Hi Tom,
As others have said, try the dummy load at the antenna end of the cable and see if there is any desense. Then try disconnecting the antenna input to the receiver from the duplexer and place a dummy load on the receiver. Turn on the transmitter and see if you still have desense. If you do then your receiver is probably picking up RF from the antenna and causing the problem. Since you do not get the desense with a dummy load on the duplexer output this will verify/eliminate direct radiation from the antenna. 73 Gary K4FMX _____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Elmore Sent: Wednesday, October 01, 2008 12:06 PM To: [email protected] 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 ? Thank You Tom Elmore KA1NVZ Anchorage, Alaska
