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

Magnus Danielson magnus at rubidium.dyndns.org
Thu Oct 2 02:10:26 EDT 2014


The character of starting high/low and then stabilize some 5-30 min 
later is typical of oven oscillators. Underdamped ovens have been seen 
before, I have even seen one on the brink of oscillation.

TCXO will not have the same wide range, as it compensate for the 


On 10/01/2014 10:11 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> 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???
> Dave
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