Re: [time-nuts] Phase measurement of my GPSDO

[Matthias Welwarsky]

On Mittwoch, 12. August 2020 13:23:57 CEST Tobias Pluess wrote:
> On the picture `gpsdo_180_210.png` one can see the last 30 hours of my
> measured data. During this time, the DAC value need to change only by 9
> counts. I think the DAC value has a slight trend to go lower and lower,
> this is perhaps because my OCXO was new and is still a bit aging. Phase
> error stays within +/-15ns during the whole time!

TimeLab can tell you the linear drift from the imported data.

> As I still don't have a proper DMTD system or anything similar which allows
> me to `quickly` estimate the stability of my device, I made some
> experiments and imported my logged data int Timelab. This can be seen in
> the picture `timelab_estimated_from_dac.png`. The blue curve results when I
> analyse the phase error. As expected, since this is essentially the
> performance of the 1PPS signal, the curve goes lower and lower. (I imported
> this data as "phase difference" and scaled it with 1e-9).
> The pink curve results when I let Timelab analyse the DAC values. This idea
> is actually from a colleague on this list. It assumes that the OCXO is
> perfectly stable and the only instability comes from the DAC being
> disturbed by the 1PPS noise. To analyse this, I imported the data as
> "Frequency Difference" and scaled it appropriately (scaling factor is
> 7.6e-12 as I have approx. 5 to 6Hz tuning range of the OCXO per 16 Bits). I
> am not sure how accurate this estimation will be, but if it is only close
> to the reality then it appears that my GPSDO has a stability in the range
> 1e-12. According to John's comparisons here:
> 
> http://www.ke5fx.com/gpscomp.htm
> 
> this would mean it is slightly better than a BG7TBL and quite a bit worse
> than a Tbolt with 10811A oscillator.

The DAC analysis tells you mainly how much "instability" the regulation causes 
for a given tau. The GPSDO output can not be better than this value. 
Typically, it's worse than the DAC ADEV. I've been doing some simulations with 
TvBs GPSDO simulator a while ago (might have posted some graphs here, cannot 
quite remember), the DAC ADEV (or MDEV) starts to influence the OCXO 
performance when they become close. 

> Comments welcome. I hope I get my two Rb standards soon and can then do
> some DMTD tests.

Looking forward to seeing some actual measurements!

> 
> 
> Tobias
> HB9FSX
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Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Dear Colleagues

I have made some tests with my self-made GPSDO which we discussed on this
very list.
I was allowed to install it at my workplace and put the antenna on the
roof, with almost 360° free sky view.
(I will have to compare different oscillators anyways, so I could install
mine as well. I have also ordered some Rb standards which I will use for
further comparisons.)

OK what I did so far is just log the output of my GPSDO to a text file. My
software which runs on the GPSDO outputs every second the 1PPS phase error,
the OCXO current, board temperature, DAC value, #of satellites tracked and
the position accuracy.
The phase error is measured with a builtin TIC and is the time difference
between the 1PPS signal from the GPS module vs. the 1PPS signal derived
from my OCXO and is the input to my control loop which then forms a PLL.

I thought, maybe the measurements are of interest for some members of this
group, this is why I post this message and uploaded some of my measurement
data here:

https://hb9fsx.ch/files/gpsdo/measurement/

on the jpg images, one can see my antenna location. It is not optimal, I
know, but far better than at home on my window still! (unfortunately, I
could not use this very nice Trimble antenna seen on one of the pictures.)

In the Lady Heather screenshot, one can see, for comparison, the satellites
tracked by my GPSDO compared to the ones tracked by a commercial GPSDO.
Nice to see that the C/N0 values and the SV IDs seem to be the same, from
this I conclude that my PCB layout of the RF part seems to be acceptable
(otherwise the signal reception would be degraded I assume).

So far, my GPSDO runs for 210 hours and continuously logs its data. On the
picture `gpsdo_0_210.png` one can see the data from the full run. The
x-axis is in hours (obviously). Also note that I cut off the first couple
of minutes of the logged data (just because the control loop needs to
settle there and therefore the phase error is not so nice and would disrupt
the y-axis). Apparently, the phase error never becomes larger than +/-20ns.

On the picture `gpsdo_180_210.png` one can see the last 30 hours of my
measured data. During this time, the DAC value need to change only by 9
counts. I think the DAC value has a slight trend to go lower and lower,
this is perhaps because my OCXO was new and is still a bit aging. Phase
error stays within +/-15ns during the whole time!

On the image `gpsdo_pos_to_timing.png` one can see when the GPS receiver
automatically switches from positioning to timing mode. At the beginning, I
started a self-survey where I specified a desired position accuracy of
200mm. (What would be a sensible value for the desired position accuracy?)
On the lowest chart, I added the position standard deviation reported by
the GPS module. We can clearly see, at about time 9h, that the 200mm limit
is reached and the module switches from positioning mode to timing mode. At
this time, we can also see how the jitter behaviour of the phase error
changes slightly. I assume this is because the timing mode offers a better
jitter performance of the 1PPS output and therefore my phase error in the
end also becomes less noisy.

The last plot I have so far is `gpsdo_switch_filters.png` which is the data
recorded during the initial startup phase. In my GPSDO control software, I
use a PI controller where I automatically change the P and I coefficients
depending on how stable the phase error was previously. We can see that up
to approx. 0.35h, the DAC output follows the phase error rather quickly.
For startup, I optimised my control loop such that it has a time constant
of approx. 10sec, which allows the phase error to stabilise quickly. At
0.35h, the phase error was within certain limits for long enough time such
that the control software decides to switch the P and I coefficients such
that the control loop's time constant becomes approx. 100sec. From there
on, we can see how the DAC output immediately becomes more quiet and
stable. Later, the time constant is again increased to 1000sec. (I don't
know whether this is good for the OCXO I have - but somewhere I read that
the Oscilloquartz STAR4 uses 200sec as default but it could be much more,
this is why I increased it on my unit to 400sec.)

As I still don't have a proper DMTD system or anything similar which allows
me to `quickly` estimate the stability of my device, I made some
experiments and imported my logged data int Timelab. This can be seen in
the picture `timelab_estimated_from_dac.png`. The blue curve results when I
analyse the phase error. As expected, since this is essentially the
performance of the 1PPS signal, the curve goes lower and lower. (I imported
this data as "phase difference" and scaled it with 1e-9).
The pink curve results when I let Timelab analyse the DAC values. This idea
is actually from a colleague on this list. It assumes that the OCXO is
perfectly stable and the only instability comes from the DAC being
disturbed by the 1PPS 

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

An OP37 may  not function well as a diode clamped limiter since the loop gain 
is <5 during limiting.
A unity gain stable opamp would likely be better.

Bruce
> On 17 April 2020 at 09:26 Bob kb8tq  wrote:
> 
> 
> Hi
> 
> The OP-37 is fine as long as the gain is over 5X. Under that gain level, you 
> need to run an OP-27. The OP-07 is pretty noisy. 
> 
> Limiter circuits have been covered in a lot of detail. One quick read is at:
> 
> http://www.ko4bb.com/getsimple/index.php?id=bruces-zero-crossing-detectors 
> 
> 
> That page and the others Bruce did go into a lot of detail on the how and 
> why of this kind of limiter. There are other resources out there as well. 
> 
> So yes, there are circuits that work better for this than others. 
> 
> Bob
> 
> > On Apr 16, 2020, at 3:46 PM, Tobias Pluess  wrote:
> > 
> > Hey Bob
> > 
> > awesome, I actually have found some OP-07 and OP-37 in my junkbox! going to
> > build an amplifier now for my mixers. Is it a wise idea to add diodes to
> > prevent the amplifier from clipping?
> > For example I would have done it similar to this
> > 
> > https://www.allaboutcircuits.com/technical-articles/an-op-amp-limiter-how-to-limit-the-amplitude-of-amplified-signals/
> > 
> > but I don't know whether this is a timenuts-grade circuit.
> > 
> > 
> > Tobias
> > 
> > 
> > On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> > 
> >> Hi
> >> 
> >>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >>> 
> >>> Hi Bob
> >>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >>> 
> >>> Maybe I have some good OpAmps for this purpose in my box. I will try it!
> >> of
> >> 
> >> You need something that is quiet (like the OP-37) and has a pretty good
> >> slew
> >> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> >> one.
> >> 
> >>> course I saw that my setup was not ideal as there was a bit of noise on
> >> the
> >>> signals which I guess does lead to some jitter in the trigger circuit and
> >>> therefore decreases my measurement noise floor.
> >> 
> >> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> >> digits.
> >> Net result is a measurement that’s good in the vicinity of parts in 10^-13
> >> 
> >>> 
> >>> Can you say something about how it would be done using a TIC?
> >>> I don't have two identically good counters, but the HP 5335A could be
> >> used
> >>> as TIC, couldn't it.
> >> 
> >> The standard way of doing the test is to run two counters / two TIC/s /
> >> two whatever’s.
> >> I know of no practical way to do it with a single 5335.
> >> 
> >>> 
> >>> And the offset source I used is not directly the HP 10811, but the HP
> >> 8663A
> >>> Signal generator internally uses a 10811 as reference source. But I
> >> didn't
> >>> wait for days for it to warm up properly. (Should I?)
> >> 
> >> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
> >> you
> >> use the 10811, it needs to be on for a while. How long very much depends
> >> on
> >> just how long it’s been off. Best to keep it on all the time.
> >> 
> >>> 
>  Fun !!!
> >>> Yea, of course! :-)
> >>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> >>> myself. I use TimeLab to see what numbers I should expect, and then I
> >> want
> >>> to compute it all myself in Matlab because I want to see how it actually
> >>> works. ;-)
> >> 
> >> Be careful any time you code this stuff for the first time. It’s amazingly
> >> easy
> >> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> >> you should not code it up yourself. I generally do it in Excel or in C.
> >> 
> >> Bob
> >> 
> >>> 
> >>> 
> >>> Best
> >>> Tobias
> >>> 
> >>> 
> >>> 
> >>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >>> 
>  Hi
>  
>  Ok, first the math:
>  
>  If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>  
>  10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>  
>  You get to add a 6 to what Time Lab shows you.
>  
>  If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>  gets you to 1x10^-10
>  
>  So, what’s going on?
>  
>  You can’t feed the mixer outputs straight into a counter. The counter
>  front
>  end does not handle LF audio sine waves very well. You need to do an
>  op-amp based limiter. A pair of OP-37’s in each leg ( or something
>  similar)
>  should do the trick.
>  
>  Second, the offset source needs to be pretty good. A 10811 tuned high
> >> with
>  both the mechanical trim and the EFC is a pretty good choice to start
> >> out.
>  
>  If you only have one counter, simply ignore the second channel. You are
> >> now
>  running a single mixer. It still works as a comparison between the
> >> offset
>  oscillator
>  and your DUT.
>  
>  If you want to do it 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hey Bob

awesome, I actually have found some OP-07 and OP-37 in my junkbox! going to
build an amplifier now for my mixers. Is it a wise idea to add diodes to
prevent the amplifier from clipping?
For example I would have done it similar to this

https://www.allaboutcircuits.com/technical-articles/an-op-amp-limiter-how-to-limit-the-amplitude-of-amplified-signals/

but I don't know whether this is a timenuts-grade circuit.


Tobias


On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:

> Hi
>
> > On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> > awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >
> > Maybe I have some good OpAmps for this purpose in my box. I will try it!
> of
>
> You need something that is quiet (like the OP-37) and has a pretty good
> slew
> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> one.
>
> > course I saw that my setup was not ideal as there was a bit of noise on
> the
> > signals which I guess does lead to some jitter in the trigger circuit and
> > therefore decreases my measurement noise floor.
>
> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> digits.
> Net result is a measurement that’s good in the vicinity of parts in 10^-13
>
> >
> > Can you say something about how it would be done using a TIC?
> > I don't have two identically good counters, but the HP 5335A could be
> used
> > as TIC, couldn't it.
>
> The standard way of doing the test is to run two counters / two TIC/s /
> two whatever’s.
> I know of no practical way to do it with a single 5335.
>
> >
> > And the offset source I used is not directly the HP 10811, but the HP
> 8663A
> > Signal generator internally uses a 10811 as reference source. But I
> didn't
> > wait for days for it to warm up properly. (Should I?)
>
> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
> you
> use the 10811, it needs to be on for a while. How long very much depends
> on
> just how long it’s been off. Best to keep it on all the time.
>
> >
> >> Fun !!!
> > Yea, of course! :-)
> > I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> > myself. I use TimeLab to see what numbers I should expect, and then I
> want
> > to compute it all myself in Matlab because I want to see how it actually
> > works. ;-)
>
> Be careful any time you code this stuff for the first time. It’s amazingly
> easy
> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> you should not code it up yourself. I generally do it in Excel or in C.
>
> Bob
>
> >
> >
> > Best
> > Tobias
> >
> >
> >
> > On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> Ok, first the math:
> >>
> >> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
> >>
> >> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
> >>
> >> You get to add a 6 to what Time Lab shows you.
> >>
> >> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
> >> gets you to 1x10^-10
> >>
> >> So, what’s going on?
> >>
> >> You can’t feed the mixer outputs straight into a counter. The counter
> >> front
> >> end does not handle LF audio sine waves very well. You need to do an
> >> op-amp based limiter. A pair of OP-37’s in each leg ( or something
> >> similar)
> >> should do the trick.
> >>
> >> Second, the offset source needs to be pretty good. A 10811 tuned high
> with
> >> both the mechanical trim and the EFC is a pretty good choice to start
> out.
> >>
> >> If you only have one counter, simply ignore the second channel. You are
> now
> >> running a single mixer. It still works as a comparison between the
> offset
> >> oscillator
> >> and your DUT.
> >>
> >> If you want to do it properly as a DMTD, then you set up two counters.
> One
> >> to measure mixer A and the other to measure mixer B.  Set them both up
> to
> >> measure frequency. Time tag the data files so you know which reading
> >> matches up with which.
> >>
> >> Fun !!!
> >>
> >> Bob
> >>
> >>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi again Bob
> >>>
> >>> I tried to do some measurements with a DMTD!
> >>> In my junk box I found a little PCB from earlier experiments on that
> >> topic,
> >>> with a power splitter and two SRA-3H mixers, it was even already wired
> >> for
> >>> the DMTD configuration. So I gave it a try!
> >>> As "transfer oscillator" I used my HP 8663A signal generator, and set
> it
> >>> high in frequency by 10 Hz. To the two mixers, I connected the two
> 10MHz
> >>> signals and at the mixer outputs, I put a little lowpass filter with
> >> 100Hz
> >>> corner frequency.
> >>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
> >> tried
> >>> to feed them directly into the HP 5335A TIC and used the TI mode to
> >> measure
> >>> the delay between the two signals.
> >>> This gives 10 readings/sec, which I try to process with TimeLab.
> >>> It does give some interesting graphs, but I don't 

Re: [time-nuts] Phase measurement of my GPSDO

[John Ackermann N8UR]

It's a feature not a bug. :-)

I was going to address possible out-of-sequence output in this update,
but after lots and lots of thinking and experiments, and discussions
with a few bright folks on this list, I've come to the conclusion that
there is no 100% reliable way to do sample ordering within the TICC,
unless you provide it with additional information about the test
configuration and guarantee the integrity of the incoming signals.

It seems trivial to just sort samples if you make some assumptions: that
both channels are providing data at the same rate, that neither one will
ever glitch, and that both of them will always be present.

But... what if chA is at 1 PPS and chB is at 10 PPS?  What if you're
only measuring one channel?  Those could be solved by telling the TICC
what the configuration is, or doing some sort of signal analysis at the
start of the run, but that adds a lot of complexity to the code (and
operation).

And then, what if chA goes away during the measurement but chB keeps on
ticking?  What if one of the DUTs glitches so there is a missing sample?
 Or an extra one?  Those occurrences will screw up any attempt at
sequencing.

Apart from that, there is a subtle quirk in the TICC architecture
(thanks to TVB for spotting this) -- because of the way the TDC7200 chip
works, if a sample arrives on each input nearly simultaneously, you
cannot tell which one occurred first until *after* both samples are
processed.  Because there are non-deterministic latencies in the
processing loop, there can be a situation where, for example, chB has a
slightly earlier timestamp but is processed after chA. So you can get an
output file where the timestamps are not always in ascending order.

I was originally going to say that addressing this particular problem in
the firmware would be sensitive to all the gotchas mentioned in the
previous paragraphs.  But as I was typing I realized that there might be
a fairly simple way to guarantee that the output is at least in
increasing-timestamp order. That doesn't guarantee chA/chB sequencing,
though.  I'll play with this idea when I get a chance.

But taken all together, it is *much* easier to sequence the data outside
the TICC than within it.  Something like:

tail -f /dev/ttyUSB0 | tee >(grep "chA" > chA.dat) >(grep "chB" > chB.dat)

should do it. (Check the syntax; I didn't actually try this out but have
used the idea in the past.)

John
(whose hair, at least what's left of it, is more gray after having
wrestled with this for the last several months)


On 4/14/20 1:10 PM, Bob kb8tq wrote:
> Hi
> 
> Have you tried it with the latest firmware update?
> 
> I’ve never seen the problem here.
> 
> Bob
> 
>> On Apr 14, 2020, at 1:05 PM, Taka Kamiya via time-nuts 
>>  wrote:
>>
>> Bob, Tobias, et al
>>
>> TICC (TAPR) isn't problem free either.  It has a tendency to get TimeLab 
>> confused on data from port A and port B.  The data stream has identifier on 
>> them but TimeLab discards it.  Then it expects A and B comes alternately.  I 
>> communicated with both developers but for time being, the solution is to 
>> record the data and inspect. 
>>
>> --- 
>> (Mr.) Taka Kamiya
>> KB4EMF / ex JF2DKG
>>
>>
>>On Tuesday, April 14, 2020, 7:48:34 AM EDT, Bob kb8tq  
>> wrote:  
>>
>> Hi
>>
>> If the phase slips are “well behaved” they can be handled. The problem 
>> with a dual channel setup is that they are often not well behaved.  The
>> period is 100 ns so a frequency drift of 1 ppb will put you in trouble in 
>> under 2 minutes. 
>>
>> The only real answer is to do it properly and time tag the two outputs. 
>> Any other approach will get you yelling and screaming at the test set. 
>> Playing with two counters and not time tagging is in the “yelling and 
>> screaming” category as well. 
>>
>> Get a TAPPR TICC if you really want to do a DMTD. 
>>
>> Of course you *could* just use a single mixer. That works fine with the 
>> counter you already have. It will give you an A to B test just like a 
>> DMTD. The only limitation is the need to tune at least one of the 
>> oscillators 
>> in each pair. 
>>
>> There is no requirement that you tune only one. If both are tunable, 
>> you could tune one to the high end of its range and the other to the low 
>> end. 
>> With most OCXO’s, there is plenty of tune range. 
>>
>> Bob
>>
>>> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
>>>
>>> Hey Bob
>>>
>>> ok now I see your point! you talk about the phase spillovers. Timelab and
>>> also Stable32 can correct for them, so it shouldn't be a problem, right?
>>>
>>> But I agree, if you cannot correct for the spillovers it becomes even more
>>> difficult.
>>>
>>>
>>> Tobias
>>>
>>> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
>>>
 Hi

 The gotcha with using a conventional counter (as opposed to a time tagger)
 is that you never know when things are going to “slip” past each other.
 When they
 do you get a major burp 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

Have you tried it with the latest firmware update?

I’ve never seen the problem here.

Bob

> On Apr 14, 2020, at 1:05 PM, Taka Kamiya via time-nuts 
>  wrote:
> 
> Bob, Tobias, et al
> 
> TICC (TAPR) isn't problem free either.  It has a tendency to get TimeLab 
> confused on data from port A and port B.  The data stream has identifier on 
> them but TimeLab discards it.  Then it expects A and B comes alternately.  I 
> communicated with both developers but for time being, the solution is to 
> record the data and inspect. 
> 
> --- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> 
> 
>On Tuesday, April 14, 2020, 7:48:34 AM EDT, Bob kb8tq  
> wrote:  
> 
> Hi
> 
> If the phase slips are “well behaved” they can be handled. The problem 
> with a dual channel setup is that they are often not well behaved.  The
> period is 100 ns so a frequency drift of 1 ppb will put you in trouble in 
> under 2 minutes. 
> 
> The only real answer is to do it properly and time tag the two outputs. 
> Any other approach will get you yelling and screaming at the test set. 
> Playing with two counters and not time tagging is in the “yelling and 
> screaming” category as well. 
> 
> Get a TAPPR TICC if you really want to do a DMTD. 
> 
> Of course you *could* just use a single mixer. That works fine with the 
> counter you already have. It will give you an A to B test just like a 
> DMTD. The only limitation is the need to tune at least one of the oscillators 
> in each pair. 
> 
> There is no requirement that you tune only one. If both are tunable, 
> you could tune one to the high end of its range and the other to the low end. 
> With most OCXO’s, there is plenty of tune range. 
> 
> Bob
> 
>> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
>> 
>> Hey Bob
>> 
>> ok now I see your point! you talk about the phase spillovers. Timelab and
>> also Stable32 can correct for them, so it shouldn't be a problem, right?
>> 
>> But I agree, if you cannot correct for the spillovers it becomes even more
>> difficult.
>> 
>> 
>> Tobias
>> 
>> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
>> 
>>> Hi
>>> 
>>> The gotcha with using a conventional counter (as opposed to a time tagger)
>>> is that you never know when things are going to “slip” past each other.
>>> When they
>>> do you get a major burp in your data. Bill’s setup is running a time
>>> tagger ….
>>> 
>>> ( = It runs an internal time count, each edge gets “labeled” with a
>>> precise time
>>> stamp that is good to nanoseconds or picoseconds. A Time Interval Counter
>>> simply measures the time between edges. That sounds like the same thing,
>>> but
>>> it’s not quite ….)
>>> 
>>> 
 On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
 
 Hi Bob
 
 Riley suggests to use a single TIC
 
 http://wriley.com/A%20Small%20DMTD%20System.pdf
 
 when you look at the block diagram Fig. 4, you can see that one TIC
>>> allows
 to compare two oscillators.
 I don't know exactly how, though :-)
>>> 
>>> The gotcha with using a conventional counter (as opposed to a time tagger)
>>> is that you never know when things are going to “slip” past each other.
>>> When they
>>> do you get a major burp in your data. Bill’s setup is running a time
>>> tagger ….
>>> 
 
 OK and I see your point on the 8663. I will try to use another reference!
 I definitely didn't keep mine on for a long time. I didn't use the signal
 generator for a while now, so it was unplugged for a few months. I assume
 that's far from optimal for the 10811's stability.
>>> 
>>> Best approach is to mount your reference off on it’s own and just power
>>> it. That way
>>> you don’t wear out all the guts of a fancy piece of gear.
>>> 
>>> Bob
>>> 
 
 
 Tobias
 
 
 
 On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
 
> Hi
> 
>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
>> 
>> Hi Bob
>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
>> 
>> Maybe I have some good OpAmps for this purpose in my box. I will try
>>> it!
> of
> 
> You need something that is quiet (like the OP-37) and has a pretty good
> slew
> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> one.
> 
>> course I saw that my setup was not ideal as there was a bit of noise on
> the
>> signals which I guess does lead to some jitter in the trigger circuit
>>> and
>> therefore decreases my measurement noise floor.
> 
> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> digits.
> Net result is a measurement that’s good in the vicinity of parts in
>>> 10^-13
> 
>> 
>> Can you say something about how it would be done using a TIC?
>> I don't have two identically good counters, but the HP 5335A could be
> used
>> as TIC, couldn't it.
> 
> The standard way of doing 

Re: [time-nuts] Phase measurement of my GPSDO

[Taka Kamiya via time-nuts]

Bob, Tobias, et al

TICC (TAPR) isn't problem free either.  It has a tendency to get TimeLab 
confused on data from port A and port B.  The data stream has identifier on 
them but TimeLab discards it.  Then it expects A and B comes alternately.  I 
communicated with both developers but for time being, the solution is to record 
the data and inspect. 

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Tuesday, April 14, 2020, 7:48:34 AM EDT, Bob kb8tq  
wrote:  
 
 Hi

If the phase slips are “well behaved” they can be handled. The problem 
with a dual channel setup is that they are often not well behaved.  The
period is 100 ns so a frequency drift of 1 ppb will put you in trouble in 
under 2 minutes. 

The only real answer is to do it properly and time tag the two outputs. 
Any other approach will get you yelling and screaming at the test set. 
Playing with two counters and not time tagging is in the “yelling and 
screaming” category as well. 

Get a TAPPR TICC if you really want to do a DMTD. 

Of course you *could* just use a single mixer. That works fine with the 
counter you already have. It will give you an A to B test just like a 
DMTD. The only limitation is the need to tune at least one of the oscillators 
in each pair. 

There is no requirement that you tune only one. If both are tunable, 
you could tune one to the high end of its range and the other to the low end. 
With most OCXO’s, there is plenty of tune range. 

Bob

> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
> 
> Hey Bob
> 
> ok now I see your point! you talk about the phase spillovers. Timelab and
> also Stable32 can correct for them, so it shouldn't be a problem, right?
> 
> But I agree, if you cannot correct for the spillovers it becomes even more
> difficult.
> 
> 
> Tobias
> 
> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
> 
>> Hi
>> 
>> The gotcha with using a conventional counter (as opposed to a time tagger)
>> is that you never know when things are going to “slip” past each other.
>> When they
>> do you get a major burp in your data. Bill’s setup is running a time
>> tagger ….
>> 
>> ( = It runs an internal time count, each edge gets “labeled” with a
>> precise time
>> stamp that is good to nanoseconds or picoseconds. A Time Interval Counter
>> simply measures the time between edges. That sounds like the same thing,
>> but
>> it’s not quite ….)
>> 
>> 
>>> On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bob
>>> 
>>> Riley suggests to use a single TIC
>>> 
>>> http://wriley.com/A%20Small%20DMTD%20System.pdf
>>> 
>>> when you look at the block diagram Fig. 4, you can see that one TIC
>> allows
>>> to compare two oscillators.
>>> I don't know exactly how, though :-)
>> 
>> The gotcha with using a conventional counter (as opposed to a time tagger)
>> is that you never know when things are going to “slip” past each other.
>> When they
>> do you get a major burp in your data. Bill’s setup is running a time
>> tagger ….
>> 
>>> 
>>> OK and I see your point on the 8663. I will try to use another reference!
>>> I definitely didn't keep mine on for a long time. I didn't use the signal
>>> generator for a while now, so it was unplugged for a few months. I assume
>>> that's far from optimal for the 10811's stability.
>> 
>> Best approach is to mount your reference off on it’s own and just power
>> it. That way
>> you don’t wear out all the guts of a fancy piece of gear.
>> 
>> Bob
>> 
>>> 
>>> 
>>> Tobias
>>> 
>>> 
>>> 
>>> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
>>> 
 Hi
 
> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> 
> Maybe I have some good OpAmps for this purpose in my box. I will try
>> it!
 of
 
 You need something that is quiet (like the OP-37) and has a pretty good
 slew
 rate. Past that, there are a lot of candidates. The TI OPA-228 family is
 one.
 
> course I saw that my setup was not ideal as there was a bit of noise on
 the
> signals which I guess does lead to some jitter in the trigger circuit
>> and
> therefore decreases my measurement noise floor.
 
 Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
 digits.
 Net result is a measurement that’s good in the vicinity of parts in
>> 10^-13
 
> 
> Can you say something about how it would be done using a TIC?
> I don't have two identically good counters, but the HP 5335A could be
 used
> as TIC, couldn't it.
 
 The standard way of doing the test is to run two counters / two TIC/s /
 two whatever’s.
 I know of no practical way to do it with a single 5335.
 
> 
> And the offset source I used is not directly the HP 10811, but the HP
 8663A
> Signal generator internally uses a 10811 as reference source. But I
 didn't
> wait for days for it to warm 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

> On Apr 14, 2020, at 11:01 AM, Tobias Pluess  wrote:
> 
> Hi Bob
> 
> yes I totally agree, you can save a lot of space by having those USB boxes
> for almost every measurement.
> However I am happy that we have at work the "old school stuff" (by which I
> don't mean we have old equipment, actually it is pretty modern) because in
> my opinion the user experience is much better if you have buttons to press
> and knobs to rotate. I don't like the scopes where you have to set up
> everything via touchscreen, and I don't like the USB scopes. Therefore I am
> actually quite happy with the kind of equipment that sits in its own box,
> the disadvantage is that it needs space. However I think this is only a
> concern for the homelab, where space is limited. A place where they don't
> have the space to install a proper network analyzer is perhaps a bit ...
> funny, I'd say. But for home usage you're probably right. However many of
> the USB things have lots of drawbacks the "pro" equipment doesn't have. But
> perhaps we are wandering off the subject a bit now :-)

I have more space on my home bench than I did on any bench at any
place I ever worked. I have never worked at a location (or visited one) where
full sized / old style network analyzers were deployed to all dozen or three 
engineering benches. Same thing with 3048 style phase noise test sets. 
For phase noise, the issue was spur pickup as much as anything else. The
USB stuff actually is *better* than the old gear in that regard. 

> 
>> Lots of projects started and never fully completed. I have piles and
> piles of them ….
> 
> yeah I know. I have them as well. Not piles, but certainly quite a few. But
> I have also piles of stuff I have finished. For instance from time to time
> I try to manufacture RF waveguide components like directional couplers and
> bandpass filters and the like. While I don't actually need them I simply
> want to see whether I could make them and how precise it is possible. (it
> is possible quite accurately up to perhaps 80GHz, above that precision
> becomes an issue). And as you know especially the waveguide stuff is bulky
> :-) I even once made my own N connectors just to see whether it was
> possible. (it is, as well. When gold plated or at least polished, they look
> very similar to the commercial ones.)
> 
> But this is definitely seriously off-topic ;-) To ask a back-to-topic
> question: you said you wrote your own programs to extract ADEV from
> timetagged data. Could you give a hint on how you "massage" (as you said)
> the data from the time tagger to get proper phase info and ADEV?

I wrote the first stuff back in the 70’s. It got redone several times as I
moved from plant to plant over the years. By the late 90’s these systems
began to fade out in industry. 

Normally the code looks for jumps and then makes arbitrary decisions
about how to “patch” them. With a time tagger, most of the problems are
actually dropouts in the data. How you fill those depends on what you
are doing ( you may re-do the run ). Simply putting in the phase data
from the previous point is an alternative. 

Bob


> 
> Tobias
> 
> 
> On Tue, Apr 14, 2020 at 2:51 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> The whole “volume of clutter” on the desk / bench / around the lab /
>> basement
>> is one of the many drivers getting me to move over to some of the more
>> modern USB based measurement gear. You can swap out 400 lb of cranky
>> (but useful )  gear from the 1960’s for what would fit in a small
>> backpack.
>> 
>> Even at work, the same sort of drivers applied. A USB based box was
>> something
>> that you could have a dozen of out on many benches. The big beast setup
>> hulked
>> away on it’s own bench over in the corner. A lot more got done with the
>> little boxes.
>> 
>> There are a lot of grades of USB gear. I’m not suggesting that my $100
>> network
>> analyzer competes for accuracy with a shiny new R or Keysight device. It
>> just
>> *might* do as good a job as the broken down pile of gear from 1968 though.
>> For
>> a bit more than $100, I could get a better USB version ….
>> 
>> =
>> 
>> Can you build your own TICC / scope / network analyzer / PC / television?
>> Sure you can. It’s just parts put together in this or that fashion.
>> Getting one to the
>> point that it measures up with what you can buy will take a while (likely
>> a couple
>> of passes).
>> 
>> Your time is “free" since this is a hobby. Does that really include 40
>> hours a week
>> for a year to get this or that pass done? At least to me … nope. How about
>> the lab
>> full of application specific test gear to get this piece of gear debugged
>> *before* you
>> can use it ? Hmmm….
>> 
>> Simply getting the board laid out is the easy part of any of this. On a
>> normal
>> product design, the work to get to that point is maybe 10% of the effort
>> put in
>> to get the job done. A home project may be even more lopsided since it
>> likely
>> is the first time you have done this 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bob

yes I totally agree, you can save a lot of space by having those USB boxes
for almost every measurement.
However I am happy that we have at work the "old school stuff" (by which I
don't mean we have old equipment, actually it is pretty modern) because in
my opinion the user experience is much better if you have buttons to press
and knobs to rotate. I don't like the scopes where you have to set up
everything via touchscreen, and I don't like the USB scopes. Therefore I am
actually quite happy with the kind of equipment that sits in its own box,
the disadvantage is that it needs space. However I think this is only a
concern for the homelab, where space is limited. A place where they don't
have the space to install a proper network analyzer is perhaps a bit ...
funny, I'd say. But for home usage you're probably right. However many of
the USB things have lots of drawbacks the "pro" equipment doesn't have. But
perhaps we are wandering off the subject a bit now :-)

> Lots of projects started and never fully completed. I have piles and
piles of them ….

yeah I know. I have them as well. Not piles, but certainly quite a few. But
I have also piles of stuff I have finished. For instance from time to time
I try to manufacture RF waveguide components like directional couplers and
bandpass filters and the like. While I don't actually need them I simply
want to see whether I could make them and how precise it is possible. (it
is possible quite accurately up to perhaps 80GHz, above that precision
becomes an issue). And as you know especially the waveguide stuff is bulky
:-) I even once made my own N connectors just to see whether it was
possible. (it is, as well. When gold plated or at least polished, they look
very similar to the commercial ones.)

But this is definitely seriously off-topic ;-) To ask a back-to-topic
question: you said you wrote your own programs to extract ADEV from
timetagged data. Could you give a hint on how you "massage" (as you said)
the data from the time tagger to get proper phase info and ADEV?

Tobias


On Tue, Apr 14, 2020 at 2:51 PM Bob kb8tq  wrote:

> Hi
>
> The whole “volume of clutter” on the desk / bench / around the lab /
> basement
> is one of the many drivers getting me to move over to some of the more
> modern USB based measurement gear. You can swap out 400 lb of cranky
> (but useful )  gear from the 1960’s for what would fit in a small
> backpack.
>
> Even at work, the same sort of drivers applied. A USB based box was
> something
> that you could have a dozen of out on many benches. The big beast setup
> hulked
> away on it’s own bench over in the corner. A lot more got done with the
> little boxes.
>
> There are a lot of grades of USB gear. I’m not suggesting that my $100
> network
> analyzer competes for accuracy with a shiny new R or Keysight device. It
> just
> *might* do as good a job as the broken down pile of gear from 1968 though.
> For
> a bit more than $100, I could get a better USB version ….
>
> =
>
> Can you build your own TICC / scope / network analyzer / PC / television?
> Sure you can. It’s just parts put together in this or that fashion.
> Getting one to the
> point that it measures up with what you can buy will take a while (likely
> a couple
> of passes).
>
> Your time is “free" since this is a hobby. Does that really include 40
> hours a week
> for a year to get this or that pass done? At least to me … nope. How about
> the lab
> full of application specific test gear to get this piece of gear debugged
> *before* you
> can use it ? Hmmm….
>
> Simply getting the board laid out is the easy part of any of this. On a
> normal
> product design, the work to get to that point is maybe 10% of the effort
> put in
> to get the job done. A home project may be even more lopsided since it
> likely
> is the first time you have done this or that.
>
> Lots of twists and turns. Lots of projects started and never fully
> completed.
> I have piles and piles of them ….
>
> Bob
>
> > On Apr 14, 2020, at 8:15 AM, Tobias Pluess  wrote:
> >
> > Hi Bob
> > yes sure I know. At least my homebrew GPSDO and the STAR4 GPSDO I have
> are
> > always powered, but since they don't take much space on my desk that's
> > okay. But for the signal generators (or SpecAn etc) it is a completely
> > different story; I usually take them from the shelf when I need them and
> > put them back afterwards, because they simply take too much space away.
> And
> > my home lab has only limited space, unfortunately. I am thinking since
> > months about a better setup (how arrange everything, how to stack my
> > equipment and such) but it is not so easy because simply stacking all
> > equipment on top of each other is unsatisfactory (in that case one needs
> in
> > general the instrument at the very top, which is simply too far away
> :-)).
> > The 8663A is a nice machine, but it would fill my desk already by 50%, so
> > no way to leave it there (and therefore I cannot keep it powered).
> >
> > 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

The whole “volume of clutter” on the desk / bench / around the lab / basement 
is one of the many drivers getting me to move over to some of the more 
modern USB based measurement gear. You can swap out 400 lb of cranky 
(but useful )  gear from the 1960’s for what would fit in a small backpack. 

Even at work, the same sort of drivers applied. A USB based box was something 
that you could have a dozen of out on many benches. The big beast setup hulked 
away on it’s own bench over in the corner. A lot more got done with the little 
boxes.

There are a lot of grades of USB gear. I’m not suggesting that my $100 network 
analyzer competes for accuracy with a shiny new R or Keysight device. It just
*might* do as good a job as the broken down pile of gear from 1968 though. For 
a bit more than $100, I could get a better USB version ….

=

Can you build your own TICC / scope / network analyzer / PC / television? 
Sure you can. It’s just parts put together in this or that fashion. Getting one 
to the
point that it measures up with what you can buy will take a while (likely a 
couple
of passes). 

Your time is “free" since this is a hobby. Does that really include 40 hours a 
week 
for a year to get this or that pass done? At least to me … nope. How about the 
lab 
full of application specific test gear to get this piece of gear debugged 
*before* you
can use it ? Hmmm….

Simply getting the board laid out is the easy part of any of this. On a normal 
product design, the work to get to that point is maybe 10% of the effort put in
to get the job done. A home project may be even more lopsided since it likely
is the first time you have done this or that. 

Lots of twists and turns. Lots of projects started and never fully completed. 
I have piles and piles of them ….

Bob

> On Apr 14, 2020, at 8:15 AM, Tobias Pluess  wrote:
> 
> Hi Bob
> yes sure I know. At least my homebrew GPSDO and the STAR4 GPSDO I have are
> always powered, but since they don't take much space on my desk that's
> okay. But for the signal generators (or SpecAn etc) it is a completely
> different story; I usually take them from the shelf when I need them and
> put them back afterwards, because they simply take too much space away. And
> my home lab has only limited space, unfortunately. I am thinking since
> months about a better setup (how arrange everything, how to stack my
> equipment and such) but it is not so easy because simply stacking all
> equipment on top of each other is unsatisfactory (in that case one needs in
> general the instrument at the very top, which is simply too far away :-)).
> The 8663A is a nice machine, but it would fill my desk already by 50%, so
> no way to leave it there (and therefore I cannot keep it powered).
> 
> Tobias
> 
> 
> On Tue, Apr 14, 2020 at 1:54 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>>> On Apr 14, 2020, at 2:31 AM, Tobias Pluess  wrote:
>>> 


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Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi

yes sure I agree that it is hard to beat. But from a
commercial perspective, any hobby is more or less nonsense - the same is
true for my own GPSDO. I just could have bought one and would be finished.
But making my own is more interesting ;-) I'll see whether I buy a TAPR
TICC. Maybe it would come in handy to have something I can compare with.


Tobias



On Tue., 14 Apr. 2020, 14:27 Bob kb8tq,  wrote:

> Hi
>
> Indeed all a time tagger does is spit out picoseconds since some arbitrary
> start point. Some run on and on forever ( counting up to pretty big numbers
> in the process). Others roll over at a pre-defined point. You then massage
> the data to take those out.
>
> I’d suggest that the “software/ firmware included” and “fully debugged”
> nature
> of the TAPR TICC make it pretty hard to beat unless you are planning to
> build a
> couple dozen ….
>
>
> Bob
>
> > On Apr 14, 2020, at 8:11 AM, Tobias Pluess  wrote:
> >
> > G'day
> >
> > OK I see I must do it with time tagging :-)
> > Is it correct that the time tagging just spits out the time (in ns, for
> > example) when the rising edge on the A or B input occured? and then, you
> > calculate the phase by subtracting the time tags for the A channel from
> the
> > time tags for the B channel?
> > Riley also says that DMTD works better with time tagging, so I am not
> > surprised that you recommend it as well. However I hoped that some simple
> > measurements (only to get a ballpark figure) would be possible with my
> > current setup.
> > In fact, since I read the Riley paper about the DMTD system he built, I
> > have had my own design on my bucket list since quite a while. I planned
> to
> > make my own time-tag counter with two TDC7200 as interpolators, to get ps
> > resolution, very similar to the TAPR TICC.
> >
> >
> > Tobias
> >
> >
> > On Tue, Apr 14, 2020 at 1:48 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> If the phase slips are “well behaved” they can be handled. The problem
> >> with a dual channel setup is that they are often not well behaved.  The
> >> period is 100 ns so a frequency drift of 1 ppb will put you in trouble
> in
> >> under 2 minutes.
> >>
> >> The only real answer is to do it properly and time tag the two outputs.
> >> Any other approach will get you yelling and screaming at the test set.
> >> Playing with two counters and not time tagging is in the “yelling and
> >> screaming” category as well.
> >>
> >> Get a TAPPR TICC if you really want to do a DMTD.
> >>
> >> Of course you *could* just use a single mixer. That works fine with the
> >> counter you already have. It will give you an A to B test just like a
> >> DMTD. The only limitation is the need to tune at least one of the
> >> oscillators
> >> in each pair.
> >>
> >> There is no requirement that you tune only one. If both are tunable,
> >> you could tune one to the high end of its range and the other to the low
> >> end.
> >> With most OCXO’s, there is plenty of tune range.
> >>
> >> Bob
> >>
> >>> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
> >>>
> >>> Hey Bob
> >>>
> >>> ok now I see your point! you talk about the phase spillovers. Timelab
> and
> >>> also Stable32 can correct for them, so it shouldn't be a problem,
> right?
> >>>
> >>> But I agree, if you cannot correct for the spillovers it becomes even
> >> more
> >>> difficult.
> >>>
> >>>
> >>> Tobias
> >>>
> >>> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
> >>>
>  Hi
> 
>  The gotcha with using a conventional counter (as opposed to a time
> >> tagger)
>  is that you never know when things are going to “slip” past each
> other.
>  When they
>  do you get a major burp in your data. Bill’s setup is running a time
>  tagger ….
> 
>  ( = It runs an internal time count, each edge gets “labeled” with a
>  precise time
>  stamp that is good to nanoseconds or picoseconds. A Time Interval
> >> Counter
>  simply measures the time between edges. That sounds like the same
> thing,
>  but
>  it’s not quite ….)
> 
> 
> > On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> >
> > Riley suggests to use a single TIC
> >
> > http://wriley.com/A%20Small%20DMTD%20System.pdf
> >
> > when you look at the block diagram Fig. 4, you can see that one TIC
>  allows
> > to compare two oscillators.
> > I don't know exactly how, though :-)
> 
>  The gotcha with using a conventional counter (as opposed to a time
> >> tagger)
>  is that you never know when things are going to “slip” past each
> other.
>  When they
>  do you get a major burp in your data. Bill’s setup is running a time
>  tagger ….
> 
> >
> > OK and I see your point on the 8663. I will try to use another
> >> reference!
> > I definitely didn't keep mine on for a long time. I didn't use the
> >> signal
> > generator for a while now, so it was unplugged for a few months. I
> >> assume
> > that's far 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

Indeed all a time tagger does is spit out picoseconds since some arbitrary 
start point. Some run on and on forever ( counting up to pretty big numbers
in the process). Others roll over at a pre-defined point. You then massage 
the data to take those out. 

I’d suggest that the “software/ firmware included” and “fully debugged” nature 
of the TAPR TICC make it pretty hard to beat unless you are planning to build a 
couple dozen ….


Bob
 
> On Apr 14, 2020, at 8:11 AM, Tobias Pluess  wrote:
> 
> G'day
> 
> OK I see I must do it with time tagging :-)
> Is it correct that the time tagging just spits out the time (in ns, for
> example) when the rising edge on the A or B input occured? and then, you
> calculate the phase by subtracting the time tags for the A channel from the
> time tags for the B channel?
> Riley also says that DMTD works better with time tagging, so I am not
> surprised that you recommend it as well. However I hoped that some simple
> measurements (only to get a ballpark figure) would be possible with my
> current setup.
> In fact, since I read the Riley paper about the DMTD system he built, I
> have had my own design on my bucket list since quite a while. I planned to
> make my own time-tag counter with two TDC7200 as interpolators, to get ps
> resolution, very similar to the TAPR TICC.
> 
> 
> Tobias
> 
> 
> On Tue, Apr 14, 2020 at 1:48 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> If the phase slips are “well behaved” they can be handled. The problem
>> with a dual channel setup is that they are often not well behaved.  The
>> period is 100 ns so a frequency drift of 1 ppb will put you in trouble in
>> under 2 minutes.
>> 
>> The only real answer is to do it properly and time tag the two outputs.
>> Any other approach will get you yelling and screaming at the test set.
>> Playing with two counters and not time tagging is in the “yelling and
>> screaming” category as well.
>> 
>> Get a TAPPR TICC if you really want to do a DMTD.
>> 
>> Of course you *could* just use a single mixer. That works fine with the
>> counter you already have. It will give you an A to B test just like a
>> DMTD. The only limitation is the need to tune at least one of the
>> oscillators
>> in each pair.
>> 
>> There is no requirement that you tune only one. If both are tunable,
>> you could tune one to the high end of its range and the other to the low
>> end.
>> With most OCXO’s, there is plenty of tune range.
>> 
>> Bob
>> 
>>> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
>>> 
>>> Hey Bob
>>> 
>>> ok now I see your point! you talk about the phase spillovers. Timelab and
>>> also Stable32 can correct for them, so it shouldn't be a problem, right?
>>> 
>>> But I agree, if you cannot correct for the spillovers it becomes even
>> more
>>> difficult.
>>> 
>>> 
>>> Tobias
>>> 
>>> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
>>> 
 Hi
 
 The gotcha with using a conventional counter (as opposed to a time
>> tagger)
 is that you never know when things are going to “slip” past each other.
 When they
 do you get a major burp in your data. Bill’s setup is running a time
 tagger ….
 
 ( = It runs an internal time count, each edge gets “labeled” with a
 precise time
 stamp that is good to nanoseconds or picoseconds. A Time Interval
>> Counter
 simply measures the time between edges. That sounds like the same thing,
 but
 it’s not quite ….)
 
 
> On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> 
> Riley suggests to use a single TIC
> 
> http://wriley.com/A%20Small%20DMTD%20System.pdf
> 
> when you look at the block diagram Fig. 4, you can see that one TIC
 allows
> to compare two oscillators.
> I don't know exactly how, though :-)
 
 The gotcha with using a conventional counter (as opposed to a time
>> tagger)
 is that you never know when things are going to “slip” past each other.
 When they
 do you get a major burp in your data. Bill’s setup is running a time
 tagger ….
 
> 
> OK and I see your point on the 8663. I will try to use another
>> reference!
> I definitely didn't keep mine on for a long time. I didn't use the
>> signal
> generator for a while now, so it was unplugged for a few months. I
>> assume
> that's far from optimal for the 10811's stability.
 
 Best approach is to mount your reference off on it’s own and just power
 it. That way
 you don’t wear out all the guts of a fancy piece of gear.
 
 Bob
 
> 
> 
> Tobias
> 
> 
> 
> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> 
>> Hi
>> 
>>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bob
>>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
>>> 
>>> Maybe I have some good OpAmps for this purpose in my box. I will try
 it!
>> of
>> 
>> You need 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bob
yes sure I know. At least my homebrew GPSDO and the STAR4 GPSDO I have are
always powered, but since they don't take much space on my desk that's
okay. But for the signal generators (or SpecAn etc) it is a completely
different story; I usually take them from the shelf when I need them and
put them back afterwards, because they simply take too much space away. And
my home lab has only limited space, unfortunately. I am thinking since
months about a better setup (how arrange everything, how to stack my
equipment and such) but it is not so easy because simply stacking all
equipment on top of each other is unsatisfactory (in that case one needs in
general the instrument at the very top, which is simply too far away :-)).
The 8663A is a nice machine, but it would fill my desk already by 50%, so
no way to leave it there (and therefore I cannot keep it powered).

Tobias


On Tue, Apr 14, 2020 at 1:54 PM Bob kb8tq  wrote:

> Hi
>
> > On Apr 14, 2020, at 2:31 AM, Tobias Pluess  wrote:
> >
> > Hi Taka
> > good to know you're working on the same stuff :-)
> > I also think that this is the goal, sort of. But apparently there are
> some
> > pitfalls. I hope the experts on this type of measurement (Bob) can give
> > more hints ;-)
> >
> > Btw good to know your 10811 took 2 months to settle. In that case I will
> > try to give mine also more time from power up until I do measurements.
> But
> > keeping the 8663 powered on is almost no option for me - my homelab is
> > simply too small and from time to time I therefore have to tidy it up a
> bit
> > and put some of the equipment in another shelf.
>
> You will need the ability to keep stuff on power. That’s true of pretty
> much
> any frequency standard. Indeed the compromise is often made with a Cs
> standard since they only have just so many running hours before they
> run out of “fuel”. Anything that’s OCXO or Rb based …. leave it on power.
>
> One of the side effects of being locked down is that there is *lots* of
> time
> to pick up the clutter and *really* get organized. It’s a amazing just how
> many weeks that sort of work has soaked up here :)
>
> Bob
>
> >
> >
> > Tobias
> >
> >
> > On Tue., 14 Apr. 2020, 01:19 Taka Kamiya via time-nuts, <
> > time-nuts@lists.febo.com> wrote:
> >
> >> I am working on pretty much the same thing.  My HP105B has an HP11801
> >> inside.  There is no telling how long it has been off.  Frequency
> wandered
> >> ALL OVER THE PLACE.  It took 2 months of continuous operation to settle
> >> down and just do the normal aging/drifting.
> >>
> >> I have a same question as you do.  How come not just one HP5335?  Your
> >> test setup has two output.  One goes to start, the other goes to stop.
> >> Measure the time interval.  Isn't that the goal?
> >>
> >> ---
> >> (Mr.) Taka Kamiya
> >> KB4EMF / ex JF2DKG
> >>
> >>
> >>On Monday, April 13, 2020, 5:53:52 PM EDT, Bob kb8tq 
> >> wrote:
> >>
> >> Hi
> >>
> >>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi Bob
> >>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >>>
> >>> Maybe I have some good OpAmps for this purpose in my box. I will try
> it!
> >> of
> >>
> >> You need something that is quiet (like the OP-37) and has a pretty good
> >> slew
> >> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> >> one.
> >>
> >>> course I saw that my setup was not ideal as there was a bit of noise on
> >> the
> >>> signals which I guess does lead to some jitter in the trigger circuit
> and
> >>> therefore decreases my measurement noise floor.
> >>
> >> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> >> digits.
> >> Net result is a measurement that’s good in the vicinity of parts in
> 10^-13
> >>
> >>>
> >>> Can you say something about how it would be done using a TIC?
> >>> I don't have two identically good counters, but the HP 5335A could be
> >> used
> >>> as TIC, couldn't it.
> >>
> >> The standard way of doing the test is to run two counters / two TIC/s /
> >> two whatever’s.
> >> I know of no practical way to do it with a single 5335.
> >>
> >>>
> >>> And the offset source I used is not directly the HP 10811, but the HP
> >> 8663A
> >>> Signal generator internally uses a 10811 as reference source. But I
> >> didn't
> >>> wait for days for it to warm up properly. (Should I?)
> >>
> >> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of
> how
> >> you
> >> use the 10811, it needs to be on for a while. How long very much depends
> >> on
> >> just how long it’s been off. Best to keep it on all the time.
> >>
> >>>
>  Fun !!!
> >>> Yea, of course! :-)
> >>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> >>> myself. I use TimeLab to see what numbers I should expect, and then I
> >> want
> >>> to compute it all myself in Matlab because I want to see how it
> actually
> >>> works. ;-)
> >>
> >> Be careful any time you code this 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

G'day

OK I see I must do it with time tagging :-)
Is it correct that the time tagging just spits out the time (in ns, for
example) when the rising edge on the A or B input occured? and then, you
calculate the phase by subtracting the time tags for the A channel from the
time tags for the B channel?
Riley also says that DMTD works better with time tagging, so I am not
surprised that you recommend it as well. However I hoped that some simple
measurements (only to get a ballpark figure) would be possible with my
current setup.
In fact, since I read the Riley paper about the DMTD system he built, I
have had my own design on my bucket list since quite a while. I planned to
make my own time-tag counter with two TDC7200 as interpolators, to get ps
resolution, very similar to the TAPR TICC.


Tobias


On Tue, Apr 14, 2020 at 1:48 PM Bob kb8tq  wrote:

> Hi
>
> If the phase slips are “well behaved” they can be handled. The problem
> with a dual channel setup is that they are often not well behaved.  The
> period is 100 ns so a frequency drift of 1 ppb will put you in trouble in
> under 2 minutes.
>
> The only real answer is to do it properly and time tag the two outputs.
> Any other approach will get you yelling and screaming at the test set.
> Playing with two counters and not time tagging is in the “yelling and
> screaming” category as well.
>
> Get a TAPPR TICC if you really want to do a DMTD.
>
> Of course you *could* just use a single mixer. That works fine with the
> counter you already have. It will give you an A to B test just like a
> DMTD. The only limitation is the need to tune at least one of the
> oscillators
> in each pair.
>
> There is no requirement that you tune only one. If both are tunable,
> you could tune one to the high end of its range and the other to the low
> end.
> With most OCXO’s, there is plenty of tune range.
>
> Bob
>
> > On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
> >
> > Hey Bob
> >
> > ok now I see your point! you talk about the phase spillovers. Timelab and
> > also Stable32 can correct for them, so it shouldn't be a problem, right?
> >
> > But I agree, if you cannot correct for the spillovers it becomes even
> more
> > difficult.
> >
> >
> > Tobias
> >
> > On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
> >
> >> Hi
> >>
> >> The gotcha with using a conventional counter (as opposed to a time
> tagger)
> >> is that you never know when things are going to “slip” past each other.
> >> When they
> >> do you get a major burp in your data. Bill’s setup is running a time
> >> tagger ….
> >>
> >> ( = It runs an internal time count, each edge gets “labeled” with a
> >> precise time
> >> stamp that is good to nanoseconds or picoseconds. A Time Interval
> Counter
> >> simply measures the time between edges. That sounds like the same thing,
> >> but
> >> it’s not quite ….)
> >>
> >>
> >>> On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi Bob
> >>>
> >>> Riley suggests to use a single TIC
> >>>
> >>> http://wriley.com/A%20Small%20DMTD%20System.pdf
> >>>
> >>> when you look at the block diagram Fig. 4, you can see that one TIC
> >> allows
> >>> to compare two oscillators.
> >>> I don't know exactly how, though :-)
> >>
> >> The gotcha with using a conventional counter (as opposed to a time
> tagger)
> >> is that you never know when things are going to “slip” past each other.
> >> When they
> >> do you get a major burp in your data. Bill’s setup is running a time
> >> tagger ….
> >>
> >>>
> >>> OK and I see your point on the 8663. I will try to use another
> reference!
> >>> I definitely didn't keep mine on for a long time. I didn't use the
> signal
> >>> generator for a while now, so it was unplugged for a few months. I
> assume
> >>> that's far from optimal for the 10811's stability.
> >>
> >> Best approach is to mount your reference off on it’s own and just power
> >> it. That way
> >> you don’t wear out all the guts of a fancy piece of gear.
> >>
> >> Bob
> >>
> >>>
> >>>
> >>> Tobias
> >>>
> >>>
> >>>
> >>> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> >>>
>  Hi
> 
> > On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> > awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >
> > Maybe I have some good OpAmps for this purpose in my box. I will try
> >> it!
>  of
> 
>  You need something that is quiet (like the OP-37) and has a pretty
> good
>  slew
>  rate. Past that, there are a lot of candidates. The TI OPA-228 family
> is
>  one.
> 
> > course I saw that my setup was not ideal as there was a bit of noise
> on
>  the
> > signals which I guess does lead to some jitter in the trigger circuit
> >> and
> > therefore decreases my measurement noise floor.
> 
>  Typically a good limiter takes you from 3 or 4 digits up to 6 or 7
> good
>  digits.
>  Net result is a measurement that’s good in the vicinity of parts in
> >> 10^-13
> 
> >
> 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

> On Apr 14, 2020, at 2:31 AM, Tobias Pluess  wrote:
> 
> Hi Taka
> good to know you're working on the same stuff :-)
> I also think that this is the goal, sort of. But apparently there are some
> pitfalls. I hope the experts on this type of measurement (Bob) can give
> more hints ;-)
> 
> Btw good to know your 10811 took 2 months to settle. In that case I will
> try to give mine also more time from power up until I do measurements. But
> keeping the 8663 powered on is almost no option for me - my homelab is
> simply too small and from time to time I therefore have to tidy it up a bit
> and put some of the equipment in another shelf.

You will need the ability to keep stuff on power. That’s true of pretty much
any frequency standard. Indeed the compromise is often made with a Cs
standard since they only have just so many running hours before they
run out of “fuel”. Anything that’s OCXO or Rb based …. leave it on power. 

One of the side effects of being locked down is that there is *lots* of time
to pick up the clutter and *really* get organized. It’s a amazing just how 
many weeks that sort of work has soaked up here :)

Bob

> 
> 
> Tobias
> 
> 
> On Tue., 14 Apr. 2020, 01:19 Taka Kamiya via time-nuts, <
> time-nuts@lists.febo.com> wrote:
> 
>> I am working on pretty much the same thing.  My HP105B has an HP11801
>> inside.  There is no telling how long it has been off.  Frequency wandered
>> ALL OVER THE PLACE.  It took 2 months of continuous operation to settle
>> down and just do the normal aging/drifting.
>> 
>> I have a same question as you do.  How come not just one HP5335?  Your
>> test setup has two output.  One goes to start, the other goes to stop.
>> Measure the time interval.  Isn't that the goal?
>> 
>> ---
>> (Mr.) Taka Kamiya
>> KB4EMF / ex JF2DKG
>> 
>> 
>>On Monday, April 13, 2020, 5:53:52 PM EDT, Bob kb8tq 
>> wrote:
>> 
>> Hi
>> 
>>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bob
>>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
>>> 
>>> Maybe I have some good OpAmps for this purpose in my box. I will try it!
>> of
>> 
>> You need something that is quiet (like the OP-37) and has a pretty good
>> slew
>> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
>> one.
>> 
>>> course I saw that my setup was not ideal as there was a bit of noise on
>> the
>>> signals which I guess does lead to some jitter in the trigger circuit and
>>> therefore decreases my measurement noise floor.
>> 
>> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
>> digits.
>> Net result is a measurement that’s good in the vicinity of parts in 10^-13
>> 
>>> 
>>> Can you say something about how it would be done using a TIC?
>>> I don't have two identically good counters, but the HP 5335A could be
>> used
>>> as TIC, couldn't it.
>> 
>> The standard way of doing the test is to run two counters / two TIC/s /
>> two whatever’s.
>> I know of no practical way to do it with a single 5335.
>> 
>>> 
>>> And the offset source I used is not directly the HP 10811, but the HP
>> 8663A
>>> Signal generator internally uses a 10811 as reference source. But I
>> didn't
>>> wait for days for it to warm up properly. (Should I?)
>> 
>> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
>> you
>> use the 10811, it needs to be on for a while. How long very much depends
>> on
>> just how long it’s been off. Best to keep it on all the time.
>> 
>>> 
 Fun !!!
>>> Yea, of course! :-)
>>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
>>> myself. I use TimeLab to see what numbers I should expect, and then I
>> want
>>> to compute it all myself in Matlab because I want to see how it actually
>>> works. ;-)
>> 
>> Be careful any time you code this stuff for the first time. It’s amazingly
>> easy
>> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
>> you should not code it up yourself. I generally do it in Excel or in C.
>> 
>> Bob
>> 
>>> 
>>> 
>>> Best
>>> Tobias
>>> 
>>> 
>>> 
>>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
>>> 
 Hi
 
 Ok, first the math:
 
 If your offset oscillator is 10 Hz high at 10 MHz, you have a:
 
 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
 
 You get to add a 6 to what Time Lab shows you.
 
 If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
 gets you to 1x10^-10
 
 So, what’s going on?
 
 You can’t feed the mixer outputs straight into a counter. The counter
 front
 end does not handle LF audio sine waves very well. You need to do an
 op-amp based limiter. A pair of OP-37’s in each leg ( or something
 similar)
 should do the trick.
 
 Second, the offset source needs to be pretty good. A 10811 tuned high
>> with
 both the mechanical trim and the EFC is a pretty good choice 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

If the phase slips are “well behaved” they can be handled. The problem 
with a dual channel setup is that they are often not well behaved.  The
period is 100 ns so a frequency drift of 1 ppb will put you in trouble in 
under 2 minutes. 

The only real answer is to do it properly and time tag the two outputs. 
Any other approach will get you yelling and screaming at the test set. 
Playing with two counters and not time tagging is in the “yelling and 
screaming” category as well. 

Get a TAPPR TICC if you really want to do a DMTD. 

Of course you *could* just use a single mixer. That works fine with the 
counter you already have. It will give you an A to B test just like a 
DMTD. The only limitation is the need to tune at least one of the oscillators 
in each pair. 

There is no requirement that you tune only one. If both are tunable, 
you could tune one to the high end of its range and the other to the low end. 
With most OCXO’s, there is plenty of tune range. 

Bob

> On Apr 14, 2020, at 2:23 AM, Tobias Pluess  wrote:
> 
> Hey Bob
> 
> ok now I see your point! you talk about the phase spillovers. Timelab and
> also Stable32 can correct for them, so it shouldn't be a problem, right?
> 
> But I agree, if you cannot correct for the spillovers it becomes even more
> difficult.
> 
> 
> Tobias
> 
> On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:
> 
>> Hi
>> 
>> The gotcha with using a conventional counter (as opposed to a time tagger)
>> is that you never know when things are going to “slip” past each other.
>> When they
>> do you get a major burp in your data. Bill’s setup is running a time
>> tagger ….
>> 
>> ( = It runs an internal time count, each edge gets “labeled” with a
>> precise time
>> stamp that is good to nanoseconds or picoseconds. A Time Interval Counter
>> simply measures the time between edges. That sounds like the same thing,
>> but
>> it’s not quite ….)
>> 
>> 
>>> On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bob
>>> 
>>> Riley suggests to use a single TIC
>>> 
>>> http://wriley.com/A%20Small%20DMTD%20System.pdf
>>> 
>>> when you look at the block diagram Fig. 4, you can see that one TIC
>> allows
>>> to compare two oscillators.
>>> I don't know exactly how, though :-)
>> 
>> The gotcha with using a conventional counter (as opposed to a time tagger)
>> is that you never know when things are going to “slip” past each other.
>> When they
>> do you get a major burp in your data. Bill’s setup is running a time
>> tagger ….
>> 
>>> 
>>> OK and I see your point on the 8663. I will try to use another reference!
>>> I definitely didn't keep mine on for a long time. I didn't use the signal
>>> generator for a while now, so it was unplugged for a few months. I assume
>>> that's far from optimal for the 10811's stability.
>> 
>> Best approach is to mount your reference off on it’s own and just power
>> it. That way
>> you don’t wear out all the guts of a fancy piece of gear.
>> 
>> Bob
>> 
>>> 
>>> 
>>> Tobias
>>> 
>>> 
>>> 
>>> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
>>> 
 Hi
 
> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> 
> Maybe I have some good OpAmps for this purpose in my box. I will try
>> it!
 of
 
 You need something that is quiet (like the OP-37) and has a pretty good
 slew
 rate. Past that, there are a lot of candidates. The TI OPA-228 family is
 one.
 
> course I saw that my setup was not ideal as there was a bit of noise on
 the
> signals which I guess does lead to some jitter in the trigger circuit
>> and
> therefore decreases my measurement noise floor.
 
 Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
 digits.
 Net result is a measurement that’s good in the vicinity of parts in
>> 10^-13
 
> 
> Can you say something about how it would be done using a TIC?
> I don't have two identically good counters, but the HP 5335A could be
 used
> as TIC, couldn't it.
 
 The standard way of doing the test is to run two counters / two TIC/s /
 two whatever’s.
 I know of no practical way to do it with a single 5335.
 
> 
> And the offset source I used is not directly the HP 10811, but the HP
 8663A
> Signal generator internally uses a 10811 as reference source. But I
 didn't
> wait for days for it to warm up properly. (Should I?)
 
 The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of
>> how
 you
 use the 10811, it needs to be on for a while. How long very much depends
 on
 just how long it’s been off. Best to keep it on all the time.
 
> 
>> Fun !!!
> Yea, of course! :-)
> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> myself. I use TimeLab to see what numbers I should expect, and then I
 want
> to 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Taka
good to know you're working on the same stuff :-)
I also think that this is the goal, sort of. But apparently there are some
pitfalls. I hope the experts on this type of measurement (Bob) can give
more hints ;-)

Btw good to know your 10811 took 2 months to settle. In that case I will
try to give mine also more time from power up until I do measurements. But
keeping the 8663 powered on is almost no option for me - my homelab is
simply too small and from time to time I therefore have to tidy it up a bit
and put some of the equipment in another shelf.


Tobias


On Tue., 14 Apr. 2020, 01:19 Taka Kamiya via time-nuts, <
time-nuts@lists.febo.com> wrote:

> I am working on pretty much the same thing.  My HP105B has an HP11801
> inside.  There is no telling how long it has been off.  Frequency wandered
> ALL OVER THE PLACE.  It took 2 months of continuous operation to settle
> down and just do the normal aging/drifting.
>
> I have a same question as you do.  How come not just one HP5335?  Your
> test setup has two output.  One goes to start, the other goes to stop.
> Measure the time interval.  Isn't that the goal?
>
> ---
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>
>
> On Monday, April 13, 2020, 5:53:52 PM EDT, Bob kb8tq 
> wrote:
>
>  Hi
>
> > On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> > awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >
> > Maybe I have some good OpAmps for this purpose in my box. I will try it!
> of
>
> You need something that is quiet (like the OP-37) and has a pretty good
> slew
> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> one.
>
> > course I saw that my setup was not ideal as there was a bit of noise on
> the
> > signals which I guess does lead to some jitter in the trigger circuit and
> > therefore decreases my measurement noise floor.
>
> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> digits.
> Net result is a measurement that’s good in the vicinity of parts in 10^-13
>
> >
> > Can you say something about how it would be done using a TIC?
> > I don't have two identically good counters, but the HP 5335A could be
> used
> > as TIC, couldn't it.
>
> The standard way of doing the test is to run two counters / two TIC/s /
> two whatever’s.
> I know of no practical way to do it with a single 5335.
>
> >
> > And the offset source I used is not directly the HP 10811, but the HP
> 8663A
> > Signal generator internally uses a 10811 as reference source. But I
> didn't
> > wait for days for it to warm up properly. (Should I?)
>
> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
> you
> use the 10811, it needs to be on for a while. How long very much depends
> on
> just how long it’s been off. Best to keep it on all the time.
>
> >
> >> Fun !!!
> > Yea, of course! :-)
> > I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> > myself. I use TimeLab to see what numbers I should expect, and then I
> want
> > to compute it all myself in Matlab because I want to see how it actually
> > works. ;-)
>
> Be careful any time you code this stuff for the first time. It’s amazingly
> easy
> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> you should not code it up yourself. I generally do it in Excel or in C.
>
> Bob
>
> >
> >
> > Best
> > Tobias
> >
> >
> >
> > On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> Ok, first the math:
> >>
> >> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
> >>
> >> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
> >>
> >> You get to add a 6 to what Time Lab shows you.
> >>
> >> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
> >> gets you to 1x10^-10
> >>
> >> So, what’s going on?
> >>
> >> You can’t feed the mixer outputs straight into a counter. The counter
> >> front
> >> end does not handle LF audio sine waves very well. You need to do an
> >> op-amp based limiter. A pair of OP-37’s in each leg ( or something
> >> similar)
> >> should do the trick.
> >>
> >> Second, the offset source needs to be pretty good. A 10811 tuned high
> with
> >> both the mechanical trim and the EFC is a pretty good choice to start
> out.
> >>
> >> If you only have one counter, simply ignore the second channel. You are
> now
> >> running a single mixer. It still works as a comparison between the
> offset
> >> oscillator
> >> and your DUT.
> >>
> >> If you want to do it properly as a DMTD, then you set up two counters.
> One
> >> to measure mixer A and the other to measure mixer B.  Set them both up
> to
> >> measure frequency. Time tag the data files so you know which reading
> >> matches up with which.
> >>
> >> Fun !!!
> >>
> >> Bob
> >>
> >>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi again Bob
> >>>
> >>> I tried to do some measurements with a DMTD!
> >>> In my junk box I 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hey Bob

ok now I see your point! you talk about the phase spillovers. Timelab and
also Stable32 can correct for them, so it shouldn't be a problem, right?

But I agree, if you cannot correct for the spillovers it becomes even more
difficult.


Tobias

On Tue., 14 Apr. 2020, 01:38 Bob kb8tq,  wrote:

> Hi
>
> The gotcha with using a conventional counter (as opposed to a time tagger)
> is that you never know when things are going to “slip” past each other.
> When they
> do you get a major burp in your data. Bill’s setup is running a time
> tagger ….
>
> ( = It runs an internal time count, each edge gets “labeled” with a
> precise time
> stamp that is good to nanoseconds or picoseconds. A Time Interval Counter
> simply measures the time between edges. That sounds like the same thing,
> but
> it’s not quite ….)
>
>
> > On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> >
> > Riley suggests to use a single TIC
> >
> > http://wriley.com/A%20Small%20DMTD%20System.pdf
> >
> > when you look at the block diagram Fig. 4, you can see that one TIC
> allows
> > to compare two oscillators.
> > I don't know exactly how, though :-)
>
> The gotcha with using a conventional counter (as opposed to a time tagger)
> is that you never know when things are going to “slip” past each other.
> When they
> do you get a major burp in your data. Bill’s setup is running a time
> tagger ….
>
> >
> > OK and I see your point on the 8663. I will try to use another reference!
> > I definitely didn't keep mine on for a long time. I didn't use the signal
> > generator for a while now, so it was unplugged for a few months. I assume
> > that's far from optimal for the 10811's stability.
>
> Best approach is to mount your reference off on it’s own and just power
> it. That way
> you don’t wear out all the guts of a fancy piece of gear.
>
> Bob
>
> >
> >
> > Tobias
> >
> >
> >
> > On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> >
> >> Hi
> >>
> >>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi Bob
> >>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >>>
> >>> Maybe I have some good OpAmps for this purpose in my box. I will try
> it!
> >> of
> >>
> >> You need something that is quiet (like the OP-37) and has a pretty good
> >> slew
> >> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> >> one.
> >>
> >>> course I saw that my setup was not ideal as there was a bit of noise on
> >> the
> >>> signals which I guess does lead to some jitter in the trigger circuit
> and
> >>> therefore decreases my measurement noise floor.
> >>
> >> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> >> digits.
> >> Net result is a measurement that’s good in the vicinity of parts in
> 10^-13
> >>
> >>>
> >>> Can you say something about how it would be done using a TIC?
> >>> I don't have two identically good counters, but the HP 5335A could be
> >> used
> >>> as TIC, couldn't it.
> >>
> >> The standard way of doing the test is to run two counters / two TIC/s /
> >> two whatever’s.
> >> I know of no practical way to do it with a single 5335.
> >>
> >>>
> >>> And the offset source I used is not directly the HP 10811, but the HP
> >> 8663A
> >>> Signal generator internally uses a 10811 as reference source. But I
> >> didn't
> >>> wait for days for it to warm up properly. (Should I?)
> >>
> >> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of
> how
> >> you
> >> use the 10811, it needs to be on for a while. How long very much depends
> >> on
> >> just how long it’s been off. Best to keep it on all the time.
> >>
> >>>
>  Fun !!!
> >>> Yea, of course! :-)
> >>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> >>> myself. I use TimeLab to see what numbers I should expect, and then I
> >> want
> >>> to compute it all myself in Matlab because I want to see how it
> actually
> >>> works. ;-)
> >>
> >> Be careful any time you code this stuff for the first time. It’s
> amazingly
> >> easy
> >> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest
> that
> >> you should not code it up yourself. I generally do it in Excel or in C.
> >>
> >> Bob
> >>
> >>>
> >>>
> >>> Best
> >>> Tobias
> >>>
> >>>
> >>>
> >>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >>>
>  Hi
> 
>  Ok, first the math:
> 
>  If your offset oscillator is 10 Hz high at 10 MHz, you have a:
> 
>  10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
> 
>  You get to add a 6 to what Time Lab shows you.
> 
>  If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>  gets you to 1x10^-10
> 
>  So, what’s going on?
> 
>  You can’t feed the mixer outputs straight into a counter. The counter
>  front
>  end does not handle LF audio sine waves very well. You need to do an
>  op-amp based limiter. A pair of OP-37’s in each leg ( or something
> 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi


> On Apr 13, 2020, at 7:18 PM, Taka Kamiya via time-nuts 
>  wrote:
> 
> I am working on pretty much the same thing.  My HP105B has an HP11801 inside. 
>  There is no telling how long it has been off.  Frequency wandered ALL OVER 
> THE PLACE.  It took 2 months of continuous operation to settle down and just 
> do the normal aging/drifting.  

Which edge comes first? 

There’s no way to know the answer to that. The counter very much wants 
to have the “first edge” on the start and the “next edge” on stop. 

Bob

> 
> I have a same question as you do.  How come not just one HP5335?  Your test 
> setup has two output.  One goes to start, the other goes to stop.  Measure 
> the time interval.  Isn't that the goal?
> 
> --- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
> 
> 
>On Monday, April 13, 2020, 5:53:52 PM EDT, Bob kb8tq  
> wrote:  
> 
> Hi
> 
>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
>> 
>> Hi Bob
>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
>> 
>> Maybe I have some good OpAmps for this purpose in my box. I will try it! of
> 
> You need something that is quiet (like the OP-37) and has a pretty good slew
> rate. Past that, there are a lot of candidates. The TI OPA-228 family is one. 
> 
>> course I saw that my setup was not ideal as there was a bit of noise on the
>> signals which I guess does lead to some jitter in the trigger circuit and
>> therefore decreases my measurement noise floor.
> 
> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good 
> digits. 
> Net result is a measurement that’s good in the vicinity of parts in 10^-13
> 
>> 
>> Can you say something about how it would be done using a TIC?
>> I don't have two identically good counters, but the HP 5335A could be used
>> as TIC, couldn't it.
> 
> The standard way of doing the test is to run two counters / two TIC/s / two 
> whatever’s.
> I know of no practical way to do it with a single 5335.
> 
>> 
>> And the offset source I used is not directly the HP 10811, but the HP 8663A
>> Signal generator internally uses a 10811 as reference source. But I didn't
>> wait for days for it to warm up properly. (Should I?)
> 
> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how you
> use the 10811, it needs to be on for a while. How long very much depends on 
> just how long it’s been off. Best to keep it on all the time. 
> 
>> 
>>> Fun !!!
>> Yea, of course! :-)
>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
>> myself. I use TimeLab to see what numbers I should expect, and then I want
>> to compute it all myself in Matlab because I want to see how it actually
>> works. ;-)
> 
> Be careful any time you code this stuff for the first time. It’s amazingly 
> easy 
> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> you should not code it up yourself. I generally do it in Excel or in C. 
> 
> Bob
> 
>> 
>> 
>> Best
>> Tobias
>> 
>> 
>> 
>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
>> 
>>> Hi
>>> 
>>> Ok, first the math:
>>> 
>>> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>>> 
>>> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>>> 
>>> You get to add a 6 to what Time Lab shows you.
>>> 
>>> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>>> gets you to 1x10^-10
>>> 
>>> So, what’s going on?
>>> 
>>> You can’t feed the mixer outputs straight into a counter. The counter
>>> front
>>> end does not handle LF audio sine waves very well. You need to do an
>>> op-amp based limiter. A pair of OP-37’s in each leg ( or something
>>> similar)
>>> should do the trick.
>>> 
>>> Second, the offset source needs to be pretty good. A 10811 tuned high with
>>> both the mechanical trim and the EFC is a pretty good choice to start out.
>>> 
>>> If you only have one counter, simply ignore the second channel. You are now
>>> running a single mixer. It still works as a comparison between the offset
>>> oscillator
>>> and your DUT.
>>> 
>>> If you want to do it properly as a DMTD, then you set up two counters. One
>>> to measure mixer A and the other to measure mixer B.  Set them both up to
>>> measure frequency. Time tag the data files so you know which reading
>>> matches up with which.
>>> 
>>> Fun !!!
>>> 
>>> Bob
>>> 
 On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
 
 Hi again Bob
 
 I tried to do some measurements with a DMTD!
 In my junk box I found a little PCB from earlier experiments on that
>>> topic,
 with a power splitter and two SRA-3H mixers, it was even already wired
>>> for
 the DMTD configuration. So I gave it a try!
 As "transfer oscillator" I used my HP 8663A signal generator, and set it
 high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
 signals and at the mixer outputs, I put a little lowpass filter with
>>> 100Hz
 corner frequency.
 The 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

The gotcha with using a conventional counter (as opposed to a time tagger)
is that you never know when things are going to “slip” past each other. When 
they
do you get a major burp in your data. Bill’s setup is running a time tagger ….

( = It runs an internal time count, each edge gets “labeled” with a precise time
stamp that is good to nanoseconds or picoseconds. A Time Interval Counter 
simply measures the time between edges. That sounds like the same thing, but 
it’s not quite ….) 


> On Apr 13, 2020, at 6:11 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> 
> Riley suggests to use a single TIC
> 
> http://wriley.com/A%20Small%20DMTD%20System.pdf
> 
> when you look at the block diagram Fig. 4, you can see that one TIC allows
> to compare two oscillators.
> I don't know exactly how, though :-)

The gotcha with using a conventional counter (as opposed to a time tagger)
is that you never know when things are going to “slip” past each other. When 
they
do you get a major burp in your data. Bill’s setup is running a time tagger ….

> 
> OK and I see your point on the 8663. I will try to use another reference!
> I definitely didn't keep mine on for a long time. I didn't use the signal
> generator for a while now, so it was unplugged for a few months. I assume
> that's far from optimal for the 10811's stability.

Best approach is to mount your reference off on it’s own and just power it. 
That way
you don’t wear out all the guts of a fancy piece of gear.

Bob

> 
> 
> Tobias
> 
> 
> 
> On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:
> 
>> Hi
>> 
>>> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bob
>>> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
>>> 
>>> Maybe I have some good OpAmps for this purpose in my box. I will try it!
>> of
>> 
>> You need something that is quiet (like the OP-37) and has a pretty good
>> slew
>> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
>> one.
>> 
>>> course I saw that my setup was not ideal as there was a bit of noise on
>> the
>>> signals which I guess does lead to some jitter in the trigger circuit and
>>> therefore decreases my measurement noise floor.
>> 
>> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
>> digits.
>> Net result is a measurement that’s good in the vicinity of parts in 10^-13
>> 
>>> 
>>> Can you say something about how it would be done using a TIC?
>>> I don't have two identically good counters, but the HP 5335A could be
>> used
>>> as TIC, couldn't it.
>> 
>> The standard way of doing the test is to run two counters / two TIC/s /
>> two whatever’s.
>> I know of no practical way to do it with a single 5335.
>> 
>>> 
>>> And the offset source I used is not directly the HP 10811, but the HP
>> 8663A
>>> Signal generator internally uses a 10811 as reference source. But I
>> didn't
>>> wait for days for it to warm up properly. (Should I?)
>> 
>> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
>> you
>> use the 10811, it needs to be on for a while. How long very much depends
>> on
>> just how long it’s been off. Best to keep it on all the time.
>> 
>>> 
 Fun !!!
>>> Yea, of course! :-)
>>> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
>>> myself. I use TimeLab to see what numbers I should expect, and then I
>> want
>>> to compute it all myself in Matlab because I want to see how it actually
>>> works. ;-)
>> 
>> Be careful any time you code this stuff for the first time. It’s amazingly
>> easy
>> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
>> you should not code it up yourself. I generally do it in Excel or in C.
>> 
>> Bob
>> 
>>> 
>>> 
>>> Best
>>> Tobias
>>> 
>>> 
>>> 
>>> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
>>> 
 Hi
 
 Ok, first the math:
 
 If your offset oscillator is 10 Hz high at 10 MHz, you have a:
 
 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
 
 You get to add a 6 to what Time Lab shows you.
 
 If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
 gets you to 1x10^-10
 
 So, what’s going on?
 
 You can’t feed the mixer outputs straight into a counter. The counter
 front
 end does not handle LF audio sine waves very well. You need to do an
 op-amp based limiter. A pair of OP-37’s in each leg ( or something
 similar)
 should do the trick.
 
 Second, the offset source needs to be pretty good. A 10811 tuned high
>> with
 both the mechanical trim and the EFC is a pretty good choice to start
>> out.
 
 If you only have one counter, simply ignore the second channel. You are
>> now
 running a single mixer. It still works as a comparison between the
>> offset
 oscillator
 and your DUT.
 
 If you want to do it properly as a DMTD, then you set up two counters.
>> One
 to measure mixer A and the other to measure 

Re: [time-nuts] Phase measurement of my GPSDO

[Taka Kamiya via time-nuts]

I am working on pretty much the same thing.  My HP105B has an HP11801 inside.  
There is no telling how long it has been off.  Frequency wandered ALL OVER THE 
PLACE.  It took 2 months of continuous operation to settle down and just do the 
normal aging/drifting.  

I have a same question as you do.  How come not just one HP5335?  Your test 
setup has two output.  One goes to start, the other goes to stop.  Measure the 
time interval.  Isn't that the goal?

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Monday, April 13, 2020, 5:53:52 PM EDT, Bob kb8tq  wrote: 
 
 
 Hi

> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> 
> Maybe I have some good OpAmps for this purpose in my box. I will try it! of

You need something that is quiet (like the OP-37) and has a pretty good slew
rate. Past that, there are a lot of candidates. The TI OPA-228 family is one. 

> course I saw that my setup was not ideal as there was a bit of noise on the
> signals which I guess does lead to some jitter in the trigger circuit and
> therefore decreases my measurement noise floor.

Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good digits. 
Net result is a measurement that’s good in the vicinity of parts in 10^-13

> 
> Can you say something about how it would be done using a TIC?
> I don't have two identically good counters, but the HP 5335A could be used
> as TIC, couldn't it.

The standard way of doing the test is to run two counters / two TIC/s / two 
whatever’s.
I know of no practical way to do it with a single 5335.

> 
> And the offset source I used is not directly the HP 10811, but the HP 8663A
> Signal generator internally uses a 10811 as reference source. But I didn't
> wait for days for it to warm up properly. (Should I?)

The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how you
use the 10811, it needs to be on for a while. How long very much depends on 
just how long it’s been off. Best to keep it on all the time. 

> 
>> Fun !!!
> Yea, of course! :-)
> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> myself. I use TimeLab to see what numbers I should expect, and then I want
> to compute it all myself in Matlab because I want to see how it actually
> works. ;-)

Be careful any time you code this stuff for the first time. It’s amazingly easy 
( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
you should not code it up yourself. I generally do it in Excel or in C. 

Bob

> 
> 
> Best
> Tobias
> 
> 
> 
> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Ok, first the math:
>> 
>> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>> 
>> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>> 
>> You get to add a 6 to what Time Lab shows you.
>> 
>> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>> gets you to 1x10^-10
>> 
>> So, what’s going on?
>> 
>> You can’t feed the mixer outputs straight into a counter. The counter
>> front
>> end does not handle LF audio sine waves very well. You need to do an
>> op-amp based limiter. A pair of OP-37’s in each leg ( or something
>> similar)
>> should do the trick.
>> 
>> Second, the offset source needs to be pretty good. A 10811 tuned high with
>> both the mechanical trim and the EFC is a pretty good choice to start out.
>> 
>> If you only have one counter, simply ignore the second channel. You are now
>> running a single mixer. It still works as a comparison between the offset
>> oscillator
>> and your DUT.
>> 
>> If you want to do it properly as a DMTD, then you set up two counters. One
>> to measure mixer A and the other to measure mixer B.  Set them both up to
>> measure frequency. Time tag the data files so you know which reading
>> matches up with which.
>> 
>> Fun !!!
>> 
>> Bob
>> 
>>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
>>> 
>>> Hi again Bob
>>> 
>>> I tried to do some measurements with a DMTD!
>>> In my junk box I found a little PCB from earlier experiments on that
>> topic,
>>> with a power splitter and two SRA-3H mixers, it was even already wired
>> for
>>> the DMTD configuration. So I gave it a try!
>>> As "transfer oscillator" I used my HP 8663A signal generator, and set it
>>> high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
>>> signals and at the mixer outputs, I put a little lowpass filter with
>> 100Hz
>>> corner frequency.
>>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
>> tried
>>> to feed them directly into the HP 5335A TIC and used the TI mode to
>> measure
>>> the delay between the two signals.
>>> This gives 10 readings/sec, which I try to process with TimeLab.
>>> It does give some interesting graphs, but I don't know yet how to
>> correctly
>>> set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in
>> 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bob

Riley suggests to use a single TIC

http://wriley.com/A%20Small%20DMTD%20System.pdf

when you look at the block diagram Fig. 4, you can see that one TIC allows
to compare two oscillators.
I don't know exactly how, though :-)

OK and I see your point on the 8663. I will try to use another reference!
I definitely didn't keep mine on for a long time. I didn't use the signal
generator for a while now, so it was unplugged for a few months. I assume
that's far from optimal for the 10811's stability.


Tobias



On Mon., 13 Apr. 2020, 23:53 Bob kb8tq,  wrote:

> Hi
>
> > On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> >
> > Hi Bob
> > awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> >
> > Maybe I have some good OpAmps for this purpose in my box. I will try it!
> of
>
> You need something that is quiet (like the OP-37) and has a pretty good
> slew
> rate. Past that, there are a lot of candidates. The TI OPA-228 family is
> one.
>
> > course I saw that my setup was not ideal as there was a bit of noise on
> the
> > signals which I guess does lead to some jitter in the trigger circuit and
> > therefore decreases my measurement noise floor.
>
> Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good
> digits.
> Net result is a measurement that’s good in the vicinity of parts in 10^-13
>
> >
> > Can you say something about how it would be done using a TIC?
> > I don't have two identically good counters, but the HP 5335A could be
> used
> > as TIC, couldn't it.
>
> The standard way of doing the test is to run two counters / two TIC/s /
> two whatever’s.
> I know of no practical way to do it with a single 5335.
>
> >
> > And the offset source I used is not directly the HP 10811, but the HP
> 8663A
> > Signal generator internally uses a 10811 as reference source. But I
> didn't
> > wait for days for it to warm up properly. (Should I?)
>
> The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how
> you
> use the 10811, it needs to be on for a while. How long very much depends
> on
> just how long it’s been off. Best to keep it on all the time.
>
> >
> >> Fun !!!
> > Yea, of course! :-)
> > I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> > myself. I use TimeLab to see what numbers I should expect, and then I
> want
> > to compute it all myself in Matlab because I want to see how it actually
> > works. ;-)
>
> Be careful any time you code this stuff for the first time. It’s amazingly
> easy
> ( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
> you should not code it up yourself. I generally do it in Excel or in C.
>
> Bob
>
> >
> >
> > Best
> > Tobias
> >
> >
> >
> > On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> Ok, first the math:
> >>
> >> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
> >>
> >> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
> >>
> >> You get to add a 6 to what Time Lab shows you.
> >>
> >> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
> >> gets you to 1x10^-10
> >>
> >> So, what’s going on?
> >>
> >> You can’t feed the mixer outputs straight into a counter. The counter
> >> front
> >> end does not handle LF audio sine waves very well. You need to do an
> >> op-amp based limiter. A pair of OP-37’s in each leg ( or something
> >> similar)
> >> should do the trick.
> >>
> >> Second, the offset source needs to be pretty good. A 10811 tuned high
> with
> >> both the mechanical trim and the EFC is a pretty good choice to start
> out.
> >>
> >> If you only have one counter, simply ignore the second channel. You are
> now
> >> running a single mixer. It still works as a comparison between the
> offset
> >> oscillator
> >> and your DUT.
> >>
> >> If you want to do it properly as a DMTD, then you set up two counters.
> One
> >> to measure mixer A and the other to measure mixer B.  Set them both up
> to
> >> measure frequency. Time tag the data files so you know which reading
> >> matches up with which.
> >>
> >> Fun !!!
> >>
> >> Bob
> >>
> >>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> >>>
> >>> Hi again Bob
> >>>
> >>> I tried to do some measurements with a DMTD!
> >>> In my junk box I found a little PCB from earlier experiments on that
> >> topic,
> >>> with a power splitter and two SRA-3H mixers, it was even already wired
> >> for
> >>> the DMTD configuration. So I gave it a try!
> >>> As "transfer oscillator" I used my HP 8663A signal generator, and set
> it
> >>> high in frequency by 10 Hz. To the two mixers, I connected the two
> 10MHz
> >>> signals and at the mixer outputs, I put a little lowpass filter with
> >> 100Hz
> >>> corner frequency.
> >>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
> >> tried
> >>> to feed them directly into the HP 5335A TIC and used the TI mode to
> >> measure
> >>> the delay between the two signals.
> >>> This gives 10 readings/sec, which I try 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

If you don’t have a spare 10811, they run about $50 to $80 on eBay. With some 
intensive shopping, 5334 or 5335 counters are in the same vicinity. Shipping on
the counters is a bit more than shipping on the 10811’s :) 

This guy:

https://www.ebay.com/itm/HP-10811-60111-10-MHz-High-Stability-Crystal-Oscillator-with-circuit-card/253425674730?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
 


Will toss in a board that has the mating connector on it. Rumor has it that 
he’ll accept
an offer for $50 if you buy 4 pieces. The “junk” rate on his parts is no worse 
than the 
typical eBay run of the mill. The up side is that 1 in 10 actually are quite 
good (for 10811’s). 

Bob

> On Apr 13, 2020, at 5:31 PM, ew via time-nuts  
> wrote:
> 
> If you have an extra 10811 use it as an offset all mine tune 20 Hz + and I 
> have used it as offset at 5 MHz , 10 Hz at 10 MHz all will do.
> Bert Kehren
> In a message dated 4/13/2020 5:07:38 PM Eastern Standard Time, 
> tplu...@ieee.org writes:
> 
> Hi Bob
> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> 
> Maybe I have some good OpAmps for this purpose in my box. I will try it! of
> course I saw that my setup was not ideal as there was a bit of noise on the
> signals which I guess does lead to some jitter in the trigger circuit and
> therefore decreases my measurement noise floor.
> 
> Can you say something about how it would be done using a TIC?
> I don't have two identically good counters, but the HP 5335A could be used
> as TIC, couldn't it.
> 
> And the offset source I used is not directly the HP 10811, but the HP 8663A
> Signal generator internally uses a 10811 as reference source. But I didn't
> wait for days for it to warm up properly. (Should I?)
> 
>> Fun !!!
> Yea, of course! :-)
> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> myself. I use TimeLab to see what numbers I should expect, and then I want
> to compute it all myself in Matlab because I want to see how it actually
> works. ;-)
> 
> 
> Best
> Tobias
> 
> 
> 
> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Ok, first the math:
>> 
>> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>> 
>> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>> 
>> You get to add a 6 to what Time Lab shows you.
>> 
>> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>> gets you to 1x10^-10
>> 
>> So, what’s going on?
>> 
>> You can’t feed the mixer outputs straight into a counter. The counter
>> front
>> end does not handle LF audio sine waves very well. You need to do an
>> op-amp based limiter. A pair of OP-37’s in each leg ( or something
>> similar)
>> should do the trick.
>> 
>> Second, the offset source needs to be pretty good. A 10811 tuned high with
>> both the mechanical trim and the EFC is a pretty good choice to start out.
>> 
>> If you only have one counter, simply ignore the second channel. You are now
>> running a single mixer. It still works as a comparison between the offset
>> oscillator
>> and your DUT.
>> 
>> If you want to do it properly as a DMTD, then you set up two counters. One
>> to measure mixer A and the other to measure mixer B.  Set them both up to
>> measure frequency. Time tag the data files so you know which reading
>> matches up with which.
>> 
>> Fun !!!
>> 
>> Bob
>> 
>>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
>>> 
>>> Hi again Bob
>>> 
>>> I tried to do some measurements with a DMTD!
>>> In my junk box I found a little PCB from earlier experiments on that
>> topic,
>>> with a power splitter and two SRA-3H mixers, it was even already wired
>> for
>>> the DMTD configuration. So I gave it a try!
>>> As "transfer oscillator" I used my HP 8663A signal generator, and set it
>>> high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
>>> signals and at the mixer outputs, I put a little lowpass filter with
>> 100Hz
>>> corner frequency.
>>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
>> tried
>>> to feed them directly into the HP 5335A TIC and used the TI mode to
>> measure
>>> the delay between the two signals.
>>> This gives 10 readings/sec, which I try to process with TimeLab.
>>> It does give some interesting graphs, but I don't know yet how to
>> correctly
>>> set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in
>> the
>>> order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
>>> simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
>>> this would mean that my real ADEV is in the range of 1e-11 to 1e-12,
>> which
>>> is indeed my target value, BUT I expect that things are not that simple.
>>> (i.e. what if I didn't set the transfer oscillator high by +10Hz but only
>>> by 9.9Hz for 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

> On Apr 13, 2020, at 5:06 PM, Tobias Pluess  wrote:
> 
> Hi Bob
> awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)
> 
> Maybe I have some good OpAmps for this purpose in my box. I will try it! of

You need something that is quiet (like the OP-37) and has a pretty good slew
rate. Past that, there are a lot of candidates. The TI OPA-228 family is one. 

> course I saw that my setup was not ideal as there was a bit of noise on the
> signals which I guess does lead to some jitter in the trigger circuit and
> therefore decreases my measurement noise floor.

Typically a good limiter takes you from 3 or 4 digits up to 6 or 7 good digits. 
Net result is a measurement that’s good in the vicinity of parts in 10^-13

> 
> Can you say something about how it would be done using a TIC?
> I don't have two identically good counters, but the HP 5335A could be used
> as TIC, couldn't it.

The standard way of doing the test is to run two counters / two TIC/s / two 
whatever’s.
I know of no practical way to do it with a single 5335.

> 
> And the offset source I used is not directly the HP 10811, but the HP 8663A
> Signal generator internally uses a 10811 as reference source. But I didn't
> wait for days for it to warm up properly. (Should I?)

The 8663 synthesizer adds a *lot* of crud to the 10811. Regardless of how you
use the 10811, it needs to be on for a while. How long very much depends on 
just how long it’s been off. Best to keep it on all the time. 

> 
>> Fun !!!
> Yea, of course! :-)
> I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
> myself. I use TimeLab to see what numbers I should expect, and then I want
> to compute it all myself in Matlab because I want to see how it actually
> works. ;-)

Be careful any time you code this stuff for the first time. It’s amazingly easy 
( = I’ve done it ….) to make minor errors. That’s in no way to suggest that
you should not code it up yourself. I generally do it in Excel or in C. 

Bob

> 
> 
> Best
> Tobias
> 
> 
> 
> On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> Ok, first the math:
>> 
>> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>> 
>> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>> 
>> You get to add a 6 to what Time Lab shows you.
>> 
>> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
>> gets you to 1x10^-10
>> 
>> So, what’s going on?
>> 
>> You can’t feed the mixer outputs straight into a counter. The counter
>> front
>> end does not handle LF audio sine waves very well. You need to do an
>> op-amp based limiter. A pair of OP-37’s in each leg ( or something
>> similar)
>> should do the trick.
>> 
>> Second, the offset source needs to be pretty good. A 10811 tuned high with
>> both the mechanical trim and the EFC is a pretty good choice to start out.
>> 
>> If you only have one counter, simply ignore the second channel. You are now
>> running a single mixer. It still works as a comparison between the offset
>> oscillator
>> and your DUT.
>> 
>> If you want to do it properly as a DMTD, then you set up two counters. One
>> to measure mixer A and the other to measure mixer B.  Set them both up to
>> measure frequency. Time tag the data files so you know which reading
>> matches up with which.
>> 
>> Fun !!!
>> 
>> Bob
>> 
>>> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
>>> 
>>> Hi again Bob
>>> 
>>> I tried to do some measurements with a DMTD!
>>> In my junk box I found a little PCB from earlier experiments on that
>> topic,
>>> with a power splitter and two SRA-3H mixers, it was even already wired
>> for
>>> the DMTD configuration. So I gave it a try!
>>> As "transfer oscillator" I used my HP 8663A signal generator, and set it
>>> high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
>>> signals and at the mixer outputs, I put a little lowpass filter with
>> 100Hz
>>> corner frequency.
>>> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
>> tried
>>> to feed them directly into the HP 5335A TIC and used the TI mode to
>> measure
>>> the delay between the two signals.
>>> This gives 10 readings/sec, which I try to process with TimeLab.
>>> It does give some interesting graphs, but I don't know yet how to
>> correctly
>>> set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in
>> the
>>> order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
>>> simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
>>> this would mean that my real ADEV is in the range of 1e-11 to 1e-12,
>> which
>>> is indeed my target value, BUT I expect that things are not that simple.
>>> (i.e. what if I didn't set the transfer oscillator high by +10Hz but only
>>> by 9.9Hz for example).
>>> Can you give some hints on that?
>>> Of course I also did the noise floor test (i.e. I fed the 10MHz signal
>> into
>>> a power splitter and connected the two outputs to my DMTD with two
>>> 

Re: [time-nuts] Phase measurement of my GPSDO

[ew via time-nuts]

If you have an extra 10811 use it as an offset all mine tune 20 Hz + and I have 
used it as offset at 5 MHz , 10 Hz at 10 MHz all will do.
Bert Kehren
In a message dated 4/13/2020 5:07:38 PM Eastern Standard Time, tplu...@ieee.org 
writes:

Hi Bob
awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)

Maybe I have some good OpAmps for this purpose in my box. I will try it! of
course I saw that my setup was not ideal as there was a bit of noise on the
signals which I guess does lead to some jitter in the trigger circuit and
therefore decreases my measurement noise floor.

Can you say something about how it would be done using a TIC?
I don't have two identically good counters, but the HP 5335A could be used
as TIC, couldn't it.

And the offset source I used is not directly the HP 10811, but the HP 8663A
Signal generator internally uses a 10811 as reference source. But I didn't
wait for days for it to warm up properly. (Should I?)

> Fun !!!
Yea, of course! :-)
I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
myself. I use TimeLab to see what numbers I should expect, and then I want
to compute it all myself in Matlab because I want to see how it actually
works. ;-)


Best
Tobias



On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:

> Hi
>
> Ok, first the math:
>
> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>
> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>
> You get to add a 6 to what Time Lab shows you.
>
> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
> gets you to 1x10^-10
>
> So, what’s going on?
>
> You can’t feed the mixer outputs straight into a counter. The counter
> front
> end does not handle LF audio sine waves very well. You need to do an
> op-amp based limiter. A pair of OP-37’s in each leg ( or something
> similar)
> should do the trick.
>
> Second, the offset source needs to be pretty good. A 10811 tuned high with
> both the mechanical trim and the EFC is a pretty good choice to start out.
>
> If you only have one counter, simply ignore the second channel. You are now
> running a single mixer. It still works as a comparison between the offset
> oscillator
> and your DUT.
>
> If you want to do it properly as a DMTD, then you set up two counters. One
> to measure mixer A and the other to measure mixer B.  Set them both up to
> measure frequency. Time tag the data files so you know which reading
> matches up with which.
>
> Fun !!!
>
> Bob
>
> > On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> >
> > Hi again Bob
> >
> > I tried to do some measurements with a DMTD!
> > In my junk box I found a little PCB from earlier experiments on that
> topic,
> > with a power splitter and two SRA-3H mixers, it was even already wired
> for
> > the DMTD configuration. So I gave it a try!
> > As "transfer oscillator" I used my HP 8663A signal generator, and set it
> > high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
> > signals and at the mixer outputs, I put a little lowpass filter with
> 100Hz
> > corner frequency.
> > The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
> tried
> > to feed them directly into the HP 5335A TIC and used the TI mode to
> measure
> > the delay between the two signals.
> > This gives 10 readings/sec, which I try to process with TimeLab.
> > It does give some interesting graphs, but I don't know yet how to
> correctly
> > set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in
> the
> > order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
> > simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
> > this would mean that my real ADEV is in the range of 1e-11 to 1e-12,
> which
> > is indeed my target value, BUT I expect that things are not that simple.
> > (i.e. what if I didn't set the transfer oscillator high by +10Hz but only
> > by 9.9Hz for example).
> > Can you give some hints on that?
> > Of course I also did the noise floor test (i.e. I fed the 10MHz signal
> into
> > a power splitter and connected the two outputs to my DMTD with two
> > different lenghts of cables. This gave results starting at 1e-4 going
> down
> > to 1e-7, maybe it would have gone even lower but I measured only for a
> > couple of minutes.)
> >
> > Can you give some hints on that?
> >
> > Best
> > Tobias
> > HB9FSX
> >
> >
> >
> >
> > On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> >>
> >>> Hi
> >>>
> >>> The quick way to do this is with a single mixer. Take something like an
> >>> old
> >>> 10811 and use the coarse tune to set it high in frequency by 5 to 10
> Hz.
> >>>
> >>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
> tone.
> >>> That tone is the *difference* between the 10811 and your device under
> >>> test.
> >>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >>>
> >>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> >>> shift
> >>> ( 0.1 ppm ). At 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bob
awesome, thanks! of course it is 1e6, not 1e7, I got a mistake :-)

Maybe I have some good OpAmps for this purpose in my box. I will try it! of
course I saw that my setup was not ideal as there was a bit of noise on the
signals which I guess does lead to some jitter in the trigger circuit and
therefore decreases my measurement noise floor.

Can you say something about how it would be done using a TIC?
I don't have two identically good counters, but the HP 5335A could be used
as TIC, couldn't it.

And the offset source I used is not directly the HP 10811, but the HP 8663A
Signal generator internally uses a 10811 as reference source. But I didn't
wait for days for it to warm up properly. (Should I?)

> Fun !!!
Yea, of course! :-)
I already implemented the ADEV, MDEV and TDEV calculations in Matlab by
myself. I use TimeLab to see what numbers I should expect, and then I want
to compute it all myself in Matlab because I want to see how it actually
works. ;-)


Best
Tobias



On Mon, Apr 13, 2020 at 10:50 PM Bob kb8tq  wrote:

> Hi
>
> Ok, first the math:
>
> If your offset oscillator is 10 Hz high at 10 MHz, you have a:
>
> 10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD
>
> You get to add a 6 to what Time Lab shows you.
>
> If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
> gets you to 1x10^-10
>
> So, what’s going on?
>
> You can’t feed the mixer outputs straight into a counter. The counter
> front
> end does not handle LF audio sine waves very well. You need to do an
> op-amp based limiter. A pair of OP-37’s in each leg ( or something
> similar)
> should do the trick.
>
> Second, the offset source needs to be pretty good. A 10811 tuned high with
> both the mechanical trim and the EFC is a pretty good choice to start out.
>
> If you only have one counter, simply ignore the second channel. You are now
> running a single mixer. It still works as a comparison between the offset
> oscillator
> and your DUT.
>
> If you want to do it properly as a DMTD, then you set up two counters. One
> to measure mixer A and the other to measure mixer B.  Set them both up to
> measure frequency. Time tag the data files so you know which reading
> matches up with which.
>
> Fun !!!
>
> Bob
>
> > On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> >
> > Hi again Bob
> >
> > I tried to do some measurements with a DMTD!
> > In my junk box I found a little PCB from earlier experiments on that
> topic,
> > with a power splitter and two SRA-3H mixers, it was even already wired
> for
> > the DMTD configuration. So I gave it a try!
> > As "transfer oscillator" I used my HP 8663A signal generator, and set it
> > high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
> > signals and at the mixer outputs, I put a little lowpass filter with
> 100Hz
> > corner frequency.
> > The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I
> tried
> > to feed them directly into the HP 5335A TIC and used the TI mode to
> measure
> > the delay between the two signals.
> > This gives 10 readings/sec, which I try to process with TimeLab.
> > It does give some interesting graphs, but I don't know yet how to
> correctly
> > set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in
> the
> > order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
> > simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
> > this would mean that my real ADEV is in the range of 1e-11 to 1e-12,
> which
> > is indeed my target value, BUT I expect that things are not that simple.
> > (i.e. what if I didn't set the transfer oscillator high by +10Hz but only
> > by 9.9Hz for example).
> > Can you give some hints on that?
> > Of course I also did the noise floor test (i.e. I fed the 10MHz signal
> into
> > a power splitter and connected the two outputs to my DMTD with two
> > different lenghts of cables. This gave results starting at 1e-4 going
> down
> > to 1e-7, maybe it would have gone even lower but I measured only for a
> > couple of minutes.)
> >
> > Can you give some hints on that?
> >
> > Best
> > Tobias
> > HB9FSX
> >
> >
> >
> >
> > On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> >>
> >>> Hi
> >>>
> >>> The quick way to do this is with a single mixer. Take something like an
> >>> old
> >>> 10811 and use the coarse tune to set it high in frequency by 5 to 10
> Hz.
> >>>
> >>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
> tone.
> >>> That tone is the *difference* between the 10811 and your device under
> >>> test.
> >>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >>>
> >>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> >>> shift
> >>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> change
> >>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase
> ).
> >>>
> >>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
> not
> >>> that
> 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

Ok, first the math:

If your offset oscillator is 10 Hz high at 10 MHz, you have a:

10,000,000 / 10 = 1,000,000 : 1 multiplier in front of the DMTD

You get to add a 6 to what Time Lab shows you.

If you are getting an ADEV at 1 second of 1x10^-4 then that multiplier
gets you to 1x10^-10

So, what’s going on? 

You can’t feed the mixer outputs straight into a counter. The counter front 
end does not handle LF audio sine waves very well. You need to do an 
op-amp based limiter. A pair of OP-37’s in each leg ( or something similar) 
should do the trick.

Second, the offset source needs to be pretty good. A 10811 tuned high with 
both the mechanical trim and the EFC is a pretty good choice to start out. 

If you only have one counter, simply ignore the second channel. You are now
running a single mixer. It still works as a comparison between the offset 
oscillator 
and your DUT.

If you want to do it properly as a DMTD, then you set up two counters. One
to measure mixer A and the other to measure mixer B.  Set them both up to 
measure frequency. Time tag the data files so you know which reading 
matches up with which. 

Fun !!!

Bob

> On Apr 13, 2020, at 3:18 PM, Tobias Pluess  wrote:
> 
> Hi again Bob
> 
> I tried to do some measurements with a DMTD!
> In my junk box I found a little PCB from earlier experiments on that topic,
> with a power splitter and two SRA-3H mixers, it was even already wired for
> the DMTD configuration. So I gave it a try!
> As "transfer oscillator" I used my HP 8663A signal generator, and set it
> high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
> signals and at the mixer outputs, I put a little lowpass filter with 100Hz
> corner frequency.
> The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I tried
> to feed them directly into the HP 5335A TIC and used the TI mode to measure
> the delay between the two signals.
> This gives 10 readings/sec, which I try to process with TimeLab.
> It does give some interesting graphs, but I don't know yet how to correctly
> set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in the
> order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
> simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
> this would mean that my real ADEV is in the range of 1e-11 to 1e-12, which
> is indeed my target value, BUT I expect that things are not that simple.
> (i.e. what if I didn't set the transfer oscillator high by +10Hz but only
> by 9.9Hz for example).
> Can you give some hints on that?
> Of course I also did the noise floor test (i.e. I fed the 10MHz signal into
> a power splitter and connected the two outputs to my DMTD with two
> different lenghts of cables. This gave results starting at 1e-4 going down
> to 1e-7, maybe it would have gone even lower but I measured only for a
> couple of minutes.)
> 
> Can you give some hints on that?
> 
> Best
> Tobias
> HB9FSX
> 
> 
> 
> 
> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
>> 
>>> Hi
>>> 
>>> The quick way to do this is with a single mixer. Take something like an
>>> old
>>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>>> 
>>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
>>> That tone is the *difference* between the 10811 and your device under
>>> test.
>>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>>> 
>>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
>>> shift
>>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
>>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>>> 
>>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
>>> that
>>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>>> second.
>>> 
>>> The reason its not quite that simple is that the input circuit on the
>>> counter
>>> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
>>> RF signal. Instead of getting 9 digits a second, you probably will get
>>> three
>>> *good* digits a second and another 6 digits of noise.
>>> 
>>> The good news is that an op amp used as a preamp ( to get you up to maybe
>>> 32 V p-p rather than a volt or so) and another op amp or three as
>>> limiters will
>>> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
>>> and low pass filter ( DC offsets can be a problem ….) and you have a
>>> working
>>> device that gets into the parts in 10^-13 with your 5335.
>>> 
>>> It all can be done with point to point wiring. No need for a PCB layout.
>>> Be
>>> careful that the +/- 18V supplies to the op amp *both* go on and off at
>>> the
>>> same time ….
>>> 
>>> Bob
>>> 
>> 
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Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi again Bob

I tried to do some measurements with a DMTD!
In my junk box I found a little PCB from earlier experiments on that topic,
with a power splitter and two SRA-3H mixers, it was even already wired for
the DMTD configuration. So I gave it a try!
As "transfer oscillator" I used my HP 8663A signal generator, and set it
high in frequency by 10 Hz. To the two mixers, I connected the two 10MHz
signals and at the mixer outputs, I put a little lowpass filter with 100Hz
corner frequency.
The output signals from the two SRA-3 mixers are almost 0.5Vpp, so I tried
to feed them directly into the HP 5335A TIC and used the TI mode to measure
the delay between the two signals.
This gives 10 readings/sec, which I try to process with TimeLab.
It does give some interesting graphs, but I don't know yet how to correctly
set up TimeLab for this kind of measurement. I.e. now, I get an ADEV in the
order of 1e-4 (at tau=1sec) to 1e-5 (at tau=500sec). So does that mean I
simply need to multiply this with 1e-7 to get the *real* ADEV at 10MHz?
this would mean that my real ADEV is in the range of 1e-11 to 1e-12, which
is indeed my target value, BUT I expect that things are not that simple.
(i.e. what if I didn't set the transfer oscillator high by +10Hz but only
by 9.9Hz for example).
Can you give some hints on that?
Of course I also did the noise floor test (i.e. I fed the 10MHz signal into
a power splitter and connected the two outputs to my DMTD with two
different lenghts of cables. This gave results starting at 1e-4 going down
to 1e-7, maybe it would have gone even lower but I measured only for a
couple of minutes.)

Can you give some hints on that?

Best
Tobias
HB9FSX




On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
>
>> Hi
>>
>> The quick way to do this is with a single mixer. Take something like an
>> old
>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>>
>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
>> That tone is the *difference* between the 10811 and your device under
>> test.
>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>>
>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
>> shift
>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>>
>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
>> that
>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>> second.
>>
>> The reason its not quite that simple is that the input circuit on the
>> counter
>> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
>> RF signal. Instead of getting 9 digits a second, you probably will get
>> three
>> *good* digits a second and another 6 digits of noise.
>>
>> The good news is that an op amp used as a preamp ( to get you up to maybe
>> 32 V p-p rather than a volt or so) and another op amp or three as
>> limiters will
>> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
>> and low pass filter ( DC offsets can be a problem ….) and you have a
>> working
>> device that gets into the parts in 10^-13 with your 5335.
>>
>> It all can be done with point to point wiring. No need for a PCB layout.
>> Be
>> careful that the +/- 18V supplies to the op amp *both* go on and off at
>> the
>> same time ….
>>
>> Bob
>>
>
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Re: [time-nuts] Phase measurement of my GPSDO

[John Ackermann N8UR]

Hi Tobias --

Several years ago, with a bunch of help from Bruce and John Miles, I did
a very high isolation, very low phase noise buffer amp design that TAPR
sold for a limited run.  It's built with surface mount parts but they
are user-friendly sized.

Details and schematic are at https://www.febo.com/pages/TNS-BUF.  The
TAPR product page and link to manual are at
https://tapr.org/product/tns-buf-isolation-amplifier/

It is possible we might still have some bare boards available; I need to
check on that.  It's also possible that if there's enough interest, we
could do another small production run (we'd need at least 25 orders to
make it economically feasible).

John


On 4/3/20 8:09 PM, Tobias Pluess wrote:
> Hi Bruce
> 
> the NIST design you mentioned - do you mean that publication where they
> used 2N's for a diode ring mixer? if so I can perhaps build this as
> well because I think I even have some 2Ns in my home lab :-)
> Concerning the RPD vs. TUF mixers - what is the actual property which makes
> the RPD "better" than the TUF?
> 
> Thanks,
> Tobias
> 
> On Sat., 4 Apr. 2020, 02:01 Bruce Griffiths, 
> wrote:
> 
>> Tobias
>>
>> That would certainly work for a start and have a better performance that a
>> counter front end.
>> The performance can be estimated using the tools at the link Bob provided.
>> Lower noise opamps will improve the performance somewhat.
>> A wider bandwidth opamp with a higher slew rate may be useful for the
>> final stage of a Collins style zero crossing  detector.
>> The RPD series of phase detectors will have better performance than the
>> TUF-1.
>> For the ultimate performance at low offset frequencies one can build a
>> mixer using diode connected BJTs as NIST have done.
>>
>> Bruce
>>> On 04 April 2020 at 12:38 Tobias Pluess  wrote:
>>>
>>>
>>> Hi Bruce
>>>
>>> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
>> AD8626.
>>> So, if I connect the OpAmps appropriately with some diode limiters as you
>>> suggest, would you say this would give an acceptable DMTD system?
>>> If so it sounds like something that can easily be built on a breadbord or
>>> in manhattan style, as Bob already mentioned. That would be really cool.
>>> I think a while ago I asked a question which goes in a similar direction
>> -
>>> which mixers are better as phase detectors (to build a PLL for phase
>> noise
>>> measurement) and which ones should be used as actual mixers (like in this
>>> case).
>>>
>>>
>>> Tobias
>>> HB9FSX
>>>
>>> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, >>
>>> wrote:
>>>
 One can merely add diodes to the opamp feedback network form a feedback
 limiter and maintain the opamp outputs within the range for which the
>> opamp
 is well behaved whilst maintaining the increase in slew rate for the
>> output.

 Bruce
> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
>
>
> Jup, some of them even have phase reversal when they are overloaded,
>> so
 it
> is perhaps not a good idea in general, but I think there are opamps
>> which
> are specified for this.
>
> Tobias
>
>
> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
 wrote:
>
>> Caution: opamps make terrible limiters- their overload behavior is
>> generally ugly
>> and unpredictable.  It's much better to use a genuine level
 comparator, and
>> wire it
>> up so that it has a modest amount of hysteresis.
>>
>> Dana
>>
>>
>> On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
>>
>>> Hi
>>>
>>> The quick way to do this is with a single mixer. Take something
>> like
 an
>> old
>>> 10811 and use the coarse tune to set it high in frequency by 5
>> to 10
 Hz.
>>>
>>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz
>> audio
 tone.
>>> That tone is the *difference* between the 10811 and your device
>> under
>>> test.
>>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>>>
>>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very
 small
>>> shift
>>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
 change
>>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
 increase ).
>>>
>>> *IF* you could tack that on to the ADEV plot of your 5335 ( no,
>> it’s
 not
>>> that
>>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>>> second.
>>>
>>> The reason its not quite that simple is that the input circuit
>> on the
>>> counter
>>> really does not handle a 10 Hz audio tone as well as it handles
>> a 10
 MHz
>>> RF signal. Instead of getting 9 digits a second, you probably
>> will
 get
>>> three
>>> *good* digits a second and another 6 digits of noise.
>>>
>>> The good news is that an op amp used as a preamp ( to get you up
>> to
 maybe
>>> 32 V p-p rather than a volt or so) and 

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

Tobias

The diode connected BJT (2N) mixer is compared with various commercial 
mixers and phase detectors in a NIST paper that has a graph showing the PN of 
various mixers as a function of offset frequency.

The RPD series phase detectors have a higher output and lower PN than most 
mixers.
The output depends on the input characteristics of the lowpass filter at the IF 
output.
A capacitive load at this port increases the output at the expense of isolation 
between ports etc.
These interactions are clearly shown in Spice simulations of such mixers.

Bruce 

> On 04 April 2020 at 13:09 Tobias Pluess  wrote:
> 
> 
> Hi Bruce
> 
> the NIST design you mentioned - do you mean that publication where they
> used 2N's for a diode ring mixer? if so I can perhaps build this as
> well because I think I even have some 2Ns in my home lab :-)
> Concerning the RPD vs. TUF mixers - what is the actual property which makes
> the RPD "better" than the TUF?
> 
> Thanks,
> Tobias
> 
> On Sat., 4 Apr. 2020, 02:01 Bruce Griffiths, 
> wrote:
> 
> > Tobias
> >
> > That would certainly work for a start and have a better performance that a
> > counter front end.
> > The performance can be estimated using the tools at the link Bob provided.
> > Lower noise opamps will improve the performance somewhat.
> > A wider bandwidth opamp with a higher slew rate may be useful for the
> > final stage of a Collins style zero crossing  detector.
> > The RPD series of phase detectors will have better performance than the
> > TUF-1.
> > For the ultimate performance at low offset frequencies one can build a
> > mixer using diode connected BJTs as NIST have done.
> >
> > Bruce
> > > On 04 April 2020 at 12:38 Tobias Pluess  wrote:
> > >
> > >
> > > Hi Bruce
> > >
> > > I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
> > AD8626.
> > > So, if I connect the OpAmps appropriately with some diode limiters as you
> > > suggest, would you say this would give an acceptable DMTD system?
> > > If so it sounds like something that can easily be built on a breadbord or
> > > in manhattan style, as Bob already mentioned. That would be really cool.
> > > I think a while ago I asked a question which goes in a similar direction
> > -
> > > which mixers are better as phase detectors (to build a PLL for phase
> > noise
> > > measurement) and which ones should be used as actual mixers (like in this
> > > case).
> > >
> > >
> > > Tobias
> > > HB9FSX
> > >
> > > On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths,  > >
> > > wrote:
> > >
> > > > One can merely add diodes to the opamp feedback network form a feedback
> > > > limiter and maintain the opamp outputs within the range for which the
> > opamp
> > > > is well behaved whilst maintaining the increase in slew rate for the
> > output.
> > > >
> > > > Bruce
> > > > > On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> > > > >
> > > > >
> > > > > Jup, some of them even have phase reversal when they are overloaded,
> > so
> > > > it
> > > > > is perhaps not a good idea in general, but I think there are opamps
> > which
> > > > > are specified for this.
> > > > >
> > > > > Tobias
> > > > >
> > > > >
> > > > > On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> > > > wrote:
> > > > >
> > > > > > Caution: opamps make terrible limiters- their overload behavior is
> > > > > > generally ugly
> > > > > > and unpredictable.  It's much better to use a genuine level
> > > > comparator, and
> > > > > > wire it
> > > > > > up so that it has a modest amount of hysteresis.
> > > > > >
> > > > > > Dana
> > > > > >
> > > > > >
> > > > > > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> > > > > >
> > > > > > > Hi
> > > > > > >
> > > > > > > The quick way to do this is with a single mixer. Take something
> > like
> > > > an
> > > > > > old
> > > > > > > 10811 and use the coarse tune to set it high in frequency by 5
> > to 10
> > > > Hz.
> > > > > > >
> > > > > > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz
> > audio
> > > > tone.
> > > > > > > That tone is the *difference* between the 10811 and your device
> > under
> > > > > > > test.
> > > > > > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > > > > > >
> > > > > > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very
> > > > small
> > > > > > > shift
> > > > > > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> > > > change
> > > > > > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
> > > > increase ).
> > > > > > >
> > > > > > > *IF* you could tack that on to the ADEV plot of your 5335 ( no,
> > it’s
> > > > not
> > > > > > > that
> > > > > > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > > > > > second.
> > > > > > >
> > > > > > > The reason its not quite that simple is that the input circuit
> > on the
> > > > > > > counter
> > > > > > > really does not handle a 10 Hz audio tone as well as it handles
> > a 10
> > > > MHz
> > > > > > > RF signal. Instead of 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

A single mixer compares two devices. Provided you can offset the frequency
of one of your devices, it does exactly what you need to do.

Bob

> On Apr 3, 2020, at 7:56 PM, Tobias Pluess  wrote:
> 
> Hey Bob
> 
> hmm how would a *single mixer* design look like? in the end I need to
> compare *two* clock signals, so a single mixer won't be of much use, would
> it?
> 
> Tobias
> 
> On Sat., 4 Apr. 2020, 01:51 Bob kb8tq,  wrote:
> 
>> Hi
>> 
>> A *single mixer* setup is something that can be done quickly and easily.
>> The *dual mixer* setup brings in a bunch of issues that are far more
>> easily handled on a good PCB layout.
>> 
>> Either way, it is going to work far better with the right sort of low noise
>> ( = single digit nanovolt per root hz …) op amps than with whatever
>> you happen across first ….
>> 
>> Bob
>> 
>>> On Apr 3, 2020, at 7:38 PM, Tobias Pluess  wrote:
>>> 
>>> Hi Bruce
>>> 
>>> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
>> AD8626.
>>> So, if I connect the OpAmps appropriately with some diode limiters as you
>>> suggest, would you say this would give an acceptable DMTD system?
>>> If so it sounds like something that can easily be built on a breadbord or
>>> in manhattan style, as Bob already mentioned. That would be really cool.
>>> I think a while ago I asked a question which goes in a similar direction
>> -
>>> which mixers are better as phase detectors (to build a PLL for phase
>> noise
>>> measurement) and which ones should be used as actual mixers (like in this
>>> case).
>>> 
>>> 
>>> Tobias
>>> HB9FSX
>>> 
>>> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, >> 
>>> wrote:
>>> 
 One can merely add diodes to the opamp feedback network form a feedback
 limiter and maintain the opamp outputs within the range for which the
>> opamp
 is well behaved whilst maintaining the increase in slew rate for the
>> output.
 
 Bruce
> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> 
> 
> Jup, some of them even have phase reversal when they are overloaded, so
 it
> is perhaps not a good idea in general, but I think there are opamps
>> which
> are specified for this.
> 
> Tobias
> 
> 
> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
 wrote:
> 
>> Caution: opamps make terrible limiters- their overload behavior is
>> generally ugly
>> and unpredictable.  It's much better to use a genuine level
 comparator, and
>> wire it
>> up so that it has a modest amount of hysteresis.
>> 
>> Dana
>> 
>> 
>> On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
>> 
>>> Hi
>>> 
>>> The quick way to do this is with a single mixer. Take something like
 an
>> old
>>> 10811 and use the coarse tune to set it high in frequency by 5 to 10
 Hz.
>>> 
>>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
 tone.
>>> That tone is the *difference* between the 10811 and your device under
>>> test.
>>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>>> 
>>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very
 small
>>> shift
>>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
 change
>>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
 increase ).
>>> 
>>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
 not
>>> that
>>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>>> second.
>>> 
>>> The reason its not quite that simple is that the input circuit on the
>>> counter
>>> really does not handle a 10 Hz audio tone as well as it handles a 10
 MHz
>>> RF signal. Instead of getting 9 digits a second, you probably will
 get
>>> three
>>> *good* digits a second and another 6 digits of noise.
>>> 
>>> The good news is that an op amp used as a preamp ( to get you up to
 maybe
>>> 32 V p-p rather than a volt or so) and another op amp or three as
>> limiters
>>> will
>>> get you up around 6 or 7 good digits. Toss in a cap or two as a high
 pass
>>> and low pass filter ( DC offsets can be a problem ….) and you have a
>>> working
>>> device that gets into the parts in 10^-13 with your 5335.
>>> 
>>> It all can be done with point to point wiring. No need for a PCB
 layout.
>>> Be
>>> careful that the +/- 18V supplies to the op amp *both* go on and off
 at
>>> the
>>> same time ….
>>> 
>>> Bob
>>> 
 On Apr 3, 2020, at 5:13 AM, Tobias Pluess 
 wrote:
 
 hi John
 
 yes I know the DMTD method, and indeed I am planing to build my own
>> DMTD
 system, something similar to the "Small DMTD system" published by
>> Riley (
 https://www.wriley.com/A Small DMTD System.pdf).
 However I am unsure whether 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bruce

the NIST design you mentioned - do you mean that publication where they
used 2N's for a diode ring mixer? if so I can perhaps build this as
well because I think I even have some 2Ns in my home lab :-)
Concerning the RPD vs. TUF mixers - what is the actual property which makes
the RPD "better" than the TUF?

Thanks,
Tobias

On Sat., 4 Apr. 2020, 02:01 Bruce Griffiths, 
wrote:

> Tobias
>
> That would certainly work for a start and have a better performance that a
> counter front end.
> The performance can be estimated using the tools at the link Bob provided.
> Lower noise opamps will improve the performance somewhat.
> A wider bandwidth opamp with a higher slew rate may be useful for the
> final stage of a Collins style zero crossing  detector.
> The RPD series of phase detectors will have better performance than the
> TUF-1.
> For the ultimate performance at low offset frequencies one can build a
> mixer using diode connected BJTs as NIST have done.
>
> Bruce
> > On 04 April 2020 at 12:38 Tobias Pluess  wrote:
> >
> >
> > Hi Bruce
> >
> > I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
> AD8626.
> > So, if I connect the OpAmps appropriately with some diode limiters as you
> > suggest, would you say this would give an acceptable DMTD system?
> > If so it sounds like something that can easily be built on a breadbord or
> > in manhattan style, as Bob already mentioned. That would be really cool.
> > I think a while ago I asked a question which goes in a similar direction
> -
> > which mixers are better as phase detectors (to build a PLL for phase
> noise
> > measurement) and which ones should be used as actual mixers (like in this
> > case).
> >
> >
> > Tobias
> > HB9FSX
> >
> > On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths,  >
> > wrote:
> >
> > > One can merely add diodes to the opamp feedback network form a feedback
> > > limiter and maintain the opamp outputs within the range for which the
> opamp
> > > is well behaved whilst maintaining the increase in slew rate for the
> output.
> > >
> > > Bruce
> > > > On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> > > >
> > > >
> > > > Jup, some of them even have phase reversal when they are overloaded,
> so
> > > it
> > > > is perhaps not a good idea in general, but I think there are opamps
> which
> > > > are specified for this.
> > > >
> > > > Tobias
> > > >
> > > >
> > > > On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> > > wrote:
> > > >
> > > > > Caution: opamps make terrible limiters- their overload behavior is
> > > > > generally ugly
> > > > > and unpredictable.  It's much better to use a genuine level
> > > comparator, and
> > > > > wire it
> > > > > up so that it has a modest amount of hysteresis.
> > > > >
> > > > > Dana
> > > > >
> > > > >
> > > > > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> > > > >
> > > > > > Hi
> > > > > >
> > > > > > The quick way to do this is with a single mixer. Take something
> like
> > > an
> > > > > old
> > > > > > 10811 and use the coarse tune to set it high in frequency by 5
> to 10
> > > Hz.
> > > > > >
> > > > > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz
> audio
> > > tone.
> > > > > > That tone is the *difference* between the 10811 and your device
> under
> > > > > > test.
> > > > > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > > > > >
> > > > > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very
> > > small
> > > > > > shift
> > > > > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> > > change
> > > > > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
> > > increase ).
> > > > > >
> > > > > > *IF* you could tack that on to the ADEV plot of your 5335 ( no,
> it’s
> > > not
> > > > > > that
> > > > > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > > > > second.
> > > > > >
> > > > > > The reason its not quite that simple is that the input circuit
> on the
> > > > > > counter
> > > > > > really does not handle a 10 Hz audio tone as well as it handles
> a 10
> > > MHz
> > > > > > RF signal. Instead of getting 9 digits a second, you probably
> will
> > > get
> > > > > > three
> > > > > > *good* digits a second and another 6 digits of noise.
> > > > > >
> > > > > > The good news is that an op amp used as a preamp ( to get you up
> to
> > > maybe
> > > > > > 32 V p-p rather than a volt or so) and another op amp or three as
> > > > > limiters
> > > > > > will
> > > > > > get you up around 6 or 7 good digits. Toss in a cap or two as a
> high
> > > pass
> > > > > > and low pass filter ( DC offsets can be a problem ….) and you
> have a
> > > > > > working
> > > > > > device that gets into the parts in 10^-13 with your 5335.
> > > > > >
> > > > > > It all can be done with point to point wiring. No need for a PCB
> > > layout.
> > > > > > Be
> > > > > > careful that the +/- 18V supplies to the op amp *both* go on and
> off
> > > at
> > > > > > the
> > > > > > same time ….
> > > 

Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

Tobias

That would certainly work for a start and have a better performance that a 
counter front end.
The performance can be estimated using the tools at the link Bob provided.
Lower noise opamps will improve the performance somewhat.
A wider bandwidth opamp with a higher slew rate may be useful for the final 
stage of a Collins style zero crossing  detector. 
The RPD series of phase detectors will have better performance than the TUF-1.
For the ultimate performance at low offset frequencies one can build a mixer 
using diode connected BJTs as NIST have done.

Bruce
> On 04 April 2020 at 12:38 Tobias Pluess  wrote:
> 
> 
> Hi Bruce
> 
> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps AD8626.
> So, if I connect the OpAmps appropriately with some diode limiters as you
> suggest, would you say this would give an acceptable DMTD system?
> If so it sounds like something that can easily be built on a breadbord or
> in manhattan style, as Bob already mentioned. That would be really cool.
> I think a while ago I asked a question which goes in a similar direction -
> which mixers are better as phase detectors (to build a PLL for phase noise
> measurement) and which ones should be used as actual mixers (like in this
> case).
> 
> 
> Tobias
> HB9FSX
> 
> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, 
> wrote:
> 
> > One can merely add diodes to the opamp feedback network form a feedback
> > limiter and maintain the opamp outputs within the range for which the opamp
> > is well behaved whilst maintaining the increase in slew rate for the output.
> >
> > Bruce
> > > On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> > >
> > >
> > > Jup, some of them even have phase reversal when they are overloaded, so
> > it
> > > is perhaps not a good idea in general, but I think there are opamps which
> > > are specified for this.
> > >
> > > Tobias
> > >
> > >
> > > On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> > wrote:
> > >
> > > > Caution: opamps make terrible limiters- their overload behavior is
> > > > generally ugly
> > > > and unpredictable.  It's much better to use a genuine level
> > comparator, and
> > > > wire it
> > > > up so that it has a modest amount of hysteresis.
> > > >
> > > > Dana
> > > >
> > > >
> > > > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> > > >
> > > > > Hi
> > > > >
> > > > > The quick way to do this is with a single mixer. Take something like
> > an
> > > > old
> > > > > 10811 and use the coarse tune to set it high in frequency by 5 to 10
> > Hz.
> > > > >
> > > > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
> > tone.
> > > > > That tone is the *difference* between the 10811 and your device under
> > > > > test.
> > > > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > > > >
> > > > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very
> > small
> > > > > shift
> > > > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> > change
> > > > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
> > increase ).
> > > > >
> > > > > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
> > not
> > > > > that
> > > > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > > > second.
> > > > >
> > > > > The reason its not quite that simple is that the input circuit on the
> > > > > counter
> > > > > really does not handle a 10 Hz audio tone as well as it handles a 10
> > MHz
> > > > > RF signal. Instead of getting 9 digits a second, you probably will
> > get
> > > > > three
> > > > > *good* digits a second and another 6 digits of noise.
> > > > >
> > > > > The good news is that an op amp used as a preamp ( to get you up to
> > maybe
> > > > > 32 V p-p rather than a volt or so) and another op amp or three as
> > > > limiters
> > > > > will
> > > > > get you up around 6 or 7 good digits. Toss in a cap or two as a high
> > pass
> > > > > and low pass filter ( DC offsets can be a problem ….) and you have a
> > > > > working
> > > > > device that gets into the parts in 10^-13 with your 5335.
> > > > >
> > > > > It all can be done with point to point wiring. No need for a PCB
> > layout.
> > > > > Be
> > > > > careful that the +/- 18V supplies to the op amp *both* go on and off
> > at
> > > > > the
> > > > > same time ….
> > > > >
> > > > > Bob
> > > > >
> > > > > > On Apr 3, 2020, at 5:13 AM, Tobias Pluess 
> > wrote:
> > > > > >
> > > > > > hi John
> > > > > >
> > > > > > yes I know the DMTD method, and indeed I am planing to build my own
> > > > DMTD
> > > > > > system, something similar to the "Small DMTD system" published by
> > > > Riley (
> > > > > > https://www.wriley.com/A Small DMTD System.pdf).
> > > > > > However I am unsure whether that will help much in this case,
> > because
> > > > all
> > > > > > what the DMTD does is to mix the 10MHz signals down to some 1Hz
> > Signal
> > > > or
> > > > > > so which can be measured more easily, and I already have 1Hz
> > signals

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hey Bob

hmm how would a *single mixer* design look like? in the end I need to
compare *two* clock signals, so a single mixer won't be of much use, would
it?

Tobias

On Sat., 4 Apr. 2020, 01:51 Bob kb8tq,  wrote:

> Hi
>
> A *single mixer* setup is something that can be done quickly and easily.
> The *dual mixer* setup brings in a bunch of issues that are far more
> easily handled on a good PCB layout.
>
> Either way, it is going to work far better with the right sort of low noise
> ( = single digit nanovolt per root hz …) op amps than with whatever
> you happen across first ….
>
> Bob
>
> > On Apr 3, 2020, at 7:38 PM, Tobias Pluess  wrote:
> >
> > Hi Bruce
> >
> > I have some TUF-1 mixers in my junk box as well as some JFET OpAmps
> AD8626.
> > So, if I connect the OpAmps appropriately with some diode limiters as you
> > suggest, would you say this would give an acceptable DMTD system?
> > If so it sounds like something that can easily be built on a breadbord or
> > in manhattan style, as Bob already mentioned. That would be really cool.
> > I think a while ago I asked a question which goes in a similar direction
> -
> > which mixers are better as phase detectors (to build a PLL for phase
> noise
> > measurement) and which ones should be used as actual mixers (like in this
> > case).
> >
> >
> > Tobias
> > HB9FSX
> >
> > On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths,  >
> > wrote:
> >
> >> One can merely add diodes to the opamp feedback network form a feedback
> >> limiter and maintain the opamp outputs within the range for which the
> opamp
> >> is well behaved whilst maintaining the increase in slew rate for the
> output.
> >>
> >> Bruce
> >>> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> >>>
> >>>
> >>> Jup, some of them even have phase reversal when they are overloaded, so
> >> it
> >>> is perhaps not a good idea in general, but I think there are opamps
> which
> >>> are specified for this.
> >>>
> >>> Tobias
> >>>
> >>>
> >>> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
> >> wrote:
> >>>
>  Caution: opamps make terrible limiters- their overload behavior is
>  generally ugly
>  and unpredictable.  It's much better to use a genuine level
> >> comparator, and
>  wire it
>  up so that it has a modest amount of hysteresis.
> 
>  Dana
> 
> 
>  On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> 
> > Hi
> >
> > The quick way to do this is with a single mixer. Take something like
> >> an
>  old
> > 10811 and use the coarse tune to set it high in frequency by 5 to 10
> >> Hz.
> >
> > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
> >> tone.
> > That tone is the *difference* between the 10811 and your device under
> > test.
> > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >
> > If you measured the 10 MHz on the DUT, that 1 Hz would be a very
> >> small
> > shift
> > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
> >> change
> > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
> >> increase ).
> >
> > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
> >> not
> > that
> > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > second.
> >
> > The reason its not quite that simple is that the input circuit on the
> > counter
> > really does not handle a 10 Hz audio tone as well as it handles a 10
> >> MHz
> > RF signal. Instead of getting 9 digits a second, you probably will
> >> get
> > three
> > *good* digits a second and another 6 digits of noise.
> >
> > The good news is that an op amp used as a preamp ( to get you up to
> >> maybe
> > 32 V p-p rather than a volt or so) and another op amp or three as
>  limiters
> > will
> > get you up around 6 or 7 good digits. Toss in a cap or two as a high
> >> pass
> > and low pass filter ( DC offsets can be a problem ….) and you have a
> > working
> > device that gets into the parts in 10^-13 with your 5335.
> >
> > It all can be done with point to point wiring. No need for a PCB
> >> layout.
> > Be
> > careful that the +/- 18V supplies to the op amp *both* go on and off
> >> at
> > the
> > same time ….
> >
> > Bob
> >
> >> On Apr 3, 2020, at 5:13 AM, Tobias Pluess 
> >> wrote:
> >>
> >> hi John
> >>
> >> yes I know the DMTD method, and indeed I am planing to build my own
>  DMTD
> >> system, something similar to the "Small DMTD system" published by
>  Riley (
> >> https://www.wriley.com/A Small DMTD System.pdf).
> >> However I am unsure whether that will help much in this case,
> >> because
>  all
> >> what the DMTD does is to mix the 10MHz signals down to some 1Hz
> >> Signal
>  or
> >> so which can be measured more easily, and I already have 1Hz
> >> signals
>  (the
> >> 1PPS) which I am 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

A *single mixer* setup is something that can be done quickly and easily.
The *dual mixer* setup brings in a bunch of issues that are far more 
easily handled on a good PCB layout. 

Either way, it is going to work far better with the right sort of low noise
( = single digit nanovolt per root hz …) op amps than with whatever 
you happen across first ….

Bob

> On Apr 3, 2020, at 7:38 PM, Tobias Pluess  wrote:
> 
> Hi Bruce
> 
> I have some TUF-1 mixers in my junk box as well as some JFET OpAmps AD8626.
> So, if I connect the OpAmps appropriately with some diode limiters as you
> suggest, would you say this would give an acceptable DMTD system?
> If so it sounds like something that can easily be built on a breadbord or
> in manhattan style, as Bob already mentioned. That would be really cool.
> I think a while ago I asked a question which goes in a similar direction -
> which mixers are better as phase detectors (to build a PLL for phase noise
> measurement) and which ones should be used as actual mixers (like in this
> case).
> 
> 
> Tobias
> HB9FSX
> 
> On Fri., 3 Apr. 2020, 23:09 Bruce Griffiths, 
> wrote:
> 
>> One can merely add diodes to the opamp feedback network form a feedback
>> limiter and maintain the opamp outputs within the range for which the opamp
>> is well behaved whilst maintaining the increase in slew rate for the output.
>> 
>> Bruce
>>> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
>>> 
>>> 
>>> Jup, some of them even have phase reversal when they are overloaded, so
>> it
>>> is perhaps not a good idea in general, but I think there are opamps which
>>> are specified for this.
>>> 
>>> Tobias
>>> 
>>> 
>>> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow 
>> wrote:
>>> 
 Caution: opamps make terrible limiters- their overload behavior is
 generally ugly
 and unpredictable.  It's much better to use a genuine level
>> comparator, and
 wire it
 up so that it has a modest amount of hysteresis.
 
 Dana
 
 
 On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
 
> Hi
> 
> The quick way to do this is with a single mixer. Take something like
>> an
 old
> 10811 and use the coarse tune to set it high in frequency by 5 to 10
>> Hz.
> 
> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio
>> tone.
> That tone is the *difference* between the 10811 and your device under
> test.
> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> 
> If you measured the 10 MHz on the DUT, that 1 Hz would be a very
>> small
> shift
> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the
>> change
> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X
>> increase ).
> 
> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s
>> not
> that
> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> second.
> 
> The reason its not quite that simple is that the input circuit on the
> counter
> really does not handle a 10 Hz audio tone as well as it handles a 10
>> MHz
> RF signal. Instead of getting 9 digits a second, you probably will
>> get
> three
> *good* digits a second and another 6 digits of noise.
> 
> The good news is that an op amp used as a preamp ( to get you up to
>> maybe
> 32 V p-p rather than a volt or so) and another op amp or three as
 limiters
> will
> get you up around 6 or 7 good digits. Toss in a cap or two as a high
>> pass
> and low pass filter ( DC offsets can be a problem ….) and you have a
> working
> device that gets into the parts in 10^-13 with your 5335.
> 
> It all can be done with point to point wiring. No need for a PCB
>> layout.
> Be
> careful that the +/- 18V supplies to the op amp *both* go on and off
>> at
> the
> same time ….
> 
> Bob
> 
>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess 
>> wrote:
>> 
>> hi John
>> 
>> yes I know the DMTD method, and indeed I am planing to build my own
 DMTD
>> system, something similar to the "Small DMTD system" published by
 Riley (
>> https://www.wriley.com/A Small DMTD System.pdf).
>> However I am unsure whether that will help much in this case,
>> because
 all
>> what the DMTD does is to mix the 10MHz signals down to some 1Hz
>> Signal
 or
>> so which can be measured more easily, and I already have 1Hz
>> signals
 (the
>> 1PPS) which I am comparing.
>> Or do you suggest to use the DMTD and use a higher frequency at its
>> outputs, say 10Hz or so, and then average for 10 samples  to
>> increase
 the
>> resolution?
>> 
>> Thanks
>> Tobias
>> HB9FSX
>> 
>> 
>> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
>> 
 b) if I want to measure 1e-11 or even 1e-12 at 1sec - what
>> resolution
>>> does
 my counter need? If the above was true, I would 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Gerhard

ah yes I didn't know that only old OpAmps have the phase reversal problem.
At least in the data sheets for some newer types it is sometimes explicitly
mentioned - "no phase reversal" - but for others it is not, and so far I
never was enough interested in this problem to find out that it only
happens for the JFET ones, but good to know! unless it is mentioned
explicitly, I usually assume that it can happen because it once caused me
some serious troubles and headache in a circuit board which was not
designed by me, but which I had to debug. At that time I did not yet know
about this property of some amps.

Tobias

On Fri., 3 Apr. 2020, 23:42 Gerhard Hoffmann, 
wrote:

>
> Am 03.04.20 um 23:08 schrieb Bruce Griffiths:
> > One can merely add diodes to the opamp feedback network form a feedback
> limiter and maintain the opamp outputs within the range for which the opamp
> is well behaved whilst maintaining the increase in slew rate for the output.
>
> Has anybody here  ever tried the OPA698 / OPA699 limiting op amps?
>
> http://www.ti.com/lit/ds/symlink/opa698.pdf
>
> A lower 1/f corner would be appreciated, and slightly less noise.
>
> >> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> >>
> >>
> >> Jup, some of them even have phase reversal when they are overloaded, so
> it
> >> is perhaps not a good idea in general, but I think there are opamps
> which
> >> are specified for this.
>
> That phase reversal thing is a misfeature of old JFET-OpAmps when
>
> overdriven at the input. It created weird behavior of feedback loops.
>
> Newer ones have that corrected.
>
>
> Cheers, Gerhard
>
>
>
>
>
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Re: [time-nuts] Phase measurement of my GPSDO

[Charles Steinmetz]

Gerhard wrote:


Has anybody here  ever tried the OPA698 / OPA699 limiting op amps?
A lower 1/f corner would be appreciated, and slightly less noise.


I haven't used the TI parts, but I have used the similar AD parts 
(AD8036/8037) quite a bit, with excellent results.  The input noise is 
lower than the TI parts', and the 1/f corner is much lower (low 100s of 
Hz as opposed to above 10kHz for the OPA698/699).


Best regards,

Charles



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Re: [time-nuts] Phase measurement of my GPSDO

[Gerhard Hoffmann]

Am 03.04.20 um 23:08 schrieb Bruce Griffiths:

One can merely add diodes to the opamp feedback network form a feedback limiter 
and maintain the opamp outputs within the range for which the opamp is well 
behaved whilst maintaining the increase in slew rate for the output.


Has anybody here  ever tried the OPA698 / OPA699 limiting op amps?

http://www.ti.com/lit/ds/symlink/opa698.pdf

A lower 1/f corner would be appreciated, and slightly less noise.


On 04 April 2020 at 04:26 Tobias Pluess  wrote:


Jup, some of them even have phase reversal when they are overloaded, so it
is perhaps not a good idea in general, but I think there are opamps which
are specified for this.


That phase reversal thing is a misfeature of old JFET-OpAmps when

overdriven at the input. It created weird behavior of feedback loops.

Newer ones have that corrected.


Cheers, Gerhard





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Re: [time-nuts] Phase measurement of my GPSDO

[Bruce Griffiths]

One can merely add diodes to the opamp feedback network form a feedback limiter 
and maintain the opamp outputs within the range for which the opamp is well 
behaved whilst maintaining the increase in slew rate for the output.

Bruce
> On 04 April 2020 at 04:26 Tobias Pluess  wrote:
> 
> 
> Jup, some of them even have phase reversal when they are overloaded, so it
> is perhaps not a good idea in general, but I think there are opamps which
> are specified for this.
> 
> Tobias
> 
> 
> On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow  wrote:
> 
> > Caution: opamps make terrible limiters- their overload behavior is
> > generally ugly
> > and unpredictable.  It's much better to use a genuine level comparator, and
> > wire it
> > up so that it has a modest amount of hysteresis.
> >
> > Dana
> >
> >
> > On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> >
> > > Hi
> > >
> > > The quick way to do this is with a single mixer. Take something like an
> > old
> > > 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
> > >
> > > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> > > That tone is the *difference* between the 10811 and your device under
> > > test.
> > > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> > >
> > > If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> > > shift
> > > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> > > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
> > >
> > > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> > > that
> > > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > > second.
> > >
> > > The reason its not quite that simple is that the input circuit on the
> > > counter
> > > really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> > > RF signal. Instead of getting 9 digits a second, you probably will get
> > > three
> > > *good* digits a second and another 6 digits of noise.
> > >
> > > The good news is that an op amp used as a preamp ( to get you up to maybe
> > > 32 V p-p rather than a volt or so) and another op amp or three as
> > limiters
> > > will
> > > get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
> > > and low pass filter ( DC offsets can be a problem ….) and you have a
> > > working
> > > device that gets into the parts in 10^-13 with your 5335.
> > >
> > > It all can be done with point to point wiring. No need for a PCB layout.
> > > Be
> > > careful that the +/- 18V supplies to the op amp *both* go on and off at
> > > the
> > > same time ….
> > >
> > > Bob
> > >
> > > > On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> > > >
> > > > hi John
> > > >
> > > > yes I know the DMTD method, and indeed I am planing to build my own
> > DMTD
> > > > system, something similar to the "Small DMTD system" published by
> > Riley (
> > > > https://www.wriley.com/A Small DMTD System.pdf).
> > > > However I am unsure whether that will help much in this case, because
> > all
> > > > what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal
> > or
> > > > so which can be measured more easily, and I already have 1Hz signals
> > (the
> > > > 1PPS) which I am comparing.
> > > > Or do you suggest to use the DMTD and use a higher frequency at its
> > > > outputs, say 10Hz or so, and then average for 10 samples  to increase
> > the
> > > > resolution?
> > > >
> > > > Thanks
> > > > Tobias
> > > > HB9FSX
> > > >
> > > >
> > > > On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> > > >
> > > >>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> > > >> does
> > > >>> my counter need? If the above was true, I would expect that a 1ps
> > > >>> resolution (and an even better stability!) was required to measure
> > ADEV
> > > >> of
> > > >>> 1e-12, The fact that the (as far as I know) world's most recent,
> > > >>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> > > >>> resolution, but people are still able to measure even 1e-14 shows
> > that
> > > my
> > > >>> assumption is wrong. So how are the measurement resolution and the
> > ADEV
> > > >>> related to each other? I plan to build my own TIC based on a TDC7200,
> > > >> which
> > > >>> would offer some 55ps of resolution, but how low could I go with
> > that?
> > > >>
> > > >> That sounds like a simple question but it's not.  There are a few
> > > >> different approaches to look into:
> > > >>
> > > >> 1) Use averaging with your existing counter.  Some counters can yield
> > > >> readings in the 1E-12 region at t=1s even though their single-shot
> > > jitter
> > > >> is much worse than that.  They do this by averaging  hundreds or
> > > thousands
> > > >> of samples for each reading they report.  Whether (and when) this is
> > > >> acceptable is a complex topic in itself, too much so to explain
> > quickly.
> > > >> Search for information on the effects of 

Re: [time-nuts] Phase measurement of my GPSDO

[John Ackermann N8UR]

Your counter can measure 1e-9 *at 1 Hz*  but you are feeding it with 10
MHz's worth of noise, so divide the reading by the factor of the down
mixing (1e7) so the result is 1e-16 -- you are multiplying the effective
noise.

Though as Bob says, you don't get close to 7 digits of improvement
without paying attention to a lot of other details.

John


On 4/3/20 11:59 AM, Tobias Pluess wrote:
> Hi John
> 
> Yes, I totally agree with you and I also understand the difference.
> But what I still don't understand is the following:
> Obviously, my 5335A is not accurate/precise enough to measure below 1e-9
> for short tau. Currently I am comparing the 1PPS signals, but when I change
> that and use the DMTD method, I will still compare some 1Hz signals, and
> the counter is still not able to resolve stuff that is lower than 1e-9. So
> why would the DMTD work better?
> I totally see that the error is somehow multiplied, but if my GPSDO is good
> (which I hope it is :-)) the error will still be very small - perhaps in
> the 1e-9 or 1e-10 region, so too low for my 5335A. Not?
> 
> 
> Tobias
> 
> On Fri, Apr 3, 2020 at 5:34 PM John Ackermann N8UR  wrote:
> 
>> I think the difference is between *mixing* or *dividing* down to a low
>> frequency.
>>
>> When you divide, you divide the noise along with the carrier frequency.
>>
>> When you mix, you "translate" the noise.  If the signal bounces around
>> 0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is
>> also divided by 1e7 so the ratio remains the same.
>>
>> But if you mix via a 9.999 999 MHz local oscillator, now your output at
>> 1 Hz still has 0.1 Hz of noise on it.  i.e., it's the same absolute
>> value of noise as you started with.  So you measure that absolute value
>> but don't compare it to the mixed down 1 Hz frequency, compare it to the
>> original 10 MHz frequency.  It's basically an error multiplier.
>>
>> John
>> 
>>
>> On 4/3/20 11:25 AM, Tobias Pluess wrote:
>>> Hi again Bob,
>>>
>>> yes you describe a simple DMTD measurement. But could you tell me what
>> the
>>> difference is between that and comparing the 1PPS pulses?
>>> I mean, I could set the 10811 high in frequency by just 1Hz, and then it
>>> would result in two 1Hz signals which are then compared.
>>> Which is essentially the same as comparing two 1PPS signals, isn't it?
>>> Ok there is a minor difference: since the 1PPS signals are divided down
>>> from 10MHz, their noise is also divided down, which is not the case for
>> the
>>> DMTD.
>>> However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
>>> region, and apparently, the 5335A is not suitable for those, at least not
>>> with the desired stability, is it?
>>>
>>>
>>> Tobias
>>>
>>> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
>>>
 Hi

 The quick way to do this is with a single mixer. Take something like an
>> old
 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.

 Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
 That tone is the *difference* between the 10811 and your device under
 test.
 If the DUT moves 1 Hz, the audio tone changes by 1 Hz.

 If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
 shift
 ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
 in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase
>> ).

 *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
 that
 simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
 second.

 The reason its not quite that simple is that the input circuit on the
 counter
 really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
 RF signal. Instead of getting 9 digits a second, you probably will get
 three
 *good* digits a second and another 6 digits of noise.

 The good news is that an op amp used as a preamp ( to get you up to
>> maybe
 32 V p-p rather than a volt or so) and another op amp or three as
>> limiters
 will
 get you up around 6 or 7 good digits. Toss in a cap or two as a high
>> pass
 and low pass filter ( DC offsets can be a problem ….) and you have a
 working
 device that gets into the parts in 10^-13 with your 5335.

 It all can be done with point to point wiring. No need for a PCB layout.
 Be
 careful that the +/- 18V supplies to the op amp *both* go on and off at
 the
 same time ….

 Bob

> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
>
> hi John
>
> yes I know the DMTD method, and indeed I am planing to build my own
>> DMTD
> system, something similar to the "Small DMTD system" published by
>> Riley (
> https://www.wriley.com/A Small DMTD System.pdf).
> However I am unsure whether that will help much in this case, because
>> all
> what the DMTD does is to mix the 10MHz 

Re: [time-nuts] Phase measurement of my GPSDO

[Taka Kamiya via time-nuts]

I had trouble understanding this as well.
Your PPS is derived from 10MHz internally by variety of method but usually by 
dividing of some kind.  So the error rate of 10MHz and PPS is usually the same 
of similar.  Please note, I said RATE.  If one moves by 1%, the other moves 1%.
DMTD is mixing.  Take 10MHz and mix 10MHz + 10Hz.  The product is 20MHz + 10Hz, 
and 10Hz.  You cut off the former and use the latter.  Assuming your I/F source 
is completely stable, If the source moves 10Hz, your result moves 10Hz as well. 
 10Hz output suddenly becomes 20Hz.  100% increase.
I hope you can see 100% change is easier to measure than 1% change.
I have HP5335A as well as HP53132A.  I've been using the latter but they work 
similarly.  Multiple measurement and averaging.  You can actually see the 
fluctuation.  But as John and Bob said, they show better than the reality.  

I hate to tell you this, but an only way to really understand this is to 
actually try it.  I spent 2 months on this stuff and now I vaguely understand 
it.  Well, understand it enough to tell you what I just said.  Just reading 
about it, it sounds very difficult and confusing.

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Friday, April 3, 2020, 12:01:18 PM EDT, Tobias Pluess  
wrote:  
 
 Hi John

Yes, I totally agree with you and I also understand the difference.
But what I still don't understand is the following:
Obviously, my 5335A is not accurate/precise enough to measure below 1e-9
for short tau. Currently I am comparing the 1PPS signals, but when I change
that and use the DMTD method, I will still compare some 1Hz signals, and
the counter is still not able to resolve stuff that is lower than 1e-9. So
why would the DMTD work better?
I totally see that the error is somehow multiplied, but if my GPSDO is good
(which I hope it is :-)) the error will still be very small - perhaps in
the 1e-9 or 1e-10 region, so too low for my 5335A. Not?


Tobias

On Fri, Apr 3, 2020 at 5:34 PM John Ackermann N8UR  wrote:

> I think the difference is between *mixing* or *dividing* down to a low
> frequency.
>
> When you divide, you divide the noise along with the carrier frequency.
>
> When you mix, you "translate" the noise.  If the signal bounces around
> 0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is
> also divided by 1e7 so the ratio remains the same.
>
> But if you mix via a 9.999 999 MHz local oscillator, now your output at
> 1 Hz still has 0.1 Hz of noise on it.  i.e., it's the same absolute
> value of noise as you started with.  So you measure that absolute value
> but don't compare it to the mixed down 1 Hz frequency, compare it to the
> original 10 MHz frequency.  It's basically an error multiplier.
>
> John
> 
>
> On 4/3/20 11:25 AM, Tobias Pluess wrote:
> > Hi again Bob,
> >
> > yes you describe a simple DMTD measurement. But could you tell me what
> the
> > difference is between that and comparing the 1PPS pulses?
> > I mean, I could set the 10811 high in frequency by just 1Hz, and then it
> > would result in two 1Hz signals which are then compared.
> > Which is essentially the same as comparing two 1PPS signals, isn't it?
> > Ok there is a minor difference: since the 1PPS signals are divided down
> > from 10MHz, their noise is also divided down, which is not the case for
> the
> > DMTD.
> > However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
> > region, and apparently, the 5335A is not suitable for those, at least not
> > with the desired stability, is it?
> >
> >
> > Tobias
> >
> > On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> The quick way to do this is with a single mixer. Take something like an
> old
> >> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
> >>
> >> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> >> That tone is the *difference* between the 10811 and your device under
> >> test.
> >> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >>
> >> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> >> shift
> >> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> >> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase
> ).
> >>
> >> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> >> that
> >> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> >> second.
> >>
> >> The reason its not quite that simple is that the input circuit on the
> >> counter
> >> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> >> RF signal. Instead of getting 9 digits a second, you probably will get
> >> three
> >> *good* digits a second and another 6 digits of noise.
> >>
> >> The good news is that an op amp used as a preamp ( to get you up to
> maybe
> >> 32 V p-p rather than a volt or so) and another op amp or three as
> limiters
> >> will
> >> get you up around 6 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

Your 5335 resolves 1 ns, that is what limits it’s performance. 
If you have a gate time of 1 second, you will get 9 digits in a 
second, regardless of frequency. That’s the advantage of a
“computing counter”.

If you had a 10 Hz signal with fast enough edges, you could read
it out to 9 digits. Simply put, the ADEV you plotted would be
*identical* at 10 Hz. You would get 7x10^-10 at 1 second off of
the 10 Hz signal. 

Next you get the x 1,000,000 because you did subtraction to
get to the 10 Hz. That is totally independent of anything else
going on. It’s like putting an amplifier in front of your system.

Take that million and put it on top of the 7x10^-10 and you are
at 7x10^-16. The only limits are the standard you compare to 
and how “quiet” you can get the edges.

Bob

> On Apr 3, 2020, at 11:59 AM, Tobias Pluess  wrote:
> 
> Hi John
> 
> Yes, I totally agree with you and I also understand the difference.
> But what I still don't understand is the following:
> Obviously, my 5335A is not accurate/precise enough to measure below 1e-9
> for short tau. Currently I am comparing the 1PPS signals, but when I change
> that and use the DMTD method, I will still compare some 1Hz signals, and
> the counter is still not able to resolve stuff that is lower than 1e-9. So
> why would the DMTD work better?
> I totally see that the error is somehow multiplied, but if my GPSDO is good
> (which I hope it is :-)) the error will still be very small - perhaps in
> the 1e-9 or 1e-10 region, so too low for my 5335A. Not?
> 
> 
> Tobias
> 
> On Fri, Apr 3, 2020 at 5:34 PM John Ackermann N8UR  wrote:
> 
>> I think the difference is between *mixing* or *dividing* down to a low
>> frequency.
>> 
>> When you divide, you divide the noise along with the carrier frequency.
>> 
>> When you mix, you "translate" the noise.  If the signal bounces around
>> 0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is
>> also divided by 1e7 so the ratio remains the same.
>> 
>> But if you mix via a 9.999 999 MHz local oscillator, now your output at
>> 1 Hz still has 0.1 Hz of noise on it.  i.e., it's the same absolute
>> value of noise as you started with.  So you measure that absolute value
>> but don't compare it to the mixed down 1 Hz frequency, compare it to the
>> original 10 MHz frequency.  It's basically an error multiplier.
>> 
>> John
>> 
>> 
>> On 4/3/20 11:25 AM, Tobias Pluess wrote:
>>> Hi again Bob,
>>> 
>>> yes you describe a simple DMTD measurement. But could you tell me what
>> the
>>> difference is between that and comparing the 1PPS pulses?
>>> I mean, I could set the 10811 high in frequency by just 1Hz, and then it
>>> would result in two 1Hz signals which are then compared.
>>> Which is essentially the same as comparing two 1PPS signals, isn't it?
>>> Ok there is a minor difference: since the 1PPS signals are divided down
>>> from 10MHz, their noise is also divided down, which is not the case for
>> the
>>> DMTD.
>>> However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
>>> region, and apparently, the 5335A is not suitable for those, at least not
>>> with the desired stability, is it?
>>> 
>>> 
>>> Tobias
>>> 
>>> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
>>> 
 Hi
 
 The quick way to do this is with a single mixer. Take something like an
>> old
 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
 
 Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
 That tone is the *difference* between the 10811 and your device under
 test.
 If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
 
 If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
 shift
 ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
 in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase
>> ).
 
 *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
 that
 simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
 second.
 
 The reason its not quite that simple is that the input circuit on the
 counter
 really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
 RF signal. Instead of getting 9 digits a second, you probably will get
 three
 *good* digits a second and another 6 digits of noise.
 
 The good news is that an op amp used as a preamp ( to get you up to
>> maybe
 32 V p-p rather than a volt or so) and another op amp or three as
>> limiters
 will
 get you up around 6 or 7 good digits. Toss in a cap or two as a high
>> pass
 and low pass filter ( DC offsets can be a problem ….) and you have a
 working
 device that gets into the parts in 10^-13 with your 5335.
 
 It all can be done with point to point wiring. No need for a PCB layout.
 Be
 careful that the +/- 18V supplies to the op amp *both* go on and off at
 the
 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi John

Yes, I totally agree with you and I also understand the difference.
But what I still don't understand is the following:
Obviously, my 5335A is not accurate/precise enough to measure below 1e-9
for short tau. Currently I am comparing the 1PPS signals, but when I change
that and use the DMTD method, I will still compare some 1Hz signals, and
the counter is still not able to resolve stuff that is lower than 1e-9. So
why would the DMTD work better?
I totally see that the error is somehow multiplied, but if my GPSDO is good
(which I hope it is :-)) the error will still be very small - perhaps in
the 1e-9 or 1e-10 region, so too low for my 5335A. Not?


Tobias

On Fri, Apr 3, 2020 at 5:34 PM John Ackermann N8UR  wrote:

> I think the difference is between *mixing* or *dividing* down to a low
> frequency.
>
> When you divide, you divide the noise along with the carrier frequency.
>
> When you mix, you "translate" the noise.  If the signal bounces around
> 0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is
> also divided by 1e7 so the ratio remains the same.
>
> But if you mix via a 9.999 999 MHz local oscillator, now your output at
> 1 Hz still has 0.1 Hz of noise on it.  i.e., it's the same absolute
> value of noise as you started with.  So you measure that absolute value
> but don't compare it to the mixed down 1 Hz frequency, compare it to the
> original 10 MHz frequency.  It's basically an error multiplier.
>
> John
> 
>
> On 4/3/20 11:25 AM, Tobias Pluess wrote:
> > Hi again Bob,
> >
> > yes you describe a simple DMTD measurement. But could you tell me what
> the
> > difference is between that and comparing the 1PPS pulses?
> > I mean, I could set the 10811 high in frequency by just 1Hz, and then it
> > would result in two 1Hz signals which are then compared.
> > Which is essentially the same as comparing two 1PPS signals, isn't it?
> > Ok there is a minor difference: since the 1PPS signals are divided down
> > from 10MHz, their noise is also divided down, which is not the case for
> the
> > DMTD.
> > However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
> > region, and apparently, the 5335A is not suitable for those, at least not
> > with the desired stability, is it?
> >
> >
> > Tobias
> >
> > On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> The quick way to do this is with a single mixer. Take something like an
> old
> >> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
> >>
> >> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> >> That tone is the *difference* between the 10811 and your device under
> >> test.
> >> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >>
> >> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> >> shift
> >> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> >> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase
> ).
> >>
> >> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> >> that
> >> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> >> second.
> >>
> >> The reason its not quite that simple is that the input circuit on the
> >> counter
> >> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> >> RF signal. Instead of getting 9 digits a second, you probably will get
> >> three
> >> *good* digits a second and another 6 digits of noise.
> >>
> >> The good news is that an op amp used as a preamp ( to get you up to
> maybe
> >> 32 V p-p rather than a volt or so) and another op amp or three as
> limiters
> >> will
> >> get you up around 6 or 7 good digits. Toss in a cap or two as a high
> pass
> >> and low pass filter ( DC offsets can be a problem ….) and you have a
> >> working
> >> device that gets into the parts in 10^-13 with your 5335.
> >>
> >> It all can be done with point to point wiring. No need for a PCB layout.
> >> Be
> >> careful that the +/- 18V supplies to the op amp *both* go on and off at
> >> the
> >> same time ….
> >>
> >> Bob
> >>
> >>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> >>>
> >>> hi John
> >>>
> >>> yes I know the DMTD method, and indeed I am planing to build my own
> DMTD
> >>> system, something similar to the "Small DMTD system" published by
> Riley (
> >>> https://www.wriley.com/A Small DMTD System.pdf).
> >>> However I am unsure whether that will help much in this case, because
> all
> >>> what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal
> or
> >>> so which can be measured more easily, and I already have 1Hz signals
> (the
> >>> 1PPS) which I am comparing.
> >>> Or do you suggest to use the DMTD and use a higher frequency at its
> >>> outputs, say 10Hz or so, and then average for 10 samples  to increase
> the
> >>> resolution?
> >>>
> >>> Thanks
> >>> Tobias
> >>> HB9FSX
> >>>
> >>>
> >>> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> >>>
> > b) if I 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

Without a local reference that is *better* than your expected performance, 
there is no simple way to know what’s going on. Ideally you would like
any measurement to be based on a reference that is 5X better than the
expected result (tolerance wise). If you are looking for 1x10^-12, the ideal
reference would be < 2x10^-13. 

One way around this is to build several of a given design and then compare
them to each other. You still have the issue of “common mode” noise. If 
they all drift exactly + 1 Hz per day, you will never be able to tell … 

A very normal  way to test a GPSDO design is to use a Cs standard
for the longer tau and a “known good” OCXO for the shorter tau. 

Bob

> On Apr 3, 2020, at 11:20 AM, Tobias Pluess  wrote:
> 
> Hi Bob
> 
> knowing that my counter's noise floor is terrible (even though I still
> don't understand why) I tried to measure the ADEV and MDEV of my GPSDO
> against another GPSDO.
> From the graphs, everything below tau=10s is, I would say, rubbish. But I
> tend to mistrust these complete results, as I have no means of finding out
> whether my reference is so bad or my own GPSDO. The reference is an eBay
> GPSDO, and as we all know, these are sometimes of doubtful pedigree.
> But still, below the 10s tau, the ADEV and MDEV are so close to the noise
> floor that I would say this measurement is useless.
> 
> But it still does not explain why my 5335A is so bad.
> 
> 
> Tobias
> HB9FSX
> 
> 
> On Thu, Apr 2, 2020 at 10:17 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> What you have measured *is* the noise floor of a 5335 when trying
>> to use it to measure ADEV. Anything past the numbers on your plot
>> will be “past” what the 5335 can “see”. Indeed, even when you get
>> close to those numbers, things may get a bit weird due to the fact
>> that you are measuring counter “noise” plus device noise.
>> 
>> Bob
>> 
>>> On Apr 2, 2020, at 3:13 PM, Tobias Pluess  wrote:
>>> 
>>> Hello all
>>> 
>>> in the meantime I figured out most of my problems and my GPSDO is working
>>> now with some very ugly prototype code. Today, I wanted to do some ADEV
>>> measurements.
>>> My plan was to compare the 1PPS generated from my GPSDO to the 1PPS of my
>>> Oscilloquartz STAR4; unfortunately I have nothing else (like Rb or so)
>>> which is perhaps more stable. So I try with the STAR4 and see where I
>> get.
>>> However, before I did any meaningful measurements, I wanted to see what
>> the
>>> noise floor of my test equipment is.
>>> Again, unfortunately I have nothing better than a HP 5335A with 1ns
>>> resolution in TIC mode. I measured the noise floor of the TIC as follows:
>>> the 1PPS output of my GPSDO was connected to a resistive power splitter,
>>> and then, one output of the splitter went to channel A of the TIC (START
>>> signal) while the other output from the splitter went first to a long
>> cable
>>> and then to channel B. With this, I achieved about 16ns of delay.
>>> I then used the TIC together with Timelab and measured the ADEV of this
>>> setup.
>>> As far as I understand, if the delay of the cable stays constant (which
>> it
>>> does as long as it is not moved and the temperature stays the same), all
>> I
>>> see in the ADEV plot is the ADEV of my counter itself. Right?
>>> 
>>> So I let this test run for one hour (collected 3600 samples), and the
>>> result looks terrible. See the attached file. I did the test twice; once
>> I
>>> used the STAR4 GPSDO as external reference for the counter, and once I
>> used
>>> its internal reference, which is a HP 10544A oven. As one can see, the
>> ADEV
>>> at 1sec is between 7e-10 and 8e-10. I don't know yet what numbers I can
>>> expect from my GPSDO, but from datasheets of commercial GPSDOs I saw that
>>> the ADEV shortly after powerup should be in the 1e-11 region. So how does
>>> one measure such low ADEVs?
>>> 
>>> To me, it appears that the ADEV at 1sec is roughly the counter's
>>> resolution; a bit less due to averaging. If I take averaging over 3600
>>> samples into account, I think I could expect maybe ~1ns/sqrt(3600) =
>>> 16.7e-12 as ADEV at 1 second, but we can clearly see that this is not the
>>> case. So there are two interesting questions arising:
>>> 
>>> a) I think the ADEV is so high because of the quantization error of the
>>> counter. Assume the time interval measured is right at the transition
>> from,
>>> say, 15ns to 16ns, even the smallest amount of noise will produce some
>>> alternating readings of 15ns and 16ns, which, in turn, results in an ADEV
>>> around 1e-9, right? Further, why is this effect not averaged out with
>>> sqrt(# of samples)?
>>> 
>>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
>> does
>>> my counter need? If the above was true, I would expect that a 1ps
>>> resolution (and an even better stability!) was required to measure ADEV
>> of
>>> 1e-12, The fact that the (as far as I know) world's most recent,
>>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
>>> 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

When you generate a 1 pps signal, you divide the DUT 10 MHz by 10,000,000
to get the 1 pps. If the 10 MHz moves by X%, the 1 pps moves by X% as well.

If you *subtract* the DUT from the offset OCXO, you get the *difference*
of the two frequencies. 

So with division:

10 MHz to 10 MHz + 1 Hz
1 pps goes from 1 Hz to 1.001 Hz

With subtraction:

10 MHz to 10 MHz + 10 Hz
10 Hz goes from 10 Hz to 9 Hz

=

Your 5335 is in no way “bad”. It simply is not good enough for what you want to
do. The 5313x series counters do some “fake out” stuff. Because of that, they 
can
look better than they really are. ( = they actually are about 2X to 10X better 
than 
your 5335). 

Bob

> On Apr 3, 2020, at 11:25 AM, Tobias Pluess  wrote:
> 
> Hi again Bob,
> 
> yes you describe a simple DMTD measurement. But could you tell me what the
> difference is between that and comparing the 1PPS pulses?
> I mean, I could set the 10811 high in frequency by just 1Hz, and then it
> would result in two 1Hz signals which are then compared.
> Which is essentially the same as comparing two 1PPS signals, isn't it?
> Ok there is a minor difference: since the 1PPS signals are divided down
> from 10MHz, their noise is also divided down, which is not the case for the
> DMTD.
> However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
> region, and apparently, the 5335A is not suitable for those, at least not
> with the desired stability, is it?
> 
> 
> Tobias
> 
> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> The quick way to do this is with a single mixer. Take something like an old
>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>> 
>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
>> That tone is the *difference* between the 10811 and your device under
>> test.
>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>> 
>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
>> shift
>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>> 
>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
>> that
>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>> second.
>> 
>> The reason its not quite that simple is that the input circuit on the
>> counter
>> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
>> RF signal. Instead of getting 9 digits a second, you probably will get
>> three
>> *good* digits a second and another 6 digits of noise.
>> 
>> The good news is that an op amp used as a preamp ( to get you up to maybe
>> 32 V p-p rather than a volt or so) and another op amp or three as limiters
>> will
>> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
>> and low pass filter ( DC offsets can be a problem ….) and you have a
>> working
>> device that gets into the parts in 10^-13 with your 5335.
>> 
>> It all can be done with point to point wiring. No need for a PCB layout.
>> Be
>> careful that the +/- 18V supplies to the op amp *both* go on and off at
>> the
>> same time ….
>> 
>> Bob
>> 
>>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
>>> 
>>> hi John
>>> 
>>> yes I know the DMTD method, and indeed I am planing to build my own DMTD
>>> system, something similar to the "Small DMTD system" published by Riley (
>>> https://www.wriley.com/A Small DMTD System.pdf).
>>> However I am unsure whether that will help much in this case, because all
>>> what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
>>> so which can be measured more easily, and I already have 1Hz signals (the
>>> 1PPS) which I am comparing.
>>> Or do you suggest to use the DMTD and use a higher frequency at its
>>> outputs, say 10Hz or so, and then average for 10 samples  to increase the
>>> resolution?
>>> 
>>> Thanks
>>> Tobias
>>> HB9FSX
>>> 
>>> 
>>> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
>>> 
> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
 does
> my counter need? If the above was true, I would expect that a 1ps
> resolution (and an even better stability!) was required to measure ADEV
 of
> 1e-12, The fact that the (as far as I know) world's most recent,
> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> resolution, but people are still able to measure even 1e-14 shows that
>> my
> assumption is wrong. So how are the measurement resolution and the ADEV
> related to each other? I plan to build my own TIC based on a TDC7200,
 which
> would offer some 55ps of resolution, but how low could I go with that?
 
 That sounds like a simple question but it's not.  There are a few
 different approaches to look into:
 
 1) Use averaging with your existing counter.  Some counters can yield
 readings in the 1E-12 region at t=1s even 

Re: [time-nuts] Phase measurement of my GPSDO

[John Ackermann N8UR]

I think the difference is between *mixing* or *dividing* down to a low
frequency.

When you divide, you divide the noise along with the carrier frequency.

When you mix, you "translate" the noise.  If the signal bounces around
0.1 Hz at 10 MHz (awful, I know), when you divide to 1 PPS the noise is
also divided by 1e7 so the ratio remains the same.

But if you mix via a 9.999 999 MHz local oscillator, now your output at
1 Hz still has 0.1 Hz of noise on it.  i.e., it's the same absolute
value of noise as you started with.  So you measure that absolute value
but don't compare it to the mixed down 1 Hz frequency, compare it to the
original 10 MHz frequency.  It's basically an error multiplier.

John


On 4/3/20 11:25 AM, Tobias Pluess wrote:
> Hi again Bob,
> 
> yes you describe a simple DMTD measurement. But could you tell me what the
> difference is between that and comparing the 1PPS pulses?
> I mean, I could set the 10811 high in frequency by just 1Hz, and then it
> would result in two 1Hz signals which are then compared.
> Which is essentially the same as comparing two 1PPS signals, isn't it?
> Ok there is a minor difference: since the 1PPS signals are divided down
> from 10MHz, their noise is also divided down, which is not the case for the
> DMTD.
> However, in the end I am comparing signals in the 1Hz to 5Hz or 10Hz
> region, and apparently, the 5335A is not suitable for those, at least not
> with the desired stability, is it?
> 
> 
> Tobias
> 
> On Fri, Apr 3, 2020 at 1:45 PM Bob kb8tq  wrote:
> 
>> Hi
>>
>> The quick way to do this is with a single mixer. Take something like an old
>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>>
>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
>> That tone is the *difference* between the 10811 and your device under
>> test.
>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>>
>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
>> shift
>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>>
>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
>> that
>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>> second.
>>
>> The reason its not quite that simple is that the input circuit on the
>> counter
>> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
>> RF signal. Instead of getting 9 digits a second, you probably will get
>> three
>> *good* digits a second and another 6 digits of noise.
>>
>> The good news is that an op amp used as a preamp ( to get you up to maybe
>> 32 V p-p rather than a volt or so) and another op amp or three as limiters
>> will
>> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
>> and low pass filter ( DC offsets can be a problem ….) and you have a
>> working
>> device that gets into the parts in 10^-13 with your 5335.
>>
>> It all can be done with point to point wiring. No need for a PCB layout.
>> Be
>> careful that the +/- 18V supplies to the op amp *both* go on and off at
>> the
>> same time ….
>>
>> Bob
>>
>>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
>>>
>>> hi John
>>>
>>> yes I know the DMTD method, and indeed I am planing to build my own DMTD
>>> system, something similar to the "Small DMTD system" published by Riley (
>>> https://www.wriley.com/A Small DMTD System.pdf).
>>> However I am unsure whether that will help much in this case, because all
>>> what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
>>> so which can be measured more easily, and I already have 1Hz signals (the
>>> 1PPS) which I am comparing.
>>> Or do you suggest to use the DMTD and use a higher frequency at its
>>> outputs, say 10Hz or so, and then average for 10 samples  to increase the
>>> resolution?
>>>
>>> Thanks
>>> Tobias
>>> HB9FSX
>>>
>>>
>>> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
>>>
> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
 does
> my counter need? If the above was true, I would expect that a 1ps
> resolution (and an even better stability!) was required to measure ADEV
 of
> 1e-12, The fact that the (as far as I know) world's most recent,
> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> resolution, but people are still able to measure even 1e-14 shows that
>> my
> assumption is wrong. So how are the measurement resolution and the ADEV
> related to each other? I plan to build my own TIC based on a TDC7200,
 which
> would offer some 55ps of resolution, but how low could I go with that?

 That sounds like a simple question but it's not.  There are a few
 different approaches to look into:

 1) Use averaging with your existing counter.  Some counters can yield
 readings in the 1E-12 region at t=1s even though their 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Jup, some of them even have phase reversal when they are overloaded, so it
is perhaps not a good idea in general, but I think there are opamps which
are specified for this.

Tobias


On Fri, Apr 3, 2020 at 3:30 PM Dana Whitlow  wrote:

> Caution: opamps make terrible limiters- their overload behavior is
> generally ugly
> and unpredictable.  It's much better to use a genuine level comparator, and
> wire it
> up so that it has a modest amount of hysteresis.
>
> Dana
>
>
> On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
>
> > Hi
> >
> > The quick way to do this is with a single mixer. Take something like an
> old
> > 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
> >
> > Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> > That tone is the *difference* between the 10811 and your device under
> > test.
> > If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
> >
> > If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> > shift
> > ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> > in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
> >
> > *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> > that
> > simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> > second.
> >
> > The reason its not quite that simple is that the input circuit on the
> > counter
> > really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> > RF signal. Instead of getting 9 digits a second, you probably will get
> > three
> > *good* digits a second and another 6 digits of noise.
> >
> > The good news is that an op amp used as a preamp ( to get you up to maybe
> > 32 V p-p rather than a volt or so) and another op amp or three as
> limiters
> > will
> > get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
> > and low pass filter ( DC offsets can be a problem ….) and you have a
> > working
> > device that gets into the parts in 10^-13 with your 5335.
> >
> > It all can be done with point to point wiring. No need for a PCB layout.
> > Be
> > careful that the +/- 18V supplies to the op amp *both* go on and off at
> > the
> > same time ….
> >
> > Bob
> >
> > > On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> > >
> > > hi John
> > >
> > > yes I know the DMTD method, and indeed I am planing to build my own
> DMTD
> > > system, something similar to the "Small DMTD system" published by
> Riley (
> > > https://www.wriley.com/A Small DMTD System.pdf).
> > > However I am unsure whether that will help much in this case, because
> all
> > > what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal
> or
> > > so which can be measured more easily, and I already have 1Hz signals
> (the
> > > 1PPS) which I am comparing.
> > > Or do you suggest to use the DMTD and use a higher frequency at its
> > > outputs, say 10Hz or so, and then average for 10 samples  to increase
> the
> > > resolution?
> > >
> > > Thanks
> > > Tobias
> > > HB9FSX
> > >
> > >
> > > On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> > >
> > >>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> > >> does
> > >>> my counter need? If the above was true, I would expect that a 1ps
> > >>> resolution (and an even better stability!) was required to measure
> ADEV
> > >> of
> > >>> 1e-12, The fact that the (as far as I know) world's most recent,
> > >>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> > >>> resolution, but people are still able to measure even 1e-14 shows
> that
> > my
> > >>> assumption is wrong. So how are the measurement resolution and the
> ADEV
> > >>> related to each other? I plan to build my own TIC based on a TDC7200,
> > >> which
> > >>> would offer some 55ps of resolution, but how low could I go with
> that?
> > >>
> > >> That sounds like a simple question but it's not.  There are a few
> > >> different approaches to look into:
> > >>
> > >> 1) Use averaging with your existing counter.  Some counters can yield
> > >> readings in the 1E-12 region at t=1s even though their single-shot
> > jitter
> > >> is much worse than that.  They do this by averaging  hundreds or
> > thousands
> > >> of samples for each reading they report.  Whether (and when) this is
> > >> acceptable is a complex topic in itself, too much so to explain
> quickly.
> > >> Search for information on the effects of averaging and dead time on
> > Allan
> > >> deviation to find the entrance to this fork of the rabbit hole.
> > >>
> > >> 2) Search for the term 'DMTD' and read about that.
> > >>
> > >> 3) Search for 'direct digital phase measurement' and read about that.
> > >>
> > >> 4) Search for 'tight PLL' and read about that.
> > >>
> > >> Basically, while some counters can perform averaging on a
> post-detection
> > >> basis, that's like using the tone control on a radio to reduce static
> > and
> > >> QRM.  It works, sort of, but it's too late 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hi Bob

knowing that my counter's noise floor is terrible (even though I still
don't understand why) I tried to measure the ADEV and MDEV of my GPSDO
against another GPSDO.
>From the graphs, everything below tau=10s is, I would say, rubbish. But I
tend to mistrust these complete results, as I have no means of finding out
whether my reference is so bad or my own GPSDO. The reference is an eBay
GPSDO, and as we all know, these are sometimes of doubtful pedigree.
But still, below the 10s tau, the ADEV and MDEV are so close to the noise
floor that I would say this measurement is useless.

But it still does not explain why my 5335A is so bad.


Tobias
HB9FSX


On Thu, Apr 2, 2020 at 10:17 PM Bob kb8tq  wrote:

> Hi
>
> What you have measured *is* the noise floor of a 5335 when trying
> to use it to measure ADEV. Anything past the numbers on your plot
> will be “past” what the 5335 can “see”. Indeed, even when you get
> close to those numbers, things may get a bit weird due to the fact
> that you are measuring counter “noise” plus device noise.
>
> Bob
>
> > On Apr 2, 2020, at 3:13 PM, Tobias Pluess  wrote:
> >
> > Hello all
> >
> > in the meantime I figured out most of my problems and my GPSDO is working
> > now with some very ugly prototype code. Today, I wanted to do some ADEV
> > measurements.
> > My plan was to compare the 1PPS generated from my GPSDO to the 1PPS of my
> > Oscilloquartz STAR4; unfortunately I have nothing else (like Rb or so)
> > which is perhaps more stable. So I try with the STAR4 and see where I
> get.
> > However, before I did any meaningful measurements, I wanted to see what
> the
> > noise floor of my test equipment is.
> > Again, unfortunately I have nothing better than a HP 5335A with 1ns
> > resolution in TIC mode. I measured the noise floor of the TIC as follows:
> > the 1PPS output of my GPSDO was connected to a resistive power splitter,
> > and then, one output of the splitter went to channel A of the TIC (START
> > signal) while the other output from the splitter went first to a long
> cable
> > and then to channel B. With this, I achieved about 16ns of delay.
> > I then used the TIC together with Timelab and measured the ADEV of this
> > setup.
> > As far as I understand, if the delay of the cable stays constant (which
> it
> > does as long as it is not moved and the temperature stays the same), all
> I
> > see in the ADEV plot is the ADEV of my counter itself. Right?
> >
> > So I let this test run for one hour (collected 3600 samples), and the
> > result looks terrible. See the attached file. I did the test twice; once
> I
> > used the STAR4 GPSDO as external reference for the counter, and once I
> used
> > its internal reference, which is a HP 10544A oven. As one can see, the
> ADEV
> > at 1sec is between 7e-10 and 8e-10. I don't know yet what numbers I can
> > expect from my GPSDO, but from datasheets of commercial GPSDOs I saw that
> > the ADEV shortly after powerup should be in the 1e-11 region. So how does
> > one measure such low ADEVs?
> >
> > To me, it appears that the ADEV at 1sec is roughly the counter's
> > resolution; a bit less due to averaging. If I take averaging over 3600
> > samples into account, I think I could expect maybe ~1ns/sqrt(3600) =
> > 16.7e-12 as ADEV at 1 second, but we can clearly see that this is not the
> > case. So there are two interesting questions arising:
> >
> > a) I think the ADEV is so high because of the quantization error of the
> > counter. Assume the time interval measured is right at the transition
> from,
> > say, 15ns to 16ns, even the smallest amount of noise will produce some
> > alternating readings of 15ns and 16ns, which, in turn, results in an ADEV
> > around 1e-9, right? Further, why is this effect not averaged out with
> > sqrt(# of samples)?
> >
> > b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> does
> > my counter need? If the above was true, I would expect that a 1ps
> > resolution (and an even better stability!) was required to measure ADEV
> of
> > 1e-12, The fact that the (as far as I know) world's most recent,
> > rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> > resolution, but people are still able to measure even 1e-14 shows that my
> > assumption is wrong. So how are the measurement resolution and the ADEV
> > related to each other? I plan to build my own TIC based on a TDC7200,
> which
> > would offer some 55ps of resolution, but how low could I go with that?
> >
> >
> > Best regards
> > Tobias
> > HB9FSX
> >
> >
> >
> > On Fri, Mar 20, 2020 at 5:34 PM Bob Q  wrote:
> >
> >> I have seen differences between both UCT and Oscilloquartz 8663 ocxo’s.
> >> The attached plot shows an example. Both boxes use Ublox LEA-6T
> receiver,
> >> surveyed in, AD5680 DAC 18 bit DAC, same level shift circuit and same
> >> control circuit. The reference is an LPRO-101. The Oscilloquartz ocxo
> was
> >> purchased used. Both UCT ocxo’s (only the better one is shown) were
> >> 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

If you are doing a limiter for a 5 Hz sine wave, a “normal” comparator is very 
much
not what you want to use. The slew rates involved are simply way to far below 
what
it is targeted to do. Effectively, it’s what’s in the counter input circuit 
that has already 
failed miserably trying to do this.  Think of this as a “slow sine to square 
converter”. 

For all the ugly details the discussions a few years back on the Colins style 
limiter
get into the this and that. Bruce did a nice write up at:

http://www.ko4bb.com/getsimple/index.php?id=bruces-zero-crossing-detectors

Bob

> On Apr 3, 2020, at 9:29 AM, Dana Whitlow  wrote:
> 
> Caution: opamps make terrible limiters- their overload behavior is
> generally ugly
> and unpredictable.  It's much better to use a genuine level comparator, and
> wire it
> up so that it has a modest amount of hysteresis.
> 
> Dana
> 
> 
> On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:
> 
>> Hi
>> 
>> The quick way to do this is with a single mixer. Take something like an old
>> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>> 
>> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
>> That tone is the *difference* between the 10811 and your device under
>> test.
>> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>> 
>> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
>> shift
>> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
>> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>> 
>> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
>> that
>> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
>> second.
>> 
>> The reason its not quite that simple is that the input circuit on the
>> counter
>> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
>> RF signal. Instead of getting 9 digits a second, you probably will get
>> three
>> *good* digits a second and another 6 digits of noise.
>> 
>> The good news is that an op amp used as a preamp ( to get you up to maybe
>> 32 V p-p rather than a volt or so) and another op amp or three as limiters
>> will
>> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
>> and low pass filter ( DC offsets can be a problem ….) and you have a
>> working
>> device that gets into the parts in 10^-13 with your 5335.
>> 
>> It all can be done with point to point wiring. No need for a PCB layout.
>> Be
>> careful that the +/- 18V supplies to the op amp *both* go on and off at
>> the
>> same time ….
>> 
>> Bob
>> 
>>> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
>>> 
>>> hi John
>>> 
>>> yes I know the DMTD method, and indeed I am planing to build my own DMTD
>>> system, something similar to the "Small DMTD system" published by Riley (
>>> https://www.wriley.com/A Small DMTD System.pdf).
>>> However I am unsure whether that will help much in this case, because all
>>> what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
>>> so which can be measured more easily, and I already have 1Hz signals (the
>>> 1PPS) which I am comparing.
>>> Or do you suggest to use the DMTD and use a higher frequency at its
>>> outputs, say 10Hz or so, and then average for 10 samples  to increase the
>>> resolution?
>>> 
>>> Thanks
>>> Tobias
>>> HB9FSX
>>> 
>>> 
>>> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
>>> 
> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
 does
> my counter need? If the above was true, I would expect that a 1ps
> resolution (and an even better stability!) was required to measure ADEV
 of
> 1e-12, The fact that the (as far as I know) world's most recent,
> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> resolution, but people are still able to measure even 1e-14 shows that
>> my
> assumption is wrong. So how are the measurement resolution and the ADEV
> related to each other? I plan to build my own TIC based on a TDC7200,
 which
> would offer some 55ps of resolution, but how low could I go with that?
 
 That sounds like a simple question but it's not.  There are a few
 different approaches to look into:
 
 1) Use averaging with your existing counter.  Some counters can yield
 readings in the 1E-12 region at t=1s even though their single-shot
>> jitter
 is much worse than that.  They do this by averaging  hundreds or
>> thousands
 of samples for each reading they report.  Whether (and when) this is
 acceptable is a complex topic in itself, too much so to explain quickly.
 Search for information on the effects of averaging and dead time on
>> Allan
 deviation to find the entrance to this fork of the rabbit hole.
 
 2) Search for the term 'DMTD' and read about that.
 
 3) Search for 'direct digital phase measurement' and read about that.
 
 4) Search for 

Re: [time-nuts] Phase measurement of my GPSDO

[Dana Whitlow]

Caution: opamps make terrible limiters- their overload behavior is
generally ugly
and unpredictable.  It's much better to use a genuine level comparator, and
wire it
up so that it has a modest amount of hysteresis.

Dana


On Fri, Apr 3, 2020 at 6:45 AM Bob kb8tq  wrote:

> Hi
>
> The quick way to do this is with a single mixer. Take something like an old
> 10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz.
>
> Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone.
> That tone is the *difference* between the 10811 and your device under
> test.
> If the DUT moves 1 Hz, the audio tone changes by 1 Hz.
>
> If you measured the 10 MHz on the DUT, that 1 Hz would be a very small
> shift
> ( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
> in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ).
>
> *IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not
> that
> simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1
> second.
>
> The reason its not quite that simple is that the input circuit on the
> counter
> really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
> RF signal. Instead of getting 9 digits a second, you probably will get
> three
> *good* digits a second and another 6 digits of noise.
>
> The good news is that an op amp used as a preamp ( to get you up to maybe
> 32 V p-p rather than a volt or so) and another op amp or three as limiters
> will
> get you up around 6 or 7 good digits. Toss in a cap or two as a high pass
> and low pass filter ( DC offsets can be a problem ….) and you have a
> working
> device that gets into the parts in 10^-13 with your 5335.
>
> It all can be done with point to point wiring. No need for a PCB layout.
> Be
> careful that the +/- 18V supplies to the op amp *both* go on and off at
> the
> same time ….
>
> Bob
>
> > On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> >
> > hi John
> >
> > yes I know the DMTD method, and indeed I am planing to build my own DMTD
> > system, something similar to the "Small DMTD system" published by Riley (
> > https://www.wriley.com/A Small DMTD System.pdf).
> > However I am unsure whether that will help much in this case, because all
> > what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
> > so which can be measured more easily, and I already have 1Hz signals (the
> > 1PPS) which I am comparing.
> > Or do you suggest to use the DMTD and use a higher frequency at its
> > outputs, say 10Hz or so, and then average for 10 samples  to increase the
> > resolution?
> >
> > Thanks
> > Tobias
> > HB9FSX
> >
> >
> > On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> >
> >>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> >> does
> >>> my counter need? If the above was true, I would expect that a 1ps
> >>> resolution (and an even better stability!) was required to measure ADEV
> >> of
> >>> 1e-12, The fact that the (as far as I know) world's most recent,
> >>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> >>> resolution, but people are still able to measure even 1e-14 shows that
> my
> >>> assumption is wrong. So how are the measurement resolution and the ADEV
> >>> related to each other? I plan to build my own TIC based on a TDC7200,
> >> which
> >>> would offer some 55ps of resolution, but how low could I go with that?
> >>
> >> That sounds like a simple question but it's not.  There are a few
> >> different approaches to look into:
> >>
> >> 1) Use averaging with your existing counter.  Some counters can yield
> >> readings in the 1E-12 region at t=1s even though their single-shot
> jitter
> >> is much worse than that.  They do this by averaging  hundreds or
> thousands
> >> of samples for each reading they report.  Whether (and when) this is
> >> acceptable is a complex topic in itself, too much so to explain quickly.
> >> Search for information on the effects of averaging and dead time on
> Allan
> >> deviation to find the entrance to this fork of the rabbit hole.
> >>
> >> 2) Search for the term 'DMTD' and read about that.
> >>
> >> 3) Search for 'direct digital phase measurement' and read about that.
> >>
> >> 4) Search for 'tight PLL' and read about that.
> >>
> >> Basically, while some counters can perform averaging on a post-detection
> >> basis, that's like using the tone control on a radio to reduce static
> and
> >> QRM.  It works, sort of, but it's too late in the signal chain at that
> >> point to do the job right.  You really want to limit the bandwidth
> before
> >> the signal is captured, but since that's almost never practical at RF,
> the
> >> next best thing to do is limit the bandwidth before the signal is
> >> "demodulated" (i.e., counted.)
> >>
> >> Hence items 2, 3, and 4 above.  They either limit the measurement
> >> bandwidth prior to detection, lower the frequency itself to keep the
> >> counter's inherent jitter from 

Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

The quick way to do this is with a single mixer. Take something like an old
10811 and use the coarse tune to set it high in frequency by 5 to 10 Hz. 

Then feed it into an RPD-1 mixer and pull out the 5 to 10 Hz audio tone. 
That tone is the *difference* between the 10811 and your device under test. 
If the DUT moves 1 Hz, the audio tone changes by 1 Hz. 

If you measured the 10 MHz on the DUT, that 1 Hz would be a very small shift
( 0.1 ppm ). At 10 Hz it’s a 10% change. You have “amplified” the change
in frequency by the ratio of 10 MHz to 10 Hz ( so a million X increase ). 

*IF* you could tack that on to the ADEV plot of your 5335 ( no, it’s not that 
simple) your 7x10^-10 at 1 second would become more 7x10^-16 at 1 
second. 

The reason its not quite that simple is that the input circuit on the counter 
really does not handle a 10 Hz audio tone as well as it handles a 10 MHz
RF signal. Instead of getting 9 digits a second, you probably will get three
*good* digits a second and another 6 digits of noise. 

The good news is that an op amp used as a preamp ( to get you up to maybe
32 V p-p rather than a volt or so) and another op amp or three as limiters will
get you up around 6 or 7 good digits. Toss in a cap or two as a high pass 
and low pass filter ( DC offsets can be a problem ….) and you have a working
device that gets into the parts in 10^-13 with your 5335. 

It all can be done with point to point wiring. No need for a PCB layout. Be 
careful that the +/- 18V supplies to the op amp *both* go on and off at the 
same time …. 

Bob

> On Apr 3, 2020, at 5:13 AM, Tobias Pluess  wrote:
> 
> hi John
> 
> yes I know the DMTD method, and indeed I am planing to build my own DMTD
> system, something similar to the "Small DMTD system" published by Riley (
> https://www.wriley.com/A Small DMTD System.pdf).
> However I am unsure whether that will help much in this case, because all
> what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
> so which can be measured more easily, and I already have 1Hz signals (the
> 1PPS) which I am comparing.
> Or do you suggest to use the DMTD and use a higher frequency at its
> outputs, say 10Hz or so, and then average for 10 samples  to increase the
> resolution?
> 
> Thanks
> Tobias
> HB9FSX
> 
> 
> On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:
> 
>>> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
>> does
>>> my counter need? If the above was true, I would expect that a 1ps
>>> resolution (and an even better stability!) was required to measure ADEV
>> of
>>> 1e-12, The fact that the (as far as I know) world's most recent,
>>> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
>>> resolution, but people are still able to measure even 1e-14 shows that my
>>> assumption is wrong. So how are the measurement resolution and the ADEV
>>> related to each other? I plan to build my own TIC based on a TDC7200,
>> which
>>> would offer some 55ps of resolution, but how low could I go with that?
>> 
>> That sounds like a simple question but it's not.  There are a few
>> different approaches to look into:
>> 
>> 1) Use averaging with your existing counter.  Some counters can yield
>> readings in the 1E-12 region at t=1s even though their single-shot jitter
>> is much worse than that.  They do this by averaging  hundreds or thousands
>> of samples for each reading they report.  Whether (and when) this is
>> acceptable is a complex topic in itself, too much so to explain quickly.
>> Search for information on the effects of averaging and dead time on Allan
>> deviation to find the entrance to this fork of the rabbit hole.
>> 
>> 2) Search for the term 'DMTD' and read about that.
>> 
>> 3) Search for 'direct digital phase measurement' and read about that.
>> 
>> 4) Search for 'tight PLL' and read about that.
>> 
>> Basically, while some counters can perform averaging on a post-detection
>> basis, that's like using the tone control on a radio to reduce static and
>> QRM.  It works, sort of, but it's too late in the signal chain at that
>> point to do the job right.  You really want to limit the bandwidth before
>> the signal is captured, but since that's almost never practical at RF, the
>> next best thing to do is limit the bandwidth before the signal is
>> "demodulated" (i.e., counted.)
>> 
>> Hence items 2, 3, and 4 above.  They either limit the measurement
>> bandwidth prior to detection, lower the frequency itself to keep the
>> counter's inherent jitter from dominating the measurement, or both.  You'll
>> have to use one of these methods, or another technique along the same
>> lines, if you want to measure the short-term stability of a good oscillator
>> or GPSDO.
>> 
>> -- john, KE5FX
>> 
>> 
>> 
>> ___
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the 

Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

hi John

yes I know the DMTD method, and indeed I am planing to build my own DMTD
system, something similar to the "Small DMTD system" published by Riley (
https://www.wriley.com/A Small DMTD System.pdf).
However I am unsure whether that will help much in this case, because all
what the DMTD does is to mix the 10MHz signals down to some 1Hz Signal or
so which can be measured more easily, and I already have 1Hz signals (the
1PPS) which I am comparing.
Or do you suggest to use the DMTD and use a higher frequency at its
outputs, say 10Hz or so, and then average for 10 samples  to increase the
resolution?

Thanks
Tobias
HB9FSX


On Fri, Apr 3, 2020 at 12:53 AM John Miles  wrote:

> > b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution
> does
> > my counter need? If the above was true, I would expect that a 1ps
> > resolution (and an even better stability!) was required to measure ADEV
> of
> > 1e-12, The fact that the (as far as I know) world's most recent,
> > rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> > resolution, but people are still able to measure even 1e-14 shows that my
> > assumption is wrong. So how are the measurement resolution and the ADEV
> > related to each other? I plan to build my own TIC based on a TDC7200,
> which
> > would offer some 55ps of resolution, but how low could I go with that?
>
> That sounds like a simple question but it's not.  There are a few
> different approaches to look into:
>
> 1) Use averaging with your existing counter.  Some counters can yield
> readings in the 1E-12 region at t=1s even though their single-shot jitter
> is much worse than that.  They do this by averaging  hundreds or thousands
> of samples for each reading they report.  Whether (and when) this is
> acceptable is a complex topic in itself, too much so to explain quickly.
> Search for information on the effects of averaging and dead time on Allan
> deviation to find the entrance to this fork of the rabbit hole.
>
> 2) Search for the term 'DMTD' and read about that.
>
> 3) Search for 'direct digital phase measurement' and read about that.
>
> 4) Search for 'tight PLL' and read about that.
>
> Basically, while some counters can perform averaging on a post-detection
> basis, that's like using the tone control on a radio to reduce static and
> QRM.  It works, sort of, but it's too late in the signal chain at that
> point to do the job right.  You really want to limit the bandwidth before
> the signal is captured, but since that's almost never practical at RF, the
> next best thing to do is limit the bandwidth before the signal is
> "demodulated" (i.e., counted.)
>
> Hence items 2, 3, and 4 above.  They either limit the measurement
> bandwidth prior to detection, lower the frequency itself to keep the
> counter's inherent jitter from dominating the measurement, or both.  You'll
> have to use one of these methods, or another technique along the same
> lines, if you want to measure the short-term stability of a good oscillator
> or GPSDO.
>
> -- john, KE5FX
>
>
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
___
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To unsubscribe, go to 
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Re: [time-nuts] Phase measurement of my GPSDO

[John Miles]

> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution does
> my counter need? If the above was true, I would expect that a 1ps
> resolution (and an even better stability!) was required to measure ADEV of
> 1e-12, The fact that the (as far as I know) world's most recent,
> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> resolution, but people are still able to measure even 1e-14 shows that my
> assumption is wrong. So how are the measurement resolution and the ADEV
> related to each other? I plan to build my own TIC based on a TDC7200, which
> would offer some 55ps of resolution, but how low could I go with that?

That sounds like a simple question but it's not.  There are a few different 
approaches to look into:

1) Use averaging with your existing counter.  Some counters can yield readings 
in the 1E-12 region at t=1s even though their single-shot jitter is much worse 
than that.  They do this by averaging  hundreds or thousands of samples for 
each reading they report.  Whether (and when) this is acceptable is a complex 
topic in itself, too much so to explain quickly.  Search for information on the 
effects of averaging and dead time on Allan deviation to find the entrance to 
this fork of the rabbit hole.

2) Search for the term 'DMTD' and read about that.

3) Search for 'direct digital phase measurement' and read about that.

4) Search for 'tight PLL' and read about that.

Basically, while some counters can perform averaging on a post-detection basis, 
that's like using the tone control on a radio to reduce static and QRM.  It 
works, sort of, but it's too late in the signal chain at that point to do the 
job right.  You really want to limit the bandwidth before the signal is 
captured, but since that's almost never practical at RF, the next best thing to 
do is limit the bandwidth before the signal is "demodulated" (i.e., counted.)   

Hence items 2, 3, and 4 above.  They either limit the measurement bandwidth 
prior to detection, lower the frequency itself to keep the counter's inherent 
jitter from dominating the measurement, or both.  You'll have to use one of 
these methods, or another technique along the same lines, if you want to 
measure the short-term stability of a good oscillator or GPSDO.

-- john, KE5FX



___
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Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi

What you have measured *is* the noise floor of a 5335 when trying
to use it to measure ADEV. Anything past the numbers on your plot
will be “past” what the 5335 can “see”. Indeed, even when you get 
close to those numbers, things may get a bit weird due to the fact
that you are measuring counter “noise” plus device noise. 

Bob

> On Apr 2, 2020, at 3:13 PM, Tobias Pluess  wrote:
> 
> Hello all
> 
> in the meantime I figured out most of my problems and my GPSDO is working
> now with some very ugly prototype code. Today, I wanted to do some ADEV
> measurements.
> My plan was to compare the 1PPS generated from my GPSDO to the 1PPS of my
> Oscilloquartz STAR4; unfortunately I have nothing else (like Rb or so)
> which is perhaps more stable. So I try with the STAR4 and see where I get.
> However, before I did any meaningful measurements, I wanted to see what the
> noise floor of my test equipment is.
> Again, unfortunately I have nothing better than a HP 5335A with 1ns
> resolution in TIC mode. I measured the noise floor of the TIC as follows:
> the 1PPS output of my GPSDO was connected to a resistive power splitter,
> and then, one output of the splitter went to channel A of the TIC (START
> signal) while the other output from the splitter went first to a long cable
> and then to channel B. With this, I achieved about 16ns of delay.
> I then used the TIC together with Timelab and measured the ADEV of this
> setup.
> As far as I understand, if the delay of the cable stays constant (which it
> does as long as it is not moved and the temperature stays the same), all I
> see in the ADEV plot is the ADEV of my counter itself. Right?
> 
> So I let this test run for one hour (collected 3600 samples), and the
> result looks terrible. See the attached file. I did the test twice; once I
> used the STAR4 GPSDO as external reference for the counter, and once I used
> its internal reference, which is a HP 10544A oven. As one can see, the ADEV
> at 1sec is between 7e-10 and 8e-10. I don't know yet what numbers I can
> expect from my GPSDO, but from datasheets of commercial GPSDOs I saw that
> the ADEV shortly after powerup should be in the 1e-11 region. So how does
> one measure such low ADEVs?
> 
> To me, it appears that the ADEV at 1sec is roughly the counter's
> resolution; a bit less due to averaging. If I take averaging over 3600
> samples into account, I think I could expect maybe ~1ns/sqrt(3600) =
> 16.7e-12 as ADEV at 1 second, but we can clearly see that this is not the
> case. So there are two interesting questions arising:
> 
> a) I think the ADEV is so high because of the quantization error of the
> counter. Assume the time interval measured is right at the transition from,
> say, 15ns to 16ns, even the smallest amount of noise will produce some
> alternating readings of 15ns and 16ns, which, in turn, results in an ADEV
> around 1e-9, right? Further, why is this effect not averaged out with
> sqrt(# of samples)?
> 
> b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution does
> my counter need? If the above was true, I would expect that a 1ps
> resolution (and an even better stability!) was required to measure ADEV of
> 1e-12, The fact that the (as far as I know) world's most recent,
> rocket-science grade counter (some Keysight stuff) has "only" 20ps of
> resolution, but people are still able to measure even 1e-14 shows that my
> assumption is wrong. So how are the measurement resolution and the ADEV
> related to each other? I plan to build my own TIC based on a TDC7200, which
> would offer some 55ps of resolution, but how low could I go with that?
> 
> 
> Best regards
> Tobias
> HB9FSX
> 
> 
> 
> On Fri, Mar 20, 2020 at 5:34 PM Bob Q  wrote:
> 
>> I have seen differences between both UCT and Oscilloquartz 8663 ocxo’s.
>> The attached plot shows an example. Both boxes use Ublox LEA-6T receiver,
>> surveyed in, AD5680 DAC 18 bit DAC, same level shift circuit and same
>> control circuit. The reference is an LPRO-101. The Oscilloquartz ocxo was
>> purchased used. Both UCT ocxo’s (only the better one is shown) were
>> purchased new and have 100’s of operating hours. I have also seen
>> differences with constant EFC control voltage. The differences limit what
>> performance you can achieve.___
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to 
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.


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Re: [time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Hello all

in the meantime I figured out most of my problems and my GPSDO is working
now with some very ugly prototype code. Today, I wanted to do some ADEV
measurements.
My plan was to compare the 1PPS generated from my GPSDO to the 1PPS of my
Oscilloquartz STAR4; unfortunately I have nothing else (like Rb or so)
which is perhaps more stable. So I try with the STAR4 and see where I get.
However, before I did any meaningful measurements, I wanted to see what the
noise floor of my test equipment is.
Again, unfortunately I have nothing better than a HP 5335A with 1ns
resolution in TIC mode. I measured the noise floor of the TIC as follows:
the 1PPS output of my GPSDO was connected to a resistive power splitter,
and then, one output of the splitter went to channel A of the TIC (START
signal) while the other output from the splitter went first to a long cable
and then to channel B. With this, I achieved about 16ns of delay.
I then used the TIC together with Timelab and measured the ADEV of this
setup.
As far as I understand, if the delay of the cable stays constant (which it
does as long as it is not moved and the temperature stays the same), all I
see in the ADEV plot is the ADEV of my counter itself. Right?

So I let this test run for one hour (collected 3600 samples), and the
result looks terrible. See the attached file. I did the test twice; once I
used the STAR4 GPSDO as external reference for the counter, and once I used
its internal reference, which is a HP 10544A oven. As one can see, the ADEV
at 1sec is between 7e-10 and 8e-10. I don't know yet what numbers I can
expect from my GPSDO, but from datasheets of commercial GPSDOs I saw that
the ADEV shortly after powerup should be in the 1e-11 region. So how does
one measure such low ADEVs?

To me, it appears that the ADEV at 1sec is roughly the counter's
resolution; a bit less due to averaging. If I take averaging over 3600
samples into account, I think I could expect maybe ~1ns/sqrt(3600) =
16.7e-12 as ADEV at 1 second, but we can clearly see that this is not the
case. So there are two interesting questions arising:

a) I think the ADEV is so high because of the quantization error of the
counter. Assume the time interval measured is right at the transition from,
say, 15ns to 16ns, even the smallest amount of noise will produce some
alternating readings of 15ns and 16ns, which, in turn, results in an ADEV
around 1e-9, right? Further, why is this effect not averaged out with
sqrt(# of samples)?

b) if I want to measure 1e-11 or even 1e-12 at 1sec - what resolution does
my counter need? If the above was true, I would expect that a 1ps
resolution (and an even better stability!) was required to measure ADEV of
1e-12, The fact that the (as far as I know) world's most recent,
rocket-science grade counter (some Keysight stuff) has "only" 20ps of
resolution, but people are still able to measure even 1e-14 shows that my
assumption is wrong. So how are the measurement resolution and the ADEV
related to each other? I plan to build my own TIC based on a TDC7200, which
would offer some 55ps of resolution, but how low could I go with that?


Best regards
Tobias
HB9FSX



On Fri, Mar 20, 2020 at 5:34 PM Bob Q  wrote:

> I have seen differences between both UCT and Oscilloquartz 8663 ocxo’s.
> The attached plot shows an example. Both boxes use Ublox LEA-6T receiver,
> surveyed in, AD5680 DAC 18 bit DAC, same level shift circuit and same
> control circuit. The reference is an LPRO-101. The Oscilloquartz ocxo was
> purchased used. Both UCT ocxo’s (only the better one is shown) were
> purchased new and have 100’s of operating hours. I have also seen
> differences with constant EFC control voltage. The differences limit what
> performance you can achieve.___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>
___
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[time-nuts] Phase measurement of my GPSDO

[Bob Q]

I have seen differences between both UCT and Oscilloquartz 8663 ocxo’s. The 
attached plot shows an example. Both boxes use Ublox LEA-6T receiver, surveyed 
in, AD5680 DAC 18 bit DAC, same level shift circuit and same control circuit. 
The reference is an LPRO-101. The Oscilloquartz ocxo was purchased used. Both 
UCT ocxo’s (only the better one is shown) were purchased new and have 100’s of 
operating hours. I have also seen differences with constant EFC control 
voltage. The differences limit what  performance you can achieve.___
time-nuts mailing list -- time-nuts@lists.febo.com
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and follow the instructions there.

Re: [time-nuts] Phase measurement of my GPSDO

[Attila Kinali]

On Thu, 19 Mar 2020 20:32:30 +0100
Tobias Pluess  wrote:

> The GPS phase detection happens on page 3. I use the TDC7200 as
> interpolator.
> Inside the STM32 microcontroller, I let a timer run with the 10MHz clock.
> The timer overflows to 0 when it reaches the value 999.
> Further, the 1PPS pulse from my GPS module triggers the interpolator, and
> is delayed by max. 2 clock cycles. The delayed signal stops the
> interpolator and is used as a capture event of the timer.
> So, when the OCXO has the right frequency, the captured value would always
> be the same. To determine the phase, I use the following code:
> 
> if(captured value >= 500)
> phase = 1000 - captured value;
> else
> phase = -captured value;
> 
> with the aid of this bit of code, my phase value is always perfectly in the
> interval -500 to +500. My test today was to let the OCXO run with a
> fixed voltage at its EFC input, while I recorded the resulting phase data.
> My recorded data is here:
> 
> https://hb9fsx.ch/files/gpsdo/phase.txt


I guess the units here are cycles of 10MHz/100ns?

BTW: keep in mind that you might run into metastability effects.
Depending on what the exact phase relation between your 10MHz
signal and the internal clock of the STM32 is, you might or might
not get a +/-1 cycle uncertainty due to metastability.

> 
> Now I made two plots (here: https://hb9fsx.ch/files/gpsdo/phase.png). The
> upper is the raw phase data, and I also fitted a linear function to it
> (i.e. if the OCXO has a constant frequency but has some offset from 10 MHz,
> the phase would drift linear into one direction - at least I expect it to
> do so).
> The lower plot is what results when I subtract my linear fitted function
> from the measured phase. I am wondering whether this makes some sense? One
> can see some wiggles and ripple, especially between sampel 0 and 3000. Is
> this the GPS jitter I see there?

Yes, it makes sense. I would have done a quadratic fit, as your OCXO
is just starting up and thus will have a "large" linear frequency drift,
which results in a quadratic phase drift.

The wiggles in the beginning could be uncorrected saw-tooth as Bob mentioned.
That would aproximately fit the quantization that the u-blox modules have
from their 24MHz clock. The change in the wiggles could be hanging bridges,
but it's hard to see. 

With your antenna position you will also get quite high jitter on the PPS
due to not many satellites being visible. Make sure you are running on
a well surveyed position hold to mitigate this. Or get your antenna outside.
See also the measurements that Said Jackson did a few years ago:

http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2012-December/055731.html
http://lists.febo.com/pipermail/time-nuts_lists.febo.com/2012-December/055774.html

BTW: there were some quite interesting discussions about GPSDOs in
late 2012 and early 2013. Might be worth a read.


> Further, I also imported this phase data into Timelab and determined the
> ADEV. Here is my plot:
> 
> https://hb9fsx.ch/files/gpsdo/timelab.png
> 
> This trace is kind of what I expect, but since I use a OSA/UCT 8663 double
> oven OCXO, I would have expected it to be much lower. Something in the
> 1e-12 regime perhaps? is that realistic?

You are measuring your OCXO against GPS. At short tau, GPS is going
to dominate your ADEV. See http://www.leapsecond.com/pages/m12-adev/
for reference.
BTW: You can tell the difference in MDEV. At taus >1s the OCXO
will be clearly in the flicker phase regime, while GPS will still
be in the white phase regime up to 1000-10ks.

The Timing Appnote of u-blox GPS.G6-X-11007 might give you additional
information on the expected behaviour of the u-blox modules:
https://www.u-blox.com/sites/default/files/products/documents/Timing_AppNote_(GPS.G6-X-11007).pdf

To see the actual performance of the system, you need to measure it
against a stable reference. If you have I would recommend using
a combination of 2 or more references: one stable, free running
OCXO (e.g. OSA 8607 or FE-405), an Rb standard (LRPO or PRS-10).
This way you have something that is more stable than your GPSDO
at (almost) all taus. Of course, to be sure that what you are
measuring is actually the performance of the GPSDO and not your
reference, you need to have at least 2 of each type and then
do an n-cornered hat. And yes, beyond one day, this will not
help you as the instability of the Rb standard will be the
limiting factor. That's when take out your Cs beam standard
and start measuring for real ;-)

And yes, characterizing your GPSDO is the biggest problem
of building one. Soon you will be building lots of
measurment equipment to characterize your GPSDO, get more
gadgets and gear until your garage is full of atomic clocks :-)

> As one can see at tau=800s, the
> ADEV is around 5e-11, so is this really all I can expect from this very
> sophisticated OCXO? (However I should maybe add that the OCXO is brand-new
> and has never 

Re: [time-nuts] Phase measurement of my GPSDO

[Matthias Welwarsky]

On Donnerstag, 19. März 2020 22:17:22 CET Matthias Welwarsky wrote:

> You cannot expect to see the OCXO for small tau if your reference is the
> GPS. The GPS 1PPS jitter and the quantization errors will dominate the ADEV
> graph for small tau. Once you correct the quantization error (you need to
> parse the UBX-TP5 message for that) your 1s ADEV will be in the 1e-9 range.

That would be UBX-TIM-TP, not UBX-CFG-TP5. My bad.

BR,
Matthias




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Re: [time-nuts] Phase measurement of my GPSDO

[Matthias Welwarsky]

On Donnerstag, 19. März 2020 20:32:30 CET Tobias Pluess wrote:
> My recorded data is here:
> 
> https://hb9fsx.ch/files/gpsdo/phase.txt
> 
> Now I made two plots (here: https://hb9fsx.ch/files/gpsdo/phase.png). The
> upper is the raw phase data, and I also fitted a linear function to it
> (i.e. if the OCXO has a constant frequency but has some offset from 10 MHz,
> the phase would drift linear into one direction - at least I expect it to
> do so).
> The lower plot is what results when I subtract my linear fitted function
> from the measured phase. I am wondering whether this makes some sense? One
> can see some wiggles and ripple, especially between sampel 0 and 3000. Is
> this the GPS jitter I see there?

I'd say so, yes. What type of receiver did you use? You mentioned a Ublox NEO-
M8T, did you trigger a self-survey when you started the measurement?

It looks like the receiver entered position-hold around 3100 seconds into the 
data file. At least that would explain why the wiggles became much less 
pronounced. Also, you're evidently not correcting the PPS quantization error 
yet.

> Further, I also imported this phase data into Timelab and determined the
> ADEV. Here is my plot:
> 
> https://hb9fsx.ch/files/gpsdo/timelab.png
> 
> This trace is kind of what I expect, but since I use a OSA/UCT 8663 double
> oven OCXO, I would have expected it to be much lower. Something in the
> 1e-12 regime perhaps? is that realistic? As one can see at tau=800s, the
> ADEV is around 5e-11, so is this really all I can expect from this very
> sophisticated OCXO? (However I should maybe add that the OCXO is brand-new
> and has never been used before, so maybe it has some initial aging?).
> I have no plots about the temperature, but this is quite constant.
> For the GPS module, I used an active outdoor antenna at the window ledge.
> Not optimal, but better than an indoor desktop antenna, I guess.
> 
> Is this some plausible data I have here, or do I measure complete crap?

I'd say it's plausible. I got similar results with my Rb-GPSDO when doing the 
same test.

https://www.eevblog.com/forum/projects/diy-gpsdo-project-w-stm32-tdc7200/
msg2860766/#msg2860766

You cannot expect to see the OCXO for small tau if your reference is the GPS. 
The GPS 1PPS jitter and the quantization errors will dominate the ADEV graph 
for small tau. Once you correct the quantization error (you need to parse the 
UBX-TP5 message for that) your 1s ADEV will be in the 1e-9 range.

BR,
Matthias




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Re: [time-nuts] Phase measurement of my GPSDO

[Bob kb8tq]

Hi


> On Mar 19, 2020, at 3:32 PM, Tobias Pluess  wrote:
> 
> Dear colleagues,
> as you may remember I am still working on my own GPSDO project.
> So far I have populated all the components on the PCBs I made, and I have
> written some very basic software to test everything. Currently, I am
> running following simple test:
> I set my DAC to a constant value (5 Volts at the EFC input of the OCXO),
> and then I send the phase measurement to the PC via RS-232 where I can log
> it. More on that later.
> Here is my schematic (not much has changed since last time):
> 
> https://hb9fsx.ch/files/gpsdo/gpsdo_schematic.pdf
> 
> The GPS phase detection happens on page 3. I use the TDC7200 as
> interpolator.
> Inside the STM32 microcontroller, I let a timer run with the 10MHz clock.
> The timer overflows to 0 when it reaches the value 999.
> Further, the 1PPS pulse from my GPS module triggers the interpolator, and
> is delayed by max. 2 clock cycles. The delayed signal stops the
> interpolator and is used as a capture event of the timer.
> So, when the OCXO has the right frequency, the captured value would always
> be the same. To determine the phase, I use the following code:
> 
> if(captured value >= 500)
>phase = 1000 - captured value;
> else
>phase = -captured value;
> 
> with the aid of this bit of code, my phase value is always perfectly in the
> interval -500 to +500. My test today was to let the OCXO run with a
> fixed voltage at its EFC input, while I recorded the resulting phase data.
> My recorded data is here:
> 
> https://hb9fsx.ch/files/gpsdo/phase.txt
> 
> Now I made two plots (here: https://hb9fsx.ch/files/gpsdo/phase.png). The
> upper is the raw phase data, and I also fitted a linear function to it
> (i.e. if the OCXO has a constant frequency but has some offset from 10 MHz,
> the phase would drift linear into one direction - at least I expect it to
> do so).
> The lower plot is what results when I subtract my linear fitted function
> from the measured phase. I am wondering whether this makes some sense? One
> can see some wiggles and ripple, especially between sampel 0 and 3000. Is
> this the GPS jitter I see there?
> Further, I also imported this phase data into Timelab and determined the
> ADEV. Here is my plot:
> 
> https://hb9fsx.ch/files/gpsdo/timelab.png
> 
> This trace is kind of what I expect, but since I use a OSA/UCT 8663 double
> oven OCXO, I would have expected it to be much lower. Something in the
> 1e-12 regime perhaps? is that realistic? As one can see at tau=800s, the
> ADEV is around 5e-11, so is this really all I can expect from this very
> sophisticated OCXO? (However I should maybe add that the OCXO is brand-new
> and has never been used before, so maybe it has some initial aging?).
> I have no plots about the temperature, but this is quite constant.
> For the GPS module, I used an active outdoor antenna at the window ledge.
> Not optimal, but better than an indoor desktop antenna, I guess.

That all looks like the raw / uncorrected for sawtooth output of a GPS module.

Bob


> 
> Is this some plausible data I have here, or do I measure complete crap?
> 
> It would also be great if someone would look at my code. Maybe I am doing
> something wrong when I read out the TDC7200?
> The code is here https://hb9fsx.ch/files/gpsdo/code/  and the most
> important function is perhaps get_tic().
> 
> I am looking forward to any good hints on this! :-)
> best
> Tobias
> HB9FSX
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[time-nuts] Phase measurement of my GPSDO

[Tobias Pluess]

Dear colleagues,
as you may remember I am still working on my own GPSDO project.
So far I have populated all the components on the PCBs I made, and I have
written some very basic software to test everything. Currently, I am
running following simple test:
I set my DAC to a constant value (5 Volts at the EFC input of the OCXO),
and then I send the phase measurement to the PC via RS-232 where I can log
it. More on that later.
Here is my schematic (not much has changed since last time):

https://hb9fsx.ch/files/gpsdo/gpsdo_schematic.pdf

The GPS phase detection happens on page 3. I use the TDC7200 as
interpolator.
Inside the STM32 microcontroller, I let a timer run with the 10MHz clock.
The timer overflows to 0 when it reaches the value 999.
Further, the 1PPS pulse from my GPS module triggers the interpolator, and
is delayed by max. 2 clock cycles. The delayed signal stops the
interpolator and is used as a capture event of the timer.
So, when the OCXO has the right frequency, the captured value would always
be the same. To determine the phase, I use the following code:

if(captured value >= 500)
phase = 1000 - captured value;
else
phase = -captured value;

with the aid of this bit of code, my phase value is always perfectly in the
interval -500 to +500. My test today was to let the OCXO run with a
fixed voltage at its EFC input, while I recorded the resulting phase data.
My recorded data is here:

https://hb9fsx.ch/files/gpsdo/phase.txt

Now I made two plots (here: https://hb9fsx.ch/files/gpsdo/phase.png). The
upper is the raw phase data, and I also fitted a linear function to it
(i.e. if the OCXO has a constant frequency but has some offset from 10 MHz,
the phase would drift linear into one direction - at least I expect it to
do so).
The lower plot is what results when I subtract my linear fitted function
from the measured phase. I am wondering whether this makes some sense? One
can see some wiggles and ripple, especially between sampel 0 and 3000. Is
this the GPS jitter I see there?
Further, I also imported this phase data into Timelab and determined the
ADEV. Here is my plot:

https://hb9fsx.ch/files/gpsdo/timelab.png

This trace is kind of what I expect, but since I use a OSA/UCT 8663 double
oven OCXO, I would have expected it to be much lower. Something in the
1e-12 regime perhaps? is that realistic? As one can see at tau=800s, the
ADEV is around 5e-11, so is this really all I can expect from this very
sophisticated OCXO? (However I should maybe add that the OCXO is brand-new
and has never been used before, so maybe it has some initial aging?).
I have no plots about the temperature, but this is quite constant.
For the GPS module, I used an active outdoor antenna at the window ledge.
Not optimal, but better than an indoor desktop antenna, I guess.

Is this some plausible data I have here, or do I measure complete crap?

It would also be great if someone would look at my code. Maybe I am doing
something wrong when I read out the TDC7200?
The code is here https://hb9fsx.ch/files/gpsdo/code/  and the most
important function is perhaps get_tic().

I am looking forward to any good hints on this! :-)
best
Tobias
HB9FSX
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