User's Manual Part 1

T
2
CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
Use or disclosure of information on this page is subject to the restrictions in the proprietary notice of this document.
2--9
(3) ATC Transponder Antenna Provisions
When installing transponder antennas, a TSO’d antenna should be selected. The
antenna must be vertically polarized and operate in the frequency range of 960 to
1220 MHz. Antenna impedance must be 50 ohms. Selection of a grounded or
lightning protected type antenna is required to pass the transponder bite continuity
detection circuitry, if enabled.
In dual transponder antenna installations it is important to provide adequate isolation
from each other to prevent receiver front-- end damage. A 20--inch minimum
separation of Mode S antennas from other L--Band antennas, including TCAS
antennas, must be maintained. The maximum cable length for RG-- 214/U is 30 feet
(9.144 meters). Allow adequate cable length so bends in cable have a minimum
3--inch (76 mm) radius. Selection of coax cable assemblies with moisture barrier
protection is highly recommended to minimize the effects of humidity and corrosion.
When ATC antennas are installed, the mounting area must provide a solid
mechanical base for the antenna as well as clearance for the connector. A doubler
plate is usually required when the antenna is mounted on an unsupported large
fuselage area. Never weaken aircraft structure for the sake of a good location.
Refer to the aircraft manufacturer’s specifications; reinforcements for antennas are
often built into the aircraft structure.
Doubler plates or shims, if used, must be metallic and shaped to interface the
antenna base with the contour of the aircraft fuselage. ATC antennas are not
supplie d by ACSS. All antenna installations should be in accordance with
manufacturer installation instructions.
A weather sealant should be applied around the periphery of the antenna base to
prevent seepage of water and condensation and preclude corrosion. If a sealant or
aerodynamic smoother is used, it should be applied after the antenna has been
bolted down.