[Test-Equipment] Frequency Measuring Test

Tue, 24 Sep 2002 11:10:21 -0500

When talking about frequency measurements, standard statistics does not
apply.  In fact when measuring clocks, the standard deviation does not
converge as the number of samples and measurement time increases.  To solve
this issue, the Allen variance was developed to study the behavior of
synchronized clocks.  In the case of non synchronized clocks, TVAR can be
used.  TVAR is an extension of the Modified Allen variance.

I don't know what kind of stochastic process the ionosphere follows.  If I
had an I&Q RX locked to WWW and a GPS based clock, I could make some
measurements.

Francesco

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Mike Feher
Sent: Tuesday, September 24, 2002 10:35 AM
To: Gary Chatters; [email protected]
Subject: Re: [Test-Equipment] Frequency Measuring Test

Gary -

That is of course correct, and I have not considered it. The good old rate
of change in phase as a function of time does equal a change in frequency.
However, I would not expect propagation delays to change so abruptly,
although, here again, this is out of my expertise, and, we are talking about
minute differences, so, it could well cause a measurable difference. But, it
does reaffirm my earlier statement about the measurement having to have a
statistical basis, made up of multiple measurements and intervals. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ, 07731
(732) 901-9193

----- Original Message -----
From: "Gary Chatters" <[email protected]>
To: <[email protected]>
Sent: Tuesday, September 24, 2002 10:36 AM
Subject: Re: [Test-Equipment] Frequency Measuring Test

> >
> >I do not believe that propagation delays will cause frequency measurement
> >errors. Unless we are talking about something like doppler. Plain delay
> >should have no effect. It will however have an effect on any time related
>
> Of course, delays are not going to cause errors.  The problem is in
> the variations of the delay.  Those with GPS based standards might
> find it interesting to measure WWV.
>
> I made a fairly simple set up for comparing frequency to WWV.
> A Racal 6790/GM tuned to 10MHz with its BFO offset by 60Hz is
> fed to an oscilloscope set to line triggering.  The trace would
> be fairly steady for only a few seconds before the ionosphere
> started shifting and the sine wave trace started racing across
> the screen in one direction or the other.
>
> Gary
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