[Today’s run: white house – 3 miles]
My GPSDO has been running since summer and I’ve noticed a problem with it. It will go fine for about a week, maybe less, then it will start to slow down. The change accelerates and eventually I get to the negative voltage rail for the frequency control. That’s no good. I have it do this cycle at least twice now, I don’t remember.
I have tried two different fixes so far. First, I thought maybe the oscillator was seeing a varying output impedance so I changed out the very small 50 Ohm output resistor for a quarter-watt job.
That didn’t fix the problem. So now I have added some shielding on the 10 Mhz output line and I’m running with that to see what happens.
I have also ordered another line-buffer IC which is the gizmo that processes the signal coming from the oscillator. Between that resistor and the line-buffer, I still wonder if something in the output circuit is causing the oscillator to see a changing impedance.
