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
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