Xm Satellite Radio Antenna Minimum Requirements; Antenna Mounting Considerations; Vhf Com/Gps Interference - Garmin G3X Installation Manual

Table 13-4 XM Satellite Radio Antenna Minimum Requirements
Characteristics
Frequency Range
Gain (Typical)
Noise Figure
Nominal Output Impedance
Supply Voltage
Supply Current (maximum)
Operating Temperature Gain
*For each 1 dB gain over 24 dB, add 1 dB of attenuation into the antenna cable path between the
antenna and the GDU 375.
It is the installer's responsibility to ensure that their choice of antenna meets FAA standards according to
the specific installation. This installation manual discusses only the antennas listed in
antennas may be acceptable but their installation is not covered by this manual.
There are several critical factors to take into consideration before installing an antenna for a satellite
communications system. These factors are addressed in the following sections.

13.3 Antenna Mounting Considerations

The information in this section does not pertain to in-cabin (internal) mounted antennas such as the
GA 26C, refer to the accompanying installation instructions (190-00082-00).
No special precautions need be taken to provide an electrical bonding path between the GPS Antenna and
the aircraft structure.

13.3.1 VHF COM/GPS Interference

On some installation VHF COM transceivers, Emergency Locator Transmitter (ELT) antennas, and
Direction Finder (DF) receiver antennas can re-radiate through the GPS antenna. The GDU 37X does not
interfere with its own GPS receiver. However, placement of the GPS antenna relative to a COM
transceiver and COM antenna, ELT antenna, and DF receiver antenna is critical.
Use the following guidelines, in addition to others in this document, when locating the GDU 37X and its
antennas.
• GPS Antenna—Locate as far as possible from all COM antennas and all COM
transceivers, ELT antennas, and DF antennas. The GPS antenna is less susceptible to
harmonic interference if a 1.57542 GHz notch filter is installed on the COM transceiver
antenna output.
• Locate the GDU 37X as far as possible from all COM antennas.
If a COM antenna is found to be the problem, a 1.57542 GHz notch filter (Garmin P/N 330-00067-00) may
be installed in the VHF COM coax, as close to the COM as possible.
If a COM is found to be radiating, the following can be done:
1. Replace or clean the VHF COM rack connector to ensure good coax ground.
2. Place grounding straps between the GDU 37X unit, VHF COM and a good ground.
3. Shield the VHF COM wiring harness.
190-01115-01
Rev. L
G3X Installation Manual - GPS/XM Antenna Installation
Specifications
2332.5 to 2345 MHz
24 dB*
<1.2 dB
50 ohms
3.6 to 5.5 VDC
55 mA
-50 to +85° C
Table 13-2. Other
Page 13-3