Re: [time-nuts] Tbolt issues

[ewkehren via time-nuts]

Know all that that is why we decided not to do it. Not knowing all the ins and 
outs and limits of the Tbolts that is why I asked the question to begin with
Bert Kehren




Sent from Samsung tabletCharles Steinmetz  wrote:Bert 
wrote:

> On our to do list was temperature control and clean up loop.  In order to do
> an analog clean up we need short interval changes and that is why  I went
> on the list since we have not been able to do it and looking at past  posting
> have not found data that will get us there.

To do any kind of "cleanup" at tau=1S, you need a source that is better 
at that tau than the one you are trying to clean up.  But if you have 
that, why use it to clean up something else?  Just use it as your 
standard.  (One might respond that the point would be to use the Tbolt 
to discipline the better oscillator at longer tau to correct drift, but 
you would need a very long time constant -- thousands of seconds -- 
which you cannot achieve with an analog loop.)  I do not think there is 
any realistic possibility of doing the kind of cleanup you propose in 
the analog domain.

Are you absolutely certain you tried the Tbolt with the damping set to 
10 seconds or more?  Did you let it settle for several weeks before 
deciding it wasn't doing what you need?

Perhaps you can try one last time:

1. Do a hard reset back to factory settings
2. Change TC to 500 seconds and damping to 10-12
3. Set recovery jam synch to "ON" with a threshold of 55-65 nS
4. Set recovery max offset frequency to >=1000 (this is in ppb)
5. Put it in an undisturbed location, inside a box of some kind
6. Let it sit for a month
7. Now, measure it

If this is better, but not quite good enough, try damping settings of 30 
and 100.

Alternatively, for a 10MHz reference you can just forget about and use, 
buy another PRS10 and discipline it with the PPS from the Tbolt.  I'd 
recommend buying a new one from SRS so you know that it has the PPS 
discipline feature and you could get help from SRS to optimize the 
discipline for your needs (the discipline is very adjustable and it is 
easy to get confused).

Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bert wrote:


On our to do list was temperature control and clean up loop.  In order to do
an analog clean up we need short interval changes and that is why  I went
on the list since we have not been able to do it and looking at past  posting
have not found data that will get us there.


To do any kind of "cleanup" at tau=1S, you need a source that is better 
at that tau than the one you are trying to clean up.  But if you have 
that, why use it to clean up something else?  Just use it as your 
standard.  (One might respond that the point would be to use the Tbolt 
to discipline the better oscillator at longer tau to correct drift, but 
you would need a very long time constant -- thousands of seconds -- 
which you cannot achieve with an analog loop.)  I do not think there is 
any realistic possibility of doing the kind of cleanup you propose in 
the analog domain.


Are you absolutely certain you tried the Tbolt with the damping set to 
10 seconds or more?  Did you let it settle for several weeks before 
deciding it wasn't doing what you need?


Perhaps you can try one last time:

1. Do a hard reset back to factory settings
2. Change TC to 500 seconds and damping to 10-12
3. Set recovery jam synch to "ON" with a threshold of 55-65 nS
4. Set recovery max offset frequency to >=1000 (this is in ppb)
5. Put it in an undisturbed location, inside a box of some kind
6. Let it sit for a month
7. Now, measure it

If this is better, but not quite good enough, try damping settings of 30 
and 100.


Alternatively, for a 10MHz reference you can just forget about and use, 
buy another PRS10 and discipline it with the PPS from the Tbolt.  I'd 
recommend buying a new one from SRS so you know that it has the PPS 
discipline feature and you could get help from SRS to optimize the 
discipline for your needs (the discipline is very adjustable and it is 
easy to get confused).


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

 
Yes Charles  
I was not part of or following the original Tbolt  discussions. My setup at 
the time was Loran C with Austron 2110, backed up with  Cs and 60 Khz using 
a Tracor 599H. My work was focused on FRK FRS Rb’s using  Shera with very 
good results. At the same time Juerg was using a PRS10  controlled by a Tbolt 
and feeding a OSA FO3/8600. With the demise of Loran C I  switched to Tbolt 
feeding the 2110 because I did see the frequency jumps.  Juerg’s PRS10 died 
a year ago and he replaced it with his Tbolt, expecting the  FO3 to clean 
up the Tbolt. After disappointing results on some of our work urged  him to 
do a cross matrix on all his sources and found out the FO3 did nothing to  
the Tbolt He bought his first one through Tarp. I bought 1 for him and 2 for 
me  all US sellers.  
Off list Tom has looked at Juergs data and we and he are  convinced that 
antenna and equipment is good. We have used auto tune and  variable settings. 
On our to do list was temperature control and clean up loop.  In order to do 
an analog clean up we need short interval changes and that is why  I went 
on the list since we have not been able to do it and looking at past  posting 
have not found data that will get us there. For our work frequency has  to 
be better than 1 E-11 one second, he had it with the PRS 10 setup. Unless  
some one can help us with settings that make analog loop clean up possible we 
 will not revisit Tbolt. Juerg will use it as an excellent 1pps source and 
I will  use it with the 2110 which is digital and has a 100 second  loop.We  
are already refocusing on work on a FRK/M100 GPSDO plan on having it up and 
 running with in a month, waiting for boards. Last two years distracted by 
clean  up of the Shera code before releasing it, controller for FE 5680 5650 
and FE  405.  
 
 
In a message dated 9/10/2016 5:48:49 P.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

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] 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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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] 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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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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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] Tbolt issues

[Bob kb8tq]

Hi

The problem is that ADEV is not really the best tool for measuring / modeling 
narrow band noise. There are other measures that are better. None of them 
really give you a direct connection to a band limited noise process. Without a 
model for the process, coming up with a max limit is just speculation. It is 
frighteningly easy to come up with nasty processes that look fine when viewed 
with this or that measure. The repeated requests on list for raw data are a 
direct result of people having seen this.

Bob

> On Sep 2, 2016, at 5:06 PM, Lars Walenius  wrote:
> 
> You are absolute right in that it is a that depends sort of things. 
> 
> Fast temperature changes might really be something that upsets a GPSDO 
> especially if the time constant is long. 
> 
> By taking temperature data and multiply with your oscillators temperature 
> coefficient you can do ADEV for the temperature dependence. Quite interesting 
> especially with an HVAC or the sun shining on the GPSDO! Or you can simply 
> take the maximum temperature shift x temperature coefficient for the same 
> time as your GPSDO  time constant to estimate the frequency error you can 
> have depending on the temperature. Of course that is also a that depend sort 
> of thing but at least gives an indication. Say that you have for example a 
> time constant of 1000secs and a temperature change of 2°C during 1000secs and 
> a temperature coefficient of 5E-11/°C that will give you a change of 1E-10 
> and the loop will not manage to compensate for it in time.
> 
> Lars
> 
>> From: Bob
>> Skickat: den 2 september 2016 22:00
> 
>> Since the measurement in the frequency domain is a "peak" measure, you need 
>> to convert both to frequency error and to an absolute max. If you *do* care 
>> about the one second per day (or 10 days) as some do, that is a different 
>> factor than one second out of two minutes. Since the noise is likely not to 
>> be white noise, the factor is one of those "that depends" sort of things. It 
>> includes messy stuff like the room temperature changes and the control 
>> loop's response to them. In some designs the response may be multi level. 
>> The temp transient hits the voltage reference, DAC, and crystal in the OCXO 
>> at different times...
> 
>> Bob
> 
>>> On Sep 2, 2016, at 3:08 PM, Lars Walenius  wrote:
>> 
>> I might be completely wrong with my ”quick rule of thumb” (frequency 
>> accuracy: 10x the worst ADEV at all Taus longer than the gate time). but my 
>> assumptions are these:
>> 
>> 1. You have a GPSDO. (A free running oscillator as a rubidium or OCXO will 
>> not work if that is what you call a ”normal” frequency standard).
>> 2. The GPSDO design is such that the frequency error goes towards zero the 
>> longer time you measure the frequency. Otherwise you can say nothing from 
>> the ADEV to the absolute frequency error I think.
>> 3. ADEV can be seen as the standard deviation of all differences in 
>> frequency between two nearby frequency measurements (with no dead times) 
>> multiplied with a small factor (sqrt 0.5).
>> 4. Absolute frequency errors will at least be in the same range as the 
>> differences if the long-term error is near zero.
>> 5. It will always be larger frequency errors for shorter times. My 
>> assumption is for example that at 100 seconds you have 30ppt frequency error 
>> that is 3ns drift in 100seconds, If you plot that as straight line you will 
>> also have 30ppt at all shorter ”gate times”. If the line isn´t straight you 
>> will always find ”points” that has more than 30ppt frequency errors.
>> 6. At least around the Taus similar to the time constant of the GPSDO 
>> especially the GPS noise will give peak frequency errors compared to the 
>> average that are quite high. A factor of ten may be very conservative but as 
>> can be seen in the Tbolt measurements by TvB it is quite close. With OCXO 
>> and Rb GPSDO´s that I have tried to optimize I have seen about this factor 
>> or slightly less. With the DOT050 VCTCXO the ratio was even higher, up to 14 
>> (ADEV 7E-11 1-100secs and 1E-9 max freq errors at 1 second gate time).
>> 
>> Lars
>> 
>>> From: Bob
>>> Sent: den 2 september 2016 15:20
>> 
>>> The GPSDO might have an ADEV of 1 ppt at 1 sec and that rises to 30 ppt at 
>>> 100 sec. It also might not, but let's use those numbers.
>> 
>>> ADEV is a standard deviation. You can get an idea of the magnitude of the 
>>> change reading to reading from it. It does not give you a sign for that 
>>> change. In the case above, it is a good bet that you see strings of 1 sec 
>>> data with mostly the same sign.  They have to add up to the 30X larger 
>>> number when tau gets to 100 sec.
>> 
>>> That creates a major problem if you just look at the 1 sec data. A "normal" 
>>> frequency standard does not have a rise or bump like that in the ADEV plot. 
>>> Thus the quick rule of thumb stuff falls apart. The correct way to do it 
>>> will 

Re: [time-nuts] Tbolt issues

[Lars Walenius]

You are absolute right in that it is a that depends sort of things. 

Fast temperature changes might really be something that upsets a GPSDO 
especially if the time constant is long. 

By taking temperature data and multiply with your oscillators temperature 
coefficient you can do ADEV for the temperature dependence. Quite interesting 
especially with an HVAC or the sun shining on the GPSDO! Or you can simply take 
the maximum temperature shift x temperature coefficient for the same time as 
your GPSDO  time constant to estimate the frequency error you can have 
depending on the temperature. Of course that is also a that depend sort of 
thing but at least gives an indication. Say that you have for example a time 
constant of 1000secs and a temperature change of 2°C during 1000secs and a 
temperature coefficient of 5E-11/°C that will give you a change of 1E-10 and 
the loop will not manage to compensate for it in time.

Lars

>From: Bob
>Skickat: den 2 september 2016 22:00

>Since the measurement in the frequency domain is a "peak" measure, you need to 
>convert both to frequency error and to an absolute max. If you *do* care about 
>the one second per day (or 10 days) as some do, that is a different factor 
>than one second out of two minutes. Since the noise is likely not to be white 
>noise, the factor is one of those "that depends" sort of things. It includes 
>messy stuff like the room temperature changes and the control loop's response 
>to them. In some designs the response may be multi level. The temp transient 
>hits the voltage reference, DAC, and crystal in the OCXO at different times...

>Bob

>> On Sep 2, 2016, at 3:08 PM, Lars Walenius  wrote:
> 
> I might be completely wrong with my ”quick rule of thumb” (frequency 
> accuracy: 10x the worst ADEV at all Taus longer than the gate time). but my 
> assumptions are these:
> 
> 1. You have a GPSDO. (A free running oscillator as a rubidium or OCXO will 
> not work if that is what you call a ”normal” frequency standard).
> 2. The GPSDO design is such that the frequency error goes towards zero the 
> longer time you measure the frequency. Otherwise you can say nothing from the 
> ADEV to the absolute frequency error I think.
> 3. ADEV can be seen as the standard deviation of all differences in frequency 
> between two nearby frequency measurements (with no dead times) multiplied 
> with a small factor (sqrt 0.5).
> 4. Absolute frequency errors will at least be in the same range as the 
> differences if the long-term error is near zero.
> 5. It will always be larger frequency errors for shorter times. My assumption 
> is for example that at 100 seconds you have 30ppt frequency error that is 3ns 
> drift in 100seconds, If you plot that as straight line you will also have 
> 30ppt at all shorter ”gate times”. If the line isn´t straight you will always 
> find ”points” that has more than 30ppt frequency errors.
> 6. At least around the Taus similar to the time constant of the GPSDO 
> especially the GPS noise will give peak frequency errors compared to the 
> average that are quite high. A factor of ten may be very conservative but as 
> can be seen in the Tbolt measurements by TvB it is quite close. With OCXO and 
> Rb GPSDO´s that I have tried to optimize I have seen about this factor or 
> slightly less. With the DOT050 VCTCXO the ratio was even higher, up to 14 
> (ADEV 7E-11 1-100secs and 1E-9 max freq errors at 1 second gate time).
> 
> Lars
> 
>> From: Bob
>> Sent: den 2 september 2016 15:20
> 
>> The GPSDO might have an ADEV of 1 ppt at 1 sec and that rises to 30 ppt at 
>> 100 sec. It also might not, but let's use those numbers.
> 
>> ADEV is a standard deviation. You can get an idea of the magnitude of the 
>> change reading to reading from it. It does not give you a sign for that 
>> change. In the case above, it is a good bet that you see strings of 1 sec 
>> data with mostly the same sign.  They have to add up to the 30X larger 
>> number when tau gets to 100 sec.
> 
>> That creates a major problem if you just look at the 1 sec data. A "normal" 
>> frequency standard does not have a rise or bump like that in the ADEV plot. 
>> Thus the quick rule of thumb stuff falls apart. The correct way to do it 
>> will always be to work out what the noise process is and calculate based on 
>> it. That is not a popular thing to do 
> 
>> Bob
> 
>> On Sep 2, 2016, at 6:38 AM, Lars Walenius wrote:
>> 
>> Hello Bert,
>> 
>> For me your findings look very much the same as this:
>> http://www.leapsecond.com/pages/tbolt-8d/ 
>> At least for me I should say the (absolute) frequency accuracy for this 
>> Tbolt is not better than +-1E10 with 1 or 10 seconds gate times on a 
>> counter. Maybe I am totally wrong as both Tom and Charles says that your 
>> Tbolt is bad.
>> 
>> As Bob Camp said we need a confidence interval. For me in this case it is 
>> peak values if they occur more than a couple of times. Think of  voltmeters. 
>> 

Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

Since the measurement in the frequency domain is a "peak" measure, you need to 
convert both to frequency error and to an absolute max. If you *do* care about 
the one second per day (or 10 days) as some do, that is a different factor than 
one second out of two minutes. Since the noise is likely not to be white noise, 
the factor is one of those "that depends" sort of things. It includes messy 
stuff like the room temperature changes and the control loop's response to 
them. In some designs the response may be multi level. The temp transient hits 
the voltage reference, DAC, and crystal in the OCXO at different times...

Bob

> On Sep 2, 2016, at 3:08 PM, Lars Walenius  wrote:
> 
> I might be completely wrong with my ”quick rule of thumb” (frequency 
> accuracy: 10x the worst ADEV at all Taus longer than the gate time). but my 
> assumptions are these:
> 
> 1. You have a GPSDO. (A free running oscillator as a rubidium or OCXO will 
> not work if that is what you call a ”normal” frequency standard).
> 2. The GPSDO design is such that the frequency error goes towards zero the 
> longer time you measure the frequency. Otherwise you can say nothing from the 
> ADEV to the absolute frequency error I think.
> 3. ADEV can be seen as the standard deviation of all differences in frequency 
> between two nearby frequency measurements (with no dead times) multiplied 
> with a small factor (sqrt 0.5).
> 4. Absolute frequency errors will at least be in the same range as the 
> differences if the long-term error is near zero.
> 5. It will always be larger frequency errors for shorter times. My assumption 
> is for example that at 100 seconds you have 30ppt frequency error that is 3ns 
> drift in 100seconds, If you plot that as straight line you will also have 
> 30ppt at all shorter ”gate times”. If the line isn´t straight you will always 
> find ”points” that has more than 30ppt frequency errors.
> 6. At least around the Taus similar to the time constant of the GPSDO 
> especially the GPS noise will give peak frequency errors compared to the 
> average that are quite high. A factor of ten may be very conservative but as 
> can be seen in the Tbolt measurements by TvB it is quite close. With OCXO and 
> Rb GPSDO´s that I have tried to optimize I have seen about this factor or 
> slightly less. With the DOT050 VCTCXO the ratio was even higher, up to 14 
> (ADEV 7E-11 1-100secs and 1E-9 max freq errors at 1 second gate time).
> 
> Lars
> 
>> From: Bob
>> Sent: den 2 september 2016 15:20
> 
>> The GPSDO might have an ADEV of 1 ppt at 1 sec and that rises to 30 ppt at 
>> 100 sec. It also might not, but let's use those numbers.
> 
>> ADEV is a standard deviation. You can get an idea of the magnitude of the 
>> change reading to reading from it. It does not give you a sign for that 
>> change. In the case above, it is a good bet that you see strings of 1 sec 
>> data with mostly the same sign.  They have to add up to the 30X larger 
>> number when tau gets to 100 sec.
> 
>> That creates a major problem if you just look at the 1 sec data. A "normal" 
>> frequency standard does not have a rise or bump like that in the ADEV plot. 
>> Thus the quick rule of thumb stuff falls apart. The correct way to do it 
>> will always be to work out what the noise process is and calculate based on 
>> it. That is not a popular thing to do 
> 
>> Bob
> 
>> On Sep 2, 2016, at 6:38 AM, Lars Walenius wrote:
>> 
>> Hello Bert,
>> 
>> For me your findings look very much the same as this:
>> http://www.leapsecond.com/pages/tbolt-8d/ 
>> At least for me I should say the (absolute) frequency accuracy for this 
>> Tbolt is not better than +-1E10 with 1 or 10 seconds gate times on a 
>> counter. Maybe I am totally wrong as both Tom and Charles says that your 
>> Tbolt is bad.
>> 
>> As Bob Camp said we need a confidence interval. For me in this case it is 
>> peak values if they occur more than a couple of times. Think of  voltmeters. 
>> If it is out of spec say for only a couple of hours but it happens several 
>> times say during a month or year and the voltmeters is not considered bad I 
>> should say change the spec. If I were going to use the Tbolt as a reference 
>> in a production environment with a 1 or 10 sec gate time I probably would 
>> set the internal spec to 2E-10.
>> 
>> If I understand correct the Tracor 527E has a low pass filter with a time 
>> constant of 1second so the 1 second frequency average data should be 
>> relevant.
>> 
>> As I am also interested in frequency accuracy with GPSDO´s used with 
>> frequency counters, I have a maybe far to simplistic rule of accuracy: (10x 
>> the worst ADEV at all Taus longer than the gate time). So for the Tbolt with 
>> time constant of 100 seconds it is a hump of about 1E-11 at 100seconds so at 
>> gate times shorter than 100seconds I expect to see excursions up to 1E-10. 
>> If you set the time constant to 1000seconds and the OCXO in the Thunderbolt 

Re: [time-nuts] Tbolt issues

[Lars Walenius]

I might be completely wrong with my ”quick rule of thumb” (frequency accuracy: 
10x the worst ADEV at all Taus longer than the gate time). but my assumptions 
are these:

1. You have a GPSDO. (A free running oscillator as a rubidium or OCXO will not 
work if that is what you call a ”normal” frequency standard).
2. The GPSDO design is such that the frequency error goes towards zero the 
longer time you measure the frequency. Otherwise you can say nothing from the 
ADEV to the absolute frequency error I think.
3. ADEV can be seen as the standard deviation of all differences in frequency 
between two nearby frequency measurements (with no dead times) multiplied with 
a small factor (sqrt 0.5).
4. Absolute frequency errors will at least be in the same range as the 
differences if the long-term error is near zero.
5. It will always be larger frequency errors for shorter times. My assumption 
is for example that at 100 seconds you have 30ppt frequency error that is 3ns 
drift in 100seconds, If you plot that as straight line you will also have 30ppt 
at all shorter ”gate times”. If the line isn´t straight you will always find 
”points” that has more than 30ppt frequency errors.
6. At least around the Taus similar to the time constant of the GPSDO 
especially the GPS noise will give peak frequency errors compared to the 
average that are quite high. A factor of ten may be very conservative but as 
can be seen in the Tbolt measurements by TvB it is quite close. With OCXO and 
Rb GPSDO´s that I have tried to optimize I have seen about this factor or 
slightly less. With the DOT050 VCTCXO the ratio was even higher, up to 14 (ADEV 
7E-11 1-100secs and 1E-9 max freq errors at 1 second gate time).

Lars

>From: Bob
>Sent: den 2 september 2016 15:20

>The GPSDO might have an ADEV of 1 ppt at 1 sec and that rises to 30 ppt at 100 
>sec. It also might not, but let's use those numbers.

>ADEV is a standard deviation. You can get an idea of the magnitude of the 
>change reading to reading from it. It does not give you a sign for that 
>change. In the case above, it is a good bet that you see strings of 1 sec data 
>with mostly the same sign.  They have to add up to the 30X larger number when 
>tau gets to 100 sec.

>That creates a major problem if you just look at the 1 sec data. A "normal" 
>frequency standard does not have a rise or bump like that in the ADEV plot. 
>Thus the quick rule of thumb stuff falls apart. The correct way to do it will 
>always be to work out what the noise process is and calculate based on it. 
>That is not a popular thing to do 

>Bob

> On Sep 2, 2016, at 6:38 AM, Lars Walenius wrote:
> 
> Hello Bert,
> 
> For me your findings look very much the same as this:
> http://www.leapsecond.com/pages/tbolt-8d/ 
> At least for me I should say the (absolute) frequency accuracy for this Tbolt 
> is not better than +-1E10 with 1 or 10 seconds gate times on a counter. Maybe 
> I am totally wrong as both Tom and Charles says that your Tbolt is bad.
> 
> As Bob Camp said we need a confidence interval. For me in this case it is 
> peak values if they occur more than a couple of times. Think of  voltmeters. 
> If it is out of spec say for only a couple of hours but it happens several 
> times say during a month or year and the voltmeters is not considered bad I 
> should say change the spec. If I were going to use the Tbolt as a reference 
> in a production environment with a 1 or 10 sec gate time I probably would set 
> the internal spec to 2E-10.
> 
> If I understand correct the Tracor 527E has a low pass filter with a time 
> constant of 1second so the 1 second frequency average data should be relevant.
> 
> As I am also interested in frequency accuracy with GPSDO´s used with 
> frequency counters, I have a maybe far to simplistic rule of accuracy: (10x 
> the worst ADEV at all Taus longer than the gate time). So for the Tbolt with 
> time constant of 100 seconds it is a hump of about 1E-11 at 100seconds so at 
> gate times shorter than 100seconds I expect to see excursions up to 1E-10. If 
> you set the time constant to 1000seconds and the OCXO in the Thunderbolt is 
> good to 2 to 3E-12 all the way 1-1000 seconds you probably don´t have 
> excursions higher than 2 to 3E-11 at 1-100 seconds gate times.
> 
> Lars
> 
> 
> Från: Bert Kehren via time-nuts
> Skickat: den 1 september 2016 19:09
> 
> We have been following the Tbolt power discussions but what I am missing is 
>  the main problem with Tbolts. All the power work will not improve the 
> frequency  performance of the unit because the frequency is constantly 
> changed 
> to correct  time. Tbolt is an excellent time device but not good for 
> frequency reference  past 1E-10. I noticed it when I bought it and compared 
> it with 
> my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
> digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
> OSA F3 for Tbolt clean up but  continuous bad results on our work 

Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

Just to be a bit more clear:

This is *not* something unique to the Tbolt. It shows up on all GPSDO's. There 
have been a lot of posts with data plots showing this on lots of GPSDO's. The 
issue is more basic than a goof in a control loop setting. To some extent it is 
a problem on all frequency sources. GPSDO's just happen to get looked at more 
often.

Bob

> On Sep 2, 2016, at 1:11 PM, Mark Sims  wrote:
> 
> If you don't like how the Tbolt adjusts the oscillator on your Tbolt... do it 
> yourself.   You can set up the Tbolt for manual DAC control and implement 
> your own control loop.   Warren Sarkison and I implemented a alternate 
> control PID for the Tbolt DAC.   Yep,  it's in Lady Heather.  It's been a 
> while since I've played with it.   I seem to remember people getting down 
> close to the 1E-13 range.
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[time-nuts] Tbolt issues

[Mark Sims]

If you don't like how the Tbolt adjusts the oscillator on your Tbolt... do it 
yourself.   You can set up the Tbolt for manual DAC control and implement your 
own control loop.   Warren Sarkison and I implemented a alternate control PID 
for the Tbolt DAC.   Yep,  it's in Lady Heather.  It's been a while since I've 
played with it.   I seem to remember people getting down close to the 1E-13 
range.
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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

Charles,
 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.
English not being my native language linguistics are some time a  problem
Thanks 
Bert
 
 
In a message dated 9/1/2016 6:26:32 P.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

Bert  wrote:

> maybe some one smarter than us can working with the  parameters that Tbolt
> makes available better performance can be  achieved

I am quite sure of that

> the frequency is being  changed to compensate for time

Yes, the PPS is steered by making slight  adjustments to the OCXO 
frequency.  But you can make these  adjustments as arbitrarily small as 
you want with the setup  parameters.  I run my Tbolts with pretty tight 
limits on the  frequency adjustments.

> and we do not care about ADEV, we care  about the actual
> frequency at that moment it goes in to the measuring  device

There is no "there" there.  One never makes a frequency  measurement at 
just one instant -- the measurement will ALWAYS be done  over a macro 
time interval (very often, one second, sometimes 0.1, 10,  100, or 1000 
seconds).  We never observe, and have no way to know,  the instantaneous 
frequency (as you put it, "the actual frequency at that  moment it goes 
into the measuring device") -- so how can we care about  it?  The only 
thing relevant (or even meaningful) is the average  frequency during our 
measurement interval.

xDEV tells us half of  what we want to know -- how stable our oscillator 
is from one measurement  interval to another.  We would also like to know 
what frequency it is  wobbling around -- the "centroid" frequency, if you 
will (to borrow a  geometric term).  (Mathematicians can argue for days 
about which type  of "average" is appropriate here -- the rest of us just 
pick one and carry  on.)  ADEV does not tell us this "centroid" frequency 
directly, but  it can be extracted from the same measurements we took to 
calculate  ADEV.

I think you are being misled by a belief that the linguistic  construct, 
"instantaneous frequency," has real meaning in the world.   It doesn't.

Best  regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

The GPSDO might have an ADEV of 1 ppt at 1 sec and that rises to 30 ppt at 100 
sec. It also might not, but let's use those numbers.

ADEV is a standard deviation. You can get an idea of the magnitude of the 
change reading to reading from it. It does not give you a sign for that change. 
In the case above, it is a good bet that you see strings of 1 sec data with 
mostly the same sign.  They have to add up to the 30X larger number when tau 
gets to 100 sec.

That creates a major problem if you just look at the 1 sec data. A "normal" 
frequency standard does not have a rise or bump like that in the ADEV plot. 
Thus the quick rule of thumb stuff falls apart. The correct way to do it will 
always be to work out what the noise process is and calculate based on it. That 
is not a popular thing to do 

Bob

> On Sep 2, 2016, at 6:38 AM, Lars Walenius  wrote:
> 
> Hello Bert,
> 
> For me your findings look very much the same as this:
> http://www.leapsecond.com/pages/tbolt-8d/ 
> At least for me I should say the (absolute) frequency accuracy for this Tbolt 
> is not better than +-1E10 with 1 or 10 seconds gate times on a counter. Maybe 
> I am totally wrong as both Tom and Charles says that your Tbolt is bad.
> 
> As Bob Camp said we need a confidence interval. For me in this case it is 
> peak values if they occur more than a couple of times. Think of  voltmeters. 
> If it is out of spec say for only a couple of hours but it happens several 
> times say during a month or year and the voltmeters is not considered bad I 
> should say change the spec. If I were going to use the Tbolt as a reference 
> in a production environment with a 1 or 10 sec gate time I probably would set 
> the internal spec to 2E-10.
> 
> If I understand correct the Tracor 527E has a low pass filter with a time 
> constant of 1second so the 1 second frequency average data should be relevant.
> 
> As I am also interested in frequency accuracy with GPSDO´s used with 
> frequency counters, I have a maybe far to simplistic rule of accuracy: (10x 
> the worst ADEV at all Taus longer than the gate time). So for the Tbolt with 
> time constant of 100 seconds it is a hump of about 1E-11 at 100seconds so at 
> gate times shorter than 100seconds I expect to see excursions up to 1E-10. If 
> you set the time constant to 1000seconds and the OCXO in the Thunderbolt is 
> good to 2 to 3E-12 all the way 1-1000 seconds you probably don´t have 
> excursions higher than 2 to 3E-11 at 1-100 seconds gate times.
> 
> Lars
> 
> 
> Från: Bert Kehren via time-nuts
> Skickat: den 1 september 2016 19:09
> 
> We have been following the Tbolt power discussions but what I am missing is 
>  the main problem with Tbolts. All the power work will not improve the 
> frequency  performance of the unit because the frequency is constantly 
> changed 
> to correct  time. Tbolt is an excellent time device but not good for 
> frequency reference  past 1E-10. I noticed it when I bought it and compared 
> it with 
> my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
> digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
> OSA F3 for Tbolt clean up but  continuous bad results on our work resulted in 
> a detailed analysis using a  HP53132A counter and M100, FTS44060, two 
> OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does not 
> clean up the Tbolt and we see +-4E-11  changes and old data shows even some 
> +-8 
> E-11 excursions. With the popularity of  the Tbolt an analog or digital 
> clean up loop would make sense. We are working on  both, the analog because I 
> saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not 
> plan 
> on using those Rb's but focus on M100 and FRK. 
> The collective expertise of time nuts could make a significant  contribution
> For power in critical applications we use the excellent work from Bern Kaa  
> a friend for the last twenty years and well known because of his published 
> work  in the European HAM community
> Bert Kehren
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Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

The gotcha in your approach is that you are using more than one sample out of 
the system to get frequency. Thus you are measuring over a time period. To get 
instantaneous frequency you need to base it on a single sample. There are some 
other restrictions (infinite bandwidth being the big one). 

Bob

> On Sep 2, 2016, at 2:25 AM, Bill Byrom  wrote:
> 
> The problem is that "frequency" has more than one meaning. The main
> dictionary definitions have to do with the frequency of occurrence of
> some items in a category with respect to a larger set, or the frequency
> of occurrence of some repeating event per unit of time. But we also use
> mathematical representations of waveforms containing a "frequency" or
> "angular frequency" parameter, and we can also define waveforms where
> the frequency parameter is itself a function over time. In these cases
> there obviously is an instantaneous frequency which for example
> represents the value of f at a particular value of t in sin(2 pi f t),
> where f = somefunction(t).
> 
> So you have discrete events (a rising edge, or the positive zero
> crossing of a sinusoidal waveform) which define a "frequency" property
> which only has meaning when we compare the time values of at least two
> of these events, but we also have an equation defining a sinewave, where
> the instantaneous angular frequency describes the derivative of the
> phase change vs time. You have to consider continuous as well as
> discrete systems.
> 
> In modern modulation theory the concept of vector modulation is used.
> This involves a carrier wave frequency and amplitude, then I/Q or vector
> modulation which instantaneously varies the amplitude (vector length)
> and phase (vector angle) of the signal. For a constant amplitude signal,
> the derivative of the vector modulation phase (arctangent of the I/Q
> ratio) corresponds to the instantaneous frequency.
> 
> 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 (microsecond) at a center
> frequency of 1 GHz. So there are 50,000 D/A samples each us, and
> although the average frequency over that us is 1 GHz (50 D/A
> samples/cycle), the start of the chirp is at 999 MHz (about 50.05 D/A
> samples/cycle) while the end of the chirp 1 us later is at 1001 MHz
> (about 49.95 D/A samples/cycle). In this case, the value of
> somefunction(T0 - 1 us) = 999 MHz and somefunction(T0 + 1 us) = 1001
> MHz, where T0 is the time at the middle of the chirp. There are
> obviously not an integral number of D/A samples per sinewave cycle, but
> that is no problem. The D/A has 10 bits of resolution and is not
> perfect, and the combination of jitter and other errors produces
> wideband noise and spurs smeared over the frequency range of DC to the
> Nyquist rate, but these errors are very small (many 10's of dB down from
> the desired signal).
> 
> The signal I just described creates the 2 MHz chirp in a 1 us time
> interval using 50,000 D/A samples. 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 (with instrument errors due to the limited 10-bit
> voltage resolution, amplitude errors, jitter errors, and errors from
> other sources).
> 
> 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) to create two 200 MS/s
> streams (I and Q waveforms). For the example above, the 1 us 2 MHz wide
> linear chirp is sampled with 200 I/Q points, and calculating the
> derivative (slope) of the phase - which is arctangent(I/Q) - results in
> a frequency vs time trace. So the instantaneous frequency can be
> measured with 5 ns resolution (1/200 MS/s I/Q rate) in time across that
> 1 us wide frequency chirp.
> 
> So yes, the concept of "instantaneous frequency" is valid and is used
> everyday in many practical measurements on phase locked loop frequency
> synthesizers, radars, testing Bluetooth FSK transmitters, and for many
> other applications.
> 
> --
> Bill Byrom N5BB
> 
> 
> 
>> On Thu, Sep 1, 2016, at 10:39 PM, jimlux wrote:
>>> On 9/1/16 5:51 PM, Charles Steinmetz wrote:
>>> Nick wrote:
>>> 
 On a theoretical basis, can one speak of the limit of the frequency
 observed as tau approaches zero?
 Might that in some way be the "instantaneous frequency" which people
 often think of?
>>> 
>>> That is (or is "something like") what 

Re: [time-nuts] Tbolt issues

[Lars Walenius]

Hello Tom,

What are the conditions for your charts? Are the Tbolts in locked condition or 
holdover? If locked what settings do you have for time constant and damping? Is 
it any other setting that is important?

For the frequency chart I see excursions up to +-3E-11 so not so far from the 
values that Bert gives and as I understand his TBolt might have a default 
setting of 100 seconds.

Lars


Från: Tom Van Baak<mailto:t...@leapsecond.com>
Skickat: den 1 september 2016 21:12


Hi Bert,

> because the frequency is constantly changed to correct  time.

A simple answer: you may have a bad TBolt. Was it part of the TAPR group buy, 
or did you buy it from eBay/China? If TAPR, you get a free replacement. Contact 
me off-list.

> Tbolt is an excellent time device but not good for frequency reference  past 
> 1E-10.

No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? 
reception? time constant? environment? China resoldered parts?). I appreciate 
that Juerg did lots of testing -- do you happen to have his ADEV plot?

I'm willing to help you debug this.

(1) Attached is the ADEV of 8 random TBolts that I tested recently. How does 
this compare to yours? You can see mine are all under 2e-12 at 1 s and under 
4e-12 at 100 s. On a bad day during holdover it might climb to 1e-11 at 1000 s 
but when locked GPS disciplining takes over and keeps it down to 2 or 3e-12.

(2) For locked vs. unlocked TBolt ADEV, see 
http://www.leapsecond.com/pages/gpsdo/

(3) Also attached is a frequency plot showing the typical noise and wander, 
down at the 1e-11 level. How does this compare with yours?

Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. 
Something is wrong.

/tvb

- Original Message -
From: "Bert Kehren via time-nuts" <time-nuts@febo.com>
To: <time-nuts@febo.com>
Sent: Thursday, September 01, 2016 9:54 AM
Subject: [time-nuts] Tbolt issues


> We have been following the Tbolt power discussions but what I am missing is
> the main problem with Tbolts. All the power work will not improve the
> frequency  performance of the unit because the frequency is constantly changed
> to correct  time. Tbolt is an excellent time device but not good for
> frequency reference  past 1E-10. I noticed it when I bought it and compared 
> it with
> my Tracor 527E on  the needle and ever since used an Austron 2110 with a
> digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an
> OSA F3 for Tbolt clean up but  continuous bad results on our work resulted in
> a detailed analysis using a  HP53132A counter and M100, FTS44060, two
> OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does not
> clean up the Tbolt and we see +-4E-11  changes and old data shows even some 
> +-8
> E-11 excursions. With the popularity of  the Tbolt an analog or digital
> clean up loop would make sense. We are working on  both, the analog because I
> saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not plan
> on using those Rb's but focus on M100 and FRK.
> The collective expertise of time nuts could make a significant  contribution
> For power in critical applications we use the excellent work from Bern Kaa
> a friend for the last twenty years and well known because of his published
> work  in the European HAM community
> Bert Kehren
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Re: [time-nuts] Tbolt issues

[Lars Walenius]

Hello Bert,

For me your findings look very much the same as this:
http://www.leapsecond.com/pages/tbolt-8d/ 
At least for me I should say the (absolute) frequency accuracy for this Tbolt 
is not better than +-1E10 with 1 or 10 seconds gate times on a counter. Maybe I 
am totally wrong as both Tom and Charles says that your Tbolt is bad.

As Bob Camp said we need a confidence interval. For me in this case it is peak 
values if they occur more than a couple of times. Think of  voltmeters. If it 
is out of spec say for only a couple of hours but it happens several times say 
during a month or year and the voltmeters is not considered bad I should say 
change the spec. If I were going to use the Tbolt as a reference in a 
production environment with a 1 or 10 sec gate time I probably would set the 
internal spec to 2E-10.

If I understand correct the Tracor 527E has a low pass filter with a time 
constant of 1second so the 1 second frequency average data should be relevant.

As I am also interested in frequency accuracy with GPSDO´s used with frequency 
counters, I have a maybe far to simplistic rule of accuracy: (10x the worst 
ADEV at all Taus longer than the gate time). So for the Tbolt with time 
constant of 100 seconds it is a hump of about 1E-11 at 100seconds so at gate 
times shorter than 100seconds I expect to see excursions up to 1E-10. If you 
set the time constant to 1000seconds and the OCXO in the Thunderbolt is good to 
2 to 3E-12 all the way 1-1000 seconds you probably don´t have excursions higher 
than 2 to 3E-11 at 1-100 seconds gate times.

Lars


Från: Bert Kehren via time-nuts
Skickat: den 1 september 2016 19:09

We have been following the Tbolt power discussions but what I am missing is 
 the main problem with Tbolts. All the power work will not improve the 
frequency  performance of the unit because the frequency is constantly changed 
to correct  time. Tbolt is an excellent time device but not good for 
frequency reference  past 1E-10. I noticed it when I bought it and compared it 
with 
my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
OSA F3 for Tbolt clean up but  continuous bad results on our work resulted in 
a detailed analysis using a  HP53132A counter and M100, FTS44060, two 
OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does not 
clean up the Tbolt and we see +-4E-11  changes and old data shows even some +-8 
E-11 excursions. With the popularity of  the Tbolt an analog or digital 
clean up loop would make sense. We are working on  both, the analog because I 
saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not plan 
on using those Rb's but focus on M100 and FRK. 
The collective expertise of time nuts could make a significant  contribution
For power in critical applications we use the excellent work from Bern Kaa  
a friend for the last twenty years and well known because of his published 
work  in the European HAM community
Bert Kehren
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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Jim wrote:


Instantaneous frequency does have a theoretical meaning, even if not
measureable..

If I'm processing  a linear frequency chirp, I can say that the
frequency at time t is some (f0 + t*slope).  the frequency at time
t+epsilon is different, as is the frequency at time t-epsilon.


Strictly speaking, the chirp does not have a frequency, at any time -- 
it has a *spectrum*.  We use the mathematical fiction of "instantaneous 
frequency" to express the limit as we differentiate.  This is the same 
as the use of the term in connection with FM modulation, and it is an 
abstraction -- not something real in the world (which is why it is not 
measurable, not only as a practical matter, but even in principle.)


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Gregory Maxwell]

On Fri, Sep 2, 2016 at 12:51 AM, Charles Steinmetz
 wrote:
> Now shorten the observation time to 20nS.  We see 1/5 of a complete cycle
> (72 degrees, 0.4 pi radians) of the wave.  No matter which particular 72
> degrees we see, we simply don't have enough information to reliably deduce

I do not see why you argue that.

For the purpose of discussion, lets assume you have a noiseless signal
which is stationary in frequency and amplitude over 20nS starting at
the zero crossing. Given these strong priors (single tone, constant
frequency which is not higher than one half cycle in our 20nS window,
constant amplitude, noiseless) there is exactly one frequency
consistent with any of those two observations.  If the starting phase
is unknown, I believe you need one additional observation to end up
over-determined and have an unambiguous solution again.

This kind of strong prior assumption is why sinusoidal estimators and
PLLs are able to extract tones with precision far beyond what you
would expect from taking a DFT from equivalent amount of data.

In reality, there is phase noise, non-linearities, harmonics, tidal
variations, and whatnot that make these assumptions untrue... but how
far they corrupt these assumptions depends on how useless the results
are.
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Re: [time-nuts] Tbolt issues

[Bill Byrom]

The problem is that "frequency" has more than one meaning. The main
dictionary definitions have to do with the frequency of occurrence of
some items in a category with respect to a larger set, or the frequency
of occurrence of some repeating event per unit of time. But we also use
mathematical representations of waveforms containing a "frequency" or
"angular frequency" parameter, and we can also define waveforms where
the frequency parameter is itself a function over time. In these cases
there obviously is an instantaneous frequency which for example
represents the value of f at a particular value of t in sin(2 pi f t),
where f = somefunction(t).

So you have discrete events (a rising edge, or the positive zero
crossing of a sinusoidal waveform) which define a "frequency" property
which only has meaning when we compare the time values of at least two
of these events, but we also have an equation defining a sinewave, where
the instantaneous angular frequency describes the derivative of the
phase change vs time. You have to consider continuous as well as
discrete systems.

In modern modulation theory the concept of vector modulation is used.
This involves a carrier wave frequency and amplitude, then I/Q or vector
modulation which instantaneously varies the amplitude (vector length)
and phase (vector angle) of the signal. For a constant amplitude signal,
the derivative of the vector modulation phase (arctangent of the I/Q
ratio) corresponds to the instantaneous frequency.

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 (microsecond) at a center
frequency of 1 GHz. So there are 50,000 D/A samples each us, and
although the average frequency over that us is 1 GHz (50 D/A
samples/cycle), the start of the chirp is at 999 MHz (about 50.05 D/A
samples/cycle) while the end of the chirp 1 us later is at 1001 MHz
(about 49.95 D/A samples/cycle). In this case, the value of
somefunction(T0 - 1 us) = 999 MHz and somefunction(T0 + 1 us) = 1001
MHz, where T0 is the time at the middle of the chirp. There are
obviously not an integral number of D/A samples per sinewave cycle, but
that is no problem. The D/A has 10 bits of resolution and is not
perfect, and the combination of jitter and other errors produces
wideband noise and spurs smeared over the frequency range of DC to the
Nyquist rate, but these errors are very small (many 10's of dB down from
the desired signal).

The signal I just described creates the 2 MHz chirp in a 1 us time
interval using 50,000 D/A samples. 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 (with instrument errors due to the limited 10-bit
voltage resolution, amplitude errors, jitter errors, and errors from
other sources).

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) to create two 200 MS/s
streams (I and Q waveforms). For the example above, the 1 us 2 MHz wide
linear chirp is sampled with 200 I/Q points, and calculating the
derivative (slope) of the phase - which is arctangent(I/Q) - results in
a frequency vs time trace. So the instantaneous frequency can be
measured with 5 ns resolution (1/200 MS/s I/Q rate) in time across that
1 us wide frequency chirp.

So yes, the concept of "instantaneous frequency" is valid and is used
everyday in many practical measurements on phase locked loop frequency
synthesizers, radars, testing Bluetooth FSK transmitters, and for many
other applications.

--
Bill Byrom N5BB



On Thu, Sep 1, 2016, at 10:39 PM, jimlux wrote:
> On 9/1/16 5:51 PM, Charles Steinmetz wrote:
>> Nick wrote:
>>
>>> On a theoretical basis, can one speak of the limit of the frequency
>>> observed as tau approaches zero?
>>> Might that in some way be the "instantaneous frequency" which people
>>> often think of?
>>
>> That is (or is "something like") what it **would** be, but a little
>> thought experiment will show that (and why) the linguistic
>> construction
>> is meaningless.
>>
>> The period of a 10MHz sine wave is 100nS.  Think about observing
>> it over
>> shorter and shorter (but still finite) time intervals.
>>
>> When the time interval is 100nS, we see one complete cycle (360
>> degrees,
>> 2 pi radians) of the wave.  At this point we still have **some**
>> shot at
>> deducing its frequency, because no matter at what phase we
>> start, we are
>> guaranteed to observe two peaks (one 

Re: [time-nuts] Tbolt issues

[jimlux]

On 9/1/16 5:51 PM, Charles Steinmetz wrote:

Nick wrote:


On a theoretical basis, can one speak of the limit of the frequency
observed as tau approaches zero?
Might that in some way be the "instantaneous frequency" which people
often think of?


That is (or is "something like") what it *would* be, but a little
thought experiment will show that (and why) the linguistic construction
is meaningless.

The period of a 10MHz sine wave is 100nS.  Think about observing it over
shorter and shorter (but still finite) time intervals.

When the time interval is 100nS, we see one complete cycle (360 degrees,
2 pi radians) of the wave.  At this point we still have *some* shot at
deducing its frequency, because no matter at what phase we start, we are
guaranteed to observe two peaks (one high, one low) and at least one
midpoint (e.g., zero-cross).  Our deduction (inference) will be less
accurate as the noise and distortion (harmonic content) increases, and
it won't be all that good under the best of circumstances.

Now shorten the observation time to 20nS.  We see 1/5 of a complete
cycle (72 degrees, 0.4 pi radians) of the wave.  No matter which
particular 72 degrees we see, we simply don't have enough information to
reliably deduce the frequency.


in fact, there's a whole literature on how accurate (or more precisely, 
what's the uncertainty) of the frequency estimate is.


We often measure frequencies with less than a cycle - but making some 
assumptions - measuring orbital parameters is done using a lot less than 
a complete orbit's data, but we also make the assumption of the physics 
involved.



---

Instantaneous frequency does have a theoretical meaning, even if not 
measureable..


If I'm processing  a linear frequency chirp, I can say that the 
frequency at time t is some (f0 + t*slope).  the frequency at time 
t+epsilon is different, as is the frequency at time t-epsilon.



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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Nick wrote:


On a theoretical basis, can one speak of the limit of the frequency observed as 
tau approaches zero?
Might that in some way be the "instantaneous frequency" which people often 
think of?


That is (or is "something like") what it *would* be, but a little 
thought experiment will show that (and why) the linguistic construction 
is meaningless.


The period of a 10MHz sine wave is 100nS.  Think about observing it over 
shorter and shorter (but still finite) time intervals.


When the time interval is 100nS, we see one complete cycle (360 degrees, 
2 pi radians) of the wave.  At this point we still have *some* shot at 
deducing its frequency, because no matter at what phase we start, we are 
guaranteed to observe two peaks (one high, one low) and at least one 
midpoint (e.g., zero-cross).  Our deduction (inference) will be less 
accurate as the noise and distortion (harmonic content) increases, and 
it won't be all that good under the best of circumstances.


Now shorten the observation time to 20nS.  We see 1/5 of a complete 
cycle (72 degrees, 0.4 pi radians) of the wave.  No matter which 
particular 72 degrees we see, we simply don't have enough information to 
reliably deduce the frequency.  By sampling very fast (say, every 
100fS), we at least know pretty well the trajectory of that little 
snippet of signal, and using heroic measures we can make an educated 
guess about the frequency -- but we really couldn't say we "knew" what 
the frequency was.  Our error bars are growing, growing


Now consider a 1nS sample.  Nothing we can do now will give us even a 
bad guess as to the frequency.  And finally, consider a genuine 
"instant" sample (one mathematical point of the wave form).  We have now 
reached the point where there is literally NO information about the 
frequency.  One time-voltage point could be part of a literally infinite 
number of signals, each one of a different frequency from DC to infinity.


Thus we see that the well-formed English phrase, "instantaneous 
frequency," is, literally, meaningless.  It denotes absolutely nothing.


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

Unfortunately if you read a typical text on FM modulation, "instantaneous 
frequency" comes up pretty fast. In that context it has a valid meaning. Once 
out of context, it gets you in trouble. That point is never made when the term 
is introduced.

Bob

> On Sep 1, 2016, at 8:51 PM, Charles Steinmetz  wrote:
> 
> Nick wrote:
> 
>> On a theoretical basis, can one speak of the limit of the frequency observed 
>> as tau approaches zero?
>> Might that in some way be the "instantaneous frequency" which people often 
>> think of?
> 
> That is (or is "something like") what it *would* be, but a little thought 
> experiment will show that (and why) the linguistic construction is 
> meaningless.
> 
> The period of a 10MHz sine wave is 100nS.  Think about observing it over 
> shorter and shorter (but still finite) time intervals.
> 
> When the time interval is 100nS, we see one complete cycle (360 degrees, 2 pi 
> radians) of the wave.  At this point we still have *some* shot at deducing 
> its frequency, because no matter at what phase we start, we are guaranteed to 
> observe two peaks (one high, one low) and at least one midpoint (e.g., 
> zero-cross).  Our deduction (inference) will be less accurate as the noise 
> and distortion (harmonic content) increases, and it won't be all that good 
> under the best of circumstances.
> 
> Now shorten the observation time to 20nS.  We see 1/5 of a complete cycle (72 
> degrees, 0.4 pi radians) of the wave.  No matter which particular 72 degrees 
> we see, we simply don't have enough information to reliably deduce the 
> frequency.  By sampling very fast (say, every 100fS), we at least know pretty 
> well the trajectory of that little snippet of signal, and using heroic 
> measures we can make an educated guess about the frequency -- but we really 
> couldn't say we "knew" what the frequency was.  Our error bars are growing, 
> growing
> 
> Now consider a 1nS sample.  Nothing we can do now will give us even a bad 
> guess as to the frequency.  And finally, consider a genuine "instant" sample 
> (one mathematical point of the wave form).  We have now reached the point 
> where there is literally NO information about the frequency.  One 
> time-voltage point could be part of a literally infinite number of signals, 
> each one of a different frequency from DC to infinity.
> 
> Thus we see that the well-formed English phrase, "instantaneous frequency," 
> is, literally, meaningless.  It denotes absolutely nothing.
> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Bert wrote:


maybe some one smarter than us can working with the parameters that Tbolt
makes available better performance can be achieved


I am quite sure of that


the frequency is being changed to compensate for time


Yes, the PPS is steered by making slight adjustments to the OCXO 
frequency.  But you can make these adjustments as arbitrarily small as 
you want with the setup parameters.  I run my Tbolts with pretty tight 
limits on the frequency adjustments.



and we do not care about ADEV, we care about the actual
frequency at that moment it goes in to the measuring device


There is no "there" there.  One never makes a frequency measurement at 
just one instant -- the measurement will ALWAYS be done over a macro 
time interval (very often, one second, sometimes 0.1, 10, 100, or 1000 
seconds).  We never observe, and have no way to know, the instantaneous 
frequency (as you put it, "the actual frequency at that moment it goes 
into the measuring device") -- so how can we care about it?  The only 
thing relevant (or even meaningful) is the average frequency during our 
measurement interval.


xDEV tells us half of what we want to know -- how stable our oscillator 
is from one measurement interval to another.  We would also like to know 
what frequency it is wobbling around -- the "centroid" frequency, if you 
will (to borrow a geometric term).  (Mathematicians can argue for days 
about which type of "average" is appropriate here -- the rest of us just 
pick one and carry on.)  ADEV does not tell us this "centroid" frequency 
directly, but it can be extracted from the same measurements we took to 
calculate ADEV.


I think you are being misled by a belief that the linguistic construct, 
"instantaneous frequency," has real meaning in the world.  It doesn't.


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bob kb8tq]

Hi

Frequency is a "change over time". If delta time is zero it is undefined. As 
you observe it in shorter time periods, the accuracy / stability gets worse. 
Since the error bars expand there isn't much of a limit as you go shorter. They 
are not quite the same thing, but they are related.

Bob

> On Sep 1, 2016, at 6:35 PM, Nick Sayer via time-nuts  
> wrote:
> 
> Just a stupid question...
> 
> On a theoretical basis, can one speak of the limit of the frequency observed 
> as tau approaches zero?
> 
> Might that in some way be the "instantaneous frequency" which people often 
> think of?
> 
> I rather suspect the answer is "no," but I'll ask anyway. 
> 
> Sent from my iPhone
> 
>> On Sep 1, 2016, at 3:26 PM, Charles Steinmetz  wrote:
>> 
>> Bert wrote:
>> 
>>> maybe some one smarter than us can working with the parameters that Tbolt
>>> makes available better performance can be achieved
>> 
>> I am quite sure of that
>> 
>>> the frequency is being changed to compensate for time
>> 
>> Yes, the PPS is steered by making slight adjustments to the OCXO frequency.  
>> But you can make these adjustments as arbitrarily small as you want with the 
>> setup parameters.  I run my Tbolts with pretty tight limits on the frequency 
>> adjustments.
>> 
>>> and we do not care about ADEV, we care about the actual
>>> frequency at that moment it goes in to the measuring device
>> 
>> There is no "there" there.  One never makes a frequency measurement at just 
>> one instant -- the measurement will ALWAYS be done over a macro time 
>> interval (very often, one second, sometimes 0.1, 10, 100, or 1000 seconds).  
>> We never observe, and have no way to know, the instantaneous frequency (as 
>> you put it, "the actual frequency at that moment it goes into the measuring 
>> device") -- so how can we care about it?  The only thing relevant (or even 
>> meaningful) is the average frequency during our measurement interval.
>> 
>> xDEV tells us half of what we want to know -- how stable our oscillator is 
>> from one measurement interval to another.  We would also like to know what 
>> frequency it is wobbling around -- the "centroid" frequency, if you will (to 
>> borrow a geometric term).  (Mathematicians can argue for days about which 
>> type of "average" is appropriate here -- the rest of us just pick one and 
>> carry on.)  ADEV does not tell us this "centroid" frequency directly, but it 
>> can be extracted from the same measurements we took to calculate ADEV.
>> 
>> I think you are being misled by a belief that the linguistic construct, 
>> "instantaneous frequency," has real meaning in the world.  It doesn't.
>> 
>> Best regards,
>> 
>> Charles
>> 
>> 
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Re: [time-nuts] Tbolt issues

[Charles Steinmetz]

Tom wrote:


No, again it sounds like you have a bad TBolt. Or something is wrong (antenna? 
reception? time constant? environment? China resoldered parts?). I appreciate 
that Juerg did lots of testing -- do you happen to have his ADEV plot?

Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I see. 
Something is wrong.


I second that (not that any further evidence is necessary following 
Tom's comprehensive response).  Additionally, as far as I know, the 
units Tom was testing would have had the default tuning parameters (Tom, 
please comment).  Most Tbolts I've seen can be tuned for much better 
performance than this at tau > 100 seconds, if they are equipped with a 
37265 OCXO.


Note that the Tbolt has tuning parameters that limit how far the 
frequency is allowed to wander to adjust the PPS phase -- if Bert's 
unit(s) have these parameters set to allow very fast PPS recovery, that 
could well cause the behavior he describes.


You should also check all of the other tuning parameters to see if there 
are errors in the settings.


However, rather than mucking about in the myriad tuning settings 
starting where they are now, I recommend doing a full factory reset to 
get all parameters back to the original settings.  Then (after several 
weeks of undisturbed running), compare ADEV performance with Tom's graphs.


Best regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bob Camp]

Hi

The problem with absolute frequency is the one they ran into in the 60’s (and 
before):

There is no really good way to measure it. 

You certainly can take data. The data can have lots of resolution.  That part 
has 
always been fairly easy. The problem is that  the more carefully you look, the 
larger a 
number you get. The number can grow 2, 3, 4, 5X as you look in more depth. 
There is 
no nice simple way to limit the measurement so that does not happen. This makes 
it 
a very hard thing to characterize. 

Many frequency measurement systems have built in limits. They have a bandwidth 
(often 
narrow). They have an integration time (sometimes FIR, sometimes IIR). They 
have internal 
noise processes. All of that “colors” the result. This is in addition to the 
basics of observation 
time and number of samples. Running two differently designed devices in 
parallel can result
in two very different “frequency readings”. 

We do “hand waving” conversions of ADEV (or some other variance). That gives a 
number to 
some number of decimal places. The gotcha is still that the underlying noise 
processes may or 
may not be “nice enough” for the conversion to have any meaning. That issue has 
caught a lot
of people over the years. On things like GPSDO’s, the noise processes  rarely 
are “nice”. You 
have humps and bumps from control loops and multiple noise sources. It’s a 
messy problem. 

None of this really addresses the question of “how do I characterize absolute 
frequency”. It 
simply goes back to the 1960’s and the whole reason we *have* ADEV. It is a 
quantity that
you can measure and the measure converges as you take more data. Absolute 
frequency 
diverges as you take more data. Yes, the papers explain it a lot more clearly 
with a lot more
math.  

Bob

> On Sep 1, 2016, at 5:23 PM, Bert Kehren via time-nuts  
> wrote:
> 
> maybe some one smarter than us can working with the parameters  that Tbolt 
> makes available better performance can be achieved but it is a fact  that 
> the frequency is being changed to compensate for time and Tom's frequency  
> data matches our's and we do not care about ADEV, we care about the actual  
> frequency at that moment it goes in to the measuring device and there is room 
>  
> for improvement if you are a frequency nut and are looking for ways to  
> improve. Bob made a good point.
> 
> 
> 
> In a message dated 9/1/2016 4:27:02 P.M. Eastern Daylight Time,  
> csteinm...@yandex.com writes:
> 
> Tom  wrote:
> 
>> No, again it sounds like you have a bad TBolt. Or something  is wrong 
> (antenna? reception? time constant? environment? China resoldered  parts?). I 
> appreciate that Juerg did lots of testing -- do you happen to have  his ADEV 
> plot?
>> 
>> Your claim of 1e-10 is order(s) of magnitude  worse than the TBolts that 
> I see. Something is wrong.
> 
> I second that  (not that any further evidence is necessary following 
> Tom's comprehensive  response).  Additionally, as far as I know, the 
> units Tom was testing  would have had the default tuning parameters (Tom, 
> please comment).   Most Tbolts I've seen can be tuned for much better 
> performance than this  at tau > 100 seconds, if they are equipped with a 
> 37265  OCXO.
> 
> Note that the Tbolt has tuning parameters that limit how far the  
> frequency is allowed to wander to adjust the PPS phase -- if Bert's  
> unit(s) have these parameters set to allow very fast PPS recovery, that  
> could well cause the behavior he describes.
> 
> You should also check  all of the other tuning parameters to see if there 
> are errors in the  settings.
> 
> However, rather than mucking about in the myriad tuning  settings 
> starting where they are now, I recommend doing a full factory  reset to 
> get all parameters back to the original settings.  Then  (after several 
> weeks of undisturbed running), compare ADEV performance  with Tom's graphs.
> 
> Best  regards,
> 
> Charles
> 
> 
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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

maybe some one smarter than us can working with the parameters  that Tbolt 
makes available better performance can be achieved but it is a fact  that 
the frequency is being changed to compensate for time and Tom's frequency  
data matches our's and we do not care about ADEV, we care about the actual  
frequency at that moment it goes in to the measuring device and there is room  
for improvement if you are a frequency nut and are looking for ways to  
improve. Bob made a good point.
 
 
 
In a message dated 9/1/2016 4:27:02 P.M. Eastern Daylight Time,  
csteinm...@yandex.com writes:

Tom  wrote:

> No, again it sounds like you have a bad TBolt. Or something  is wrong 
(antenna? reception? time constant? environment? China resoldered  parts?). I 
appreciate that Juerg did lots of testing -- do you happen to have  his ADEV 
plot?
>
> Your claim of 1e-10 is order(s) of magnitude  worse than the TBolts that 
I see. Something is wrong.

I second that  (not that any further evidence is necessary following 
Tom's comprehensive  response).  Additionally, as far as I know, the 
units Tom was testing  would have had the default tuning parameters (Tom, 
please comment).   Most Tbolts I've seen can be tuned for much better 
performance than this  at tau > 100 seconds, if they are equipped with a 
37265  OCXO.

Note that the Tbolt has tuning parameters that limit how far the  
frequency is allowed to wander to adjust the PPS phase -- if Bert's  
unit(s) have these parameters set to allow very fast PPS recovery, that  
could well cause the behavior he describes.

You should also check  all of the other tuning parameters to see if there 
are errors in the  settings.

However, rather than mucking about in the myriad tuning  settings 
starting where they are now, I recommend doing a full factory  reset to 
get all parameters back to the original settings.  Then  (after several 
weeks of undisturbed running), compare ADEV performance  with Tom's graphs.

Best  regards,

Charles


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Re: [time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

For us it is absolute Frequency, to me it is a measure of true  performance.
 
 
In a message dated 9/1/2016 4:52:35 P.M. Eastern Daylight Time,  
kb...@n1k.org writes:

Hi

I think one issue here is that ADEV is being used by one  “lab" and 
absolute frequency is being used by the other. 
They very much  are *not* the same thing. There isn’t even a really simple 
way to convert one  to the other. 
There will always be a big delta between those two measures.  For absolute 
frequency you will also need
some sort of confidence number  (99 % or some such thing). The details of 
why all this happens are  the
mainstay of the 1960’s (and early 70’s) papers on ADEV.  

Bob


> On Sep 1, 2016, at 3:11 PM, Tom Van Baak  <t...@leapsecond.com> wrote:
> 
> Hi Bert,
>  
>> because the frequency is constantly changed to correct   time.
> 
> A simple answer: you may have a bad TBolt. Was it part  of the TAPR group 
buy, or did you buy it from eBay/China? If TAPR, you get a  free 
replacement. Contact me off-list.
> 
>> Tbolt is an  excellent time device but not good for frequency reference  
past  1E-10.
> 
> No, again it sounds like you have a bad TBolt. Or  something is wrong 
(antenna? reception? time constant? environment? China  resoldered parts?). I 
appreciate that Juerg did lots of testing -- do you  happen to have his ADEV 
plot?
> 
> I'm willing to help you debug  this.
> 
> (1) Attached is the ADEV of 8 random TBolts that I  tested recently. How 
does this compare to yours? You can see mine are all  under 2e-12 at 1 s and 
under 4e-12 at 100 s. On a bad day during holdover it  might climb to 1e-11 
at 1000 s but when locked GPS disciplining takes over and  keeps it down to 
2 or 3e-12.
> 
> (2) For locked vs. unlocked  TBolt ADEV, see 
http://www.leapsecond.com/pages/gpsdo/
> 
> (3)  Also attached is a frequency plot showing the typical noise and 
wander, down  at the 1e-11 level. How does this compare with yours?
> 
> Your  claim of 1e-10 is order(s) of magnitude worse than the TBolts that 
I see.  Something is wrong.
> 
> /tvb
> 
> - Original  Message - 
> From: "Bert Kehren via time-nuts"  <time-nuts@febo.com>
> To: <time-nuts@febo.com>
>  Sent: Thursday, September 01, 2016 9:54 AM
> Subject: [time-nuts] Tbolt  issues
> 
> 
>> We have been following the Tbolt power  discussions but what I am 
missing is 
>> the main problem with  Tbolts. All the power work will not improve the 
>> frequency   performance of the unit because the frequency is constantly 
changed  
>> to correct  time. Tbolt is an excellent time device but not  good for 
>> frequency reference  past 1E-10. I noticed it when  I bought it and 
compared it with 
>> my Tracor 527E on  the  needle and ever since used an Austron 2110 with 
a 
>> digital 100  sec. loop for  clean up. My Swiss partner Juerg has relied 
on an  
>> OSA F3 for Tbolt clean up but  continuous bad results on our  work 
resulted in 
>> a detailed analysis using a  HP53132A  counter and M100, FTS44060, two 
>> OSA8600's and one of the best  FE405's.  The rsult is that the OSA F3 
does not 
>> clean up the  Tbolt and we see +-4E-11  changes and old data shows even 
some +-8  
>> E-11 excursions. With the popularity of  the Tbolt an analog  or digital 
>> clean up loop would make sense. We are working  on  both, the analog 
because I 
>> saw similar behavior on the  FE5680 and FE5650, we did  a GPSDO but do 
not plan 
>> on using  those Rb's but focus on M100 and FRK. 
>> The collective expertise of  time nuts could make a significant  
contribution
>> For power in  critical applications we use the excellent work from Bern 
Kaa   
>> a friend for the last twenty years and well known because of his  
published 
>> work  in the European HAM community
>>  Bert Kehren
>  
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Re: [time-nuts] Tbolt issues

[Bob Camp]

Hi

I think one issue here is that ADEV is being used by one “lab" and absolute 
frequency is being used by the other. 
They very much are *not* the same thing. There isn’t even a really simple way 
to convert one to the other. 
There will always be a big delta between those two measures. For absolute 
frequency you will also need
some sort of confidence number (99 % or some such thing). The details of why 
all this happens are the
mainstay of the 1960’s (and early 70’s) papers on ADEV. 

Bob


> On Sep 1, 2016, at 3:11 PM, Tom Van Baak <t...@leapsecond.com> wrote:
> 
> Hi Bert,
> 
>> because the frequency is constantly changed to correct  time.
> 
> A simple answer: you may have a bad TBolt. Was it part of the TAPR group buy, 
> or did you buy it from eBay/China? If TAPR, you get a free replacement. 
> Contact me off-list.
> 
>> Tbolt is an excellent time device but not good for frequency reference  past 
>> 1E-10.
> 
> No, again it sounds like you have a bad TBolt. Or something is wrong 
> (antenna? reception? time constant? environment? China resoldered parts?). I 
> appreciate that Juerg did lots of testing -- do you happen to have his ADEV 
> plot?
> 
> I'm willing to help you debug this.
> 
> (1) Attached is the ADEV of 8 random TBolts that I tested recently. How does 
> this compare to yours? You can see mine are all under 2e-12 at 1 s and under 
> 4e-12 at 100 s. On a bad day during holdover it might climb to 1e-11 at 1000 
> s but when locked GPS disciplining takes over and keeps it down to 2 or 3e-12.
> 
> (2) For locked vs. unlocked TBolt ADEV, see 
> http://www.leapsecond.com/pages/gpsdo/
> 
> (3) Also attached is a frequency plot showing the typical noise and wander, 
> down at the 1e-11 level. How does this compare with yours?
> 
> Your claim of 1e-10 is order(s) of magnitude worse than the TBolts that I 
> see. Something is wrong.
> 
> /tvb
> 
> - Original Message - 
> From: "Bert Kehren via time-nuts" <time-nuts@febo.com>
> To: <time-nuts@febo.com>
> Sent: Thursday, September 01, 2016 9:54 AM
> Subject: [time-nuts] Tbolt issues
> 
> 
>> We have been following the Tbolt power discussions but what I am missing is 
>> the main problem with Tbolts. All the power work will not improve the 
>> frequency  performance of the unit because the frequency is constantly 
>> changed 
>> to correct  time. Tbolt is an excellent time device but not good for 
>> frequency reference  past 1E-10. I noticed it when I bought it and compared 
>> it with 
>> my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
>> digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
>> OSA F3 for Tbolt clean up but  continuous bad results on our work resulted 
>> in 
>> a detailed analysis using a  HP53132A counter and M100, FTS44060, two 
>> OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does 
>> not 
>> clean up the Tbolt and we see +-4E-11  changes and old data shows even some 
>> +-8 
>> E-11 excursions. With the popularity of  the Tbolt an analog or digital 
>> clean up loop would make sense. We are working on  both, the analog because 
>> I 
>> saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not 
>> plan 
>> on using those Rb's but focus on M100 and FRK. 
>> The collective expertise of time nuts could make a significant  contribution
>> For power in critical applications we use the excellent work from Bern Kaa  
>> a friend for the last twenty years and well known because of his published 
>> work  in the European HAM community
>> Bert Kehren
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Re: [time-nuts] Tbolt issues

[Chris Caudle]

On Thu, September 1, 2016 11:54 am, Bert Kehren via time-nuts wrote:
>  All the power work will not improve the frequency  performance
> of the unit because the frequency is constantly changed
> to correct  time.

Can't you control that to a large extent with the damping and time
constant parameters?

-- 
Chris Caudle




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[time-nuts] Tbolt issues

[Bert Kehren via time-nuts]

We have been following the Tbolt power discussions but what I am missing is 
 the main problem with Tbolts. All the power work will not improve the 
frequency  performance of the unit because the frequency is constantly changed 
to correct  time. Tbolt is an excellent time device but not good for 
frequency reference  past 1E-10. I noticed it when I bought it and compared it 
with 
my Tracor 527E on  the needle and ever since used an Austron 2110 with a 
digital 100 sec. loop for  clean up. My Swiss partner Juerg has relied on an 
OSA F3 for Tbolt clean up but  continuous bad results on our work resulted in 
a detailed analysis using a  HP53132A counter and M100, FTS44060, two 
OSA8600's and one of the best FE405's.  The rsult is that the OSA F3 does not 
clean up the Tbolt and we see +-4E-11  changes and old data shows even some +-8 
E-11 excursions. With the popularity of  the Tbolt an analog or digital 
clean up loop would make sense. We are working on  both, the analog because I 
saw similar behavior on the FE5680 and FE5650, we did  a GPSDO but do not plan 
on using those Rb's but focus on M100 and FRK. 
The collective expertise of time nuts could make a significant  contribution
For power in critical applications we use the excellent work from Bern Kaa  
a friend for the last twenty years and well known because of his published 
work  in the European HAM community
Bert Kehren
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