Installation Instructions

190-01007-A3 GTN 6XX/7XX AML STC Installation Manual
Rev. 4 Page 5-91
5.7.3 VHF COM Interference Check
NOTE
Interference checks must be completed on all IFR installations.
Certain non-aviation radios, including marine transceivers, can interfere with civil aviation navigation and
surveillance equipment including the Garmin GTN. When installing GTN equipment, it is the
responsibility of the installer to ensure that the GTN modification is compatible with all previous aircraft
modifications. Garmin recommends that whenever a GTN is installed in an aircraft that has been modified
with non-aviation radios, particular care should be exercised to verify that these do not interfere with
proper function of the GTN.
Special care should also be taken to ensure that there is no interference with the GTN if non-aviation
radios are installed in an aircraft after a GTN has been installed. If interference is found, it can be
addressed by relocating antennas, rerouting cables, using filters to attenuate unintentional harmonic
frequency transmissions, or using various other techniques for elimination of the interference. It may be
necessary to remove or replace the interfering radio with a model that does not interfere with the proper
functioning of the GTN.
If you are testing a transmitter from a non-aviation device, each frequency must be verified by
transmitting for at least 30 seconds on each channel.
Once the Signal Acquisition Test has been completed successfully, perform the following steps:
1. View the Satellite Status Page and verify that at least 7 satellites have been acquired by the GTN.
2. Verify that the GPS ‘LOI’ flag is out of view.
3. Select 121.150 MHz on the COM transceiver to be tested.
4. Transmit for a period of 35 seconds.
5. Verify that the GPS ‘LOI’ flag does not come into view.
6. Repeat steps 4 and 5 for the following frequencies:
a. 25 kHz COM Channel Spacing:
121.15 MHz 131.22 MHz
121.17 MHz 131.25 MHz
121.20 MHz 131.27 MHz
121.22 MHz 131.30 MHz
121.25 MHz 131.32 MHz
131.20 MHz 131.35 MHz
b. For VHF radios with 8.33 kHz channel spacing, include the following frequencies in
addition to those listed above:
121.185 MHz 130.285 MHz
121.190 MHz 131.290 MHz
7. Repeat steps 3 through 6 for all remaining COM transceivers installed in the aircraft.
8. If the aircraft is TCAS-equipped, turn on the TCAS system and verify that GPS position remains
valid (if position is lost, the status on the GPS Status page will change to “ACQUIRING”).
9. If aircraft is SATCOM-equipped, use the SATCOM system and verify that GPS position remains
valid (if position is lost, the status on the GPS Status page will change to “ACQUIRING”).
10. If the GPS “LOI” flag comes into view, see Section 2.4.4.5 for options to improve performance.