The ARCA held its first short range 2-meter fox hunt on the 23rd of July. The great interest shown in conversations prior to the hunt, and also at the July club meeting, resulted in a poor attendance at the hunt. For most people, it is simply a lack of DF equipment. Here is a listing of some commercial DF kits and some instructions on how to build an inexpensive DF so you can join the fun.
Ramsey Electronics of Victor, N.Y. (1-800-446-2295) offers two DF kits. The Ramsey DF-1C is a hand-held lobe switching kit that sells for $74.95 plus shipping. Henry, KN4AV, has one and you can talk to him about the unit. The Ramsey DDF-l is a Doppler automatic direction indicating mobile kit that sells for $169.95 plus shipping. There is a military surplus DF antenna that you might find, the AS-2365/GR, that works on 2 meters. The Direction Finding Antenna chapter in the ARRL Antenna Book has instructions for building several units if you want to roll your own.
If you want the simplest, cheapest, and easiest to build DF, here is a set of directions. Like most DFs, this home-made one is bi-directional, with two nulls 180 degrees apart. There are no electronics: just two coax-fed dipoles, approximately a half-wavelength apart, connected in parallel. One is mounted upside down to provide a 180 degree phase shift. When the incoming signal hits both antennas at the same time, they will cancel each other out and provide a null which points the way towards (or away from) the incoming signal, which is at a right angle to a line through the two antennas. If you want a name for it, it is a Michelson Interferometer Radio Direction Finder.
Materials needed to build the unit are PVC pipe (1.5″ or 1″), a Tee fitting, two dipole antennas
(telescopic whips, solid aluminum ground rod wire, silicon bronze welding rod, or number 10 or 12 solid copper wire), RG-59 coax, RG-58 coax, and a coax connector to your HT. The drawings show the wiring and construction of the antenna. A variable is how you build and mount the antenna elements at the ends of the horizontal PVC pipe. Nothing is critical about the mounting or the lengths of the elements, as long as all antenna elements are the same length. Also, the
two RG-59 coax segments from the antenna elements to the splice must be the same length.
The RG-58 only needs to be long enough to reach your HT when you hold up, extend and rotate the antenna.
Chuck Teeters – W4MEW
Published in the August 2005 edition of The Splatter
Please note that Ramsey Electronics is no longer in business and does not sell the kits mentioned in this article. However, these kits may be found for sale online.