Wide-Range Doppler Antenna

  
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Doppler units are the `weapon of choice` among mobile T-hunters in many parts of the country. They indicate the direction of incoming VHF signals on a circular ring of light-emitting diodes or a digital display. A doppler set updates bearings almost instantaneously, so even short carrier bursts can be tracked. A doppler installation can be done quickly on just about any vehicle.
Wide-Range Doppler Antenna - schematic

It has a much lower profile than a RDF yagi or quad setup. The multi-element antenna assembly replaces your mobile whip. The control unit extracts direction information from a tone that the antenna set adds to the audio output of your VHF-FM transceiver or scanner. Excellent commercial doppler models are available for several hundred dollars, but you can build your own at a fraction of the cost. Today`s most popular do-it-yourself doppler was originated by Chuck Tavaris N4FQ of Roanoke, Virginia. Tom Curlee WB6UZZ and I made enhancements and documented the design. We named it the Roanoke Doppler in honor of N4FQ`s T-hunting grounds. Complete plans for the Roanoke Doppler are in "Transmitter Hunting-Radio Direction Finding Simplified" by Moell and Curlee. One chapter in this book thoroughly discusses the theory of RDF using the doppler principle and gives much more information about techniques, advantages and disadvantages than space here allows. The Roanoke Doppler has been built by hundreds of hams in many forms (see Photos 1 and 2 below). Several independent suppliers have made circuit boards and kits available for its controls and display. They are not affiliated with the book`s authors or publisher, so contact them directly for information on their products. Photo 1 (left). This Roanoke Doppler display box was built by Jerry Boyd WB8WFK of Albuquerque, NM. Note the 10-turn potentiometer and large dial for the...



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