receivers to be used in an aircraft. They are also required for our LA Series permanent
mounted Aircraft DF sets. These are FAA-approved (TSO) stainless steel bent whip antennas.
dual band use (121.5/243), the system contains three bent whips (two long and one slightly
shorter), a molded switchbox and antenna interconnection harness with 10 of cable,
and hardware for connection to the receiver. If operation is required on only one band,
such as VHF aircraft (121.5), the center antenna, which has no cable connected to it, may
be left off. The proper operation of the DF system is critically dependent on the proper
installation of the antennas, which work with the aircraft structure to provide the
necessary directional antenna pattern.
We know of no temporary or "inside the cabin" antennas that are satisfactory
for regular use. A portable DF set with its antennas inside the cabin of a light plane is
worse than using the planes own communications receiver and wing shadowing.
Temporary antennas mounted on struts or inspection plates can work but they depend on
details of the aircraft structure and each installation should be thoroughly tested before
In order to avoid damage to the antennas switching circuitry, the DF antennas
must be separated from transmitting antennas, the safe distance dependent on transmitter
frequency and power output. Normal comm radios do not present a problem.
In all cases, the rods are mounted crosswise of the aircraft center (left and right of
the nose). Spacing for the LAA-16 (121.5/243) is nominally 20 inches between outboard
rods, but can be from 12 to 24 inches apart to suit structural needs. Belly mounting
should be used whenever possible to keep clear of existing VHF comm and GPS antennas.
Belly mounting gives the best DF location because the aircraft structure
doesn't get in the way when flying nearly overhead. The installation instructions show how
the DF antennas can be "hot" bent for ground clearance or installed off vertical
up tp 30 degrees. Nearby CB, ADF, marker, transponder, DME, Loran, and Stormscope antennas
have little affect.
Installation on an aircraft usually requires a Form 337 by a mechanic or radio repair
technician. Sample FAA documents and installation instructions are included in both the
printed and the downloadable versions of the LA Series Operating & Maintenance Manual.
A copy of the Antenna Installation sheet is included with the antenna kit.