In sci.electronics.design, Paul Burridge
wrote:


Hi chaps,

I've decided to bite the bullet and try to build an RF filter for
40Mhz. This filter will ideally have a very, very sharp characteristic
at one single spot frequency +-20Khz and attenuate the crap out of
anything either side of this. It'll need to be tunable over a range of
say 200Khz. Can anyone give me a steer on what type of arrangement
would be best suited to fit this purpose?

I've got that deja-google feeling all over again:


http://groups.google.com/groups?hl=e...com%26rnum%3D6

I like the idea of downconverting to an IF, filtering using
standard IF technology, and (if you want the output to be the same
frequency band as the input) upconverting using the same local
oscillator as the downconverter. Just change the LO frequency (maybe
use a frequency synthesizer for stability) to do tuning.

Thanks,

p.
--

"I believe history will be kind to me, since I intend
to write it." - Winston Churchill