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I finally stopped guessing at wire routing after a lead in Dallas gave me one piece of advice
Two years ago I was installing a new transponder in a Cessna 172 and I ran the coax right alongside a bundle of power wires because it was the shortest path and it looked clean. The plane passed the ops check on the ground and I signed it off feeling pretty good about myself. About a month later the owner came back saying his transponder would drop out over the Dallas class B airspace, and I spent two full days chasing it before our shop lead walked over and asked me one question. He said, "Where's your coax running?" I told him and he just shook his head and said noise from those power lines was bleeding into the signal. We rerouted it away from the power bundle, put about 4 inches of separation between them, and the dropouts stopped completely. Now I route every antenna cable first before I even touch the power runs, and I've caught three more potential noise issues before they ever left the hangar. Has anyone else had a transponder or GPS act up only in certain airspace because of wire routing?
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amy6547h ago
Gonna push back a little here. In my experience coax routing gets blamed for a lot of stuff that has nothing to do with it, and a transponder dropping out over class B sounds way more like a weak antenna ground, a bad tray connection, or even interference from the radar environment itself. Four inches of separation is nice but plenty of tight installs run fine bundled next to power with no trouble at all, because the shielding on decent coax does its job. You also changed the routing AND re-terminated the connectors when you moved it, so you can't really say for sure it was the power wires. Not saying you're wrong, but two days chasing a ghost and one fix later doesn't prove much. Your mileage may vary.
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