<<Are people using a common ground wire for the radio PTT and any Auto Pilot
switches ?  ... If so did you try to run separate grounds ? >>

 

I have used separate ground lines for each system.

I did some testing this weekend.

I checked the impedance between ground bus, avionics racks, instrument panel and the autopilot case. -all check out good as a dead short. 

 

It is the #2 antenna (bent wip mounted to an aluminum platform in the tail cone) has a big impact on the auto pilot.  The #1 antenna (Bob Archer in the vertical stab) has a small, barely perceptible impact if tested on the ground.  Physically moving the #2 antenna from the tail cone to outside near the passenger side wing tip eliminates its interference with the autopilot completely.  With the #2 antenna removed, the #1 antenna now becomes the source of strong interference with the autopilot. 

 

still scratching my head....

 

 

Chris Zavatson

N91CZ

L360std