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

[Bob kb8tq]

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  N5TNL<uccm_gain_2_11h.gif>_______________________________________________
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