Jonathan Goodish wrote:
In article .com,
"mikem" wrote:

Jonathan Goodish wrote:
...I pulled the cover on the rear bulkhead to
look at the glideslope receiver, strobe power pack, and battery.

On your alternator whine ground loop problem, check to see how the
audio gets out of the glideslope receiver to your audio panel. My
Skylane has a rear mounted battery and the Marker Beacon receiver is
mounted on an avionics shelf near the battery.

I checked this yesterday, the case of the glideslope receiver has
continuity with ground when it is isolated from the airframe mounting
brackett and the antenna is disconnected.

OK, then the wiring to the GS receiver could well be the source of your
ground loop, just like it was in my Skylane. Here is how you can find
out: Unplug the cable where it connects to the GS Rx. If there is a
ground strap coming out of the plug your just removed from the GS Rx,
disconnect it from ground. Insulate the cable end so it cannot touch
the airframe, and go fly the airplane.

If this reduces or eliminates your ground loop, then either modify the
GS Rx, or use a 1:1 500Ohm audio isolation transformer to break the
ground loop along the audio from the GSRx to the audio panel at the
front of the airplane. Write back if you have questions?