Using ceramic resonators in SSB filters

Ladder filters using low cost standard frequency quartz resonators are well known in amateur circles, but what about ceramic resonators? Actually, they can be quite useful in lowish (half MHz) SSB filters, despite their lower Q. The reason for this is that their lower inherent impedance allows top coupled parallel resonance operation to be quite practical, which makes playing with networks that much easier. Associated network capacitor values end up being very convenient, and 'suck it and see' filter development becomes quite fun. So here are two examples, each using three resonators, that operate at about 0.5 MHz. The shunt capacitors allow some movement of resonator frequency, and the series capacitors control the coupling between stages and therefor filter width. Oh, with this topology, it is easy to arrange for 50 ohm input and output matching impedances:

455 kHz 560 kHz

It's a while since I did these, so details, other than those shown above, have become a little hazy. The 455 kHz version was fitted into a small 80m monitoring receiver, and that certainly sounds OK.

The same idea was tried at 1 MHz, but I have lost the circuit values:

3 x 1MHz resonators 4 x 1MHz resonators 5 x 1MHz resonators

I must have tried higher frequency ceramic resonators, but cannot now find any graphs of those. They probably weren't sharp enough as sideband filters, but 3.58MHz or 3.68MHz units should make good image filters for 80m receiver front-ends or transmitters, though they will only cover a portion of the band. Likewise, 14.3MHz ones for 20m.

There definitely have to be other worthwhile applications for these for instance, SSB generation for an audio RF processor - or this 0 - 20 kHz carrier frequency USB generator, built for low frequency optical comms use.

speech processor