[time-nuts] Re: GPSDO - EFC and fear

[Andy Talbot]

Does it not have a coarse adjustment [trimmer capacitor] you can use to
bring the voltage control within range?

Andy
www.g4jnt.com



On Sat, 13 Jan 2024 at 11:09, ordnit via time-nuts <time-nuts at lists.febo.com>
wrote:

> Dear list,
> I own a couple of UCCM GPSDO which have been running flawlessy for a
> couple of years. On January the 4th I decided to switch them off for
> scheduled maintenance and noticed that one unit was not locking
> properly. Thanks to the log, I realized that the EFC was near its
> maximum and, an hour later, had exceeded its maximum.
>
> I think that OCXO (Samsung STP2945LF Datecode 1245) has reached a drift
> level which is no longer recoverable by the internal DAC. I still have
> to desolder the OCXO and test it with counter + power supply, in order
> to see the amount of voltage required by the unit in order to reach (or
> approx 10MHz).
>
> Is there a way to fix it? I think that using a bunch a opamps it should
> be possible to fix it, maybe degrading the performances.
>
> In the junk kox I found an old trimble 10MHz OCXO which was removed by a
> dead GPSDO. So I powered it up ( 30+ hours) and mesured its output
> frequency with a HP50131A reading 9.999991 Hz (time gate 1s). By varying
> the Vref voltage (N6075A power supply), I managed to bring the OCXO back
> to 10MHz but... applying 5V. So I think that thix OCXO (dated back to
> 2015) has aged out too.
>
> My questions:
> - Are my assumption reasonable?
> - Is there an OCXO which can replace the STP2495LF having the same Hz
> per Volt sensibility?
>
> Thank you in advance for your help.
>
> Have a nice 2024.
>
>
> adelmo
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