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Post-Installation Configuration & Checkout
3. Check the position using the GPSstatus command. The displayed lat/lon should agree with a known
reference position.
4. Turn on other avionics one at a time and verify that the GPS LED remains steady on.
5. Check for VHF comm transmitter interference.
a)
Tune the Com 1 radio to 121.125 MHz. Listen on the frequency to ensure it is not in use,
and then transmit for 30 seconds.
b)
While transmitting, observe the 'GPS' LED. Verify that the GPS LED remains steady on. If
not, additional isolation measures will have to be taken.
c)
Repeat steps a) and b) 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
d)
Repeat for each com transmitter installed in the aircraft.
e)
If aircraft is TCAS-equipped, turn on the TCAS system and verify that GPS LED remains
steady on.
f)
If aircraft is SATCOM-equipped, use the SATCOM system and verify that GPS LED remains
steady on.
g)
If the GDL 90 is susceptible to VHF Com transmitter interference, then better isolation (or greater
separation) may be required between the GPS and VHF (or other offending system) antennas.
With some com transmitters, a 1575.42 MHz notch filter (such as Garmin AT P/N 162-1059) may
be required in series with the VHF Com antenna coax at the rear of the com unit. ELT's may re-
radiate harmonics of the VHF Com signal into the GPS band. A 1575.42 MHz notch filter on the
ELT will solve this.
Older VHF Com transmitters may emit higher levels of harmonic interference.
4.3.1.2
Interface Checkout
This section describes checks that can be carried out to verify that systems interfacing to the CNX80 are
communicating properly.
4.3.1.2.1 Air Data Computer and Altitude Encoder
Verify that the Ext LED on the front of the GDL 90 is not illuminated.
4.3.1.2.2 MX20 Display Checkout
Refer to the MX20 installation manual (P/N 560-1025-08 or later FAA approved revision) for the
following checks.
4-8
The interference check must be completed on all IFR installations.
[1]
[1]
[1] frequency is only applicable to VHF radios with 8.33 kHz channel spacing
560-1049-00 Rev B
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
NOTE
GDL 90 Installation Manual
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