![]() For the mag-mount version, the P-in-a-triangle points at the whip ends of the coaxes are connected to the magnets but remain insulated from the car body. The P-in-a-triangle symbol denotes a connection to the ground plane sheet of the one-piece version. ![]() Schematic diagram of the new wideband switcher for the Roanokeĭoppler. Impedance of switched-off whips and the impedance match at the common point.)įigure 1. (Why is it important to have diodes at each end of each coax? See Homing Inįor April 1995, which explains in detail the importance of controlling both the feedpoint It is possible to use one array to cover tens of megahertz, limited only byĪrray spacing and values of inductors and capacitors in the switcher. Coax lengths no longer limit the bandwidth of the array, so This means that the coaxes can be any reasonable length, so long as the four The new design (schematic in Figure 1 below)įeatures series PIN diodes at each end of the coax lines to the four whips. Invited several T-hunters to build and test it. In 1994, I designed an improved switching system for the Roanoke Doppler and On a 20 X 20 inch metal plate with 8 radials to provide a ground plane under The Roanoke Doppler antenna array described in TRANSMITTER HUNTING has four quarter-wavelength whips Have tried to scale the array for higher frequencies (such as the 70 centimeter The requirement for exact half-wavelengths of coax limits anĪrray to a narrow frequency range (typically 5%). I have used it on well over a hundred T-hunts. The Roanoke Doppler antenna design in the book (see Photo 3 below) works well on strong two meter Etched circuit boards are also available from several Bill Briles WØOQC of Derby, KS built his on perforated The Roanoke Doppler display circuits are designed for easy "homebrew"Ĭonstruction. This allows him to log settings for each band. Note the 10-turn potentiometer and large dial for theĬalibration control. ![]() This Roanoke Doppler display box was built by Jerry Boyd WB8WFK ofĪlbuquerque, NM. With the book's authors or publisher, so contact them directly for information Several independent suppliers have made circuit boards and kits available for The Roanoke Doppler has been built by hundreds of hams in many forms (see Photos 1 and 2 below). Much more information about techniques, advantages and disadvantages than space Thoroughly discusses the theory of RDF using the doppler principle and gives We named it the Roanoke Doppler in honor of N4FQ's T-hunting grounds.Ĭomplete plans for the Roanoke Doppler are in "Transmitter Hunting-Radioĭirection Finding Simplified" by Moell and Curlee. Tom Curlee WB6UZZ and I made enhancements and documented the design. ![]() Today's most popularĭo-it-yourself doppler was originated by Chuck Tavaris N4FQ of Roanoke, Information from a tone that the antenna set adds to the audio output of yourĮxcellent commercial doppler models are available for several hundred dollars,īut you can build your own at a fraction of the cost. The multi-element antennaĪssembly replaces your mobile whip. Much lower profile than a RDF yagi or quad setup. Updates bearings almost instantaneously, so even short carrier bursts can beĪ doppler installation can be done quickly on just about any vehicle. They indicate the direction of incoming VHF signals on aĬircular ring of light-emitting diodes or a digital display. Originally published in 73 Magazine, June 1995ĭoppler units are the "weapon of choice" among mobile T-hunters in many parts Wide-Range Doppler Antenna Wide-Range Antenna Arraysįor the Roanoke Doppler And Other Dopplers
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