Direction Finding and Fox Hunting

What is ARDF?

2008-08-23 Fox Hunt 003 KC & WDAmateur Radio Direction Finding (ARDF) is a type of radio sport.  Like all radio sports, ARDF has a very important role in building skill sets.  In this case being able to correctly trace and find the source of a radio signal has its applications in locating of emergency transponder beacons, persons lost but who have a radio and interfering transmissions. Not surprisingly this sport has its origins in the former Eastern Block of nations and was promoted by those governments because of its potential military and security applications. 

ARDF is a formal competitive sport that combines radio direction finding with orienteering. 

Generally YARS engages in a less formal activity called a "fox hunt", however we are gradually moving more and more to ARDF as we become more familiar with the activity. 

The Challenge

2008-08-23 Fox Hunt 005 RokA key challenge in ARDF or fox hunts is discerning between signals that are reflections and signals that come directly from a transmitter.  If the signal is direct, we can simply shoot up a bearing and obtain a line of bearing to the transmitter.  Several lines of bearing can be used to pinpoint the transmitter using applied geometry - triangulation.  If the signal is a reflection, it can throw one off as false lines of bearings are plotted to the object(s) that reflect the radio waves. 

To discriminate between direct and reflected signals is a bit of an art and requires some thinking about the topography of the land and the objects on it (and sometimes in the air).

There are many applications of this sport to search and rescue and the pinpointing of interfering signals.

Physical

ARDF, as a sport, attempts to fuse radio direction finding with orienteering.  It is probably one of the more physically intensive aspects of our hobby (next to erecting antenna masts and hiking around for remote operation).  YARS has not gone to orienteering yet and tends to do hiking instead.  In the winter we might do snow shoeing.

Competitive

There are international competitions and since YARS is located in North America, the ARDF rules of the International Amateur Radio Union apply (Region 2).  Generally YARS is working towards following these rules as it gains more skill and insight into how to conduct these events.

Equipment

Equipment is fairly modest:

  • One needs some fox transmitters.  This could be a person with a transceiver transmitting or it could be remote low powered transmitters that cycle on and off periodically. 
  • If orienteering is used, one will need orienteering equipment.
  • A map of the area and compass might be useful for the taking and plotting of bearings.
  • One should use use a time difference of arrival device or a directional antenna, attenuator, receiver and so forth.  A number of YARS members have built their own time difference of arrival devices from scratch or from kits (yes this is an amateur radio club - we do build this sometimes!).

Further Reading

VE8RT Guide to Fox Hunts

Mobile Fox Hunt Boundaries (VE8SS)

Foot Fox Hund Boundaries (VE8IR)

Sample Operations Instructions (VE8IR)