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R.A. Miller
R.A. Miller Industries, Inc.
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Tips for Ground Planes
for Aircraft Radio Antennas
Most radio antennas require a ground plane. The AV-534 is a good
example of an antenna that performs best with a ground plane. A ground
plane is a metal surface that is connected to the antennas ground (common).
There is no need for a ground plane when mounting an antenna on a metal
aircraft, but it can be tough to accommodate in a fiberglass aircraft such
as a sailplane.
Note: Radio antennas can be mounted inside a
fiberglass aircraft, but they would not work well if mounted inside a carbon
fiber aircraft.
Below is a note from RAMI about ground planes
for aircraft radio antennas.
A proper ground plane is one that extends
1/4 wavelength (at the operating frequency) outward in all directions
from the feed point or base of the antenna. 1/4 wavelength at aircraft
com frequencies is approximately 24 inches. So the ground plane would be
approximately 4 ft. X 4 ft. (or 4 ft. diameter) conductive surface with
the antenna mounted in the center. You can also accomplish this with (2)
four foot ( 1.22 m) long conductive wires running perpendicular to each
other and electrically connected to the shield of the transmission line
at the base of the antenna at their mid points. Similar to a base
station antenna seen at an airport terminal building. The wires can be
run inside the fuselage forward and aft and down the inside wall.
Sincerely,
Ben Ennenga
Engineering Manager / GAA Product Line Manager
RAMI
Tips for Ground
Planes for Transponder Antennas
I talked to Ben Ennenga at RAMI about transponder antenna ground planes.
Some interesting notes from that conversation are below. Thank you Ben
for the friendly and helpful support!
- A ground plane is required (of course)
with both rod style and blade style transponder antennas.
- The smallest recommended ground plane
would be 12 inches in diameter (6 inches radius).
- A ground plane works about equally well
regardless of whether it is made from a solid plate (such as aluminum)
or instead made using 2 wires in a "+" arrangement. In either case, the
radius should be at least 6 inches.
- When working with carbon fiber glider
fuselages, the antenna must be mounted on the outside of the fuselage,
but it is OK to mount the ground plane on the inside.
- The mounting screws for the RAMI AV-74
antenna are connected to the antenna ground. Therefore, you can
connect the ground plane to either or both of the mounting screws.
- It is OK for the ground plane wires ("+"
configuration) to curve and follow the inside of the glider fuselage.
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