GPS 155XL/GNC 300XL Installation Manual
P/N 190-00067-22 Rev E Page 2-1
SECTION 2
INSTALLATION
2.1
INTRODUCTION
Careful planning and consideration of the suggestions in this section are required to achieve the desired performance
and reliability from the GPS 155XL/GNC 300XL.
2.2
ANTENNA CONSIDERATIONS
2.2.1
GPS Antenna Location
The GPS 155XL/GNC 300XL GA 56 Antenna must be mounted on top of the aircraft. For best performance, select a
location with an unobstructed view of the sky above the aircraft when in level flight. Figure 2-1 illustrates a typical
GPS antenna installation. The antenna should be located at least 3 feet from transmitting antennas such as VHF
Comm, HF transmitter, DME, Transponder, and Radar.
For rotorcraft, locate the GA 56 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.
2.2.2
Communication Antenna Location (GNC 300XL)
The COMM antenna should be well removed from all projections, engines, and propellers. The ground plane surface
directly below the antenna should be a flat plane over as large an area as possible (18 inches square minimum). The
antenna should be mounted a minimum of 6 feet from any DME antennas, 4 feet from any ADF sense antennas, and 3
feet from the GNC 300XL and its GPS antenna.
The GNC 300XL COMM antenna connector is specified to have a 1.57542 GHz notch filter installed (GPN
330-00067-00) to minimize interfering harmonics.
Installations required to meet German regulation REG TP 321 ZV 034, must have Lowpass Filter (GPN 330-00157-
00) installed on the GNC 300XL COM RF connector J4 instead of the GPS Notch Filter (GPN 330-00067-00).
2.2.3
Electrical Bonding
No special precautions need to be taken to provide a bonding path between the GPS antenna and the aircraft
structure. Follow the manufacturer’s instructions for the COMM antenna (GNC 300XL).
2.2.4
Antenna Limitations
GARMIN’s GA 56 Antennas are recommended for installations where the airspeed of the aircraft will be subsonic.
In such installations, GARMIN's GA 56—Mod 1 or later—must be used. See the COMM antenna specification for
its limitations (GNC 300XL).