There has been example after example of people replacing foil/braid cable with heliax and the end result was elimination of the problem that you are experiencing. Yes, there are isolated examples of people getting away with using the foil/braid coax, but they are far and few between.
You indicate that you've terminated the duplexer into a dummy load and the problem goes away, try terminating at the antenna end, using the LMR cable, and see what you get. Chuck WB2EDV ----- Original Message ----- From: Tom Elmore To: [email protected] Sent: Wednesday, October 01, 2008 1:06 PM Subject: [Repeater-Builder] LMR-400 Cable I recently put a six meter repeater (52.810/51.110) on the air here in Anchorage, Alaska. I am feeding it with about 60 feet of LMR-400 cable and am experiencing quite a bit of desense. I did a search for "LMR-400 in duplex operation" and came across several posts from users of this list and decided to sign up and investigate some more. I am running a GE Master Pro at 100 watts into a 8 cavity Sinclair duplexer. The antenna is a Diamond co-linear mounted about 35 feet above ground at the present time. I live on a hill here in town and currently have the repeater mounted at my home qth. When I terminate the duplexer into a dummy load and look at it with the spectrum analyzer it performs very well with no desense. Connecting up the antenna is another story altogether. I have been pulling my hair out over this one thinking it must be a duplexer problem. Originally I fed the antenna with RG-213 which I know is not the best choice for repeater use but it is what I had handy at the time. I was getting desense with the RG-213 so I switched to the LMR-400 since I had a roll someone had given me. I actually think I had slightly less desense with the RG-213. Is the 400 really not that suitable for duplex operation even at 6 meters? What would be a good alternate choice ?
