Sorry about the slow response.
I'm not yet aware that is an issue. I'm still working on the basics, e.g. measuring a Kenwood TS-520 CW filter and construct fixtures. But a tuned choke or two should do it. I need a 25 femptoFarad change to . A series arrangement should be fairly insensitive to small variations in capacitance of the varactor. The first prototype will be manual air variables.
It's entirely possible that it can't be done reliably. But the only way to find out is try doing it. Unfortunately, my 8593A is misbehaving so I seem to have had a repair job take priority. I now have 500x crystals in hand.
Have Fun!
Reg
