Since Bruce hasnt responded

A cavity filter is a very narrow band filter usually of silvered copper
pipe construction. At 160MHz its going to be about 18" long and maybe 3"
dia. You might be able to get away with a helical filter instead. Thats
a copper/silverplated coil inside a silvered/copper box. I'd suggest
three coupled together if you were serious. They could then be in a
(say) 4" x 2" x 2" box.

In this case the use is as a tuned TRF receiver connected direct to a RF
measuring device. When you are close you simply watch the meter and walk
towards where it gets stronger and away from where it is weaker!

I'll comment on your other post in a moment.

Cheers Bob

Jim wrote:

I am not familiar with a "cavity filter". I'll do some Googling on that.
Can you fill me in on it's use?