I've never worked with cans or repeaters, but I've witnessed similar issues caused by oxidation/corrosion. Have you tried using a conductive grease on the housing joints and the rods?
It appears silver-based grease is suggested for all applications above 50 mhz. Good luck! Jacob Suter (unlicensed newb) From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike Besemer (WM4B) Sent: Monday, October 06, 2008 7:39 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables Okay. I got the cable dilemma sorted out thanks to some photos I'd taken earlier, but I CANNOT get the desense out of these things. Some history: The cans and the repeater were both in storage for several years. We got a 'too good to be true' deal on the site and I pulled everything out of storage. The repeater (Mark 4) and cans were both originally on 146.85. The repeater was brought back to life on 145.11 and I tuned the cans using an HP-8920A. When I was done, I had no detectable desense either into the -8920A or at the site. Fast forward 2 months. The repeater goes deaf. I make a trip to the site (about 40 minutes) and find terrible desense. I blamed the service technician who'd just installed a new repeater for the BoE at the site, tweaked up the cans and everything was fine. for about a day. The repeater sounded great and the sensitivity was fine, but it had a terrible noise on transmit after it had been at rest for a while. About 2 minutes of RF would clean it up and it would work fine until it rested again for about 40 minutes. then it all started over again. The noise was only when the squelch was open. ID's and announcements were fine. (AH-HA!) I finally got a chance to make the trip back to the site and pulled everything home with me. I took a look at the repeater, just to give it a clean bill of health. It all looked good. I made only a few minor tweaks. The cans were noisy. I could turn the bandpass screws and I'd get noise on the receiver. That's what led me to pull the cans apart (below) to inspect and clean. There was some growth on the copper further up the outer tube, but nothing by the fingerstock. I have it a nice vinegar bath and cleaned it with a paint roller stuck inside the outer tube. It cleaned up nicely and I gave it a nice bath with the garden hose and baked the whole thing in the oven until it was good and dry. The entire process was repeated for each can. The enclosure with the notch capacitor was removed for this process, and the tuning rod screws were removed from the top to let the tuning rod drop down so I could get into the outer tube. After I put it all back together, I checked the fingerstock and it all looked good. Initial tuneup with the HP-8920 went fine and I soon had the repeater running through the cans into the -8920, breaking the squelch at about -116 dB with no detectable desense. Then. I went to bed. The next day, the desense was back with a vengeance. Been tuning for 2 days now (I thought I found it last night when I found a connector spinning on one of the cables going to the T-connector) and I CANNOT get rid of it. Sometimes it sounds like an AM radio driving under a power line. sometimes it just crackles. It's got to be microarcing somewhere, but I HATE taking those cavities apart again. (BTW, the cable with the spinning connector was replaced with good, MILSPEC RG-214 and MILSPEC connectors.) Have I missed anything? I'm really starting to think that these things are beyond salvage, but I sure hate to break that news to the club! Help! 73, Mike WM4B
