and...
"...23.3.5 Antenna Grounding Plane
Although no ground plane is required, the antennas typically perform better when a ground plane is used. The ground plane should be a conductive surface as large as practical, with a minimum diameter of 8 inches. To use an antenna in aircraft with fabric or composite skin, a ground plane is recommended. It is usually installed under the skin of the aircraft, below the antenna, and is made of either aluminum sheet or of wire mesh..."
It is funny reading the install manual, there are places which seem to contradict each other.
I really have to laugh at the GMU position requirements. If you were to follow every recommended distance to determine the best mounting location, it would appear that the magnetometer needs to be flying about 10 feet outside the aircraft but in close formation...
Obviously, that isn't the case but it is funny...
In the antenna example, they talk about grounding the antenna to the ground plane but in another section, it states that the ground plane is not required...
I intend to mount the antenna on an aluminum plate within the overhead console, and ground that plate to the airframe.