[time-nuts] How does one actually do Allan variation graphs?

William H. Fite omniryx at gmail.com
Sun Nov 14 16:29:31 UTC 2010


Gentlemen,

What is a reasonable price for a 5370A?  Local guy here is trying to hawk
one to me.  Not cosmetically perfect but fully operational.

Yes, I know someone is going to say, "I got one for 50 bucks."  But really,
what is a fair price?

Thanks,

Bill




On Sun, Nov 14, 2010 at 10:48 AM, Magnus Danielson <
magnus at rubidium.dyndns.org> wrote:

> On 11/14/2010 09:41 AM, John Miles wrote:
>
>>
>>  I’ve looked at Wikipedia and I am as lost as when I started.
>>>
>>> Could someone walk me through the process step by step and also
>>> tell me what test equipment is required?
>>>
>>>
>> Besides the pointers at www.leapsecond.com , I've collected a few links
>> at http://www.ke5fx.com/stability.htm that may be helpful.
>>
>> The first .PDF link on that page is my presentation from the Microwave
>> Update conference a few weeks ago.  It was meant as an introductory
>> "Stability Measurement for Radio Nuts" talk, discussing the state of the
>> commercial art in light of what's available to hobbyists.
>>
>> The NIST links under "General timing and noise metrology", in particular
>> this one ( http://tf.nist.gov/general/pdf/2220.pdf ) are excellent.
>>
>> If you have an HP 5370A/B counter and a GPIB interface you can do a lot of
>> good measurement work.  With the appropriate software you can make
>> conventional strip-chart style plots of frequency and phase, as well as ADEV
>> and similar plots.  Unless you are a software nut you probably do not want
>> to homebrew the necessary code to do this.  Most people don't use the same
>> program for acquisition and plotting; a script or batch file does the job of
>> reading the data from the counter and spooling it to a text file, while a
>> program like Stable32 or Ulrich Bangert's (search on df6jb plotter) renders
>> the graphics.
>>
>> My own app (TimeLab) is an exception, in that it attempts to do a good job
>> at both data acquisition and rendering.  It's still under heavy
>> construction.  Right now I'm rewriting all of the acquisition routines to
>> support, among other things, the use of more than one GPIB counter at once.
>>
>> Given that you have an HP 5370 available, if you wanted a walkthrough, you
>> could try something along these lines:
>>
>> 1) Get an NI or Prologix GPIB adapter, install per manufacturer's
>> guidelines.
>>
>> 2) Download the current TimeLab beta.  You have two options here:
>>        http://www.ke5fx.com/timelab/setup.exe -- Graphically ugly but
>> better tested
>>        http://www.ke5fx.com/timelab/setup_temp.exe -- Nicer looking, but
>> more likely to have bugs, and some features have yet to be ported over to
>> the new codebase.  Use this one for the instructions below.
>>
>> 3) Decide whether you want your HP 5370A/B to run in talk-only mode or
>> addressable mode and set its DIP switch accordingly.  The software will work
>> either way since it doesn't actually try to control the counter, but for a
>> 5370 I'd use addressable mode unless you have a reason not to.
>>
>> 4) Set up a basic frequency measurement to begin with.  Feed a 10 MHz
>> signal or whatever into the STOP jack, and hit FREQ and 1s.
>>
>> 5) In TimeLab, select Acquire->Acquire from HP 5370A/B, and then select
>> the NI interface or the Prologix interface's COM port from the list.  Hit
>> the "Monitor" button and you should start seeing the counter's frequency
>> readings scroll by.  If not, find out why before going any further.
>>
>> 6) Hit "Start Measurement."  After a few readings have come in, you should
>> see your ADEV plot start to take shape.
>>
>> 7) Hit the 'f' key to switch to a frequency-difference chart, or the 'p'
>> key for a phase-difference chart.  The 'y' key will toggle the Y-axis
>> between easy-to-read round numbers and full display range.
>>
>> You can get somewhat cleaner measurements from the 5370 if you use
>> time-interval mode rather than frequency mode, but time-interval
>> measurements require a 1-pps or similar source and some additional setup
>> effort.
>>
>
> 0) Essentially whatever source you have (crystal, Rubidium, Cesium, GPSDO)
> unless you haven't done it before, turn it on well in advance. I prefer days
> over hours. Locked crystals such as Rubidium, Cesium and GPSDOs will cancel
> the last part of the oscillator drift but depending on details performance
> may be more or less compromised by this drift. I think this is one of the
> practical details one should not miss.
>
> I for one thinks that using a trigger signal such as the PPS or more
> preferably a higher frequency trigger is worthwhile, as you get a more
> stable rate of read-outs. Also, it gives a larger amount of raw data,
> allowing for the increased degrees of freedom and quicker convergence of
> estimator(s).
>
> Do use TimeLab, I think it is a great way to get going. It's also fun to
> see the curve converge as more data comes in...
>
> Cheers,
> Magnus
>
>
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