[time-nuts] Methods for comparing oscillators

Steve Rooke sar10538 at gmail.com
Tue Aug 4 03:16:26 UTC 2009


2009/8/4 Ed Palmer <ed_palmer at sasktel.net>:
> The biggest difference between the 5370 and the 5372 is the single-shot
> resolution.  The 5370 has a resolution of 20 ps while the 5372 is limited to
> 150 ps.  When measuring Allen Deviation, this difference means that for a
> Tau of 1 second, the 5370 can measure down to approx. 2e-11 while the 5372
> can only reach 1.5e-10.  Note that since many high-quality OCXOs are spec'ed
> lower than these numbers, neither counter can directly measure them and need
> help e.g. DMTD or some other heterodyne technique.

I'm not sure that the 5370A is capable of measuring without dead time
so this will affect Allen Deviation measurements unless procedures
like picket fence are used.

Yes, DMTD and similar look like the way to improve the resolution of
these instruments. Just need a practical way of implementing it.

73, Steve

> Ed
>
> Steve Rooke wrote:
>>
>> 2009/7/31 John Green <wpxs472 at gmail.com>:
>>
>>>
>>> I've been hanging around and reading long enough to understand that when
>>> measuring the differences between oscillators the preferred methods are
>>> the
>>> HP 5370A Time difference counter or the dual mixer method. I want to
>>>
>>
>> What's the difference between a HP 5370A and a HP 5372A for this type
>> of measurement?
>>
>> 73,
>> Steve
>>
>>
>>>
>>> evaluate some ocxo's and Rb sources against either a Tbolt or Z3801 and I
>>> don't have either method available. What I have used in the past is an HP
>>> Infinium scope with the reference fed to one channel which also provides
>>> sync and the DUT to the other. I have tested 2 ocxos that were so close
>>> that
>>> the two waveforms did not move by a detectable amount in a 30 minute
>>> period.
>>> I realize that this method will require very long observation times when
>>> looking at more stable sources. I am not looking to get absolute data,
>>> just
>>> comparative. Given what I have to work with, is there a better way? I use
>>> an
>>> Agilent 89441A Vector Signal Analyzer for signal quality measurements. I
>>> can
>>> see 60 Hz sidebands at least 60 or 70 db down and while I can't measure
>>> phase noise, I can  tell a clean oscillator from a dirty one. For
>>> instance,
>>> there is a world of difference between the signal generated by an HP8920
>>> and
>>> a E4430B.
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>>>
>>
>>
>>
>>
>
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-- 
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.



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