FRG-7 BFO convert to ceramic resonator

[neazoi]

Hi I wonder if I can convert the BFO (Q408) of this receiver to use a ceramic resonator without too much changes in the BFO circuit, so as not to have to alter many things onto the PCB.

Can I somehow connect a ceramic resonator there and/or maybe remove 1-2 components and convert it into a more stable one?
How about replacing this R439 with a ceramic resonator?

I see some similarities with the attached colpitts oscillator with common base.

 

[betwixt]

It might work but I doubt you would see any improvement. The SAW circuit is usually used at much higher frequencies (> 300MHz) so it may need some adapting to go down to 455KHz. You would also have problems shifting to the opposite sideband . You wouldn't want a 455KHz resonator, you would need two, one about 453.5KHz and one at 456.5KHz. Switching capaciance across it as used in the original wouldn't allow for shifting up and down but you might be able to start at 456.5KHz and 'pull' it 3KHz down with a capacitor.

Brian.

 

[neazoi]

It might work but I doubt you would see any improvement. The SAW circuit is usually used at much higher frequencies (> 300MHz) so it may need some adapting to go down to 455KHz. You would also have problems shifting to the opposite sideband . You wouldn't want a 455KHz resonator, you would need two, one about 453.5KHz and one at 456.5KHz. Switching capaciance across it as used in the original wouldn't allow for shifting up and down but you might be able to start at 456.5KHz and 'pull' it 3KHz down with a capacitor.

Brian.

I rebuilt the circuit on a breadboard and I connected a 455KHz ceramic resonator from the drain to the ground. I am not sure if it improved stability, but for sure it did not made this worst. But I am using another coil than that of the frg-7.
I noticed a decrease in frequency of 50KHz with the ceramic resonator to ground. When I added a series capacitor to the resonator to ground, the shift was less.
Also with just the ceramig resonator and no extra series capacitor I could still use the top variable capacitor to shift the frequency on USB.

But I am not sure in which places to try the resonator. Is what i did on the drain correct? What other places?