Interference Of Gps; Gtr/Gnc Mounting Considerations - Garmin GTR 225 Installation Manual

3.2.2

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. Placement of the GPS
antenna relative to a COM transceiver and COM antenna (including the GTR/GNC COM antenna), ELT
antenna, and DF receiver antenna is critical.
Use the following guidelines, in addition to others in this document, when locating the GTR/GNC and its
antennas.
 Locate the GTR/GNC as far as possible from all GPS antennas.
 Locate the COM antenna as far as possible from all GPS 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
GTR/GNC 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 GTR/GNC, VHF COM and ground.
 Shield the VHF COM wiring harness.

3.3 GTR/GNC Mounting Considerations

The GTR/GNC is designed to mount in the avionics stack in the aircraft instrument panel within view and
reach of the pilot. The primary unit location should minimize pilot head movement when transitioning
between looking outside of the cockpit and viewing/operating the GTR/GNC. The location should be such
that the GTR/GNC unit is not blocked by the glare shield on top, or by the throttles, control yoke, etc. on
the bottom. If aircraft has a throw-over yoke, be sure the yoke does not interfere with the GTR/GNC.
GTR 225/GNC 255 TSO Installation Manual
Page 3-2
190-01182-02
Rev. B