Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 01:25pm 03 Nov 2017 |
I played around with frequency pulling ceramic resonators some time ago.
The trick seems to be to buy a whole bunch, the frequencies will be all over the place. Use the highest frequency resonator out of the batch.
There was never any problem pulling the frequency low, it was reaching the high end that proved quite difficult.
I managed to get 497Khz to 503Khz from a 500Khz resonator, with 0 to +10 volts using two BB112 varicap diodes (35 to 440pF each) which is what I needed for my application.
Divided down to mains frequency that would give +/- 0.3Hz which is plenty.
It should work equally well up at 12Mhz.
Surprisingly the frequency shift versus voltage ended up being a lot more linear than I expected. +5v producing a very stable 500 Khz.
Cheers, Tony.