SYSTEM INSTALLATION MANUAL
89000016
(b)
The antenna must be mounted on the bottom and/or top surface of the aircraft and in a
vertical position when the aircraft is in level flight.
(c)
Avoid mounting the antenna within 3 feet (91.44 cm) of the ADF sense antenna or any
COMM antenna and 6 feet (182.88 cm) from the transponder and DME antennas.
(d)
In installations without a digital serial interface to the transponder, the KGX contains a
Mode A receiver to receive Mode A/C transponder control data from the transponder
antenna through the UAT antennas. The transponder antenna must be located on the
bottom of the aircraft (same as the UAT antenna).
1
The transponder antenna is recommended to be at least 6 feet (182.88 cm) and no
further than 12 feet (365.8 cm) away from the UAT antenna.
2
The transponder antenna can be as close as 3 feet (91.44 cm) if there is at least 2-3
dB of UAT antenna cable loss.
3
There must be a clear line-of-sight between the UAT antenna and the transponder
antenna with no obstructions or projections.
(e)
Where practical, plan the antenna location to keep the cable lengths as short as possible
and avoid sharp bends in the cable to minimize the VSWR.
(2)
Electrical connection to the antenna must be protected to avoid loss of efficiency as a result
of the presence of liquids or moisture. All antenna feeders must be installed in such a way
that a minimum of RF energy is radiated inside the aircraft.
B.
UAT Antenna Ground Plane
(1)
When a conventional aircraft monopole antenna is used it relies on a ground plane for correct
operation. For ideal performance the ground plane must be very large compared to the
wavelength of the transmission, which is approximately 12 inches (304.8 mm).
(2)
For a composite or fabric skinned aircraft, a metallic ground plane must be fabricated and
fitted under the antenna.
(3)
As the ground plane is made smaller, the actual dimensions of the ground plane become more
critical, and small multiples of the wavelength must be avoided. A circular ground plane must
be avoided. Rectangles or squares are much less likely to create a critical dimension that
resonates with the transmissions. The smallest practical ground plane is a square around 5.25
inches (133.35 mm) for each side.
(4)
As the size increases the performance can actually get worse, but will be better by the time the
ground plane is 30.5 inches (774.7 mm) on each side. Anything much larger than that size is
unlikely to show significant further improvement.
(5)
The thickness of the material used to construct the ground plane is not critical, provided it is
sufficiently conductive. A variety of proprietary mesh and grid solutions are available.
C.
UAT Antenna Cable
(1)
The KGX is designed to meet Class A1H/A1S requirements with an allowance of 2 to 6 dB for
loss in the connectors and cable used to connect it to the antenna.
(2)
Excessive loss degrades transmitter output power so it is recommended that the installation
cable loss be limited to the loss minimum of 2 to 5.5 dB.
(3)
Allowing 0.25 dB loss for the connector at each end of the antenna cable assembly leaves an
allowance of 1.5 to 5.0 dB loss for the cable itself.
(4)
An acceptable cable then has:
• A minimum of 1.5 dB loss for the run length but no more than 5.0 dB loss
EFFECTIVITY
ALL
Page 1022
22 Dec 2016
© Honeywell International Inc. Do not copy without express permission of Honeywell.