I was having problems with high SWR (standing wave ratio) on my ATAS 120 mobile antenna. My guess was the feedline, which was the standard tiny coax that comes with a Comet or Diamond trunk lip mount. I ordered the Coment 3D4M coax cable assemly, which has 13 feet of RG58 coax. All of a sudden my SWR on the ATAS goes down to 1:1 on 40 meters and some random RF problems are solved. Lesson -- use real coax on HF mobile, not the miniature type that's designed to go through a gap easily, but may be so-so on transmitting and sheilding RF.