[time-nuts] Lars GPSDO

[ed breya]

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