Fixed a finicky transponder with a wire tie trick

Had a KT76 that would drop its reply on cold mornings at the hangar in Anchorage. Chased ground loops for two hours before an old tech told me to zip tie the coax tight to the tray. Anyone ever seen vibration kill signal like that in a piston single?

2 comments

2 Comments

wadeg921mo ago

Did you check if the coax was actually snug against the tray before you tightened that zip tie? I had a similar thing happen with a Narco transponder in a Cherokee, and I swear it was just the cable vibrating against the metal tray that was killing the signal. The cold mornings make everything contract just a hair, and that little bit of slack can mess with the impedance. I’ve seen guys spend hours swapping out antennas when all it needed was a good solid tie-down. Just make sure the tie isn't pinching the coax too tight though, you don't want to crush the dielectric. A little dab of dielectric grease on the connector never hurts either, especially with the Alaska cold.

kelly_miller801mo ago

Zip tie the coax tight to the tray like that, yeah, it's a real thing in piston singles. I mean, vibration from the engine and prop can make the connector wiggle just enough to break the signal, especially when it's cold and things shrink a little. Always worth checking the coax isn't hanging loose before chasing electrical gremlins.