[time-nuts] GPSDO won't lock: OCXO aged out?

[paul swed]

Not sure how hard it might be to get a thermocouple into the oven. That
would give you a hint.
Regards
Paul

On Fri, Jan 15, 2021 at 8:51 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> One of the options is that the EFC has an issue.
>
> Another option is that the oven control circuit has a problem.
>
> Either one *could* put the center frequency someplace odd. If it’s the
> heater control
> (or heater set point) then indeed, the temperature sensitivity will go way
> up.
>
> Most of the OCXO’s off these boards are a sub $20 sort of item on eBay.
> How good
> are they? Who knows ….
>
> Bob
>
> > On Jan 15, 2021, at 8:18 PM, Scott Newell <newell+timenuts at n5tnl.com>
> wrote:
> >
> > Quick update: tried using an AD780 reference + op-amp to offset the EFC
> voltage. Worked great, until I slid everything back into the enclosure and
> it was tuning the OCXO too high!
> >
> > After several disassembly/mod/reassembly passes (all tuning too high
> once boxed up), I punted and went back to the simple gain stage. It's been
> locked at TFOM 2 all day, but it does seem very sensitive to air currents
> and temperature changes. I'm starting to think the oven setpoint may be
> wrong, too. (How could it lock 1 month ago with EFC <5V, but now it needs
> 8.5V to be on frequency when it's outside the enclosure? Something's fishy
> there.)
> >
> > Check out the white OSC trace in the LH screenshot--that can't be good!
> >
> > Hoping to limp by until I can find either a drop-in 5V OCXO or time to
> adapt a 12V OCXO into the box.
> >
> >
> > thanks!
> > newell
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