SD7,

Ferrite beads can be effective when there is a direct link from the transmitter via an audio cable to the intercom. In this case the offending noise is in sync with the transponder, which has no audio cable. A ferrite bead on the transponder ground alone might help, but would not likely be effective. One could certainly try it as the beads are cheap. MGL does not have a lock on ferrite beads. Go to Digikey or Mouser. Even Radio Shack has them.


There is some evidence of an offending ground loop somewhere in Andy's system. Other noises are reported to be audible. Finding the ground loop is the problem. It can be as simple as a phone jack body rubbing the frame or an improper ground. When found, there is usually one of those “AHA!!!” moments.

Other than coaching someone through on common installation errors, it is almost impossible to diagnose a ground loop problem via emails or forums. You really need to be there with a scope and a meter. Once the common errors are exhausted, it’s time to get help or go to the Avionic$ $hop.

John Pitkin