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Aircraft DF

Antennas

 

The LAA Series antennas allow the LL and LH Series Little L-PerRegister.jpg (2200 bytes) portable DF 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.

For 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 plane’s 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 use.

In order to avoid damage to the antenna’s 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.

 

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