Page 3-6 GDU 37X Installation ManualRevision C 190-01054-01Mounting the antenna under the glare shield (Figure 3-3) is a good option for XM – FIS antennas, althoughit is not typically the best option for a GPS antenna. This location results in the aft fuselage shading theantenna.Figure 3-3 Glare Shield Buried Antenna AreaDue to the excessive temperature environment and large areas of signal blockagecaused by the fuselage, mounting the antenna under the engine cowling (forwardof the firewall) is not recommended and likely will not provide adequate GPSreception.3.3.4 Antenna Doubler/Backing PlateThe antenna installation must provide adequate support for the antenna considering a maximum drag loadof 5 lbs. (at subsonic speed). When penetrating the skin with a large hole (i.e. for the coax connector) adoubler plate is required to re-instate the integrity of the aircraft skin. Never weaken the aircraft structurewhen choosing a mounting area. Make use of any available reinforcements where appropriate.3.3.5 Antenna Grounding PlaneAlthough 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 8inches. To use an antenna in aircraft with fabric or composite skin, a ground plane is recommended. It isusually installed under the skin of the aircraft, below the antenna, and is made of either aluminum sheet orof wire mesh.NOTE
