AS 680/682
Description, Operation and Maintenance Installation and Setup
ADS−B
3−9Ed. 10.07
3.1.6 Mounting Requirements and Recommendations
3.1.6.1 Installation Notes to Ground Station (RXU) and Antenna Amplifier Unit
1 ADS−B Ground−Station: If the the RXU subassembly in the SPU is intended to be used without
an AAU or other equipment is connected to it, internal jumper X3 of the RXU1 (Ref. No. 83142
71502) or X1 of the RXU2 (Ref. No. 83142 71503) needs to be removed. In addition, there is no
band−pass filter at the input of the SPU/RXU. If the RXU subassembly should be operated without
AAU, a separate dedicated 1090 MHz band−pass filter is needed at the input.
2 Antenna Amplifier Unit (AAU): The AAU requires a 12 VDC power supply otherwise it will not provide
any gain and attenuate the signal instead. If next to the ADS−B RX antenna a TX antenna is
installed, the AAU should comprise the RF limiter option to avoid RF input overload.
3. The recommendations are valid for all channels even only one channel is referred to.
3.1.6.2 Installing the ADS−B Antenna
To mount the antenna and the AAU preferably use pre−installed mounting assembly if possible. To
fulfill the installation criteria consider the following recommendations and mounting aspects:
− Ensure obstacle free line of sight to the aircraft.
− Avoid shadowing by tower structures.
− Avoid possibility of signal reflections.
− Mount antenna as high as possible, but respect cable length restrictions.
− Mount the antenna in a vertical position and align within ±0.5°.
− The antenna can be mounted on a stub or mast, max. 60.5 mm ∅ (see Fig. 2−23).
− Antenna fastening base shall have conductive connection to the tower (earth). Insulating material
or paint must not be used.
3.1.6.3 Installing the Antenna Amplifier Unit (AAU)
If the pre−installed mounting assembly is used, the AAU is already installed as part of it. To fulfill the
installation criteria consider the following recommendations and mounting aspects:
− The AAU assembly can be mounted on a stub (or short mast), min. 60.5 mm ∅.
− Always mount the AAU assembly in upright position, connectors toward bottom to provide proper
convection cooling and splash protection. Use the weather cover for protection against sun.
− The distance to the ADS−B RX antenna shall not exceed 2 m.
− Record the serial number in the installation protocol.
To connect the AAU perform following connections (refer to Fig. 3−9):
a) RF cable (e.g. optional cable 27288 04059) from AAU connector "RFin" to antenna "RFout"; cable
characteristics shall be similar to Cellflex 1/2", attenuation < 8 dB/100 m, cable length up to 2 m.
b) Earth cable to tower; recommended is a cable with more than 16 mm
2
∅. It shall be as short as
possible and be connected to the metallic tower structure.
The cable shall be fixed by mounting brackets or UV resistant cable ties. The cable shall have addi-
tional earthing/shielding to protect against lightning stroke.
The Low Noise Amplifier (LNA) input of the AAU is protected against surge and lightning by a quarter
wave stub. DC input voltages will be blocked. The AAU houses no serviceable parts.
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