Antenna Doubler/Backing Plate; Antenna Grounding Plane; Antenna Grounding - Garmin G300 Installation Manual

6.2 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.

6.3 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.

6.4 Antenna Grounding

The antenna is grounded through the mounting hardware and the coax connection. The mounting
hardware (washers and nuts) and doubler plate should make contact with an unpainted grounded surface
ensuring proper antenna grounding. It is important to have good conductivity between the coaxial shield
and the ground plane. The bottom of the antenna does not need to make contact with the ground plane
(i.e. the surface may be painted). The antenna will capacitively couple to the ground plane beneath the
paint or aircraft cover.
G300 Installation Manual – Antennas Page 6-3
190-00921-01 Revision A