Dynon Avionics SkyView System Installation Guide - Manual (Page 232)

SV-XPNDR-261/262 Installation, Configuration, and Testing
11-12 SkyView System Installation Guide - Revision S
Some of the protocols listed above may not contain all the required data for a compliant ADS-B
message, depending on the intended airspace regulations. Further information can be found in
the GPS Data section under the Transponder Settings of this chapter.
Antenna Installation
The antenna should be installed according to the manufacturer’s instructions.
The following considerations should be taken into account when siting the antenna:

The antenna should be well removed from any projections, the engine(s) and
propeller(s). It should also be well removed from landing gear doors, access doors or others
openings which will break the ground plane for the antenna.

The antenna should be mounted on the bottom surface of the aircraft and in a vertical
position when the aircraft is in level flight.

Avoid mounting the antenna within 3 feet of the ADF sense antenna or any COMM
antenna and 6 feet from the transponder to the DME antenna.

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 (voltage standing wave ratio).
Electrical connection to the antenna should be protected to avoid loss of efficiency as a result
of the presence of liquids or moisture. All antenna feeders shall be installed in such a way that a
minimum of RF energy is radiated inside the aircraft.
Antenna Ground Plane
When a conventional aircraft monopole antenna is used it relies on a ground plane for correct
behaviour. For ideal performance the ground plane should be very large compared to the
wavelength of the transmission, which is 275 mm. In a metal skinned aircraft this is usually easy
to accomplish, but is more difficult in a composite or fabric skinned aircraft. In these cases a
metallic ground plane should be fabricated and fitted under the antenna.
As the ground plane is made smaller, the actual dimensions of the ground plane become more
critical, and small multiples of the wavelength should be avoided, as should circles. 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 120 mm per side; as the
size increases the performance may actually get worse, but will be better by the time the
ground plane is 700 mm on each side. Anything much larger than that size is unlikely to show
significant further improvement.
The thickness of the material used to construct the ground plane is not critical, providing it is
sufficiently conductive. A variety of proprietary mesh and grid solutions are available.