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Av. Kit Install. Manual
190-00067-02 Rev. J
Page 9
The antenna should be located at least 3 feet from transmitting antennas such as VHF
Comm, HF transmitter, DME, Transponder, and Radar.
2.1.2 COMM ANTENNA LOCATION
The COMM antenna should be well removed from all projections, engines and
propellers. The ground plane surface directly below the antenna should be a flat plane
over as large an area as possible (18 inches square minimum).
The antenna should be mounted a minimum of 6 feet away from any DME antennas,
4 feet from any ADF sense antennas, and a minimum of 3 feet from the GNC 300 and
its GPS antenna.
The GNC 300 COMM antenna connector is specified to have installed GPN 330-00067-
00 (1.57542 GHz notch filter) to minimize interfering harmonics.
2.1.3 ELECTRICAL BONDING
No special precautions need to be taken to provide a bonding path between the GPS
antenna and the aircraft structure.
Follow the manufacturers instructions for the COMM antenna.
2.1.4 ANTENNA LIMITATIONS
GARMIN'S GA 56 Antennas are recommended for installations where the airspeed of
the aircraft will be subsonic.
GARMIN's GA 56, Mod 1 or later, must be used.
See the COMM antenna specification for its limitations.
2.1.5 VHF COMM INTERFERENCE OF GPS
On many panel-mounted aircraft, VHF COMM's can radiate strong harmonics from
the unit and antenna. The GNC 300 COMM section will not interfere with its GPS
section. However, placement of the GNC 300 GPS antenna relative to all COMM's and
COMM antenna, including its own, is critical.
Use the following guidelines, in addition to others in this document, when locating the
GNC 300 and its antennas.
GPS Antenna: Locate as far as possible from all COMM antennas
and all COMMs (including the GNC 300). The GPS
antenna will be much less sensitive to COMM antennas that
use a 1.57542 GHz notch filter.
GNC 300: Locate as far as possible from all COMM antennas.