On May 9, 2008, at 2:54 PM, [EMAIL PROTECTED] wrote: > At 5/9/2008 13:40, you wrote: >> if you are using the same wires from the cans to the tees, about >> all I >> can suggest is maybe retuning the duplexers while connected to the >> antenna. > > If there is 0 dB of desense looking into a dummy load & 30 dB into an > antenna, duplexer retuning is not the answer. The problem is > definitely > beyond the duplexer (feedline, antenna, something acting as a mixer > in the > near field, etc.) > >> Also check and recheck each section of cable between the cans, >> etc... >> Not saying this will be the answer, but at this point you seem to >> have >> little to lose by trying it. > > ..except having to retune the duplexer after you detune it looking > for the > real problem. BTDT.
Agreed. Retuning the duplexer "while connected to the antenna" is what I like to call "voodoo engineering". In other words, while it might make you feel better, it has no basis in RF engineering reality. Wave a dead chicken over the repeater while you're at it. It'll do as much good. :-) How do you tune a duplexer properly? One can at a time. If you hook it together and test it properly terminated, and it needs retuning, what's wrong? Cable lengths. If you hook it to your antenna system and it somehow magically goes out of tune? Something else is (badly) wrong. Probably an antenna system that doesn't present a 50 ohm (or anything close to it) load. The way I was taught, and the way I teach is: They put those lock nuts on the duplexer for a reason. Use 'em. (In other words, leave the duplexer alone. Tune it and forget about it.) I've yet to see a quarter wave stub in a can with a lock/jam nut tightened properly (a duplexer), go "out of tune"... no matter how many years went by since the last time it was checked. -- Nate Duehr, WY0X [EMAIL PROTECTED]
