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

IARU ARDF Rules
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.

Transmitters
The first thing you need to take on board about an IARU style DF hunt 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.

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 21	D19 - females aged below 21
M21 - males aged 21 and over	D21 - females aged 21 and over
M40 - males aged 40 and over	D35 - females aged 35 and over
M50 - males aged 50 and over	D50 - females aged 50 and over
M60 - males aged 60 and over

Typically, only the M21 class have to find all five transmitters. Classes M19, M40, M50, D19, D21 and D35 have to find four, but not the same four transmitters are allocated to each of these classes. M60 and D50 have to find just three transmitters. The transmitters that have to be found by any one competition class are announced before the start. The M/D21 age groups have no restrictions on the ages of the competitors. M/D19 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, D35, D50.

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.