Preparing for Georgia

de WM5R

My fiancee, Jen W5JEN, and I are preparing to compete in the Second USA ARDF/Radio-Orienteering Championships. In 2002, this annual event is taking place at the F.D. Roosevelt State Park near Pine Mountain, Georgia, not far from the Alabama state line, April 19-21. Even though this is the national championship, this will be our first-ever radio orienteering event. There are no qualifying meets or criteria by which competitors are allowed to enter, as there might be in national championships in Europe or Asia, where the sport is much more popular.

A tape measure yagi for two meters.

The sport is most commonly called ``Amateur Radio Direction Finding'' or ARDF. It also goes by ``radio orienteering.'' Unlike the fox-hunting that most U.S. hams do, radio orienteering does not involve automobiles. The competitions take place in the woods, and the radio orienteers must use their hand-held ARDF equipment together with a topographic map and compass to navigate on foot from transmitter to transmitter. The shortest route from on transmitter to the next may not be the fastest - successful radio orienteers must learn to plan routes that avoid difficult terrain.

The rules for radio orienteering are maintained by the International Amateur Radio Union (IARU). The ``Rules for Championships in Amateur Radio Direction Finding'' specifies five low-power (0.25 to 1.5 watt) foxes. Each fox transmits its identifier in Morse code (starting with MOE, then MOI, MOS, MOH, and MO5) for one minute, followed by the next transmitter in the sequence. The location of each transmitter is marked with an orange and white orienteering control marker that can be seen from 15 or so meters away. Competitors attempt to locate as many of the transmitters as possible, punching a card they carry with them at each transmitter, and return to the finish line before the three hour time limit. Scoring is determined primarily by the number of transmitters found and secondarily by elapsed time. The competitors starts at intervals, usually every five minutes, coinciding with the start of fox MOE's transmissions.

At the USA Championship, there will be two days of competition. On the first day, the hidden foxes will be transmitting on two meters. On the second day, the fixes transmit on 80 meters. While the hand-held receiving equipment for each day is completely different, the direction finding techniques are very similar. The times for 80 meter course are generally faster, though, as 80 meter signals tend to suffer less from reflections and multi-path, making it easier to home in on the foxes. All the foxes are 1-2 watt transmitters. The two meter foxes will use horizontally-polarized omni-directional antennas, and the 80 meter foxes will use vertical wire antennas with radials.

The map of the 2001 USA ARDF competition. The actual maps given to competitors did not show the transmitter locations! VMOE marks the two meter transmitter that sent MOE, and HMOE the 80 meter transmitter that sent MOE.

There are all sorts of equipment options to use for hand-held ARDF gear. For two meters, Jen and I are using ``tape measure'' yagis. These are three-element yagis made from 1/2'' wide metal tape measures, 1/2'' PVC tubing and joints, and a small piece of wire for a T-match. The design and (excellent) instructions are from WB2HOL and are online. Just like a tape measure, the elements are rigid but can bend when whacked into trees are stuff. We have also built ``offset attenuators'' that attach to the back of the yagi boom. In addition to attenuating the signal, these devices move it up 4MHz. The advantage to this is that when you get really close to the fox, the signal won't bypass the attenuator by traveling straight through the case of the HT!

For 80 meters, Jen and I are each building a ``FoxFinder 80'' receiver, as designed by WB8WFK. This is an 80M receiver designed specifically for ARDF. You can attenuate the signal directly with an RF gain control. It uses a magnetic loop antenna 24'' in circumference, with a separate ``sense'' antenna, and everything is built into a single hand-held case. Unfortunately, the parts list for this project is all over the map, and we've had a lot of trouble finding all the parts. Some of the ICs are no longer available, and there are many parts whose source is listed as ``author's junk box'' that turn out to be either very expensive or very hard to find. We do hope to have working receivers by April, though.

There are several classes of competition. Men and women are scored separately, and for each gender there are several age classes. At the 2002 USA Championship, the women's classes are F19, F21, F35, and F50. F19 is for women 19 and younger, F21 for women 20 through 34, F35 for women 35 to 49 and F50 for women 50 years old and older. Men's classes are similar, but not exactly the same: M19, M21, M40, M50, M60. Only F21 and M21 classes need to find all five transmitters - the other classes need find only four or three transmitters.

We will not be the only Texas hams at the 2002 event. We already know of some other competitors from the Houston area that are planning to attend.