Garmin GNS 480 Installation Manaul page 113

It is known that certain non-aviation radios, including marine transceivers, can interfere with civil
aviation navigation and surveillance equipment including the Garmin GNS 480. When installing
GNS 480 equipment in accordance with the appropriate STC, it is the responsibility of the installer
to ensure that the GNS 480 modification is compatible with all previous aircraft modifications.
Garmin recommends that whenever a GNS 480 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 GNS 480. Special care should also be taken to ensure that there is no
interference with the GNS 480 if non-aviation radios are installed in an aircraft after a GNS 480
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 GNS 480.
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.
a) Verify that at least five satellites are displayed in green boxes (with the corresponding satellite
vehicle number displayed in green on the left of the bar graph). Ensure that NO POSITION
FIX is not displayed.
Press the COM bezel key and tune the GNS 480 COM to 121.125 MHz. Listen on the
b)
frequency to ensure it is not in use, and then transmit for 35 seconds.
When the mic has been keyed for 35 seconds, a "WARNING Stuck Microphone" message
will pop-up and the COM transmitter will stop transmitting. If required to transmit for an
additional 15 seconds, the PTT switch must be momentarily released and then re-keyed to
continue transmitting – the WARNING message does not have to be cleared to continue
transmitting.
c) While transmitting, observe the signal status of each satellite being received. If the satellite
signals are significantly degraded or some satellite signals are lost during the test, continue
transmitting for another 15 seconds. Verify that the GPS position remains valid (if position is
lost, NO POSITION FIX will be displayed in place of the position data). If position is lost,
additional isolation measures will have to be taken.
If required, clear the "WARNING Stuck Microphone" message by pressing the CLR bezel
d)
key. Repeat steps b) and c) for additional frequencies as follows.
121.150 MHz
121.175 MHz
121.185 MHz
121.190 MHz
121.200 MHz
121.225 MHz
121.250 MHz
131.200 MHz
e) Repeat for each COM transmitter installed in the aircraft.
f) If aircraft is TCAS-equipped, turn on the TCAS system and verify that GPS position remains
valid (if position is lost, NO POSITION FIX is displayed in place of the position data).
GNS 480 (CNX80) Installation Manual
[1]
[1]
[1] frequency is only applicable to VHF radios with 8.33 kHz channel spacing
560-0982-01 Rev L
Post-Installation Configuration & Checkout
NOTE
NOTE
131.225 MHz
131.250 MHz
131.275 MHz
130.285 MHz
[1]
131.290 MHz
[1]
131.300 MHz
131.325 MHz
131.350 MHz
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