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
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
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.