Jim and all: Coax quality -- absolutely makes a difference.
I inherited some "previously driven" (aka used) coax from work thinking to save money -ha! It dates from before I began working at my last employer as comm tech else would never have been purchased. I found in preparing for installing connectors the shield density so poor one could not make good connections -- only useful buried in ground as radial.
I ran into the coax shield quality issue in a different situation but is the same isolation or "radiation" problem. When I increased power from 600w to 1400w on 2m eme I suddenly started blowing preamps.
There were multiple "suspects": My TR relays were not rated for 1200w nor had the Rx port isolation needed. I try to keep RF into the preamp < 0 dBm (1mw) and 1200w = +61 dBm. My relays were only spec at 45-dB isolation. Also turned out only good to 800w. I replaced all after melting down three of them!! Now using NARDA sem123N rated 1200w & 80 dB isolation.
But to the point the high emf of being installed at the antenna subjects connecting coax jumpers to high RF fields so shielding is critical. I was using RG-58. I swapped for RG-142 double-shielded coax. I also fed 12v to the preamp thru shielded power wiring (RG-6 or RG-58). Preamps has feedthru bypass caps so that path should not as critical.
So changing three things means I do not know which was the "cure" but no longer blow up preamps. Double-shielded coax is commonly used as jumpers with repeater duplexers for the same reason cited by Jim.
I wonder if better coax jumper in the shack would improve isolation from wifi type RFI? Probably couldn't hurt.
73, Ed - KL7UW http://www.kl7uw.com "Kits made by KL7UW" Dubus Mag business: [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
