Keep in mind that duplexer manufacturers used to routinely use single shielded (RG-213) cables to make up harnesses. They worked. So Bob's testing doesn't surprise me.
Chuck WB2EDV ----- Original Message ----- From: <[email protected]> To: <[email protected]> Sent: Wednesday, August 04, 2010 10:22 PM Subject: Re: [Repeater-Builder] Coax length > At 8/4/2010 14:37, you wrote: > >>---- Doug Hutchison <[email protected]> wrote: >> > Does the length of coax connecting cable between repeater and filters >> > matter? >> > >> > Doug >> > >>As long as the filters are working correctly, the cable length from the >>duplexers to the radios tx and rx does not matter. Having said that, >>remember that the shortest length of double shielded coax or HELIAX cable >>that will reach without kinks or physcial loads (binds) on the connectors >>should be used. This has nothing to do with impedeance matching, but >>rather cross talk thru cable leakage. > > Double-shielded cables aren't going to leak enough to be a concern. You > do > want to keep the length short to minimize loss. > > BTW, I once measured the isolation between a pair of ordinary RG-58 cables > on a VNA from 50 to 500 MHz. Unless the cables were twisted together, I > didn't see any coupling between them down to at least -90 dB. When they > were twisted together, I think there was ONE frequency around 500 MHz > where > there was -65 dB coupling. > >> On this same note (and knowing I'm going to stur up a hornets nest) I >> strongly advise against using the LMR type cables for ANY full duplex >> system. Any double sheilded cable which uses dissimular metals in the 2 >> (or more) shields will eventually cause rf noise . > > No argument here. > > Bob NO6B
