Garmin GDL 69/69A, Installation Manual

Page: 28 / 70

Installation Procedure
Page 2-12 GDL 69/69A Installation Manual
Revision E 190-00355-02
2.6 XM Antenna
For use with the GDL 69/69A, the GA 55, GA 55A, and GA 57 antennas are an XM Satellite Radio
antenna operating within a frequency range of 2332-2345 MHz for general aviation.
NOTE
Depending on specific installations, the installer may want to use a different make/model
of XM Satellite Radio antenna. (An alternate antenna may be used providing it meets the
minimum requirements shown in Table 1-6).
It is the installer’s responsibility to ensure that their choice of antenna meets FAA
certification standards according to the specific installation.
This installation manual
discusses only the antennas listed in Table 1-5, which is used during STC certification by
Garmin. Other antennas may be acceptable but their installation is not covered by this
manual and is outside the scope of the data approved in the GDL 69/69A STC.
There are several critical factors to take into consideration before installing an antenna for a satellite
communications system. These factors are addressed in the following sections.
2.6.1 Antenna Mounting
For installation mounting of the XM antenna listed in Table 1-5, use Garmin GA Antenna AML STC.
Verify aircraft model is listed on the AML and follow limitations defined in that STC data.
2.6.2 Antenna Grounding
NOTE
Improper grounding of the antenna is typically the primary cause of reduced
signal reception quality.
It is very important to have good conductivity between the coaxial shield and the ground plane. This is
ensured when all the fasteners properly ground the antenna base to the skin of the aircraft. The resistance
between the antenna and the skin of the aircraft should be less than 10 milliohms.
2.6.3 XM Antenna Location
As with any antenna installation, keep the following points in mind:
1. The XM Satellite signal is a line-of-sight signal. Locating antennas too close to obstructions such
as the vertical stabilizer will limit the reception of the satellite signal.
2. Maintain about three feet from heater, ignition, autopilot, and other control surface actuators and
motors. Maintain about five feet from fluorescent lamps, related ballast, air conditioners, blowers,
strobe lights and power supplies.
3. The minimum distances to be observed when selecting an antenna location are as follows:
•
1.25 inches from any passive (receive only) antenna such as a GPS or another XM.
•
5 inches from a VHF active antenna such as COM or ACARS.
•
5 inches from an active radar altimeter (4 GHz).
•
12 inches from a UHF / Microwave transmitting antenna such as a transponder, DME, active
TCAS, UAT, SATCOM, or Flitephone
.
4. The XM antenna must be mounted on top of the aircraft for greatest satellite visibility. For best
performance, select a location with an unobstructed view of the sky above the aircraft when in
level flight. Location of communication antennas too close to the XM antenna may not only
degrade the transmission through reflection, but can also absorb and re-radiate the transmission
causing a condition similar to having two COM antennas located in close proximity to each other.