Garmin GDL 90 Installation Manual

Also see for GDL 90: Installation manual

Post-Installation Configuration & Checkout560-1049-00 Rev B GDL 90 Installation Manual4-83. Check the position using the GPSstatus command. The displayed lat/lon should agree with a knownreference 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.NOTEThe interference check must be completed on all IFR installations.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. Ifnot, additional isolation measures will have to be taken.c) Repeat steps a) and b) for additional frequencies as follows.121.150 MHz 131.225 MHz121.175 MHz 131.250 MHz121.185 MHz [1] 131.275 MHz121.190 MHz [1] 130.285 MHz [1]121.200 MHz 131.290 MHz [1]121.225 MHz 131.300 MHz121.250 MHz 131.325 MHz131.200 MHz 131.350 MHz[1] frequency is only applicable to VHF radios with 8.33 kHz channel spacingd) 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 remainssteady on.f) If aircraft is SATCOM-equipped, use the SATCOM system and verify that GPS LED remainssteady on.g) If the GDL 90 is susceptible to VHF Com transmitter interference, then better isolation (or greaterseparation) 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) maybe 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 theELT will solve this.NOTEOlder VHF Com transmitters may emit higher levels of harmonic interference.4.3.1.2 Interface CheckoutThis section describes checks that can be carried out to verify that systems interfacing to the CNX80 arecommunicating properly.4.3.1.2.1 Air Data Computer and Altitude EncoderVerify that the Ext LED on the front of the GDL 90 is not illuminated.4.3.1.2.2 MX20 Display CheckoutRefer to the MX20 installation manual (P/N 560-1025-08 or later FAA approved revision) for thefollowing checks.