Garmin GDU 37X Installation Manual page 27

NOTE
The separation requirement does not apply to GPS and COM combination antennas,
provided the antenna has been tested to meet Garmin's minimum performance standards.
The separating requirement includes the combination with an XM antenna element as
well.
4a) 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.
4b) 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).
190-01054-01
Rev. D
GDU 37X Installation Manual
Page 3-4