Amateur radio direction finding (ARDF) is also known as "foxhunting", "transmitter hunting", or "T-hunts". The central activity is using a receiver equipped with a directional antenna system to obtain a bearing on a remotely located transmitter. Many variations of ARDF are practised according to the interests of the participants, mode of transport, degree of cooperation of the transmitter, and so forth.
One form which has been well standardized by the International Amateur Radio Union (IARU) has the hunters using portable receivers, searching on foot, using the bearings to guide them to the transmitter location, and observing various rules of conduct. The course consists of 5 marked transmitters all on the same frequency, defined start and end points, and a 6th transmitter on a second frequency at the finish. The 5 course transmitters on the same frequency have a transmitting schedule of one minute on and 4 minutes off, so there is always one transmitter on. The transmitters uniquely identify by sending one of MOE, MOI, MOS, MOH, or MO5 in slow Morse code. These identifications are 5 dashes followed by from 1 to 5 dots, so it is not necessary to understand morse code to determine which transmitter is currently on. Competitors attempt to find as many of the transmitters in as short a time as they can. The maximum duration of the competition is strictly limited and taking longer than the limit to return to the finish disqualifies the competitor.
The full format IARU event has separate events on separate days with one day using 80 meters and a second day using 2 meters. There are classifications of competitors according to age and gender with different numbers of transmitters required to be found.
Recent addtions to this basic on-foot game include "sprint", and "fox orienteering" which use low power transmitters in a more restricted area (sprint) or combining map navigating with ARDF (fox-or).