The catch is how steep you can get the skirt of the filter. A small multi PI filter { look like the output stage on a ZZ transmitter } using very small toroids or if posssible shielded coils could work.
Another way is to replace that rengentive receiver pile of junk section with a mixer and osc. If they still make NE602 or equ could bypass the receiver and use it as a receiver. The OSC size of that chip will work with an crystal. WOuld be a direct conversion but better than that regenative junk.
The input on a ZIP, Bit, can car whatever is a single capactor-coil combo that good as a trap but is so broad its almost usless for what they are using it for.
Grab a ARRL handbook. They have always had a nice section on filters. Its expensive but really packed with info.
Want to setup some simple tools info to construct to measure signal and also tune the receiver for max smoke so to speek. Something you can either use off the shelf tools or simple mods to maintain the electronic side. Try for a RS peg rack bld of matterials. Been so bussy on DB projects of late cant even breath. This is the only break I get!
