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 > > > > > > >