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2020-03-12

Fox Hunting



Also known as Amateur Radio Direction Finding (ARDF)


Another Great Meeting Presentation


Amateur radio direction finding (ARDF, also known as radio orienteering, radio fox hunting and radiosport) is an amateur radio sport that combines radio direction finding with the map and compass skills of orienteering. It is a timed race in which individual competitors use a topographic map, a magnetic compass and radio direction finding apparatus to navigate through diverse wooded terrain while searching for radio transmitters. The rules of the sport and international competitions are organized by the International Amateur Radio Union. The sport has been most popular in Eastern Europe, Russia, and China, where it was often used in the physical education programs in schools.

ARDF events use radio frequencies on either the two-meter or eighty-meter amateur radio bands. These two bands were chosen because of their universal availability to amateur radio licensees in all countries. The radio equipment carried by competitors on a course must be capable of receiving the signal being transmitted by the five transmitters and useful for radio direction finding, including a radio receiver, attenuator, and directional antenna. Most equipment designs integrate all three components into one handheld device. (See Wikipedia and HomingIn for additional details) 


Receiver equipment

No radio license is required. The radio equipment carried on course must be capable of receiving the signal being transmitted by the transmitters and useful for radio direction finding. This includes a radio receiver that can tune in the specific frequency of transmission being used for the event, an attenuator or variable gain control, and a directional antenna. Directional antennas are more sensitive to radio signals arriving from some directions than others.

Most equipment designs integrate all three components into one handheld device. On the two meter band, the most common directional antennas used by competitors are two or three element Yagi antennas made from flexible steel tape. This kind of antenna has a cardioid receiving pattern, which means that it has one peak direction where the received signal will be the strongest, and a null direction, 180° from the peak, in which the received signal will be the weakest. Flexible steel tape enables the antenna elements to flex and not break when encountering vegetation in the forest. 

On the eighty meter band, two common receiver design approaches are to use either a small loop antenna or an even smaller loop antenna wound around a ferrite rod. These antennas have a bidirectional receiving pattern, with two peak directions 180° apart from one another and two null directions 180° apart from one another. The peak directions are 90° offset from the null directions. A small vertical antenna element can be combined with the loop or ferrite rod antenna to change the receiving pattern to a cardioid shape, but the resulting null in the cardioid is not as sensitive as the nulls in the bidirectional receiving pattern. A switch is often used to allow the competitor to select the bidirectional or cardioid patterns at any moment. ARDF receiver equipment is designed to be lightweight and easy to operate while the competitor is in motion as well as rugged enough to withstand use in areas of thick vegetation.

Les Tocko VA7OM has designed a top notch contest grade ARDF 80m receiver that has now gone into production. It is hoped that it will be available for our annual SARC FoxHunt in May. Once sufficient quantities are in stock they will be available for general purchase. Inquiries may be sent to VA7XB@rac.ca.





Les presented a club meeting program on ARDF and the receiver on March 11, 2020, along with his cohorts Amel Krdzalic VA7KBA and Dave Miller VE7HR. He has shared his presentation slides and two videos.


Les' Slides on ARDF (PDF 5Mb) or Les' Demo with Video (PPS 170Mb)



Les' ARDF Video: Fox Placement and Strategy



A video on the use of the receiver





Our 2019 SARC FoxHunt video




Update!

Our next Fox Hunt was scheduled for May 9th, however it was postponed due to the COVID crisis. The new date is Saturday, August 29. Here is the poster:





~ Updated 2020-08-12




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