> It is about 10"x10" square and 1" high, and has SMA connectors, one
> on each side (left/right), and 9 flat-head tuning screws in the
> front (just like the ones on the small 50w duplexers).
Sounds like the filters John Danielson has been selling for the last several
years at Dayton and on his web site.
> The strange thing (why I'm posting) is the tuning behavior. Of the
> nine tuning screws, counting them 1-9 from left to right, screws 1,
> 5, and 9 all seem to adjust the passband center freq, screws 3 and 7
> seem to adjust what appears to be two notches (or one if I "pull"
> them together), and screws 2,4,6, and 8 seem to do nothing at all.
The "even" screws adjust the irises between resonators. They will only make
minor differences in the passband response and insertion loss. The notches
are usually set so that one is on the high side and one on the low side of
the passband to steepen the skirts.
> As it stands right now, based on how it plots on my 8920's tracking
> generator, it looks like it should make a halfway decent filter for
> in front of a preamp, but I'd like to tune it properly if I can
> figure out how and what kind of filter it was designed to be.
There are two versions of that filter; I forget which is the "good" one and
which is the "bad" one, but one of them doesn't work well up above 430 or
so. Make sure you check the return loss.
--- Jeff WN3A
