4.0 TRANSPONDER ANTENNA & COAX CABLE
The T2000ADSB requires an antenna tuned to 1090MHz.
4.1 Mounting
The transponder signal is primarily directed to ground stations (Radar sites), hence the antenna is
typically located on the underside of the fuselage. The position should give the antenna a full 360-degree
view of the horizon. The position should be away from other protrusions from the airframe, such as
footsteps, and undercarriage legs.
To avoid possible interference the antenna must be mounted a minimum of 0.3m (12 inches) away from
the T2000ADSB. The transponder antenna outputs high levels of RF energy and should be located at
least 1m (3ft) away from vulnerable part of the human body or be separated by a metal panel.
If the VHF comm antenna is already located on the underside of the fuselage, the transponder antenna
should be located at least 1 metre (3ft) away. The transponder antenna should be mounted 2 metres (78
inches) from a DME antenna, and 1.5 metres (58 inches) from the ADF sense antenna.
4.2 Ground Plane
In metal skin aircraft the skin forms the ground plane. To ensure a good electrical connection, it may be
necessary to remove paint/primer from the inside face of the skin, before attaching the antenna. This may
be resealed after the antenna is installed. On pressurised aircraft, the antenna should be sealed using RTV-
3145 or equivalent, to seal around the connector and mounting hardware. All antenna mounts should be
sealed around the outside for moisture protection, using RTV-3145 or equivalent.
In a composite aircraft the skin of the airframe cannot be used,
and a suitable ground plane must be fabricated. The ground
plane is typically an aluminium disc with a radius equal to the
height of the antenna (approx. 75mm or 3”). The antenna is
mounted in the centre of the ground plane.
The ground plane does not have to be circular however, but the
area should be approx the same size. Fibreglass aircraft can
mount the ground plane on the inside of the aircraft.
Although carbon fibre is a good reflector of RF, it is not a
suitable material for a ground plane. A metal ground plane is
ideal.
It is important to ensure that a good electrical contact is
established, as some antennas have sealing O-rings which can
isolate this connection.
4.3 Coaxial Cable
The T2000ADSB allows for 2dB cable loss from the unit to the antenna. The installer should consider
carefully what type of coaxial cable is to be used, so that this loss limit is not exceeded. The cable should
be terminated with a crimped BNC connector rated for 200Wpep and 2GHz such as the Amphenol
112514.
