Pilotlight11
I love flying!
I recently replaced my 8" with a 10" display and replaced the Garmin radio and Transponder with the Dynon comm and 261 Transponder. The transponder is creating a popping noise in my headset. I think I have done sufficient tests to isolate it to the transponder's output. At first I thought it was perhaps an issue with the antenna being too close to the comm antenna. My aircraft is composite so ground planes are hard to come by. I purchased a dipole antenna that does not require a ground plane. When I take the antenna 25 feet away (long cable) the popping goes away. I should note here the popping can be heard without the headset being plugged in as long as it is an ANC headset. And yes I tried three different headsets. When the antenna is brought near the headset (within 4-5 feet) the popping starts again. I called earlier today and was told this problem had been seen before and that in that case going to RG 400 cable solved the issue. Well I already have RG 400. The final clue that it is the transponder is when put into standby the popping stops. I did not experience this with the GTX300 that I removed. Avionic are grounded to their own buss, separated from all other grounds. There is actually no doubt in my mind at this point that it is the transponder, but since I can not get the antenna 25 feet away I'm looking for other suggestions. I thought it might be that the power of the 261 was greater than the 330, but they are both 250watts. I have tried individually removing the other avionics to no avail.