---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Fri 06/16/06: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:49 PM - Dual Comm Transmitter Problem (John) ________________________________ Message 1 _____________________________________ Time: 09:49:20 PM PST US From: "John" Subject: Avionics-List: Dual Comm Transmitter Problem I just now subscribed to the Avionics list in hopes that I can get some experts advice. I know absolutely nothing about radio equipment so please understand that you are talking to a dummy. 7 years ago I bought a Harmon Rocket which is equipped with a KLX135A Gps/Comm and a KY97A Transceiver. I also have a KT76A Transponder, A Rocky Mountain Encoder, and a SPA-400 Sigtronics Intercom with a Music Switcher (I believe it is a STEREOCOM-400 ). The audio panel consists of three separate toggle switches. One switch selects the radio to transmit from. The other two turn the respective receivers ON or OFF This system has worked well for me until just recently when I started having transmitter problems. Both of my receivers are excellent under all conditions. I sent my radios to Aurora for a bench check but they didn't find any problems with them. I'm not sure how good my transmissions have been over the years but I didn't get any complaints. Lately though I am being advised that my transmissions are weak, scratch and barely readable when I am only a few miles away from a station. Also, I have been getting an annoying, kind of hollow tinny background noise in my headset when I transmit from my KLX135A while the KY97A is also turned ON. The noise becomes less troublesome if I turn the volume down on the KY97A. When I transmit from the KY97A with the KLX135A turned ON, I don't hear the noise in my head set, but it too is reported to be weak and scratchy. Transmitting from either radio with the other completely turned off does not solve the problem either. I still send out weak and scratchy transmissions. I guess I must have some deteriorating wire or possibly some other kind of interference that is cutting down the signal strength before it reaches the antennas. Medford Jet Center Avionics techs tell me a big part of my problem is caused by the close proximity of the 45 degree whip antennas between the gear legs. The antennas are only 18 inches apart. They say the minimum recommended is 36 inches. I really don't have an option to relocate the antennas. I suppose if all else fails I can yank the KY97A out and use the KLX135A as my single flip-flop. I think most Rockets and RVs have only one comm anyway. I wonder what would happen if I disconnect the coax cable from the KY97A antenna. Would that have the same affect as removing the radio completely, or will the dead antenna still interfer with the KLX135A transmissions? The Jet Center Avionics shop looked at my aircraft and determined that I have poorer quality coax cable and unshielded wiring. They estimate 6 hours labor plus parts which probably shouldn't run much over $600. That is probably the best way to go. I just though I would toss this problem out there and see if any of you have had experience with something similar. John