At the moment, the phase-locking only occurs in a very short range (maybe 10 Hz).
If I amplify the output using an active/opamp filter, I should get a much higher range?
e.g. If I wanted to get to 100 kHz range, I would have to amplify?
Ultimately, I will want to slowly sweep the RF by 100 kHz or so by changing the Ref, but they don't remain phase locked over a long range.