I neglected to mention in the first post, but I also put the crystals into a 2nd repeater we have and had the same problem.
I may have to try tuning the cans on our spare 6.85 machine. Mike WM4B From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike Besemer (WM4B) Sent: Monday, October 06, 2008 8:56 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables David, Not sure what youre asking, but if youre asking about spurs, shes a clean as a whistle. VSWR is fine as well. Mike From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of David Murman Sent: Monday, October 06, 2008 8:51 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables Have you look at your transmitter when the desense starts? David -----Original Message----- 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 Id 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 whod 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 IDs 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 Id get noise on the receiver. Thats 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. Its 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? Im 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 _____________________________________________ From: Mike Besemer (WM4B) [mailto:[EMAIL PROTECTED] Sent: Sunday, October 05, 2008 9:10 PM To: 'Repeater-Builder@yahoogroups.com' Subject: DB4060 Duplexer Cables I spent the weekend working on a set of DB4060 cans (cleaning and retuning) and have managed to commit the ultimate stupidity. I had all the harnesses off and instead of MARKING them I just laid them out on the bench. Unfortunately, the bench got cleaned and the cables are now all mixed up. I can tell which 2 cables went between the cans and which went to the T-connector, but all 4-cables are different lengths. I assume that the shorter of the two cables go on the TX (high) side of the cans and the shorter go on the RX (low) side of the cans. Am I correct? Thanks for the help next time Ill mark the cables! 73, Mike WM4B
