[time-nuts] Frequency standards for different tau in Allen Dev measurement

Sun Mar 1 00:46:43 UTC 2020

Hi,

If you have a GPSDO, then PPS as re-generated from the locked oscillator
is naturally less noisy than straight from the GPS. Using a PICDIV helps
you to use another reference instead, and the TADD-2 is a useful option
to consider.

I have my TADD-2:s modified such that one of the outputs is the input
clock buffered, which is a simple wire from the clock input of the PIC
over to one of the output drivers. This gives better jitter performance
than feeding a 5 MHz or 10 MHz sine straight into a TIC channel.

However, the important is that you start measure. Even somewhat
imperfect measures is better than nothing, and taking several measures
as you do, I think you will see a pattern re-emerge in them as being the
tell-tail of your measurement limits. Consider that single-shot
resolution and white noise has a 1/tau slope on them, so eventually you
go down to the combination of the actual DUT and GPS noise, rather than
that of the PPS placement.

Cheers,
Magnus

On 2020-03-01 01:25, Taka Kamiya via time-nuts wrote:
> YES, please.  tkamiya9 at yahoo.com.
> So far, I've taken HP105B and did adev frequency reading based, T.I. based adev, and while at it, I am doing PRS-10 T.I. based.
> I have a question.  My 1 second reference for channel A is coming from GPS based 1 second.  I understand it's only 10E-8 precision on second to second basis?  Is this sufficient for OCXO and Rb based oscillators?
>
> --------------------------------------- 
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>  
>
>     On Saturday, February 29, 2020, 7:21:28 PM EST, Magnus Danielson <magnus at rubidium.se> wrote:  
>  
>  Hi,
>
> On 2020-02-29 23:10, Taka Kamiya via time-nuts wrote:
>> One question for Magnus.
>>
>> Ch A start - pps (standard)Ch B stop - DUT
>> On item 4, you said "frequency of the signal on time B".  That much is obvious.  But then you said: "give it the time-base of the period on the A-channel".  Will you explain this?
>> Say I give 1 Hz, period is 1s.  Say I give 10Hz, period is 0.1s.  Is this what you mean?
> Yes. Exactly.
>> I'm using HP5370A.  This instruction is valid on this TI counter, correct??
> Yes. It will work.
>> A request for everyone:
>> I am conducting an one hour measurement on HP105B.  Does anyone have 1 hour plot of this signal generator handy?  If so, will you DM me a copy?  For some reason, I cannot find one on the great Internet.
> I have one of the 00105 oscillator ,as mounted and free-running in a
> HP5065A, against hydrogen maser at hand. I can locate that and send you
> if you wish. It's longer than 1 hour, but you get additional precision
> from this.
>
> Cheers,
> Magnus
>
>> ------------------- clip from Magnus's previous email------------------
>> A setup I use a lot is this:
>> 1) Connect a reference oscillator to produce a 1 Hz or 10 Hz signal and
>> feed into a counter Channel A/TI-start channel. For PPS signals, I make
>> sure to trigger a but up on the rising edge not to false-trigger. For
>> some counters this means turning of automatic trigger and set it to 1 V
>> manually. It is important that no false triggers occurs.
>>
>> 2) Connect a signal under test to Channel B/TI-stop. Adjust trigger to
>> through-zero or up on the edge as suitable.
>>
>> 3) TI-mode, continuous trigger
>>
>> 4) Collect data in TimeLab, give TimeLab the frequency of the signal on
>> B-channel, give it the time-base of the period on the A-channel.
>>
>> 5) Look at data as it comes in. Look at phase view, frequency view,
>> wrapped phase. Look at the ADEV, how the upper end flaps with data, but
>> how the same tau becomes more and more stable as it comes in.---------------------
>> --------------------------------------- 
>> (Mr.) Taka Kamiya
>> KB4EMF / ex JF2DKG
>>   
>>
>>     On Friday, February 21, 2020, 9:26:47 PM EST, Magnus Danielson via time-nuts <time-nuts at lists.febo.com> wrote:  
>>   
>>   Hi Taka,
>>
>> On 2020-02-21 23:26, Taka Kamiya via time-nuts wrote:
>>> I'm sorry, I messed up.  I jumped on more advance topic than I intended.  I'm sure there were answers in the replies but they must have gone way over my head because some of original questions still remain.  I bulletized (is that a word?) the original question with my NEW understanding.  Would someone please respond for me, point-to-point?
>> No problem. No worries. I hope you end up reading these and the other
>> replies again and acquire good knowledge. I know it's like drinking from
>> a fire-hoze, but you did ask some very relevant and fair questions.
>>> 1)  A frequency counter that measures DUT basically puts out a reading every second during the measurement.  When TimeLab is well into 1000s or so, it is still reading every second; it does not change the gate time to say, 1000s.  I understand now, Adev is about phase, not the frequency.  But assuming DUT is sine wave, if there is enough phase change, frequency do change.  I think of phase change as frequency change that is less than full cycle.  So how does counters that outputs every 1 second end up in tau of 1000s?  It will entirely miss phase change that spans more than 1 cycle.
>> ADEV is about the frequency stability. ADEV can be calculated using
>> phase or frequency measures. We tend to prefer using phase measures from
>> Time-Interval Counters for these things.
>>
>> OK, so let's say that we want to output a counter which provides output
>> of frequency estimates but for a time-base which is longer than 1 s,
>> even if we output results every 1 s?
>>
>> Classically counters could not do that. You acquired a start-value,
>> waited the time-base, acquired a stop-value, calculated a result to
>> display and then arm to get a new start-value for the next result. Such
>> counters will have a limit that the rate of readings will be limited by
>> the time-base, so if it is set to 10 s, only every 10 s and output is
>> produced.
>>
>> To tackle this, one needs a counter that can interleave frequency
>> measurements, so that it generates new start-points at the update rate
>> even if the stop-point has not occurred. So, for a time-base of 10 s and
>> an update rate of 1 s, then every 1 s a new start-trigger is produced,
>> and then remembered until a stop trigger can be produced, at which time
>> the start-trigger 10 s back is used to estimate the frequency. In fact,
>> for this to work, the stop trigger time-stamp is also the start trigger
>> time-stamp for a new measurement. You can do this with any time-base
>> really, and the degree of interleaving only depends on the number of
>> start-points one can keep in memory.
>>
>>> 2)  I recall reading on TICC manual, in time interval mode, anything that's reasonably good is good enough, because it has time stamp and the count reading.  Clock is used to chunk the data.  Is this still true?  Through this discussion, I ended up with conclusion that there is no inherent advantage over TI measurement when compared to frequency measurement.  Am I understanding this correctly?
>> There is benefits in time-measures over frequency measures when one
>> monitors long-term properties. Also, as one tries to create a
>> phase-curve from frequency estimates, any rounding off errors show in an
>> slope, as there is a tiny average frequency offset from round-offs. Only
>> really good such setups does not have significant slope.
>>
>>> 3)  I understand even the BEST counter is only good for Adev nE-12 measurement. Then, with my collection of counters, HP53132A (which averages tons of short period measurement), 5335A (not enough resolution), HP5370A (interval reading is no better than frequency), TICC by TAPR,   Do I even have a chance of doing any meaningful work?  (say work with GPSDO and Rb which some of it does reach E-13)  Yes, I know now, it is NOT possible to do 1 sec Adev but say over 100 seconds?  Right now, I don't have any standard that has adev that good at 1 sec anyway.
>> The resolution of your counter tells you about where your 1/tau curve
>> will cut tau = 1 s, and it goes from there. There is a slight scaling
>> factor, but if we assume it is 1 for now, it is pretty simple. Your
>> 5335A has 1 ns single-shot resolution, this gives 1E-9 at 1 s, but 1E-10
>> at 10 s, 1E-11 at 100 s and 1E-12 at 1000 s. You see very clearly when
>> the linear slope ends and "lands" in the noise, at which time the noise
>> becomes dominant and is giving you the interesting reading. The 5370A is
>> 20 ps single-shot resolution, giving you a whopping 2E-11 at 1 s, 2E-12
>> at 10 s, 2E-13 at 100 s and 2E-14 at 1000 s. It's some serious
>> improvement. You are more likely to be limited by your oscillators as
>> ref and under test at 1000 s with that one, than the instrument itself.
>>
>>> 4)  Would one person who has infinite patience and experience guide me through getting one reading done correctly with what I already have?  That may include email and phone call.  (I speak English and Japanese)  I don't want to lower S/N of this mailing list by doing this here.  
>> I think you have contributed by asking some really good questions.
>>
>> A setup I use a lot is this:
>>
>> 1) Connect a reference oscillator to produce a 1 Hz or 10 Hz signal and
>> feed into a counter Channel A/TI-start channel. For PPS signals, I make
>> sure to trigger a but up on the rising edge not to false-trigger. For
>> some counters this means turning of automatic trigger and set it to 1 V
>> manually. It is important that no false triggers occurs.
>>
>> 2) Connect a signal under test to Channel B/TI-stop. Adjust trigger to
>> through-zero or up on the edge as suitable.
>>
>> 3) TI-mode, continuous trigger
>>
>> 4) Collect data in TimeLab, give TimeLab the frequency of the signal on
>> B-channel, give it the time-base of the period on the A-channel.
>>
>> 5) Look at data as it comes in. Look at phase view, frequency view,
>> wrapped phase. Look at the ADEV, how the upper end flaps with data, but
>> how the same tau becomes more and more stable as it comes in.
>>
>> Using even old counters this setup have helped a lot for many measures.
>> It is simple and sturdy for many measures. Remember to save traces, to
>> annotate it carefully so one can understand afterwards what one did.
>>
>> Using this setup, I swapped a HP53132A (150 ps) for a HP5335A (1 ns) and
>> then PM6853A (2 ns) to show that a particular problem did not needed the
>> best counter in the house to be well characterized.
>>
>>> 5)  One time, it was mentioned many of Adev graphs posted are basically a graph of instruments noise graph.  How do I tell when a given reading/graph is exceeding the limit of a setup?  I did do base line where same signal goes to counter's reference input and signal input.  I always have that on my chart so traces does not go below.  Is that enough?
>> Almost. It's a good start. The first slope for lower taus is due to the
>> instrument for sure. If you look carefully you will notice that the
>> actual performance shifts around, because it is more complex than just
>> being instrument limit, but it is the right ball-park for that part of
>> the plots. For the upper end, you can be limited by your device under
>> test drift. This can be handled by simply letting them be turned on
>> longer. Sub-sequent measurement will have that rising slope move more
>> and more towards higher taus and thus becomming less like a limit-issue
>> for a certain tau.
>>> I appreciate everyone's input.  I am learning a lot but just not digesting well enough.  I'd like to do DMTD after I understand the basics.
>> Good spirit. DMTD takes some care, but once you learned it, it can be a
>> magnificent tool.
>>
>> Cheers,
>> Magnus
>>
>>> --------------------------------------- 
>>> (Mr.) Taka Kamiya
>>> KB4EMF / ex JF2DKG
>>>   
>>>
>>>     On Thursday, February 20, 2020, 1:41:06 PM EST, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:  
>>>   
>>>   I have a question concerning frequency standard and their Allen deviation.  (to measure Allen Dev in frequency mode using TimeLab)
>>>
>>> It is commonly said that for shorter tau measurement, I'd need OCXO because it's short tau jitter is superior to just about anything else.  Also, it is said that for longer tau measurement, I'd need something like Rb or Cs which has superior stability over longer term.
>>> Here's the question part.  A frequency counter that measures DUT basically puts out a reading every second during the measurement.  When TimeLab is well into 1000s or so, it is still reading every second; it does not change the gate time to say, 1000s.
>>> That being the case, why this consensus of what time source to use for what tau?
>>> I recall reading on TICC, in time interval mode, anything that's reasonably good is good enough.  I'm aware TI mode and Freq mode is entirely different, but it is the same in fact that measurement is made for very short time span AT A TIME.
>>> I'm still trying to wrap my small head around this.  
>>>
>>> --------------------------------------- 
>>> (Mr.) Taka Kamiya
>>> KB4EMF / ex JF2DKG
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>>>     
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>>   
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>   
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.