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Radio Society of Great Britain
Guide to the Rules for IARU DF

The full rules can be read over the Internet (this is a .pdf file requiring Acrobat Reader) but the purpose of this page is to explain the rules as straightforwardly as possible for the newcomer.

Overview of Formats
Originally there was only one format, now referred to as the 'Classic' race. In this up to five transmitters were hunted with each competitor being given a map with only the locations of the start and finish marked.

The Sprint format has much shorter transmissions from each of ten transmitters on two different frequencies. There is a spectator beacon that has to be visited after finding the first five of the ten transmitters. This format is fast and furious and has a greater spectator appeal.

The final format is FoxOring. This is half way between Radio Direction Finding and Orienteering.

Competitions for the Blind are also organised. These take place in an area about the size of four tennis courts with a surrounding fence. Competitors are accmpanied but have to locate the transmitters unaided

Classic Races
The first thing you need to take on board about this format is that there can be as many as six transmitters on the air. Five of these are the "foxes" or hidden transmitters and these are all on the same frequency and are 'time division multiplexed'. That is to say, they come on the air one after the other.

Competitions take place on either the 3.5 or 144 MHz bands. Each transmitter is allocated a one minute slot. During this time it sends its ID in morse, but before you personally switch off, this is not a problem to anyone who does not know any morse. The transmitters are identified by the letter sequences MOE, MOI, MOS, MOH, and MO5. In morse MOE comes out as 'dah dah, dah dah dah, dit'. Click here for an audio clip of MOI which is 'dah dah, dah dah dah, dit dit'. To distinguish them, all you have to do is to count the dots at the end and the M and the O form a clear intro. Hence, the first Tx in the sequence has one dot at the end of its call, the second has two dots, the third three dots and so on.

These five transmitters are placed in the competition area which is accessible only on foot. Each transmitter is concealed to some extent but is marked with an orienteering style red and white 'kite' marker to which is attached an orienteering needle punch which must be used to punch the control card you carry as proof of finding the Tx. In important competitions, the transmitters will be 'manned' in the sense that they are under observation.

The sixth transmitter is a beacon transmitter which is on the air continuously on a different frequency. If you get totally lost then just DF this beacon to find the finish. Both frequencies are given out before the start and you may wish to have them written on your receiver as a reminder.

Siting of Foxes Transmitters cannot be placed nearer than 750 m of the start and 400 m of the finish. Also, the transmitters must be at least 400m from each other. The map you are given at the start has only the start and finish marked. In domestic competition, with the small forested areas widely available in the UK, the 750m limit is usually reduced to 400m

Classes of Competition The existence of several classes makes the sport enjoyable for all ages. In the table below, ages count from January 1st of the year in which you attain the age e.g., a man whose 60th birthday is 26 August 2003 is allowed to compete as an M60 from 1 Jan 2003. This arrangement means that competitors do not change class in mid-season.

M19 - males aged below 21W19 - females aged below 21
M21 - males aged 21 and overW21 - females aged 21 and over
M40 - males aged 40 and overW35 - females aged 35 and over
M50 - males aged 50 and overW50 - females aged 50 and over
M60 - males aged 60 and overW60 - females aged 60 and over
M70 - males aged 70 and over

The M21 class has to find all five transmitters. The number of transmitters to be found by other classes is at the discretion of the siting referee. Generally, the older the competitor, the fewer transmitters have to be found.the identity of the transmitters to be found by any each competition class are announced before the start. The M/W21 age groups have no restrictions on the ages of the competitors. M/W19 apply to the end of the calendar year in which you become 19. An M40 enters this category on the 1st January of the year in which he becomes 40 and similarly with M50, M60, M70, W35, W50, W60.

Prevention of Cheating To stop people taking furtive bearings before they start, all receivers and all competitors are separately corralled before the transmitters come on the air. The photo shows some Dutch 80m receivers laid out in the designated area. You are not allowed to communicate to anyone outside the corral.This can lead to a long wait in a big competition since starts are at 5 minute intervals. You are allowed to collect your receiver as you move into the start corridor but can only switch it on after you start. It is your responsibility to provide weather protection for your receiver while it is kept in the corral. You also need to be able to tune your receiver accurately to the stated frequency.

Dress There are no specific rules about dress. Some people wear orienteering clothing but for the majority a variety of dress is seen. Basically, anything you are comfortable in for walking (mostly) and occasionally jogging in the woods.

Safety Take a whistle and remember that the emergency signal is 6 blasts followed by a one minute interval then 6 more blasts and so on.

Time Limit There is a time limit to the competition, usually 90 minutes or two hours. If you find all the Txs but are just one second over the time limit you will be placed below anyone who is within the time limit but who has found only one Tx. Pretty galling! So make sure you have a watch and use it to ensure you are not out of time. The time limit is announced before the start.

The Sprint Format
This became an integral part of World and Region 1 Championships in 2011. It is conducted on 3.5MHz only and there are two groups of five transmitters making a total of ten 'foxes' plus one or two beacon transmitters.
Each group of five hidden transmitters operates on a different frequency; in the UK 3560kHz and 3579.5kHz are used. Each tranmitter operates for just 12 seconds and the complete cycle of each transmitter sending just once, is completed in one minute. The two groups of tranmitters both transmit at the same time and, in order to differentiate between them, one group keys the usual MOE, MOI, MOS...slowly and the other group keys fast. Slowly is about 10wpm and fast is about 14wpm.
Competitors first locate the transmitters in one group and are then obliged to visit a breacon transmitter which is visible to spectators. Then the other five hidden transmitters are located before a second 'finish' beacon is visited immediately prior to the finish. It is possible to make the spectator beacon and the finish beacon one and the same.

As at 2013 competitions of this type are offered as an additional event outside of the main events at international championships.
Typically ten ultra low power transmitters are deployed in the competition area. The approximate location of each one is marked with a circle on the map. Competitors navigate using map and compass to the location of the circle. Once there the signal from the hidden transmitter can be heard and it is then located using direction finding techniques. These competitions use the 3.5MHz band for all international events.

Competitions for the Blind
Competitions of this nature have been organised at each of the major international events 2010-2012. They are quite labour intensive to organise since each transmitter has to be manned and each competitor is accompanied during the competition.
The rules can be viewed here and there are a couple of videos on You Tube with a commentary in SerboCroat here and here
An invitation in Radcom for expressions of interest in this form of direction finding attracted no interest from UK sight impaired persons.