Antenna Considerations; Section 1 1-1 – - Garmin G300 Installation Manual

1.7 Antenna Considerations

1.7.1 GPS Antenna Location
Refer to Section 6 for GPS antenna location considerations.
1.7.2 Electrical Bonding
No special precautions need to be taken to provide a bonding path between the GPS antenna and the
aircraft structure.
1.7.3 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.
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G300 Installation Manual –Installation Overview
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