GPS 155XL/GNC 300XL Installation Manual Page 2-1
190-00067-22 Revision F
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).
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