Amateur radio direction finding (ARDF)

To give you some idea of what it is like to compete at an International ARDF event, here is an account by one of the RSGB team members at an IARU Region 1 Championships in France...

This IARU Region 1 DF Championships was my third International Event and it had all the usual 'trappings' of these things. There was the opening ceremony with a parade of national flags, some speeches of (this time) modest length and the compulsory folk dancing!

The event was organised by the French (very well) and they had taken over a self catering holiday complex in the Department of Herault near Toulouse. To solve the catering problem they put up a large marquee on the sailing club car park and we walked down there for all meals, all the presentations and the final 'hamfest'.

Day 1 - 144 MHz Competition. I intend to describe my experiences on Day 1 of the competition when the 144 MHz band was used. The procedures were the same for the 3.5MHz competition two days later although the nature of the DFing was very different.

We were bussed out from the centre at 0700hrs prompt (those who were late for the bus on Day 1 seemed to be on time on Day 2 after they had had to walk there). We were dropped off in a large taped corral in a pine wood comprising wonderful mature trees at least 60 years old. It could have been anywhere between southern Sweden and the Alps. Even though it was close to the South of France in September, it was not too warm. I envied those who had the foresight (and team back-up) to bring sleeping bags and even a tent to keep comfy while they waited. With a start interval of 5 minutes it took something of the order of four hours to work through the long start lists.

The waiting time depended on whether one had an early, middle or late start. Mine was a middle start. With about ten minutes to go to one's start time all the starters at that time from the different classes were called up. We collected our receivers but were not allowed to turn them on. We were led a short distance down the road to the start itself. Here we were issued with an almost blank orienteering map of the area. The position of the start was marked with a triangle and the finish by a double circle. Things immediately go into overdrive. In the few minutes left before you start you need to:

a. Weatherproof the map (I didn't bother because the sun had now come out and it was a nice day).
b. The rules preclude having foxes within 750 metres of the start and 400 metres of the finish and many competitors like to draw arcs onto the map to indicate these areas.
c. Finally, you need to relate the map to the surroundings and be comfortable with it before you start. There are two lanes at the start depending on your class. Without my glasses I cannot read the signs and end up starting in the wrong lane. However, this is France and no one seems to notice.

Ready, steady, Go! My start is signalled and I set off down the start lane. I switch on my receiver and MOE has just come on the air. There is a fair sized hill in front and I decide to go to the top of that to try to get some bearings reasonably free of multi-path. It took me a good five minutes to totter up there by which time MOE was back on the air at the start of the next cycle of transmissions. There is a power line crossing the top of the hill but by moving around while taking bearings, I get a reasonable set spread across about 120 degrees with the direction of the finish to the right side of this arc. The sketch below is a simplification of the map to illustrate how the planner was successful in tempting me into error!

The signal strengths vary quite a bit with Tx3 being quite loud but, for want of a better idea, I decided to go for them from left to right.

Tx1 was the leftmost Tx and I set off in that vague direction. The hills and the path network dictated that my route was rather indirect. I checked bearings as the Txs came up but tried not to waste too much time standing still on the tracks.

I got to POINT A and then made my BIG error. Trogging along a forest road I felt sure that Tx1 was pretty much straight ahead but Tx4, which had been very weak at the top of the hill, was now strong and 90 degrees left. Instead of changing my plan and picking up Tx4 I decided to carry on to Tx1 which I thought was just ahead. In fact it was not just ahead but a considerable distance away at 60 degrees right and significantly higher up. The big spur on my right had screened the direct signal from this Tx, but there was strong multipath coming down the track towards me. After a couple more transmissions and much wheezing and gasping I eventually got to Tx1.

I now realised my error and instead of being able to head along the ridge to Tx3, I was forced to drop back to the valley floor to pick up Tx4 before climbing again for Tx3. The planner had been very clever in placing Tx4 under a small cliff relatively close to the start so that the screening gave a weak signal in the vicinity of the start.

It was hard work getting to Tx3 where I blagged a drink off the guy manning the Tx since I was dehydrating fast as the day got hotter and hotter.

Just one more to find! As an M50 (old duffer!) I did not have to visit Tx2 and now just had Tx5 to get. I had been getting some rough bearings during my travels to add to the one I got at the top of the hill near the start. This gave me a vague idea of where it was and I took bearings whenever it came on the air while I was moving to its general location. As I got close, I got a good bearing with little sign of multi path and thought it must be down the steep slope to the left of the track. I pushed on along the track to try to get a good cross bearing on the next transmission.

The next bearing was full of multipath which told me I was out of line of sight of the Tx and there was significant screening between me and it. Clearly it could not be down the open slope to the left and the transmitter must be away to the right somewhere. I judged it to be near a parallel-ish track to the right over the top of a low rise. I went over there for the next transmission and was rewarded by a good clear bearing on a clump of conifers.

I dashed across there to find a couple of guys lurking in the bushes beside the Tx. After that it was hey ho for the finish. I was seriously tired by now and it was hard work getting down to the finish field. I was mighty glad to get across the line and stop running (well, tottering)!

Bob, G3ORY