Getting Started in ARDF

Your First Practice Event

de Dale Hunt WB6BYU

Your first practice event may have many people looking for five transmitters, or maybe your friend hid a transmitter down the street from your house. We will go through the hunt with you so you know what to do, and what to expect.

Let's begin with a simple hunt - only one transmitter. First, you need to know the frequency the transmitter is on, so you can tune your receiver to hear the signal. When you can hear it, take a bearing. Since there is only one transmitter, we will just go in the direction of the bearing until we reach it. We must always be aware of where we are, and where we are going. It is not uncommon for someone to find a transmitter without knowing where they actually are if they were not paying attention!

If we are in an open area, we can just start walking in the proper direction. But often that is not possible. The next best choice is to take the trail or road that runs closest to the desired direction. As you walk along, the bearing to the transmitter will change. Also, as you get closer to the transmitter, the signal will get stronger, and you may have to turn down the gain control on the receiver. If you come to another path that runs closer to the current transmitter direction, you may want to take that path. Of course, it will depend on how many paths there are and where they go relative to the where the transmitter is hidden. But keep taking bearings on the transmitter and going as near as possible to that direction.

There are two warning signs that you are close to a transmitter: the signal will be very strong and the bearing to the transmitter will change quickly as you walk along. If you are walking down a straight road and the transmitter is hidden just to the side of it, the initial bearing might point exactly along the direction of the road. If the transmitter is 500 meters away, and 50 meters to one side, the initial bearing will be only 6 degrees different from the direction of the road - not enough to notice. After walking 400 meters, the bearing will change by about 20 degrees. Another 50 meters down the road, and the bearing to the transmitter will be 45 degrees from the road, and it will change to 90 degrees in the next 50 meters. If the transmitter is closer to the path, the change in bearing will be even more sudden. (You can estimate how far the transmitter is off the road by measuring the distance between the point where the bearing is 45 degrees from the direction of the road and where it is 90 degrees from the road - this is the same distance that the transmitter is from the road.)

If it is difficult to walk off the road, then the best approach is usually to follow the road until the bearing is 90 degrees from it, then follow the bearing to the transmitter. But maybe there is a large lake in the way! Then you need to decide whether the transmitter is on this side of it or on the other side. If the signal is very strong, and the bearing moves quickly as you walk down the road, then the transmitter may be on your side. But if the signal is not as strong, and the bearing did not change as quickly, the transmitter is probably on the other side. As you get more practice, you will learn how to interpret what the receiver is telling you to make these decisions. If the transmitter is on the other side of the lake, find a path that takes you there and continue hunting.

Although you may have to make detours around objects you can not walk through, this method of following the bearing to the transmitter is simple, and will usually get you to thetransmitter. But sometimes the hunts are more difficult, with more than one transmitter.

A standard ARDF course has five transmitters, and choosing the best order in which to find them is an important part of the competition. In this case, you will generally have a topographic map of the area where the transmitters are hidden. Though the transmitter locations will not be marked on the map, the map will indicate roads, trails, elevations, and physical features such as forest, clearings, and lakes. The map should also indicate magnetic north, and there will be straight lines of magnetic north bearings at a regular interval across the map. An ARDF competition map will mark the locations of the start and the finish.

Now you are trying to keep track of all the transmitters as they transmit in turn. Especially in your first practice event, it is best to focus on actually finding the transmitters instead of trying to be fast. Once you learn the basic skills, you will be able to do it faster without making many mistakes. So, for this hunt, after you start, find a convenient place that you can accurately locate on the map to stop and take bearings. Some examples of locations that are easy to accurately locate on a map are where two trails or roads meet, where a trail enters a large clearing, the top of a well-defined hill, or where any distinctive feature such as a pit, a lone tree, or cultural artifact (i.e. an abandoned car) are marked on the map. Bearings taken while crossing large sections of terrain without distinctive features are still helpful, but it is harder to know where exactly you are on the map. Each transmitter is on for one minute at a time, and for beginners it may be difficult to take an accurate bearing and plot it on the map in that time. Don't worry about being very accurate at first - just write down the bearings you get for each transmitter, and then plot them on your map.

There are two common ways to plot a bearing. You can mount a compass to your antenna or receiver. Make sure there are no steel parts that deflect the compass needle. Mount the compass so that 0 degrees is in the direction of maximum antenna sensitivity. If you reverse the numbering around the compass dial (so that the numbers become progressively larger in a counter-clockwise direction rather than in a clockwise direction,) you can just read the number that the red end of the compass needle points to, and that is the direction the antenna is pointing. (A compass with this kind of marking is said to have a reverse bezel.) Using a protractor, draw a line in this direction on the map, starting from the point where you are standing. After you have plotted several bearings for each transmitter from several different locations, your map will be very messy, so it helps to use a different color marker for the lines to each transmitter.

Another approach is to orient the map to north using your compass, then lay the receiver on it while taking a bearing. Draw a line in the direction the receiver is pointing, starting from your current location on the map. With practice, you will find the method that works best for you.

Now we have initial bearings on all of the transmitters. This does not tell us where they are, but it gives us good information. The other thing we want to check is the signal strengths: a weak signal usually means the transmitter is further away. A strong signal means the transmitter is closer: if one signal is much stronger than the others, we may want to go to that one first because it is the closest.

Unless one transmitter is obviously closest, a good strategy is to start with the one that appears to be the furthest from the finish. (If the start and finish are at the same place, then start with the transmitter furthest at one end of the group.) As you go along, you will get more information about the exact transmitter locations, but you have enough information to get started.

Once you have chosen the first transmitter, hunt it as discussed above. Follow convenient paths such as roads or trails to get as close as possible to it before walking through the forest to find it. Because the transmitter is on for one minute and off for four minutes, it is possible to walk past it when it is not transmitting. When the signal is very strong in your receiver, watch carefully for the orange and white transmitter control flag. But do not spend too much time looking; if you do walk past it, you will find out the next time the transmitter comes on, and you can go back and find it. Each time the transmitter comes on, check the bearing to the transmitter. Correct your direction of travel if necessary. Towards the end of the one minute transmission, make a mental note of the current compass bearing. Then you can continue following the compass in the same direction until it comes on again. With practice, you will also be able to judge how close you are to the transmitter by the signal strength: this is very useful, because if the distance is further than you can run or walk in four minutes, you do not have to worry about looking for the transmitter this time while it is off.

Meanwhile, take bearings on the other transmitters while you are walking towards your first one. Once you have gone 500 meters or more, you can plot another set of bearings on your map and see where the bearing lines cross for each transmitter. Of course, no bearing is perfect, but when you have three bearing lines for a transmitter that go to the same general area, you can go there and you will probably be fairly close when the transmitter comes on.

Each transmitter should have an orange and white control flag located 75 to 100 centimeters off the ground and in a location where you can see it when you get within about ten meters of the transmitter. In competition, it will have some type of marker so you can show you actually found the transmitter. This might be an electronic device into which you push a small memory stick you carry with you (usually attached to a finger with elastic,) a punch that makes a special pattern of holes in a paper card you carry with you (perhaps stapled to your map or pinned to your shirt,) or a particular color of pencil that you use to mark a paper card you carry with you. In your excitement that you found the transmitter, make sure you remember to "punch in!"

By the time you find the first transmitter, you should have a general idea about where the other transmitters are located. You should probably also have decided the order in which you should find them. Plan the fastest route to the next one you want to find, using paths and roads where available, and trying to avoid steep hills or heavy brush that is difficult to walk through. As you hunt for the other transmitters, you will not need to plot bearings as often - just check that each bearing from your current location is consistent with where you think the transmitter is located each time it comes on.

Make sure you remember which transmitter you are looking for at all times! Otherwise you may find the same transmitter more than once, which may be good practice, but it is not the purpose of the competition. Also, try to keep track of where you are on the map as you travel. It does not help to plot a bearing on the map if you do not know where you are when you take the bearing.

Most competitions will have a time limit. Especially on your first practice, you may not have enough time to find all the transmitters. You may want to skip the ones that are the furthest away, or are the hardest to get to. Even if you only find one or two transmitters, that is a good start, and you will learn a lot that will help you do better next time.

After you find the last transmitter (or the last transmitter that you have time to find,) go to the finish area. In competition, there will be a beacon transmitter at the finish, transmitting on a different frequency than the hidden transmitters. You can tune your receiver to the finish beacon frequency and follow the bearings back. Alternatively, you can rely on your map skills to get you from where you are to the finish (which, unlike the hidden transmitters, is marked on the map.)

When you finish, think back over the hunt to see what lessons you can learn. Look at your bearings and see how close they were to the actual locations where you found the transmitter - if the errors tend to be mostly in one direction, maybe your compass is not properly aligned or is being affected by the receiver, or maybe you are not plotting the bearings properly. Perhaps you can discuss the hunt with a more experienced competitor who has just run the same course and find out what decisions they made. The best competitors always learn from their mistakes.

One problem you will find, especially when on hunting on two meters, is signal reflections and blockages. With a VHF signal, if there is a hill between you and the transmitter, it will block the signal path. The transmitter behind the hill may have a very weak signal, or you may instead pick up a stronger signal from the transmitter that is being reflected from another hill. If you have this problem, the best solution is to move and take a bearing somewhere else. Look for a hill or other high place with a clear view in the transmitter direction. Also, if you have conflicting bearings, usually those taken on the strongest signals will be the most reliable.

Reflections are rarely a problem when hunting on eighty meters. Bearings are usually clear and accurate, although if you are standing near telephone or power wires, a long fence, railroad tracks, or inside a building, the bearings may not be as accurate.


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Last updated: 8 May 2020