Hello Eric Good question and I think that my answer is probably not.
In my case, or I should say, in the case of our PD duplexers, I inherited both of them (as new lead man) in used condition. My predecessors had successfully used both of them in protected but somewhat damp locations for years without obvious problems.----same frequency pair, in primary and backup repeaters. The backup repeater was abandoned and the primary was completely rebuilt using a different new transmitter and improved sensitivity new receiver. In integration testing of the new repeater system, severe desense was found which was traced to being the result of wide band noise from the duplexers (both were tried). One was worse than the other but both produced a gob of wide band noise over the receive frequency. when the transmitter was operated. This was witnessed via spectrum analyzer on a sample "T" between the Rx port of the duplexers and the receiver. The tuning of both duplexers was checked and was found to be good, in fact, very good-----about 1.75 db thruput loss (both paths) and about 110 db Tx to Rx loss. Also, it was found that almost all of the cavity pass adjusters felt like a squeaky dry meat grinder full of chicken bones when turned. It was obvious that the problem was down with the finger stock and not in the adjuster bolts (rods) as windup in the bolts was easily felt. One eventually jammed and the other duplexer was reverse tuned but was still noisy. I can't say at this time just what went wrong inside as I haven't had time to open one for a look. The paint looks good, the adjuster bolts are a bit rusty but not bad and looking inside, with the connector-loop plate removed, no corrosion is visible and it is impossible to see the finger stock area. I made contact with a fellow in the East some time ago who had similar problems with a PD 497. He drilled holes in the top, through the inter tube protrusion and squirted contact cleaner in and successfully fixed his noise problem. He also drilled some holes in the bottom to let the excess out and replaced all of the connectors with silver body-gold pin N connectors for good measure. Another duplexer was borrowed, tuned, connected and our new repeater system was found to work perfectly with noticeably improved performance compared to that of the replaced system. Telewave was then contacted for a replacement that would fit in the space I had the PD in. Space was and still is tight as I have three repeaters (2 meters, 222,and 440), all complete with duplexers, a Link controller, power and space for several remote receiver interface units all in six foot enclosed computer system rack. Hope this answers your question-----I suspect the duplexer troubles here are the result of some corrosion and possibly some tuning with power applied abuse. I'm envisioning a complete disassembly and replating to be the fix. Scott, N6NXI I know that one of them was tuned with power applied---about 30 watts---and the problem found afterwards. ----- Original Message ----- From: Eric Lemmon To: Repeater-Builder@yahoogroups.com Sent: Thursday, November 08, 2007 7:11 PM Subject: RE: [Repeater-Builder] 2 Meter Duplexer Recommendations? Scott, Please elaborate on the "old age" problem. Are we talking about the wear and erosion that results from endless "pumping" of the center tuning element which, however slight, moves during cycles from cold when idle to warm after long transmissions? That's about the only cause of a poor contact I am aware of. Whenever I found this problem, reversing the TX/RX tuning fixed it. When you found that reversal did not help, what was your diagnosis? 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Scott Overstreet Sent: Thursday, November 08, 2007 8:54 AM To: Repeater-Builder@yahoogroups.com Cc: Scott Overstreet Subject: Re: [Repeater-Builder] 2 Meter Duplexer Recommendations? Hello Tony If we are talking in the 2 meter ham band---read on. The PD 497 series duplexer is a very good duplexer until old age sets in-----I have two of them here that have gone noisy---I should say that mine produce wide band noise when transmitter power is applied----lots of desense in spite of looking perfect on the tuneup instruments-----and they are not easily fixed----and a Tx/Rx reversal didn't help. In my case, space is tight---the 497 is shorter than most and replacement with a standard Telewave catalog unit was impossible at the low end of 2 meters . A little pleading with Telewave resulted in their making a special for me that fit nicely in place of the 497 and very nearly equaled the 497 performance which was more than enough for my application. If you are concidering a new duplexer---I suggest that you call Len Pringle (KH8A) at Telewave (1-800-331-3396) and ask about the "2 meter Ham Special" ----their PN TPRD-14556 that he had built for me. ----- Original Message ----- From: Tony L. <mailto:[EMAIL PROTECTED]> To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder@yahoogroups.com> Sent: Wednesday, November 07, 2007 8:10 PM Subject: [Repeater-Builder] 2 Meter Duplexer Recommendations? My Celwave PD 497-1-1 VHF duplexer just can't seem to provide adequate tx/rx isolation (Micor 100 watt repeater with 0.6 MHz tx/rx separation). Everything else seems to check out okay; jumper cables, connectors, receiver, and hard line. I've heard the PD 497-1-1 isn't the latest in duplexer design and was wondering what other VHF repeater owners might recommend with regard to high performing, closed spaced duplexers for moderate power applications. Thanks.
