Tom, My first question is what is the reflected power on the antenna? With duplexer loss I am guessing that you would have about 70 watts out of the duplexer, anything more than a couple watts reflected could cause problems.
Yes, the LMR series of cable is really that bad for duplexer use. Worse than that it will turn to junk inside in less than a year if anywhere near salt water. I have replaced lots of it. We avoid any cable that has aluminum foil shield here on the Oregon Coast for outside use. It will corrode up and turn to white powder inside, causing all types of site noise for just about everybody on the same tower. The other question is what type of cables are you using between the radio and duplexer? You ideally want heliax even at 50 MHz. Next best cable is silver plated double shielded coax. If you have to buy new, most of the time 1/2" ldf Andrew heliax can be found cheaper than the silver plated double shielded coax. Joe - WA7JAW --- In Repeater-Builder@yahoogroups.com, "Tom Elmore" <[EMAIL PROTECTED]> wrote: > > 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 ? > > > > > Thank You > Tom Elmore KA1NVZ > Anchorage, Alaska >
