[time-nuts] Measurement of frequency of HP 8720D option 1D5 oscillator after switch on

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Wed Oct 1 16:11:47 EDT 2014

Further to my question the other day about what type of oscillator was
used in the HP 8720D VNA, fitted with the high stability oscillator
option (1D5), here is the frequency as the instrument is switched on,
after being powered off for 2-3 hours.

The oscillator appears to start too high in frequency, overshoots
downwards, then settles down. It would be a somewhat useless exercise
collecting data for much loonger and looking at in detail, since I
don't know the accuracy of the HP spectrum analyzer. But that had been
on for at least 24 hours.

The measurement system was an HP 70000 system spectrum analyzer,
fitted with the 70310A precision frequency reference. This has not
been calibrated in years.

I will get one of those Jackson labs GPS frequency references, then I
will know what the frequency is!!

Assuming the crystal frequency is only a function of temperature, (and
I know that not to be the case), it looks as if the oven is under
damped to me.

Is this behavior typical of a TCXO, OCXO or whatever ??

Any comments???

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