Garmin GIA 63 Installation Manual page 65

For rotorcraft, locate the GPS antenna as far as possible from the main rotor hub. This reduces the
percentage of time the blade blocks the antenna. Also mount it as far below the blade surface as possible if
installing the antenna under the blade. This reduces signal distortion caused by the blades.
1. Mount the antenna as close to level as possible with respect to the normal cruise flight attitude of
the aircraft. If the normal flight attitude is not known, substitute the waterline, which is typically
referenced as level while performing a weight and balance check.
2. The GPS antenna should be mounted in a location to minimize the effects of airframe shadowing
during typical maneuvers. Typically mounting farther away from the tail section reduces signal
blockage seen by the GPS antenna.
3. The GPS antenna should ideally be located at the opposite end of the aircraft from the COM unit in
order to make the GPS less vulnerable to harmonics radiated from the COM itself.
4. The GPS antenna should be mounted no closer than two feet (edge to edge) and ideally three feet
from any VHF COM antenna or any other antenna which may emit harmonic (or other) interfer-
ence at the L1 frequency of 1575.42 MHz. An aircraft EMC check (reference VHF COM interfer-
ence check in Post Installation Checkout procedures) can verify the degradation of GPS in the
presence of interference signals. If an EMC check reveals unacceptable interference, insert a GPS
notch filter in line with the offending VHF COM or the (re-radiating) ELT transmitter.
NOTE
The separation requirement does not apply to GPS and COM combination antennas,
provided the antenna model is TSO authorized and has been tested to meet Garmin's
minimum performance standards. The separating requirement includes the combination
with an XM antenna element as well.
The GPS antenna should be mounted no closer than two feet (edge to edge) and ideally
three feet from any antennas emitting more than 25 watts of power. An aircraft EMC check
can verify the degradation of GPS in the presence of interference signals.
To minimize the effects of shadowing at 5° elevation angles, the GPS antenna should be
mounted no closer than 6 inches (edge to edge) from other antennas, including passive
antennas such as another GPS antenna or XM antenna.
5. To maintain a constant gain pattern and limit degradation by the windscreen, avoid mounting the
antenna closer than 3 inches from the windscreen.
6. For multiple GPS installations, the antennas should not be mounted in a straight line from the front
to the rear of the fuselage. Also varying the mounting location will help minimize any aircraft
shading by the wings or tail section (in a particular azimuth, when one antenna is blocked the other
antenna may have a clear view).
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Rev. Y
GIA 63 Installation Manual
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