> Ok so here's what I've got (I think)
>
> http://www.n2ckh.com/FORSALE/REPEATERS/DUPLEXERS/DB4076/DSC02678.JPG
>
> Hamvention special, 4 cavities, appears to be a DB Products
> 4076 family unit. My bench tools: HP 8924c w/ Spec Analyzer
> and Tracking Generator.
There was a guy at the Hamvention that had several sets of Decibel
four-cavity window filters, selling for $50 each, which, to the untrained
eye, would look like an older DB4076. As you said, there would be nothing
in the hole where the capacitor would be in a regular DB4076. In essecence,
what you have are just plain-jane pass cavities.
As a second means of confirming that you do, in fact, have a window filter,
is there an antenna "tee", or are the four cavities cabled together in
cascade? If the latter, then you probably have a window filter.
And as a third means of confirming, is there is a label on the front? If
not, was there any signs of a label having once been there? If not, then
that's yet one more indication that it isn't a DB4076.
Decibel made two varieties of pass cavities used in window filters in that
era. One had adjustable loops (less common), the other had fixed loops. If
your loop connectors have a rectangular chrome plate around them with
insertion loss calibration marks, you have the less-common adjustable ones.
If you just see four philips-head screws and no chromed plate around the
connectors, then yours is not adjustable.
If you have the adjustable type, you could probably use them as a pass-only
duplexer, but with mediocre isolation, even with the insertion loss cranked
up higher than you'd like. If you have the non-adjustable ones, they have
very tight coupling, so you're not going to get the isolation you'd need for
a repeater.
> Did I buy a piece of junkola? Teach me obie-wan.
Not junk, but maybe not what you were expecting...
--- Jeff WN3A
