[time-nuts] FA2 internal OCXO orientation sensitivity

[Mark Sims]

It's not due to thermal issues.  The freq change due to tip is way too fast for 
that.

---

> It’s also possible that the sensitivity is due to thermal issues.
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[time-nuts] FA-2 Frequency Counter Display

[Mark Sims]

I doubt that you can find a suitable larger replacement display.   Besides 
interface compatibility issues, a larger display will probably have more pixels 
than the FA2 firmware expects.

I have added FA1/FA2 support to Lady Heather.  It includes a command (ZF) to 
zoom the screen to a full screen frequency counter display.  A Raspberry PI 
with the 800x480 touch sceeen display works very well.   Heather supports 
running with two FA1/FA2 counters (or even an FA1 and a FA2).  

See the attached screen dump for the resulting display.  The plot stats are 
from Lady Heather's calculations and not the FA2's calculated statistics.  The 
main input device is a FA2.  The auxiliary input device is a FA1.   I'm working 
on simultaneously displaying statistics for both devices... but the PI 
touchscreen does not have enough space.



>but I'd be more than happy to have it less wee and relocate it into a larger 
>box if it was practical to replace that display with something bigger that 
>could actually be read from a bit further away than an inch or two when 
>running standalone___
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Re: [time-nuts] FA-2 questions

[djl]

I agree completely. A friend and I each had one of these and thought 
there was something wrong with each of them. The dither at 10 MHZ 
compared to a gpsdo is approximately 10 Hz. We spent many hours with the 
manual trying to find the cause of the fm to no avail. It's just a bad 
design. Unsuitable for any time-nuts use. Maybe OK for fixing pre-sdr 
ham radios. The attenuator section is pretty good. Otherwise in today's 
world a boat anchor.

Don

On 2019-10-14 16:57, Didier Juges wrote:
HP8656 and spectral purity should not be used in the same sentence. I 
had
one and the best band is VHF where it may be usable for SSB or NBFM if 
you

are not too picky. It gets worse from there going up. The worst is the
lower band (HF) because it is actually the high band mixed down.

http://www.ko4bb.com/getsimple/index.php?id=comparing-the-hp-8656a-hp-8657b-and-hp-3586a


Didier KO4BB

On Sat, Oct 12, 2019 at 10:07 PM David  wrote:


The hp8656 spectral purity may be a problem.  Residual FM for output
frequencies above 494MHz is < 15 Hz rms ( 0.3 to 3 kHz BW ).  (The B
version is better by about a factor of 2)
Dave

Perry Sandeen via time-nuts  wrote:

>Yo Bubba Dudes!,
>First, does the internal OCXO run when the power is turned off?
>Wrote:
>We are presently experimenting using a ISC570B  multiplier at 100 MHz
>and get 13 digits seeattached but the data out of the back is only 12
>digits reliable.
>Looking it up I found out that the ISC570B is a teeny - tiny IC which
>for me would pose a problem to implement.
>
>So looking at alternatives that I already had I came up with two
>possible alternative multiplier ideas.
>The first was to put the 10 MHz DUT into the external reference of my
>(boat anchor) HP signal generator set the output frequency to 200 MHz
>and put the output into the channel 1 input to get extra resolution
>digits.
>Expanding upon that, I came with more complex but what may be a better
>error multiplier reading since I have both signal generators on hand.
>First I feed the 10 MHz DUT signal into my Fluke 6080 setting the
>output to 1 GHz.  I'd then feed the reference 10 MHz signal into the
>external reference of my HP 8656 and set the output to 990 MHz.
>Next I'd feed both outputs into a
>AD8342 LF to 3.8GHZ Active Mixer Down conversion Output withBalun
>Transformer
>
>board from ebay ($23) and then feed the multiplied signal into channel
>1. (I may need a simple low pass filter.)
>
>
>This should give me a 100X error multiplication.
>
>
>Am I on the right track or am I missing something?
>
>
>Regards,
>Perrier
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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Sent with mySecureMail.
http://www.mysecurephone.eu/

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--
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304


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Re: [time-nuts] FA2 internal OCXO orientation sensitivity

[Bob kb8tq]

Hi

A lot depends on the source of the tip sensitivity. If it is acceleration then 
indeed vibration will get to you. It’s also possible that the sensitivity is due
to thermal issues. In that case, vibration will not be as big an issue.

Worst axis is about +/- 3 ppb so it could be from either source. 

Bob

> On Oct 14, 2019, at 5:45 PM, Didier Juges  wrote:
> 
> If it is sensitive to orientation, it is probably also sensitive to
> vibrations, so mobile applications may be out of the question, depending on
> your needs.
> 
> Didier KO4BB
> 
> On Mon, Oct 7, 2019 at 2:00 AM Mark Sims  wrote:
> 
>> The first time that I tried to set the FA2 internal oscillator frequency I
>> tilted the case so that the screen was facing down and the adjustment screw
>> was facing up.  I got it on frequency, but when I placed the unit with the
>> bottom of the case facing down the oscillator was 0.032 Hz off.  So I did
>> some more testing with the case in various orientations.  It looks like the
>> frequency is fairly insensitive to orientation except for tilt in the
>> front-back axis where it is around +/-1 milliHertz per 3 degrees of tilt
>> (which seems rather high to me).  If you are using the FA2 in a mobile
>> application pay close attention to the front/back tilt of the case.
>> 
>>   F:001000.001619430  bottom down
>>   F:001000.001687723
>>   F:001000.001946380
>>   F:001000.001902348
>>   F:001000.001692710
>>   F:001000.001663366
>>   F:001000.001712156
>>   F:001000.001760899
>>   F:001000.001590295
>>   F:001000.001648737
>> 
>>   F:001000.001922004 bottum up
>>   F:001000.002214679
>>   F:001000.002209653
>>   F:001000.002063463
>>   F:001000.001912133
>>   F:001000.002556087
>>   F:001000.002775519
>>   F:001000.002053697
>>   F:001000.002014587
>>   F:001000.001570725
>> 
>>   F:001000.033927950 screen down
>>   F:001000.033435257
>>   F:001000.032562128
>>   F:001000.032625399
>>   F:001000.032098574
>>   F:001000.032225335
>>   F:001000.032391257
>>   F:001000.032571790
>>   F:001000.032922928
>> 
>>   F:000999.971298357  screen up
>>   F:000999.967820455
>>   F:000999.967859533
>>   F:000999.967986393
>>   F:000999.967800925
>>   F:000999.967947314
>>   F:000999.968327835
>>   F:000999.968252960
>>   F:000999.968030373
>> 
>>   F:000999.998658455  left edge down
>>   F:000999.998985308
>>   F:001000.000419484
>>   F:001000.002063510
>>   F:001000.003292634
>>   F:001000.003956045
>> 
>>   F:001000.002448722  left edge up
>>   F:001000.002029197
>>   F:001000.001917045
>>   F:001000.001985357
>>   F:001000.002012571
>>   F:001000.001980588
>> 
>> 
>> ___
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Re: [time-nuts] FA-2 questions

[Didier Juges]

HP8656 and spectral purity should not be used in the same sentence. I had
one and the best band is VHF where it may be usable for SSB or NBFM if you
are not too picky. It gets worse from there going up. The worst is the
lower band (HF) because it is actually the high band mixed down.

http://www.ko4bb.com/getsimple/index.php?id=comparing-the-hp-8656a-hp-8657b-and-hp-3586a


Didier KO4BB

On Sat, Oct 12, 2019 at 10:07 PM David  wrote:

> The hp8656 spectral purity may be a problem.  Residual FM for output
> frequencies above 494MHz is < 15 Hz rms ( 0.3 to 3 kHz BW ).  (The B
> version is better by about a factor of 2)
> Dave
>
> Perry Sandeen via time-nuts  wrote:
>
> >Yo Bubba Dudes!,
> >First, does the internal OCXO run when the power is turned off?
> >Wrote:
> >We are presently experimenting using a ISC570B  multiplier at 100 MHz
> >and get 13 digits seeattached but the data out of the back is only 12
> >digits reliable.
> >Looking it up I found out that the ISC570B is a teeny - tiny IC which
> >for me would pose a problem to implement.
> >
> >So looking at alternatives that I already had I came up with two
> >possible alternative multiplier ideas.
> >The first was to put the 10 MHz DUT into the external reference of my
> >(boat anchor) HP signal generator set the output frequency to 200 MHz
> >and put the output into the channel 1 input to get extra resolution
> >digits.
> >Expanding upon that, I came with more complex but what may be a better
> >error multiplier reading since I have both signal generators on hand.
> >First I feed the 10 MHz DUT signal into my Fluke 6080 setting the
> >output to 1 GHz.  I'd then feed the reference 10 MHz signal into the
> >external reference of my HP 8656 and set the output to 990 MHz.
> >Next I'd feed both outputs into a
> >AD8342 LF to 3.8GHZ Active Mixer Down conversion Output withBalun
> >Transformer
> >
> >board from ebay ($23) and then feed the multiplied signal into channel
> >1. (I may need a simple low pass filter.)
> >
> >
> >This should give me a 100X error multiplication.
> >
> >
> >Am I on the right track or am I missing something?
> >
> >
> >Regards,
> >Perrier
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >___
> >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] FA-2 Frequency Counter Display

[gandalfg8--- via time-nuts]

The FA-2 really is an amazing wee beastie for the money, and can cram an 
equally amazing amount of information on to that tiny display, but I'd be more 
than happy to have it less wee and relocate it into a larger box if it was 
practical to replace that display with something bigger that could actually be 
read from a bit further away than an inch or two when running standalone:-)

I have one on soak test right now so can't strip that down for the next few 
days but just wondering if anyone has already identified the fitted display and 
if so is it likely that a larger module could be fitted without significant 
electrical modification?
I envisage either transplanting the existing innards into a larger box, or 
perhaps the complete unit as it stands to maintain screening, with box size 
depending on whatever displays might be available, and it seems to me that 
something around the size of the CNT91 display would be ideal.

Nigel, GM8PZR






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Re: [time-nuts] Question for my new GPSDO

[Tobias Pluess]

Hi Tom

thanks for your inputs.

For sure the 1PPS output will be generated in hardware. I have made good 
experiences with using a microcontroller timer: One can use an ordinary PWM 
channel and this generates very precise pulses, and no interrupts or the like 
are involved. And since the timer can be clocked directly by the 10 MHz signal, 
we can even avoid PLL jitter.

Of course I know the TAPR TICC, and I was recently thinking about buying one. 
It seems to be a really nice device. However I didn't want to add a full TICC 
to my GPSDO, but it is maybe a nice idea.

"If you plan to implement GPSDO holdover mode you will also want
timestamping, or a full 0 to 1 s time interval range. You get the idea
by now: a 100 ns range is not sufficient for a GPSDO; do the work for a
full 1 second range; look at how John's TICC uses the TDC7200."

Yes, I actually did plan to use a full 1 second time interval: as you may 
rememver from my previous GPSDO, I clocked a timer in my microcontroller with 
the 10MHz signal. The 1PPS pulse from the GPS is used as input capture; and the 
timer runs continously. When there is a rising edge on the 1PPS, the timer 
value is captured into another register, and while the timer continues to run, 
an interrupt occurs. So every second, I get an interrupt, and when I subtract 
the previous captured timer value from the current one, I should always get 
1000 if the frequency is accurate. However, when the frequency has an error 
smaller than 1 Hz, it takes longer and longer to detect this error; so I 
planned to add the TDC7200 to add further digits to my captured values, e.g. 
1000.25 or so, and this would allow to detect small frequency errors faster.




From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Tom Van Baak 
[t...@leapsecond.com]
Sent: Monday, October 14, 2019 18:08
To: time-nuts@lists.febo.com
Subject: Re: [time-nuts] Question for my new GPSDO

Have a look at the TAPR/TICC design as an example how to use the TDC7200
as a timestamping / time interval counter. The TI chip itself is
designed only for very short-range Time-of-Flight applications so the
additional coarse counter logic that John added is the also right
approach for a GPSDO. Details on the tapr.org site.

Once you have this working, it's easy to put two of them on the board:
one is used to capture GPS/1PPS and another can be used to timestamp a
user's external pulse. That turns your plain GPSDO into a device that
also includes measurement capability -- timestamping (time-tagging),
period, period average, frequency, frequency average, ADEV, etc. Very
useful.

The Trimble TBolt GPSDO is also an informative example. When
disciplining is manually disabled by command, the internal TIC still
continues to provide time interval between GPS and OCXO. This is very
useful as it allows you to measure & characterize the OCXO against GPS
without any additional instruments. This feature comes for free when you
use the timestamping model.

If you plan to implement GPSDO holdover mode you will also want
timestamping, or a full 0 to 1 s time interval range. You get the idea
by now: a 100 ns range is not sufficient for a GPSDO; do the work for a
full 1 second range; look at how John's TICC uses the TDC7200.

For the 1PPS output, always derive that directly from the OCXO itself,
in h/w; don't use a CPU timer. Users tend to expect the 10 MHz and 1PPS
outputs to be in perfect h/w synchronization, without s/w bugs, without
tempco, without added CPU clock jitter.

I'm enjoying your thought process on your GPSDO design. Note that you'll
want to spend as much time developing a test bench so that you can test
what you come up with.

One other comment, do read the archive time nuts postings and blog
entries by Nick Sayer. He did a nice work with an affordable, not
extremely high-end but open source, GPSDO and that would be useful
background reading for you.

/tvb

On 10/14/2019 4:49 AM, Tobias Pluess wrote:
> Hello all together
>
> thanks for your replies so far and hints for my new GPSDO design.
> I have now designed the EFC circuit such that it is easily possible to use 
> different DAC and voltage reference models. I have also reverse-engineered 
> the circuit which is used on the Oscilloquartz GPSDO. They seem to use two 
> cascaded Sallen-Key lowpass filters with approx. 1 Hz corner frequency to 
> integrate the PWM signal, so I have included this circuit as well in my 
> design. This then allows later to test different DACs as well as the PWM.
>
> The next thing I am considering is the usage of the TDC7200 as an 
> interpolator. I know this topic has been discussed often, but some issues 
> still remain.
> I have attached the schematic how I planned to use the TDC7200. The 1PPS 
> pulse from the GPS module is definitely longer than 100ns, so the logic 1 
> will be clocked into the first flip-flop after max. 100ns. The 2nd flip-flop 
> gives a further delay of 100ns. So, the 

Re: [time-nuts] FA2 internal OCXO orientation sensitivity

[Didier Juges]

If it is sensitive to orientation, it is probably also sensitive to
vibrations, so mobile applications may be out of the question, depending on
your needs.

Didier KO4BB

On Mon, Oct 7, 2019 at 2:00 AM Mark Sims  wrote:

> The first time that I tried to set the FA2 internal oscillator frequency I
> tilted the case so that the screen was facing down and the adjustment screw
> was facing up.  I got it on frequency, but when I placed the unit with the
> bottom of the case facing down the oscillator was 0.032 Hz off.  So I did
> some more testing with the case in various orientations.  It looks like the
> frequency is fairly insensitive to orientation except for tilt in the
> front-back axis where it is around +/-1 milliHertz per 3 degrees of tilt
> (which seems rather high to me).  If you are using the FA2 in a mobile
> application pay close attention to the front/back tilt of the case.
>
>F:001000.001619430  bottom down
>F:001000.001687723
>F:001000.001946380
>F:001000.001902348
>F:001000.001692710
>F:001000.001663366
>F:001000.001712156
>F:001000.001760899
>F:001000.001590295
>F:001000.001648737
>
>F:001000.001922004 bottum up
>F:001000.002214679
>F:001000.002209653
>F:001000.002063463
>F:001000.001912133
>F:001000.002556087
>F:001000.002775519
>F:001000.002053697
>F:001000.002014587
>F:001000.001570725
>
>F:001000.033927950 screen down
>F:001000.033435257
>F:001000.032562128
>F:001000.032625399
>F:001000.032098574
>F:001000.032225335
>F:001000.032391257
>F:001000.032571790
>F:001000.032922928
>
>F:000999.971298357  screen up
>F:000999.967820455
>F:000999.967859533
>F:000999.967986393
>F:000999.967800925
>F:000999.967947314
>F:000999.968327835
>F:000999.968252960
>F:000999.968030373
>
>F:000999.998658455  left edge down
>F:000999.998985308
>F:001000.000419484
>F:001000.002063510
>F:001000.003292634
>F:001000.003956045
>
>F:001000.002448722  left edge up
>F:001000.002029197
>F:001000.001917045
>F:001000.001985357
>F:001000.002012571
>F:001000.001980588
>
>
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
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Re: [time-nuts] Question for my new GPSDO

[Jim Harman]

On Mon, Oct 14, 2019 at 12:09 PM Tom Van Baak  wrote:

> ...
> One other comment, do read the archive time nuts postings and blog
> entries by Nick Sayer. He did a nice work with an affordable, not
> extremely high-end but open source, GPSDO and that would be useful
> background reading for you.
>
> /tvb
>

Tobias,

I suggest you also review the GPSDO design by Lars Walenius described here
https://www.eevblog.com/forum/projects/lars-diy-gpsdo-with-arduino-and-1ns-resolution-tic/


which is the basis for Nick Sayer's design. Lars has unfortunately passed
away, but I have worked extensively with his hardware and software and have
made some improvements which I would be happy to share with you off list if
you are interested.

Also if you are interested in pursuing a PWM based DAC, I suggest you
review this article
https://www.edn.com/design/analog/4460665/Fast-PWM-DAC-has-no-ripple
which describes a sample and hold technique for reducing the output noise
of a PWM DAC. The article also has references to other PWM noise reducing
techniques.

--Jim Harman
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Re: [time-nuts] Question for my new GPSDO

[Bob kb8tq]

Hi

You probably will find that comparing the 1 pps to 10 MHz directly gives you
a rollover problem that is difficult to deal with. Comparing it to something 
much 
lower in frequency is the more normal approach.

Bob

> On Oct 14, 2019, at 6:49 AM, Tobias Pluess  wrote:
> 
> Hello all together
> 
> thanks for your replies so far and hints for my new GPSDO design.
> I have now designed the EFC circuit such that it is easily possible to use 
> different DAC and voltage reference models. I have also reverse-engineered 
> the circuit which is used on the Oscilloquartz GPSDO. They seem to use two 
> cascaded Sallen-Key lowpass filters with approx. 1 Hz corner frequency to 
> integrate the PWM signal, so I have included this circuit as well in my 
> design. This then allows later to test different DACs as well as the PWM.
> 
> The next thing I am considering is the usage of the TDC7200 as an 
> interpolator. I know this topic has been discussed often, but some issues 
> still remain.
> I have attached the schematic how I planned to use the TDC7200. The 1PPS 
> pulse from the GPS module is definitely longer than 100ns, so the logic 1 
> will be clocked into the first flip-flop after max. 100ns. The 2nd flip-flop 
> gives a further delay of 100ns. So, the TDC7200 is started on the rising edge 
> of the 1PPS, and stopped with the delayed signal, such that the measurement 
> time ranges betwenn >100ns and <200ns.
> OK so the TDC7200 measures the phase difference between the 10MHz and the 
> 1PPS. To measure the actual frequency, the 1PPS will be used on an input 
> capture of a microcontroller (STM32F407 or something).
> To trigger the input capture, should I use the same signal as for starting 
> the TDC7200, or should I use one of its delayed versions? I think it does not 
> really matter, but I am unsure.
> Further, I also want my GPSDO to output an 1PPS pulse which is aligned to 
> UTC. This 1PPS is generated with an ordinary timer. However, if I do that, 
> the resulting pulse will have an arbitrary phase compared to the GPS module, 
> so how would one deal with that? Actually, one should measure the phase 
> difference between the two 1PPS signals, but this would be even more 
> complicated.
> 
> I also don't know whether metastability could be an issue with my circuit, 
> because in the unlocked state, the 1PPS could change its state any time ond 
> so, setup or hold time of the first flip-flop is maybe violated. But I have 
> no idea how that problem should be resolved or whether it actually is a 
> problem.
> 
> Tobias
> HB9FSX
> 
> 
> 
> 
> From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq 
> [kb...@n1k.org]
> Sent: Wednesday, October 09, 2019 16:25
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Question for my new GPSDO
> 
> Hi
> 
> Indeed some OCXO’s have VCXO return pins. If you take a look at how they
> get used ….hmmm…. the pin doesn’t get used properly. From trying to *get*
> designers to use that sort of pin, indeed their reaction normally was “no can 
> do”.
> 
> Bob
> 
>> On Oct 9, 2019, at 2:28 AM, Tobias Pluess  wrote:
>> 
>> Hi Bob
>> 
>> thanks for your explanation with the Telecom Rb. I am going to make the same 
>> calculations for my OCXOs I plan to use.
>> The ground pin current modulating the EFC is also interesting. I never 
>> thought about that, but indeed, this is true and thus having common ground 
>> pins for the heater and the EFC makes "accurate" tuning more complicated ;-)
>> maybe this is the reason for the old HP 10544A and 10811A having separate 
>> ground pins for the heater and the oscillator circuit?
>> 
>> 
>> Tobias
>> 
>> 
>> From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq 
>> [kb...@n1k.org]
>> Sent: Tuesday, October 08, 2019 17:18
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Question for my new GPSDO
>> 
>> Hi
>> 
>> What is the temperature stability of the OCXO you plan to use? In the case of
>> open windows, what is the *dynamic* temperature stability of the OCXO?
>> What is the tuning range of the EFC on the OCXO?
>> 
>> The wider the EFC range on the OCXO, the more the tempco of the control 
>> system
>> impacts the output. With a small enough range, you may not need a very good
>> DAC at all. With a super big EFC range then the requirements go up.
>> 
>> As long as the EFC stability is better than the OCXO’s temperature 
>> stability, there
>> really is no benefit to improving it.
>> 
>> One example of all this is not an OCXO, but it’s the same sort of idea. A 
>> Telecom Rb
>> might have a tuning range of +/- 2 ppb. It also might have a tempco of 0.1 
>> ppb over
>> a 50 degree range. That comes out to 0.002 ppb / K. It also comes out to 
>> 1,000 ppm/K
>> in terms of the tuning range. (2/0.002). 100 ppm resistors / Dac’s / 
>> references would
>> be ove

Re: [time-nuts] Question for my new GPSDO

[Tom Van Baak]

Have a look at the TAPR/TICC design as an example how to use the TDC7200 
as a timestamping / time interval counter. The TI chip itself is 
designed only for very short-range Time-of-Flight applications so the 
additional coarse counter logic that John added is the also right 
approach for a GPSDO. Details on the tapr.org site.


Once you have this working, it's easy to put two of them on the board: 
one is used to capture GPS/1PPS and another can be used to timestamp a 
user's external pulse. That turns your plain GPSDO into a device that 
also includes measurement capability -- timestamping (time-tagging), 
period, period average, frequency, frequency average, ADEV, etc. Very 
useful.


The Trimble TBolt GPSDO is also an informative example. When 
disciplining is manually disabled by command, the internal TIC still 
continues to provide time interval between GPS and OCXO. This is very 
useful as it allows you to measure & characterize the OCXO against GPS 
without any additional instruments. This feature comes for free when you 
use the timestamping model.


If you plan to implement GPSDO holdover mode you will also want 
timestamping, or a full 0 to 1 s time interval range. You get the idea 
by now: a 100 ns range is not sufficient for a GPSDO; do the work for a 
full 1 second range; look at how John's TICC uses the TDC7200.


For the 1PPS output, always derive that directly from the OCXO itself, 
in h/w; don't use a CPU timer. Users tend to expect the 10 MHz and 1PPS 
outputs to be in perfect h/w synchronization, without s/w bugs, without 
tempco, without added CPU clock jitter.


I'm enjoying your thought process on your GPSDO design. Note that you'll 
want to spend as much time developing a test bench so that you can test 
what you come up with.


One other comment, do read the archive time nuts postings and blog 
entries by Nick Sayer. He did a nice work with an affordable, not 
extremely high-end but open source, GPSDO and that would be useful 
background reading for you.


/tvb

On 10/14/2019 4:49 AM, Tobias Pluess wrote:

Hello all together

thanks for your replies so far and hints for my new GPSDO design.
I have now designed the EFC circuit such that it is easily possible to use 
different DAC and voltage reference models. I have also reverse-engineered the 
circuit which is used on the Oscilloquartz GPSDO. They seem to use two cascaded 
Sallen-Key lowpass filters with approx. 1 Hz corner frequency to integrate the 
PWM signal, so I have included this circuit as well in my design. This then 
allows later to test different DACs as well as the PWM.

The next thing I am considering is the usage of the TDC7200 as an interpolator. 
I know this topic has been discussed often, but some issues still remain.
I have attached the schematic how I planned to use the TDC7200. The 1PPS pulse from 
the GPS module is definitely longer than 100ns, so the logic 1 will be clocked into 
the first flip-flop after max. 100ns. The 2nd flip-flop gives a further delay of 
100ns. So, the TDC7200 is started on the rising edge of the 1PPS, and stopped with 
the delayed signal, such that the measurement time ranges betwenn >100ns and 
<200ns.
OK so the TDC7200 measures the phase difference between the 10MHz and the 1PPS. 
To measure the actual frequency, the 1PPS will be used on an input capture of a 
microcontroller (STM32F407 or something).
To trigger the input capture, should I use the same signal as for starting the 
TDC7200, or should I use one of its delayed versions? I think it does not 
really matter, but I am unsure.
Further, I also want my GPSDO to output an 1PPS pulse which is aligned to UTC. 
This 1PPS is generated with an ordinary timer. However, if I do that, the 
resulting pulse will have an arbitrary phase compared to the GPS module, so how 
would one deal with that? Actually, one should measure the phase difference 
between the two 1PPS signals, but this would be even more complicated.

I also don't know whether metastability could be an issue with my circuit, 
because in the unlocked state, the 1PPS could change its state any time ond so, 
setup or hold time of the first flip-flop is maybe violated. But I have no idea 
how that problem should be resolved or whether it actually is a problem.

Tobias
HB9FSX




From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq 
[kb...@n1k.org]
Sent: Wednesday, October 09, 2019 16:25
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Question for my new GPSDO

Hi

Indeed some OCXO’s have VCXO return pins. If you take a look at how they
get used ….hmmm…. the pin doesn’t get used properly. From trying to *get*
designers to use that sort of pin, indeed their reaction normally was “no can 
do”.

Bob


On Oct 9, 2019, at 2:28 AM, Tobias Pluess  wrote:

Hi Bob

thanks for your explanation with the Telecom Rb. I am going to make the same 
calculations for my OCXOs I plan to use.
The ground 

Re: [time-nuts] FA-2 questions

[ed breya]

Hal wrote:

"dickw1ksz at gmail.com 
 said: 
>/provide frequencies at 72.5, 725 and 7,975 MHz that are /


What's interesting about 72.5, 725, or 7975 MHz?"

Nothing, unless you're using those frequencies. But, if you want to 
multiply up to expand the resolution of a counter, anything you can use 
that will work well enough at 10 MHz reference, in conjunction with a 
little math, can help a lot.


Perry, I'd suggest that you can use a number of old PLO "brick" type 
oscillators that are commonly available - if they can operate well (or 
be easily modified) with 10 MHz reference. Most were intended for 100 
MHz-ish inputs, but will also be just fine at lower frequencies - but 
consider the extra phase noise. The actual output frequency can be 
almost anything as long as it's big enough for sufficient 
multiplication. Simple calculations to get the desired scaling and info.


I have a bunch of 5 GHz PLOs that work fine with 10 MHz in, planned for 
a two-stage multiplier. I just happen to have been working on this 
differential frequency counter project over the last few days, and have 
the design worked out for the high frequency range stage 1000x (delta 
+/- 2 kHz gives +/- 2 MHz). It takes in two 10 MHz signals, and provides 
an output IF of 10 MHz plus 1000x the frequency difference between the 
inputs. One input is taken as the reference, converted to 5040 MHz and 
90 MHz LOs. The other input is converted to 5000 MHz (500x), and mixed 
down to 40 MHz IF. This is then doubled to 80 MHz (2x), then mixed with 
the 90 MHz down to 10 MHz, netting 1000x the difference. This can be 
viewed on a suitable counter (1 Hz resolution at 1 second gate) at 
modest frequency. The display is 10 MHz plus 1000x the difference, or 
say 8-12 MHz range, representing 9,998-10.002 MHz. Essentially, it takes 
the middle three zeros (or nines) out of the 10 MHz shown on the 
counter, while expanding so the 1 Hz digit represents 1 mHz, and so on.


The other (similar but specially modified) 1000x multiplier will be 
cascaded in front of or behind this one, depending on how things work 
out. The first 1000x is easy, but the second is of course, a whole 
'nother story - the two cascaded would be similar in noise to 
multiplying up to 10 THz. The plan so far is for the +/-2 Hz range to 
provide E6 multiplication, so 1 uHz resolution at 1 second gate - or 
maybe 10 seconds, or more, depending on how things work out. My 
experiments indicate that I can go pretty far with it, once things are 
clean enough. Right now I'm fighting line noise mostly, which dwarfs the 
random close-in phase noise. I can't even even get a second stage to 
lock with my experimental setup, but expect much better results once I 
build a very clean power supply for it, and fix the numerous ground loops.


So anyway, a good old-school PLO can help with pretty good 
multiplication factors, so may be worth considering, especially for 
one-time use, or to avoid having to commit a piece of regular test gear 
to the application. Also note that nobody in their right mind would use 
the approach I've outline above - except for me, since I have lots of 
the right kinds of microwave pieces, and it's a lot of fun.


Good luck.

Ed



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Re: [time-nuts] Question for my new GPSDO

[Tobias Pluess]

Hello all together

thanks for your replies so far and hints for my new GPSDO design.
I have now designed the EFC circuit such that it is easily possible to use 
different DAC and voltage reference models. I have also reverse-engineered the 
circuit which is used on the Oscilloquartz GPSDO. They seem to use two cascaded 
Sallen-Key lowpass filters with approx. 1 Hz corner frequency to integrate the 
PWM signal, so I have included this circuit as well in my design. This then 
allows later to test different DACs as well as the PWM.

The next thing I am considering is the usage of the TDC7200 as an interpolator. 
I know this topic has been discussed often, but some issues still remain.
I have attached the schematic how I planned to use the TDC7200. The 1PPS pulse 
from the GPS module is definitely longer than 100ns, so the logic 1 will be 
clocked into the first flip-flop after max. 100ns. The 2nd flip-flop gives a 
further delay of 100ns. So, the TDC7200 is started on the rising edge of the 
1PPS, and stopped with the delayed signal, such that the measurement time 
ranges betwenn >100ns and <200ns.
OK so the TDC7200 measures the phase difference between the 10MHz and the 1PPS. 
To measure the actual frequency, the 1PPS will be used on an input capture of a 
microcontroller (STM32F407 or something).
To trigger the input capture, should I use the same signal as for starting the 
TDC7200, or should I use one of its delayed versions? I think it does not 
really matter, but I am unsure.
Further, I also want my GPSDO to output an 1PPS pulse which is aligned to UTC. 
This 1PPS is generated with an ordinary timer. However, if I do that, the 
resulting pulse will have an arbitrary phase compared to the GPS module, so how 
would one deal with that? Actually, one should measure the phase difference 
between the two 1PPS signals, but this would be even more complicated.

I also don't know whether metastability could be an issue with my circuit, 
because in the unlocked state, the 1PPS could change its state any time ond so, 
setup or hold time of the first flip-flop is maybe violated. But I have no idea 
how that problem should be resolved or whether it actually is a problem.

Tobias
HB9FSX




From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq 
[kb...@n1k.org]
Sent: Wednesday, October 09, 2019 16:25
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Question for my new GPSDO

Hi

Indeed some OCXO’s have VCXO return pins. If you take a look at how they
get used ….hmmm…. the pin doesn’t get used properly. From trying to *get*
designers to use that sort of pin, indeed their reaction normally was “no can 
do”.

Bob

> On Oct 9, 2019, at 2:28 AM, Tobias Pluess  wrote:
>
> Hi Bob
>
> thanks for your explanation with the Telecom Rb. I am going to make the same 
> calculations for my OCXOs I plan to use.
> The ground pin current modulating the EFC is also interesting. I never 
> thought about that, but indeed, this is true and thus having common ground 
> pins for the heater and the EFC makes "accurate" tuning more complicated ;-)
> maybe this is the reason for the old HP 10544A and 10811A having separate 
> ground pins for the heater and the oscillator circuit?
>
>
> Tobias
>
> 
> From: time-nuts [time-nuts-boun...@lists.febo.com] on behalf of Bob kb8tq 
> [kb...@n1k.org]
> Sent: Tuesday, October 08, 2019 17:18
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Question for my new GPSDO
>
> Hi
>
> What is the temperature stability of the OCXO you plan to use? In the case of
> open windows, what is the *dynamic* temperature stability of the OCXO?
> What is the tuning range of the EFC on the OCXO?
>
> The wider the EFC range on the OCXO, the more the tempco of the control system
> impacts the output. With a small enough range, you may not need a very good
> DAC at all. With a super big EFC range then the requirements go up.
>
> As long as the EFC stability is better than the OCXO’s temperature stability, 
> there
> really is no benefit to improving it.
>
> One example of all this is not an OCXO, but it’s the same sort of idea. A 
> Telecom Rb
> might have a tuning range of +/- 2 ppb. It also might have a tempco of 0.1 
> ppb over
> a 50 degree range. That comes out to 0.002 ppb / K. It also comes out to 
> 1,000 ppm/K
> in terms of the tuning range. (2/0.002). 100 ppm resistors / Dac’s / 
> references would
> be overkill in this case.
>
> None of that gets into the issue of dynamic change. Pretty much every 
> component
> you will find is rated for a gradual rather than fast change. The impact of a 
> fast change
> can be orders of magnitude worse than a slower change. ( so indeed, don’t 
> open the
> window :) )
>
> ===
>
> If you want to go a bit nuts (this being time nuts):
>
> A change in the temperature changes the current through the OCXO heater. That

Re: [time-nuts] HP105B HP 105B 1 amp fuse blowing

[shouldbe q931]

On Fri, Oct 11, 2019 at 10:00 PM Dana Whitlow  wrote:
>
> I once read that Supercapacitors come up short in handling really short
> spikes,
> and that this is not due to physical inductance arising from the
> structure.  Rather,
> the issue was of a subtle (to me) electrochemical nature.
>
> Can anyone either confirm or refute this?  Inquiring minds want to know.
>
> Dana
>

Granted the usage is different, but some time ago most HPE/Dell RAID
controllers moved from using battery (usually NiCad) backed cache
modules, to using flash backed cache with a supercapacitor to power
the transfer from cache to flash.

One would hope that as these are used to protect data integrity, that
HPE and Dell did their homework. I certainly have appreciated no
longer having to replace failed battery packs in servers (-:

Cheers

Arne

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