Well now--- I've got two 2 meter Phelps-Dodge duplexers that tune beautifully but are unusable in duplex service do to receiver desense-----internal microarcs between failed silver plated movable and fixed parts of the center element in a couple of the cavities of each.
Also, some time ago, I had a 2 meter Hustler antenna---the 3 section one--- go bad on our repeater-----it heard fine and showed good VSWR but desensed badly when the transmitter was on. A total disassembly and cleanup of all connections---aluminum tube slip fits and bolted connections and reassembly with anti-corrosion dope and shrink tubing to keep the weather out fixed it. In your case it sounds like you may have a bad "antenna" port coax "T" on your duplexer or the mating antenna feedline connector or a bad connector somewhere up the feedline----I've seen that too-----micro arcs. And LMR-400 or 9913 cable with a loose connector will do it too. Then you could have a loose random connection somewhere in your tower/antenna structure-----something like a coax connector making and breaking connection to the antenna support structure-----this will often make high level random "static" type noise------look for anything that is loose. Scott, N6NXI ----- Original Message ----- From: Dan Cation To: Repeater-Builder@yahoogroups.com Sent: Saturday, September 29, 2007 4:14 PM Subject: [Repeater-Builder] Duplexer and noise question Hi everyone - new to the group looking for help on a strange problem. I've been involved with two repeaters in Southeast Kansas (Humboldt - 147.18 and 442.900) for over 30 years and work in Electronics, although not in radio. A couple months ago we lost both repeaters when we had a flood in this area - I took the Wacom duplexer apart and cleaned any obvious corrosion or such and assumed it would be fine - it tuned up without any trouble and there was almost no corrosion. I replaced as many of the T connectors as I could and carefully cleaned any that remained and made new cables of the correct length. I have built a new repeater but am now having a problem with intermittent buzzing sometimes when the transmitter is up - it will hold the receiver open and cover any signals that aren't pretty strong. Comes on whenever the transmitter comes up but not always - sometimes it is fine. I have tried 3 different transmitters - a Midland 3400, a Midland 340A and even a couple Icom rigs - makes no difference. Same for receivers - makes no difference. Never shows up unless the duplexer is hooked to an antenna - works fine on a dummy load. Tried two different antennas as well. The noise sounds like bad line noise, but I can't hear it except on the repeater. The repeater is at my house right now, but I intend to haul it back to the site to see if it shows up there as well when I can get time to do it. Anyone else ever ran into this kind of thing?
