Total posts : 45366
Pursue your idea using the variable cap but here’s another thought which worked for me. My loading coil is wound on a 3 1/2 inch diameter Plexiglas tube and as a means of tweaking the tuning I added a 5 turn movable winding in series with the coil and mounted on the coil form with the loading coil. The 5 turns are lashed together with wire ties and slides easily on the core which is how I make the fine adjustment. When adjusted for resonance this coil is about 1 inch from the main coil. Moving it back and forth about 1 inch pulls the resonant frequency +/- 10 kHz. There is nothing magic about 5 turns since more or less will work. It can be wired series aiding or opposing as required.
It took a bit of experimenting to get it right but the precision it gives is worth the effort. I started with the intent of building a varometer but this was easier.