Installation Instructions

GTN 6XX/7XX AML STC Installation Manual 190-01007-A3
Page 2-22 Rev. 4
2.4.4.5 Interference of GPS
On some installations, VHF COM transceivers, Emergency Locator Transmitter (ELT) antennas, and
Direction Finder (DF) receiver antennas can re-radiate harmonics that can potentially interfere with the
GPS antenna. The GTN unit 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 635/650/750
COM antenna), ELT antenna, and DF receiver antenna is important.
Use the following guidelines, in addition to others in this document, when locating the GTN unit and its
antennas.
• GPS/WAAS antenna—Locate as far as possible from all COM antennas and all COM
transceivers (including the GTN unit COM), ELT antennas, and DF receiver antennas. The
GPS/WAAS 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 unit 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 635/650/750 transmitter.
If a COM is found to be radiating, the following can be done:
1. Replace or clean VHF COM rack connector to ensure good coaxial ground.
2. Place a grounding brace between the GTN unit, VHF COM and ground.
3. Shield the VHF COM wiring harness.
2.4.4.6 COM and NAV Antenna Installation Considerations
Install the COM and NAV antennas according to the manufacturer’s recommendations, and obtain FAA
approval. (Other FAA approval for installation of the COM and NAV antennas are required, and is not a
part of this STC.) Ensure that the COM and NAV antennas are electrically bonded to the aircraft. Avoid
running other wires and coaxial cables near the NAV antenna cable. If there are two separate COM
antennas, attempt to run the COM coaxial cables independently of each other and provide zonal
separation as much as possible in the aircraft to avoid loss of both COMs in a single event.
2.4.4.6.1 NAV Antenna Cable Splitter/Diplexer Considerations
The GTN 650/750 includes one NAV antenna input. It is recommended that a single
VOR/Localizer/Glideslope antenna be used for the installation. Some installations will require the use of
a splitter or diplexer. Use Splitter, Garmin P/N 013-00112-00 or Comant Diplexer, P/N CI 507. Refer to
Figure E-18 for splitter and diplexer installation wiring details. Install the splitter and diplexer in
accordance with Section 3.3.3.
2.4.4.6.2 Marker Beacon Antenna Installation Considerations
Install the marker beacon antenna according to the manufacturer’s recommendations. (Other FAA
approval for installation of the marker beacon antenna is required, and is not a part of this STC.) The
marker beacon antenna should be mounted on a flat surface on the underside of the aircraft body. Mount
the marker beacon antenna so that there is a minimum of structure between it and the ground radio
stations. Locate it as far as possible from transmitter antennas.
NOTE
Do not install the antenna inside the aircraft fuselage. Installing the antenna inside the
aircraft fuselage limits the antenna reception, especially on metal aircraft and increases