Pilot's Guide

6
Garmin GTS Traffic Systems
190-00587-02 Rev. B
Antennas
The GTS Traffic Systems use one or two dedicated externally-mounted
antennas to transmit transponder interrogations to other aircraft. The same
antenna or antennas are used to receive transponder replies and ADS-B
broadcasts from other aircraft.
A directional antenna on top of the aircraft is always required and is used to
determine the bearing to the intruder aircraft. Interrogations transmitted from
the top antenna are directional, which reduces the number of transponders that
reply to the interrogation and reduces congestion on the 1090 MHz frequency.
An optional second antenna may be installed on the bottom of the aircraft
to improve performance. A bottom mounted antenna adds additional visibility
for targets that could be shaded from the top antenna (for example, targets
that are underneath the aircraft). The bottom antenna may be a directional
antenna or an omni-directional antenna. If a directional antenna is installed on
the bottom, it may be used to determine the bearing to the intruder aircraft
(omni-directional antennas cannot determine bearing). The bearing accuracy
of a bottom directional antenna on a fixed gear airplane may be less than that
of the top antenna, due to the presence of the landing gear. Bearing from the
bottom antenna on a retractable gear airplane is not used when the landing
gear is extended. Interrogations transmitted from the bottom antenna are always
omni-directional, regardless of the antenna type.
Directional Antennas
GA 58 Directional Antenna
The GA 58 is a directional four-element antenna that may be installed on the
top and/or bottom of the aircraft.
Figure 2 GA 58 Directional Antenna