Page 2-2 GPS 155XL/GNC300 XL Installation Manual
Revision F 190-00067-22
2.2.5 VHF Comm Interference of GPS
On many panel-mounted aircraft installations, VHF Communication radios can radiate strong harmonics
from the comm transceivers and their antenna. The GNC 300XL COMM section will not interfere with
its GPS section. However, placement of the GNC 300XL GPS antenna relative to a COMM and COMM
antenna, including its own, is critical.
Figure 2-1. GPS Antenna Installation Considerations
Use the following guidelines, in addition to others in this document, when locating the GPS 155XL/GNC
300XL and its antenna(s).
• GPS Antenna—Locate as far as possible from all COMM antennas and all COMMs (including
the GNC 300XL). The GPS antenna will be much less sensitive to COMM antennas that use a
1.57542 GHz notch filter.
• GPS 155XL/GNC 300XL—Locate as far as possible from all COMM antennas.
If a COMM antenna is found to be the problem, a 1.57542 GHz notch filter (GPN 330-00067-00) may be
installed in the VHF COMM coax, as close to the COMM as possible. This filter (GPN 330-00067-00) is
required for the GNC 300XL transmitter.
If a COMM is found to be radiating, the following can be done:
• Replace or clean the VHF COMM rack connector to ensure a good coax ground.
• Place a grounding brace between the GNC 300XL, the VHF COMM, and ground.
• Shield the VHF COMM wiring harness.
2.2.6 Comm Antenna Installation Instructions (GNC 300XL)
Install the COMM antenna according to the manufacturer's recommendations.
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