Installation Procedures
190-01810-00 GDL 82 TSO Installation Manual
Rev. 5 Page 6-9
To reduce or eliminate signal interference, signal loss of the GPS antenna cable assembly, including connectors and
adapters, must be between 1.5 dB and 6.5 dB. Coaxial connectors and adapters, i.e., TNC to BNC, 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. To maintain integrity of the SBAS signal, the GPS antenna coaxial cable must have a minimum of two
shields (e.g., RG-400 or RG-142B).
For short runs with less than 1.5 dB loss, increase the cable length until the loss is between 1.5 dB to 6.5 dB. Coil any
additional cable.
During the post-installation checkout, evaluate susceptibility to harmonics of VHF COM transmitters. If problems arise,
better isolation or distance may be required between the GPS and COM antennas. To reduce or eliminate the harmonic
interference, install 1575.42 MHz notch filter in series with the antenna coax of the VHF COM transceiver. A notch
filter is available from Garmin (P/N 330-00067-00).
If a VHF COM transmitter causes problems with the GPS on selected frequencies, as listed in the post-installation
checkout, the problem may be due to the ELT. To verify, disconnect the ELT antenna coax at the ELT unit. If the ELT is
causing the problem, contact the ELT manufacturer or replace the ELT.
6.4.2 GPS Antenna Doubler
1. Secure the antenna with the following.
• #8 washers (qty 4)
• 8-32 (qty 4) self-locking nuts or suitable nutplates installed on the doubler
2. Torque the four supplied 8-32 stainless steel screws 12-15 in-lbs. Torque should be evenly applied across all
mounting screws to avoid deformation of the mounting area.
3. Use a TNC plug to connect the GPS coaxial cable to the antenna.
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