Antenna Considerations - Garmin G3X Installation Manual

19.5 Antenna Considerations

This section contains mounting location considerations for the antennas required for the GTR 20. For
mounting the COM antenna, refer to the aircraft manufacturer's data.
19.5.1 COM Antenna Location
The GTR 20 COM 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
inch square, minimum). The antenna should be mounted a minimum of six feet from any DME or other
COM antennas, and four feet from any ADF sense antennas. The COM antenna should also be mounted as
far as practical from the ELT antenna. Some ELTs have exhibited re-radiation problems that cause
interference with other radios, including GPS. This can happen when the COM (GTR 20 or any other
COM) is transmitting on certain frequencies such as 121.15 or 121.175 MHz, which may cause the ELT
output circuit to oscillate from the signal coming in on the ELT antenna coax.
If simultaneous use of two COM transceivers is desired (split-COM or simul-comm), the COM antennas
should be spaced for maximum isolation. A configuration of one topside antenna and one bottom side
antenna is recommended. The GTR 20 requires a transmit interlock.
Simultaneous COM performance varies significantly across installations and is affected by both the
isolation between the COM antennas and the separation of the tuned frequencies. Each installation should
be individually examined to determine the expected performance of simultaneous COM.
NOTE
Canadian installations are required to meet Industry Canada specifications for maximum
radiation as documented in Radio Specifications Standard 102 (RSS-102). For more
information about RF exposure and related Canadian regulatory compliance, contact:
Manager, Radio Equipment Standards
Industry Canada
365 Laurier Avenue
Ottawa, Ontario
K1A 0C8
In accordance with Canadian Radio Specifications Standard 102 (RSS 102), an RF safety
separation distance of 26 cm from the antenna should be maintained for an RF field
strength exposure to persons of less than the 10W/m
Under Industry Canada regulations, this radio transmitter may only operate using an
antenna of a type and maximum (or lesser) gain approved for the transmitter by Industry
Canada. To reduce potential radio interference to other users, the antenna type and its
gain should be so chosen that the equivalent isotropically radiated power (e.i.r.p.) is not
more than that necessary for successful communication.
The GTR 20 has been approved by Industry Canada to operate with the antenna types
listed below. Antenna types not included in this list, having a gain greater than the
maximum gain indicated for that type, are strictly prohibited for use with this device.
A COM Antenna that meets TSO-C37( ) and C38( ) or TSO-C169( ), 50W, vertically
polarized. Maximum gain of 1 dBi with an impedance of 50 Ω.
190-01115-01
Rev. AA
2
occupational safety limit.
G3X/G3X Touch Installation Manual - GTR 20 Installation
Page 19-5