Vor/Loc Antenna Location; Glideslope Antenna Location; Electrical Bonding; Interference Of Gps - Garmin GTN 625 Installation Manual

3.5.3

VOR/LOC Antenna Location

The GTN VOR/LOC antenna should be well removed from all projections, engines and propellers. It
should have as clear a field of sight as possible. The antenna must be mounted along the centerline of the
aircraft, minimizing the lateral offset. Install the antennas according to the manufacturer's
recommendations. Avoid running other wires and coaxial cables near the VOR/LOC antenna cable.
3.5.4

Glideslope Antenna Location

The GTN glideslope antenna should be well removed from all projections, engines and propellers. It
should have as clear a field of sight as possible. Install the antenna according to the manufacturer's
recommendations.
3.5.5

Electrical Bonding

Ensure that the GPS/SBAS/NAV/COM antennas are electrically bonded to the aircraft. Follow the aircraft
manufacturer's instructions for the NAV and COM antenna installations, or obtain other FAA approval.
3.5.6

Interference of GPS

On some installations, VHF COM transceivers, Emergency Locator Transmitter (ELT) antennas, and
Direction Finder (DF) receiver antennas can re-radiate through the GPS antenna. The GTN COM does not
interfere with its own GPS section. However, placement of the GPS antenna relative to a COM transceiver
and COM antenna (including the GTN COM antenna), ELT antenna, and DF receiver antenna is critical.
Use the following guidelines, in addition to others in this document, when locating the GTN and its
antennas.

GPS Antenna—Locate as far as possible from all COM antennas and all COM transceivers
(including the GTN COM), ELT antennas, and DF receiver 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 GTN 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. This filter is not required for the GTN
transmitter.
If a COM is found to be radiating, the following can be done:
 Replace or clean VHF COM rack connector to ensure good coax ground.
 Place a grounding brace between the GTN, VHF COM and ground.
 Shield the VHF COM wiring harness.
190-01004-02
Rev. F
GTN 625/635/650 TSO Installation Manual
Page 3-9