Installation
GDL 90 Capstone Upgrade Instructions 560-1057-00 Rev A
2-5
from vibration and located in a convenient location for easy connection to a computer as the computer
will be used to configure and troubleshoot the GDL 90. The length for this cable should not exceed 20
feet.
Figure 2-3: APM and Maintenance Connector Installation
2.5.1.3 Antenna
Connectors
UAT antenna cables from the previous UAT system need to be modified (or extended if not of sufficient
reach) to right-angle coax connectors (Part No. 162-0043). Refer to Figure 2-5 for assembly instructions.
CAUTION
Operating the GDL 90 with no RF terminations on the Top or Bottom UAT Antenna
ports can result in equipment damage. Always operate the GDL 90 with the Top and
Bottom UAT Antenna ports terminated with a VSWR ratio of 3.0:1 or less.
For the GPS connection, there are 3 wiring options as depicted in Figure 2-4. GPS signal connection to
the MX20 shall be disconnected and rerouted to the GDL 90. If only one GPS antenna is installed, a
signal splitter may be used to provide GPS signal to the GX60 and the GDL 90 as long as the primary
navigator, the GX60, provides power to the splitter and the total cable loss from the antenna to the GDL
90 is from 3 to 7 db. If SatCom is installed on the aircraft, the cable loss shall be 3 dB minimum to
ensure proper interference rejection from SatCom. The coaxial connectors and adapters, such as TNC to
BNC and signal splitter, add additional loss to the cable and should be considered when computing the
cable loss. A typical loss of 0.2 dB can be used for each connection. The typical cable loss for 20 feet of
RG-400 coax with a connector one each end is 4 dB.
During the post-installation checkout, susceptibility to harmonics of VHF comm. transmitters will be
evaluated. If problems arise, then better isolation, or distance, may be required between the GPS and
