VFO for UHF (144-148mhz) Help please!
Can you check what is changing?
For me is these relative big variance & I think its a self heating effect, or it will be heated from the environment!?...
You can/must select some temp coefficient adjusted capacitors, but you have to know what is & how much changing.
Formerly by tube tranceivers it was an allday busines some oscillator to build with different & parallel/serial connected & selected Tc + Value capacitors & from begining so to design
_ also their are temp compensated.
In your case is possible not a metell case relevant, but a thermal isolation_if the other effects as capacitances to environment & supply changing effects arent relevant...
Try it pls with an extra stabilysed small supply/Zener & good filtering for your VCO, plus separating/buffer amps!...
With relative simple technique it must be possible to build oscillators up to so GHz & at 10^-5,-6.
These means a stability of 10th of KHz & more and not only in couple of seconds...
I had a project so 17 years ago with two synthesyzers in that_ at 510 & 840MHz, so as I remember their are ca: 10^-6, I didnt used selected Tc capacitors but NP0 & the circuit was built with a short RG 174 Coaxial cable (practically λ/4)as resonant elements
K.