Radio interference

[prhutson]

First flight with the ADI Pilot II today. When I engage TRK, there is no significant additional hum, but when I engage ALT hold, I get the squeal of the step motor circuit in my headphones. Suggestions for an easy fix, or will this require a trip to the avionics shop?
Thanks
Paul

[TrutrakTech]

Make sure your pitch servo is not grounded locally and is grounded with the rest of the AP system. Check to see if your headphone jacks are isolated from the airframe by nylon or fabric washers.

[prhutson]

Lucas:
Thanks for the chance to visit and discuss this issue on the Glastar. To confirm the results from my flight home, the noise was apparently caused by two things:
1. I was pulling 14V off of the end of the bus on a string of avionics circuit breakers at the far end of the bus from the Avionics master. Moving the power wire for the A/P to the Master switch itself helped greatly.
2. My servos shared a ground with the ground plate for COM1 that had been installed by an avionics shop, but were also grounded to the aircraft cage through the servo mounting plate - hence a ground loop of the electrical kind. We removed the grounding wire (and I removed the ground that went to the COM1 ground plate).
The result on the flight home was quiet - I couldn't perceive any squeal or steps from the autopilot. Thanks!
Paul

[TrutrakTech]

Paul,

That's excellent news! I'm glad we were able to get everything straightened out for you. Thanks again!