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

Tim Shoppa tshoppa at gmail.com
Thu Oct 2 08:53:59 EDT 2014


As to "oscillation": most older octal style crystal ovens have no
proportional control at all, they are simply a bimetallic
click-on-click-off thermostatic switch that is on or off, and after initial
warmup they cycle up and down every few minutes.

A tiny fraction of the better octal crystal ovens have some proportional
heater control.

Tim N3QE

On Thu, Oct 2, 2014 at 2:10 AM, Magnus Danielson <magnus at rubidium.dyndns.org
> wrote:

> David,
>
> 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
> temperature.
>
> Cheers,
> Magnus
>
>
> 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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