Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Warren wrote:


The most important thing to get good Tbolt frequency performance is the
antenna, with good sky view and correct location setting.


Agreed.  Nothing will go right if the antenna, sky view, and surveyed 
location are not as good as you can get them.



The Tbolts damping setting is what controls how much 'freq noise' is
added to correct for time error (i.e. Phase error).  You can set it to
optimize whatever you want.A damping of 0.7 adds ~25% freq overshoot
noise and gives you the lowest phase error.


Meaning, it corrects the PPS position as quickly as practicable but 
horses the frequency around quite a bit to do it and overshoots before 
settling.



A damping of 1.0 adds ~10% freq overshoot noise and any time/phase error
takes about 3 times longer to correct.

A damping of 1.25 adds <5% freq overshoot noise and the time error takes ~6
times longer to correct.

With a damping setting of 2, less that 1% of freq noise is added to correct
for time errors and phase errors takes >>10 longer to correct.

With a damping of >=10, the time correcting is so slow that time/phase
correction can take days, and there is *no* added freq noise.


These are good rules of thumb.  Someone who is interested solely in a 
frequency reference is well advised to set the damping >>2.  I think I 
ended up around 6-12.  There was a minor improvement if I increased it 
to 50, but then recovery from holdover took longer than I was prepared 
to wait.


Speaking of which -- recovery from holdover will be slow when a Tbolt is 
tuned this way, so do everything you can to speed it up.  Allow "jam" 
setting of the PPS when the error reaches, say, 65-75nS during recovery, 
and also allow quite a lot of frequency error during recovery (IIRC, you 
can allow the Tbolt to vary the oscillator up to parts in 10e-9 during 
recovery).  Then, DO NOT USE THE 10MHz OUTPUT WHEN THE TBOLT IS IN 
RECOVERY.  Wait until it is fully recovered.


And again (back to the first item), make sure everything about your 
antenna system and location is in perfect order, so it will only very 
rarely go into holdover.  ALSO, make sure that the Tbolt sees a nice 
thermal environment, either by actively controlling the temperature 
surrounding the Tbolt itself, or by isolating it from ambient so the 
oven can always keep up with any changes.  The latter is my preferred 
technique -- see old list messages discussing "cast aluminum boxes", 
"thermal mass," "thermal inertia," and "thermal capacitance."  But there 
is nothing wrong with active control, either, and LH can do that for you 
with a few external parts.


Best regards,

Charles


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[time-nuts] Lady Heather's Tbolt oscillator auto-tune function

[Mark Sims]

Here's a little info on Lady Heather's oscillator autotune function for the 
Thunderbolt GPSDO:

The autotune function tries to optimize the settings for the oscillator 
disciplining parameters, antenna signal mask angle, and the signal level 
amplitude mask beyond what the default setting (which are more for telecom 
timing applications) are.

To use the auto-tune function the receiver should be warmed up and stable.  
Manually set the antenna mask angle to a low value (say 0-5 degrees) with the 
FE keyboard command and set the signal level mask to a low value (1 AMU,  20-30 
dBc) with the FL command.  Clear the signal level log with the CS command. Let 
the receiver collect signal level data for several hours (overnight is good).  
The data collected is used to determine where your signal levels begin to drop 
vs the satellite elevation angles.  

Since the unit should be locked and stable, the current DAC setting is where 
the oscillator is at 10.000 MHz and will be set in EEPROM as the initial 
DAC setting. The tbolt uses this value to speed up locking the oscillator when 
powering up.

Then issue the autotune command (&a).  This will put the DAC into manual 
control mode and step the DAC control voltage 5 mV high and then low and 
measure how the oscillator frequency changes.  This takes a few minutes to 
complete.  This is used to determine the oscillator voltage gain.   The 
calculated value seems to be quite accurate.  Tbolts set up for external 
oscillators can be used to determine unknown 10 MHz oscillator EFC 
characteristics.

Next,  Lady Heather sets the loop time constant to 500 seconds and the damping 
to 1.0   These value seem to be  good conservative general purpose values for a 
typical unit and should not cause any loop stability issues.

Finally, Lady Heather sets the antenna mask angle setting to where the signal 
level starts to drop off rapidly and the signal level mask value to 30 dBc (or 
1 AMU unit).   After the auto-tune completes, the antenna mask angle setting 
might need to be manually set to a lower value...  it tends to find that the 
signal level falls off at a higher angle than one might expect.  You can check 
the signal level vs elevation plot with the SAE keyboard command (or ZE in the 
next release will show the plot zoomed to full screen).   High antenna mask 
angles cause more satellite constellation changes which is not good.  Low 
antenna mask angles subjects the receiver to multi-path effects which is also 
not good.  You are damned if you do and damned if you don't...








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Re: [time-nuts] ke5fx.com - something's up

[Glenn Little WB4UIV]

Try the wayback machine: 



This is an archive of many websites.

73
Glenn
WB4UIV

On 9/10/2016 6:48 PM, Nick Sayer via time-nuts wrote:

I tried to look for Lady Heather docs today, but it appears like the ke5fx 
domain is… funky.

The name servers are NS1.PENDINGRENEWALDELETION.COM and there are other 
indications that maybe the domain lapsed…?
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--
---
Glenn LittleARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIVwb4...@arrl.netAMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
---
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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bert wrote:


Looks like we are not the only ones trying to improve frequency
performance and hopefully some one will share settings.


You are coming very late to the Tbolt party.  There was a veritable 
blizzard of posts about optimizing Tbolt performance, which began maybe 
10 or 11 years ago (??) and lasted for several years, and a steady 
trickle since then.  Everything that is possible to be said was posted, 
often several times.  Go back in the list archives and read this 
material -- it will answer all of your questions (and lots more that you 
haven't asked yet).


Best regards,

Charles


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Re: [time-nuts] ke5fx.com - something's up

[John Miles]

Hmm.  Gotta be some kind of DNS glitch, it's not due for renewal as far as I 
can see.  I'll look into it, thanks.

-- john, KE5FX
Miles Design LLC

> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Nick Sayer
> via time-nuts
> Sent: Saturday, September 10, 2016 3:48 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] ke5fx.com - something's up
> 
> I tried to look for Lady Heather docs today, but it appears like the ke5fx 
> domain
> is… funky.
> 
> The name servers are NS1.PENDINGRENEWALDELETION.COM and there are
> other indications that maybe the domain lapsed…?
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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bob wrote:


The one thing that autotune seems to do well is to come up with the actual 
sensitivity of the OCXO you have. It depends on a few things to do this so it 
might go wrong. I’ve never seen it come up with the wrong number. It then 
appears to drop in a gain and damping that make more sense than the original 
numbers. Since it is a pre-defined pair of numbers, it is indeed a “one size 
fits all” solution.


Warren, who I understand provided the algorithms for the autotune 
routine, has advocated in a number of list postings damping factors much 
lower than what I consider optimal (and in some cases below the factory 
default of 1.2).  Also, in the case of my units, the autotune function 
adjusted the tuning rate parameter (OCXO sensitivity) for substantially 
increased loop gain, which effectively decreased the damping even 
further.  So, one of the results [long ago, and with my very small 
sample of Tbolts] was to adjust the loop toward and even into instability.


It also seemed to tinker with parameters I didn't expect it to change, 
which is why I had to do a hard reset rather than just re-program the 
settings that I had changed as a result of my prior experimentation.


Again, I have no idea why it did this, and it is very possible that the 
autotune routine on current versions of LH works perfectly and gives an 
optimum tuning very painlessly.  But back when I tried it, with my two 
Tbolts, it made them pretty much unusable.


No big deal -- just evaluate the operation of your Tbolt after using the 
autotune routine, and if you find that it did not produce the results 
you hoped for, be prepared to do a hard reset and tune it manually.  If 
it works well, then great!


Best regards,

Charles


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[time-nuts] ke5fx.com - something's up

[Nick Sayer via time-nuts]

I tried to look for Lady Heather docs today, but it appears like the ke5fx 
domain is… funky.

The name servers are NS1.PENDINGRENEWALDELETION.COM and there are other 
indications that maybe the domain lapsed…?
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Re: [time-nuts] Tbolt issues

[ws at Yahoo via time-nuts]

Bert 
a) 1e-10 freq error, Sounds to me like you have a typical TBolt with near
factory default setting. 
The most important thing to get good Tbolt frequency performance is the
antenna, with good sky view and correct location setting. 

After that there are some 'basic' Tbolt setting and things that can be done
that will get it close to the best, within say 2 to one.

 
Other comments in text below and attached graph.


***
Bert Kehren wrote in part:
 
>would you mind sharing 1 second frequency data that you get out of the
>tbolt to get an idea what is possible. 
>Looks like we are not the only ones trying to improve frequency performance
>and hopefully some will share settings.
>For us it is absolute Frequency, to me it is a measure of true
>performance.

 a)Attached is data plotted from a modified Tbolt that has a 1 sec ADEV of
1e-12. 
This shows that its 100ms "instantaneous" freq error varies from 1 to 3e-11.
As long the frequency counter is not resolution limited, the 0.1sec, 1sec,
10sec, and 100 sec sampled plots all had about the same peak to peak freq
error just with less high freq fuzz, 

***
>Tbolt is an excellent time device but not good for frequency reference 
> past 1E-10 because the frequency is constantly changed to correct time. 
 
a) The Tbolts damping setting is what controls how much 'freq noise' is
added to correct for time error (i.e. Phase error).

You can set it to optimize whatever you want.
Many time-nuts use Phase error, not frequency error as the indicator of
performance, so I tend to set the damping low to minimize the phase error.
When the gain is set correct, damping of 0.707 gives ideal critical damped
phase error correction response. 
A damping of 1.2 gives a nice compromise for frequency response correction.


A damping of 0.7 adds ~25% freq overshoot noise and gives you the lowest
phase error.

A damping of 1.0 adds ~10% freq overshoot noise and any time/phase error
takes about 3 times longer to correct.

A damping of 1.25 adds <5% freq overshoot noise and the time error takes ~6
times longer to correct.

With a damping setting of 2, less that 1% of freq noise is added to correct
for time errors and phase errors takes >>10 longer to correct.

With a damping of >=10, the time correcting is so slow that time/phase
correction can take days, and there is *no* added freq noise.


***
>With the popularity of the Tbolt an analog or digital clean up loop would
make sense. 
>My Swiss partner Juerg has relied on an OSA F3 for Tbolt clean up but has
had continuous bad results . 
>The result is that the OSA F3 does not clean up the Tbolt and we see
+-4E-11 changes and old data shows even some +-8E-11 excursions. 
 
a) The Tbolt control loop is already a clean up controller, it is cleaning
up the noisy GPS freq signal.
What I have found is that with a properly setup TBolt, an addition clean up
Osc does not help to give better low frequency stability because the peak to
peak noise output is pretty much constant whether the cleanup bandwidth is
set at 0.1sec, 1sec, 10sec, 30sec or 100 sec.
And of course you'd need a cleanup oscillator that is more stable that the
Tbolt over the cleanup time period.
If you have the low noise clean up oscillator, what works better is let the
Tbolt discipline it directly as an external oscillator.
 

ws



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[time-nuts] FS: Z3801A

[Joseph Gray]

Fully functional (in use now). Has been upgraded to an Oncore VP GPS
module (more sensitive than the original). I replaced several caps on
the DC-DC board with low-ESR parts (it wasn't necessary, but I didn't
like the look of some of them). Includes DC power supply, but no
antenna. $300 OBO. Shipping extra. Reply offline.

Joe Gray
W5JG
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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

Charles
would you mind sharing 1 second frequency data that you get out of the  
tbolt to get an idea what is possible. Looks like we are not the only ones  
trying to improve frequency performance and hopefully some one will share  
settings.
Bert Kehren
 
 
In a message dated 9/10/2016 6:42:17 A.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

Bert  wrote:

>  would you please share your settings, this is exactly  what we are  
looking
>  for. We are doing it by trial and  error but your expertise will help 
greatly.

Well, I spent the holiday  weekend looking for the "safe place" where I 
recorded my final Tbolt  tuning parameters -- without success.  After I 
tuned them and  qualified them as fit for long-term duty, I disconnected 
the com ports and  stashed them away in a very quiet and hard to access 
location with just  the 10MHz coax connected, so I can't use the comms to 
extract the  parameters without disturbing the Tbolts (which have now 
settled nicely,  undisturbed for ~10 years).

But what I did wasn't rocket science -- I  just read up on the tuning 
parameters, determined which ones would likely  affect the stability of 
the 10MHz output, made some educated guesses about  the likely best 
settings, and started playing.  It took me several  weeks of 
experimentation (on and off), and the parameters I settled on  were 
somewhat different between the two units I kept (primarily, the loop  
time constant and damping, which ideally should be set to complement the  
particular OCXO in each unit).

I recommend extreme caution when you  hear suggestions to use low loop 
damping, or to monkey very much with the  oscillator scale factor.  I 
found that high damping (far above the  1.2 default value) worked best 
for my units.  (Like you, I care most  about the stability and accuracy 
of the 10MHz output.  I don't even  have the PPS turned on.)

Before you do anything else, I strongly  suggest a full factory reset to 
put everything into a known state, and  work from there.

You have received some advice to use the "autotune"  routine in Lady 
Heather.  I seem to recall several people reporting  that it worked well 
for them, and there is nothing to lose by trying  it.  However, in my 
case it screwed up the tuning of both units so  badly that I had to do 
factory resets and then re-enter my custom  parameters.  I might have 
been using a version of LH that didn't have  the latest autotune code, or 
perhaps the autotune function needs to start  from factory default 
settings, or maybe the phase of the moon was wrong --  but I was sure 
glad I had recorded the tuning parameters I worked out by  experiment, so 
I didn't have to start over again!  Just be prepared  to do another 
factory reset and start experimenting if autotune doesn't  work to your 
liking.

So, I would suggest: (1) do a full factory  reset, let it run for a few 
weeks, and take data; (2) use the autotune  routine, let it run for a few 
weeks, and take data.  If you are not  satisfied with the results at this 
point, (3) do another full factory  reset and begin experimenting manually.

Best  regards,

Charles


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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bert wrote:


 would you please share your settings, this is exactly what we are  looking
 for. We are doing it by trial and error but your expertise will help greatly.


Well, I spent the holiday weekend looking for the "safe place" where I 
recorded my final Tbolt tuning parameters -- without success.  After I 
tuned them and qualified them as fit for long-term duty, I disconnected 
the com ports and stashed them away in a very quiet and hard to access 
location with just the 10MHz coax connected, so I can't use the comms to 
extract the parameters without disturbing the Tbolts (which have now 
settled nicely, undisturbed for ~10 years).


But what I did wasn't rocket science -- I just read up on the tuning 
parameters, determined which ones would likely affect the stability of 
the 10MHz output, made some educated guesses about the likely best 
settings, and started playing.  It took me several weeks of 
experimentation (on and off), and the parameters I settled on were 
somewhat different between the two units I kept (primarily, the loop 
time constant and damping, which ideally should be set to complement the 
particular OCXO in each unit).


I recommend extreme caution when you hear suggestions to use low loop 
damping, or to monkey very much with the oscillator scale factor.  I 
found that high damping (far above the 1.2 default value) worked best 
for my units.  (Like you, I care most about the stability and accuracy 
of the 10MHz output.  I don't even have the PPS turned on.)


Before you do anything else, I strongly suggest a full factory reset to 
put everything into a known state, and work from there.


You have received some advice to use the "autotune" routine in Lady 
Heather.  I seem to recall several people reporting that it worked well 
for them, and there is nothing to lose by trying it.  However, in my 
case it screwed up the tuning of both units so badly that I had to do 
factory resets and then re-enter my custom parameters.  I might have 
been using a version of LH that didn't have the latest autotune code, or 
perhaps the autotune function needs to start from factory default 
settings, or maybe the phase of the moon was wrong -- but I was sure 
glad I had recorded the tuning parameters I worked out by experiment, so 
I didn't have to start over again!  Just be prepared to do another 
factory reset and start experimenting if autotune doesn't work to your 
liking.


So, I would suggest: (1) do a full factory reset, let it run for a few 
weeks, and take data; (2) use the autotune routine, let it run for a few 
weeks, and take data.  If you are not satisfied with the results at this 
point, (3) do another full factory reset and begin experimenting manually.


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bob Camp]

Hi

> On Sep 10, 2016, at 6:40 AM, Charles Steinmetz  wrote:
> 
> Bert wrote:
> 
>> would you please share your settings, this is exactly what we are  looking
>> for. We are doing it by trial and error but your expertise will help greatly.
> 
> Well, I spent the holiday weekend looking for the "safe place" where I 
> recorded my final Tbolt tuning parameters -- without success.  After I tuned 
> them and qualified them as fit for long-term duty, I disconnected the com 
> ports and stashed them away in a very quiet and hard to access location with 
> just the 10MHz coax connected, so I can't use the comms to extract the 
> parameters without disturbing the Tbolts (which have now settled nicely, 
> undisturbed for ~10 years).
> 
> But what I did wasn't rocket science -- I just read up on the tuning 
> parameters, determined which ones would likely affect the stability of the 
> 10MHz output, made some educated guesses about the likely best settings, and 
> started playing.  It took me several weeks of experimentation (on and off), 
> and the parameters I settled on were somewhat different between the two units 
> I kept (primarily, the loop time constant and damping, which ideally should 
> be set to complement the particular OCXO in each unit).
> 
> I recommend extreme caution when you hear suggestions to use low loop 
> damping, or to monkey very much with the oscillator scale factor.  I found 
> that high damping (far above the 1.2 default value) worked best for my units. 
>  (Like you, I care most about the stability and accuracy of the 10MHz output. 
>  I don't even have the PPS turned on.)
> 
> Before you do anything else, I strongly suggest a full factory reset to put 
> everything into a known state, and work from there.
> 
> You have received some advice to use the "autotune" routine in Lady Heather.  
> I seem to recall several people reporting that it worked well for them, and 
> there is nothing to lose by trying it.  However, in my case it screwed up the 
> tuning of both units so badly that I had to do factory resets and then 
> re-enter my custom parameters.  I might have been using a version of LH that 
> didn't have the latest autotune code, or perhaps the autotune function needs 
> to start from factory default settings, or maybe the phase of the moon was 
> wrong -- but I was sure glad I had recorded the tuning parameters I worked 
> out by experiment, so I didn't have to start over again!  Just be prepared to 
> do another factory reset and start experimenting if autotune doesn't work to 
> your liking.

The one thing that autotune seems to do well is to come up with the actual 
sensitivity of the OCXO you have. It depends on a few things to do this so it 
might go wrong. I’ve never seen it come up with the wrong number. It then 
appears to drop in a gain and damping that make more sense than the original 
numbers. Since it is a pre-defined pair of numbers, it is indeed a “one size 
fits all” solution. 

Bob

> 
> So, I would suggest: (1) do a full factory reset, let it run for a few weeks, 
> and take data; (2) use the autotune routine, let it run for a few weeks, and 
> take data.  If you are not satisfied with the results at this point, (3) do 
> another full factory reset and begin experimenting manually.
> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] "Instantaneous frequency" [WAS: Tbolt issues]

[Charles Steinmetz]

Bill wrote:

[lots and lots of snippage - the original message was posted on 9/2 for 
those who want to review it]



we can also define waveforms where the
frequency parameter is itself a function over time.


Agreed.


In these cases there obviously is an instantaneous frequency


"Obviously"?  Hardly.


the instantaneous angular frequency describes the derivative of the
phase change vs time.


Right.  As I said, the so-called "instantaneous frequency" is a 
mathematical fiction that describes the result of a differentiation with 
respect to a waveform that is constantly changing in frequency.  Like 
many mathematical concepts, it is abstract -- it has no real existence 
in the world.



At work I deal with equipment which generates RF signal using a 50 GS/s
maximum sampling rate D/A converter, which provides one sample every 20
ps. I can create a linear frequency up-chirp using this instrument with
a frequency modulation slope of 2 MHz per us



The 10-bit resolution voltage values
of each of those samples (spaced by 20 ps) select the closest D/A values
which represent the sine function with an "instantaneous frequency"
given by somefunction (which in this case is a linear ramp). So you can
think of this as a discrete system which is changing the instantaneous
frequency every 20 ps


Yes, you "can think of it as..." and "it represents" "instantaneous 
frequency."  But again, that is just a mathematical fiction, *not* a 
real feature of the signal in the world.  There is no instantaneous 
frequency, but (like many mathematical constructs) it can be a useful 
fiction.



On the measurement side, I have an instrument with a 16-bit 400 MS/s A/D
which can sample a superheterodyne downconverted signal at an IF
frequency over a 165 MHz span. Those samples are run through a DDC
(digital downconverter using a Hilbert filter)


Note that both of these hardware examples operate in the finite time 
domain, not the instantaneous (infinitessimal time) domain.  They are no 
different from my example at 10MHz, except that the decimal point has 
been moved several decades.  But no matter how short a finite interval 
you use, it is still an infinity away from "instantaneous" (a single 
point in time of zero duration).


In both cases, the so-called "instantaneous frequency" is derived by 
differentiating a finite-time measurement.  In neither case is the 
frequency measured instantaneously.  It *cannot* be, either in practice 
or, more importantly, in theory, for a very good reason -- it is not a 
real entity, it is only a mathematical fiction.  Useful to we engineers, 
but not real.


Best regards,

Charles


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