On May 8, 3:03 pm, "Lumpy" wrote:
K7ITM wrote:
...(I've built several somewhat similar filters using
copper clad for the shielding, and they work quite well.)
Would a suggested design be helpful?..

I would like to hear of your designs, please.
Particularly how you physically work the
copper fabrication/solder etc.

Thanks -

Craig 'Lumpy' Lemke

www.n0eq.com

Hi Lumpy,

I'm fortunate to have access to a shear that cuts fiberglass/epoxy
board stock reasonably cleanly. I use all double-sided stock, copper-
clad on both sides. I typically set up the stop for, say, 2 inches,
and make a bunch of square pieces. They'll become end pieces and
partitions between "cells". Then I cut a couple 2 inch wide strips
using the same setup; these will be the sides, and they are whatever
length I need. The base piece is typically a quarter inch wider (or a
bit more) and the same length as the sides. I plan out where I need
holes, and punch them in the partitions and end pieces (or sides, if
that's what I want). Then I tack one of the square pieces just short
of the end of the base, so I can solder it to the base on both sides.
Same on the other end. Then side pieces go in, tack-soldered to the
base and the two end pieces. Avoid tacking where partitions will go.
Put in partitions where you want, and tack them. Then run a bead of
solder along each place where two pieces of copper-clad come
together. Occasionally I'll also put in something to support coils or
wires, too. Then I built the filter...soldering some parts to the
copper clad for ground.

Some filters I can get by with a minimum of partitions. I would
expect for a sharp cutoff filter like the "FD adjacent band" filter
that I'd need to use a partition to separate any two adjacent
resonators.

When I first started making filters this way, I was expecting to have
to seal off the open end of each cavity. The description above only
puts copper-clad on five of the six sides of each cell. I was amazed
to find that it's practically never necessary to do that. For
example, I have a 1MHz bandpass filter that has stops specifically at
2MHz and 3MHz. I used it to clean up the output of a signal generator
so I can test for harmonic distortion. That filter shows about 120dB
attenuation at 2 and 3 MHz, in spite of the open-topped cells.

If a picture would help, I'd be happy to send one via email.

Cheers,
Tom