Sorry to hear you got the proverbial shaft. But all's not lost. If you
need a duplexer, I'll trade you a Motorola T1504 (pass/reject) duplexer in
good shape that I had on my table at Dayton that didn't sell. I was asking
$125 for it. I'll trade you straight across if you pick up shipping in both
directions, and I'll even tune it on the VNA and send you the plots.
I bought two sets of those window filters from the same guy, but I knew what
they were, caveat emptor is the golden rule at Dayton or any other hamfest.
Actually I think I gave him $75 for the pair, and I took the two
cleanest/newest ones he had (the newer dark-tan ones).
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Josh
> Sent: Saturday, May 29, 2010 9:27 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Re: Help Needed (Guidance and
> advice) tuning a DB Products Duplexer
>
>
>
> Certainly not what I was expecting... Yeah, I bought one from
> 'that guy'. It's more than an untrained eye - he straight
> lied to me... said 'under these caps are where you'll tune
> the capacitors' - I should have popped one off and looked
> down the hole. Maybe he was clued in, maybe he wasnt - either
> way, that's what I bought. Dangit :P
>
> So if all I have are pass cavities.... what 'are' they good for ?
>
> Guess I've got to find another dupelxer.
>
> j
>
> --- In Repeater-Builder@yahoogroups.com
> <mailto:Repeater-Builder%40yahoogroups.com> , "Jeff DePolo"
> <j...@...> wrote:
> >
> > > 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
> >
>
>
>
>
>
