[time-nuts] Re: repair of an HP E1938A OCXO

[Wilko Bulte]

hello Chris,

You are correct, the EFC is shorted right now. So, if there is a nominal EFC voltage !=0 V  required to obtain 10 MHz this explains why my oscillator is off-frequency.

In case somebody on the list can measure the EFC voltage with the oven being GPS disciplined we can get this clarified Inthink.

I unfortunately do not have the GPSD board(s), I just have the O of the whole GPSDO system. In case someone has a GPSD board available for the good cause I would be interested, for obvious reasons.

cheers,
Wilko

> On 1 Jul 2025, at 14:52, Chris Caudle via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> On Thursday, June 26, 2025 3:47:48 PM Central Daylight Time Bob Camp via time-
> nuts wrote:
>> There really is no practical way to get an accurate temperature sensor
>> inside the oven / on the crystal, without upsetting the operation of the
>> device.
> 
> Do you really need to measure the temperature independently?  I don't fully
> understand the control scheme and the differences between C mode and B mode,
> but if you get the oven to the right temperature, will that not set the
> oscillator output back to within spec?  I recall the original description was
> the measurement was with EFC connected to 0V, so I guess you would need to
> know what the nominal value of the EFC should be for on-target frequency.
> Am I thinking too simplistically?  Is there a range of oven temperatures where
> the output is close to nominal but the temperature coefficient is not optimal?
> 
> --
> Chris Caudle
> 
> 
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