Garmin GTS 8 Series Installation Manual page 22

2.2.1.1 TAS/TCAS Antenna Location
To achieve proper interrogation and surveillance volumes the following GTS 8XX antenna installation
guidelines should be followed.
The GTS 8XX requires a top-mounted directional antenna. An optional bottom mounted directional or
L-band monopole antenna can be installed in conjunction with the top-mounted directional antenna.
Antenna locations are critical to maintain the surveillance coverage across all azimuth and elevation
angles. Locations shall be chosen so the top mounted and bottom mounted antenna will represent same
range and bearing to an intruder. The mounting location, geometry, and surroundings of the antenna can
affect the system performance. The following guidance provides information to aid the installer in
ensuring that the most optimum location is selected for the installation of the antenna. Because meeting
all of these installations guidelines may not be possible on all aircraft, these guidelines are listed in order
of importance to achieve optimum performance. The installer must use best judgment to balance the
installation guidelines.
Installations must be thoroughly tested to verify that performance degradation as a result of antenna
placement is not an issue for the TAS/TCAS system as well as other systems.
1. As far as physically possible, the top directional antenna shall be mounted at the most forward
location.
2. The TAS/TCAS antenna(s) shall be mounted on the aircraft skin so that the horizontal base is
horizontal to within +/-5° in longitudinal and lateral axes when the aircraft is in level flight.
3. The TAS/TCAS antenna(s) shall be mounted on a flat section of the fuselage to reduce the gap
formed between the base plate and the fuselage when normal mounting torque is applied.
4. It is recommended that all antennas be mounted at least 20 inches away (measured from center to
center) from the TAS/TCAS antenna(s).
5. Ground plane considerations shall include minimization of any discontinuities such as overlapped
un-riveted airframe skins, cowlings, or hatches. It is recommended that all such discontinuities be
at least 18 inches from the nearest edge of the TAS/TCAS antenna.
6. For installations using a bottom mounted antenna, it is recommended that the top and bottom
antennas be located near the same vertical line through the aircraft such that they represent the
same range and bearing to an intruder.
7. The top and bottom mounted TAS/TCAS Antenna shall be as close as possible to the aircraft
centerline.
8. It is recommended that no antenna be mounted in front of the TAS/TCAS antenna(s).
Page 2-4
Revision 4TP
GTS 8XX/GPA 65 Installation Manual
190-00587-00