I'd recommend that once you get things figured out and tuned up to
nominal running conditions, you should narrow the offset pot range, and
use good low-TC resistors to make up most of the network R, with the pot
having as small an effect as practical. BTW I don't see the pot in the
pictures, but I do in the schematic.
You may want to consider lowering the entire network resistance by
scaling everything down, say ten times lower or more. This would reduce
noise, and lessen effects from the varicap bias (leakage) current in the
OCXO. Also, I have seen a number of OCXOs with an internal termination
resistor (like 50-100 k) on the tuning line - that has spoiled a lot of
fun for me, having to worry about the characteristics of that resistor,
and including it in the deal. With an unknown or unspecified OCXO, it's
good to check for any unwanted extra parts.
It may help the stability to put some insulation around the tuning
resistor network and maybe the DAC too, especially if the waste heat
from the OCXO is significant.
Ed
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