Comm Radio Reception Issue

[jwpalmer]

Going to substitute a different coax this weekend. Did check both the shielding and the center conductor for resistance and grounding, no problems there, but I did not use a milli-ohm meter so there may still be a problem I couldn't see. Antenna is in the usual place , next to the wing root behind my head on the roof. Hanover (KOFP) is flat as a pancake so no other obstructions, first indication of a problem was when I couldn't raise Potomac Approach for flight following, then my inability to get the ATIS at my destination until REALLY close to the airport. I keep my plane in a hanger so moisture should not be a problem, plane is always dry. I'm hoping that it will turn out to be the coax at this point. Its a cheap fix.

Being essentially NORAD is keeping me grounded as far as long trips are concerned, too close to the DC SFRA and all the Class C in SE VA. And it has put my instrument instruction on hold. Quick trips around the pattern just don't have the allure they did when I was a student pilot.

Thanks for the continued support
John

[FredMa]

Hopefully it will be one of the end connectors, same as fangzz problem, and they can simply cut it off and install another one. What happens is some people are a little too aggresive when cutting the insulation material on the coax and cut it too deeply. This causes a gap between the center conductor and the shielding that acts like a short when the radio is transmitting similar to an ignition system that has an ignition lead that is (leaking) high voltage to ground causing weak ignition. the RF signal is leaking to ground through the cut in insulation to the shielding causing weak RF signal. Hope that is a better explanation. Since there is a gap, it will read as infinite resistance with a volt meter set on low range. That is why it has to be checked with a megger. A megger applies a high voltage and measures if there is any leakage to ground, like a high tension lead tester does on an ignition system. If the simple and inexpensive parts don't prove to be the cause, unfortunately the radio will need to be checked. Hopefully you will find and fix the problem before reaching that point as the cost of repair could take a sudden and sharp rise, that is why I was saving the best for last on my suggestions.

[jwpalmer]

Fred: It was a great suggestion and makes real good sense. Put new ends on the coax but had the same issues. Put the radio in another plane wired for the SL30 to eliminate possibility of my plane being the problem. Got the dreaded COM FAILURE message. Off to Garmin she goes. Thanks everybody for the troubleshooting help!

John