Installation Procedures
GDL 90 Installation Manual
560-1049-02 Rev. B
2-9
Suggestion:
Temporarily locate the GPS antenna with coax connected to the
GDL 90
and check the GPS
performance as described in the GPS Checkout in the Equipment Operational/Functional Test Section.
Once a suitable location has been verified, permanently mount the antenna.
NOTE
If using an approved GPS antenna that was already on the aircraft, or if mounting the
antenna closer than recommended distance from other antennas, conduct the
GPS
Checkout
test in the
Equipment Operational/Functional Test
. If the GDL 90 installation
passes the test, then the GPS antenna performance is acceptable.
RF connectors and RG-400 coax cable are included in the installation kit. Assembly instructions for the
connectors are included in Figure 2-7. Proper assembly of the connectors is critical to GPS receiver
performance and reliability. Other equivalent airworthy parts may be used.
Cable Loss:
The cable loss from the GPS antenna shall be at least 3 dB and shall not be greater than 7 dB. RG-400
cable up to 35 feet long can be used. For longer lengths, use low-loss 50
Ω
coax.
The GDL 90 is not approved for installation on aircraft that have SATCOM equipment installed.
When calculating cable losses, include the loss due to each connector or RF adapter (typically 0.2 dB )
used in the GPS antenna cable assembly.
GPS Splitter:
If a GPS splitter is used with an existing GPS antenna, allow 3.5 dB for each branch of a 2-way splitter.
Routing and Checkout:
Once the antenna mounting position has been prepared, route the coax cable from the antenna to the GDL
90.
During the post-installation checkout, evaluate the GPS susceptibility to harmonics from all VHF
transmitters on the aircraft. See Section 4.3.1.1 for specific procedures. If interference with the GDL 90
GPS is found, the problem must be resolved before the installation is completed. Interference may be
minimized through using of double shielded VHF antenna coax, VHF radio grounding and shielding,
increasing the distance between the GPS and comm antennas, or by installing a 1575.42 MHz notch filter
in series with the antenna coax of the VHF comm transceiver.
If a VHF comm transmitter causes interference with GPS reception, the problem may be due to the ELT.
This can be verified by disconnecting the ELT antenna coax at the ELT unit and repeating the test. If the
ELT is found to cause the problem, then contact the ELT manufacturer or replace the ELT.
Содержание GDL 90
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Страница 8: ...Table of Contents vi 560 1049 02 Rev B GDL 90 Installation Manual Notes ...
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