So picture 4ZQ resting peacefully in her hangar. Power on, WX500 on as well as the Apollo MX20 which displays lightning strikes from the Stormscope antenna.
There are nine fluorescent light fixtures overhead and when turned on, each is clearly shown on the MX20 in relative position to the plane. Normal.
The WX500 antenna is located in the floor behind the co-pilot seat and about 12" forward of the baggage bulkhead. The STec pitch servo is located as per installation drawings on the right side of the elevator pushrod tunnel. In the air and with autopilot off, the MX20 display is quiet. Turn AP on and the display begins to show random strikes all around the plane. Turn AP off and clearing the display makes the problem go away. So it would appear that EMF from the pitch servo motor (which is constantly twitching ever so slightly, while waiting for the altitude hold clutch to engage), could be the source of my problem. I'm going to try to shield the pitch servo motor in a sort of Farraday cage using copper wire screen mesh and see if this helps. Anybody else with a similar problem/solution?

Angier Ames
N4ZQ