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G900X/G950 Installation and Maintenance Manual – Garmin GPS WAAS Antenna
Page 12-9
190-00719-00
Revision D
Mounting the antenna under the glare shield is a good option for XM – FIS antennas, it typically is not the
best option for your WAAS GPS antenna. This location results in the aft fuselage shading the antenna.
Figure 12-4. Glare Shield Buried Antenna Area
NOTE
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 WAAS reception in all areas of
the United States.
12.5.5 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.
12.5.6 Antenna Grounding Plane
Although no ground plane is required, the antennas typically perform better is 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.