Garrecht Avionik GmbH
VT-01 Transponder
Installation Manual - english -
Document:
01.0200.11E
Revision: 1.3
30
7. Antenna installation
7.1. General
Any type of suitable transponder antenna may be used for connection to VT-01.
Antenna installation should be done by qualified personal only. It is strongly recommend to follow the
step by step instruction below:
•
Generally, follow the instructions of FAA AC 42.13-2B regarding antenna
installation.
•
Select a suitable position for installing the antenna. The manufacturer of
your aircraft should give you detailed information regarding this issue.
•
Mount the transponder antenna as described by the antenna manufacturer.
•
To prevent damages by moisture, seal all antenna mounts.
•
When choosing a position for installation, always be sure not to damage
structural devices of the airframe.
•
For antenna installation in pressurized aircraft, follow the special
instructions of FAA AC 42.13-2B.
7.2. Special instructions for antenna installation in composite aircraft
7.2.1. Mounting Preparation
The electrical bonding of the antenna to the aircraft ground is extremely important. If this is not done
properly, antenna performance characteristics may become distorted and nulls may appear in the
antenna radiation pattern. This, in turn, may cause erratic navigational readings or signal drop out.
The electrical bonding of antennas to composite aircraft is best accomplished by direct metal-to-metal
contact of the antenna mounting hardware to an internal ground plane. To do this, you must have the
mounting screws, washers and nuts make direct contact to the internal ground plane with the use of a
backing plate. The backing plate must make direct contact to the internal ground plane. Sandwich the
aircraft skin and internal ground plane between the antenna base plate and internally mounted
backing plate. To test the electrical bonding of the blade to the aircraft, a reading of .003 ohms
between the antenna base plate and ground should be achieved.
7.2.2. Ground Plane Size
UHF antennas will require a metal ground plane size of 24” by 24” OR LARGER. “As large as
practical” will assure optimum antenna performance. Most other antennas may also use the 24” by 24”
rule, but with ground planes, larger is always better.
After installation, double check that a reading of .003 ohms between the antenna base plate and
ground has been achieved.
