Antenna Doubler/Backing Plate; Antenna Grounding Plane; Glare Shield Buried Antenna Area - Garmin GDU 37X Installation Manual

Mounting the antenna under the glare shield (Figure 3-3) is a good option for XM – FIS antennas, although
it is not typically the best option for a GPS antenna. This location results in the aft fuselage shading the
antenna.
Due to the excessive temperature environment and large areas of signal blockage
caused by the fuselage, mounting the antenna under the engine cowling (forward
of the firewall) is not recommended and likely will not provide adequate GPS
reception.

3.3.4 Antenna Doubler/Backing Plate

The antenna installation must provide adequate support for the antenna considering a maximum drag load
of 5 lbs. (at subsonic speed). When penetrating the skin with a large hole (i.e. for the coax connector) a
doubler plate is required to re-instate the integrity of the aircraft skin. Never weaken the aircraft structure
when choosing a mounting area. Make use of any available reinforcements where appropriate.

3.3.5 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.
Page 3-6
Revision C
Figure 3-3 Glare Shield Buried Antenna Area
NOTE
GDU 37X Installation Manual
190-01054-01