190-01115-01 G3X™/G3X Touch™ Avionics Installation Manual
Rev. AV Page 20-4
20.4 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.
20.4.1 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 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 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 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 provide good coax ground.
2. Place grounding straps between the GDU unit, VHF COM, and a good ground.
3. Shield the VHF COM wiring harness.
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