On Sat, 26 Jul 2003 21:20:18 -0700, Watson A.Name - 'Watt Sun'
wrote:

In article , mentioned...

Take a look at lowband filters and duplexers from CellWave, Telewave,
etc.
Your filter is going to be a coaxial cavity about 2mx20cm with piston
for tuning.
I am sure there are some better approaches to your task

How about a helical resonator. They're smaller than a cavity, maybe
not as high Q, but still higher than lumped constant tuned circuit.
They're tunable, but I'm not sure how much.

I'd like to live long enough to see a helical at 40MHz that can
'attenuate the hell" out of signals outside the Fr+/-20kHz channel.