Garmin GTX 3x5 Series Installation Manual page 34

3. The GPS antenna should be mounted no closer than two feet from any VHF COM antenna or any
other antenna which may emit harmonic interference at the L1 frequency of 1575.42 MHz. An
aircraft EMC check (see section ??) can verify the degradation of GPS in the presence of
interference signals. If an EMC check reveals unacceptable interference, either insert a GPS notch
filter in line with the offending VHF COM or the (re-radiating) ELT transmitter, or select a
different GPS antenna location.
NOTE
When mounting a combination antenna, the recommended distance of two feet or more is
not applicable to the distance between the antenna elements of the combination antenna
(ex. GPS and COM, GPS and XM) provided the combination antenna is TSO authorized
and has been tested to meet Garmin's minimum performance standards. See table 1-10 for
approved antennas.
4. The GPS antenna should be mounted no closer than two feet from any antennas emitting more than
25 watts. An aircraft EMC check can verify the degradation of GPS in the presence of potential
interference signals.
5. To minimize the effects of shadowing at 5° elevation angles, the GPS antenna must be mounted no
closer than nine inches (center to center) from other antennas, including passive antennas such as
another GPS or XM antenna.
6. To maintain a constant gain pattern and limit degradation by the windscreen avoid mounting the
antenna closer than three inches from the windscreen.
7. To achieve the best possible low-elevation antenna gain by minimizing pattern degradation due to
shadowing and near-field interaction a twelve inch center to center spacing between GPS antennas
is required. When practical, twelve inch center-to-center spacing must be used. If twelve inch
spacing is not practical, the maximum center-to-center spacing must be used, but never less than
nine inches. Spacing less than nine inches results in unacceptable antenna pattern degradation.
190-01499-02
Rev. 1
GTX 3x5 TSO Installation Manual
Page 3-8