[ARDF] Re: Protractors, 80m accuracy

[Charles E. Scharlau]

Sam Smith wrote:
More than anything be able to predict how quickly you can
cover the terrain, and practice thinking while under physical
exertion.

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Hi Sam,

I think we are in substantial agreement. I don't have the experience that you do in orienteering, but it seems to me that in ARDF you've got a whole lot more data to process in a short period of time than you do in orienteering, especially near the start of the race. The problem I see with using orienteering methods comes from the differences between orienteering and ARDF. In orienteering, you don't have to worry too much about where controls 3, 4 and 5 are located on your map while you're trying to navigate from control 1 to control 2. Nor do you concern yourself with deciding in which order to find the controls. That information is all provided to you on your map. (Score-O events, however, might approximate the same challenge of choosing optimum order.)

In ARDF you've got to have an awareness of the entire map, and formulate an idea of where all the transmitters are located, before you can decide what order you're going to take the transmitters in. Your bearings are essential to determining probable transmitter locations, and therefore the optimum order you should follow.

ON 144 MHz
Bearings on the two meter band, unfortunately are often not very straightforward to interpret. Determining which bearings to believe, and which ones to distrust is key. The confidence you should put in your bearings can be affected by the terrain from which the signals appear to be emanating, and your current location and elevation. As you get closer to a transmitter, your bearings tend to improve, but not always. Should you trust your earlier bearings because they were taken at a higher elevation? Is there an explanation for why the signal seems to be getting weaker while you're going in the direction of your previous bearings? Are there reflection-creating hills in the direction of your bearings? These questions and more can often be answered with a quick look at bearings drawn on your map.

ON 3.5 MHz
On 80M the intersections of your bearing lines SHOULD almost always provide you with a more accurate indication of a transmitter's position than a seat-of-the-pants "behind that hill" estimation. If they don't, start looking around for overhead power lines, or a defective receiver.  It isn't unusual to see 80M bearing lines crossing at near right angles that intersect within 100 meters of where a transmitter is located. That means that you should be able to treat bearing crossings like you would an orienteering control point... run for it! Once you're there, you're almost guaranteed of finding the transmitter on its next cycle, if not before.

With five transmitters to find, and a finish line to navigate to, my brain is overloaded. By the time I'm on my way to the second transmitter, I'm lucky to have determined which transmitter comes next, much less remember how much confidence to put in my theories about where the three remaining transmitters might be. The job gets simpler with each transmitter found, but my memory gets fuzzier the more time and terrain that passes since the bearings were taken. Give me a map with a few bearing lines to jog my memory and I'm much better off.

Do I need to practice thinking while under physical exertion? Definitely, that is a serious problem for me. 

Do I need to improve my location awareness and route selection? Those are more problematic for me than thinking while running! 

Do I need a photographic memory of the best bearings I took 45 minutes and 7 kilometers ago? No, just let me plot them quickly (and as accurately as possible without stopping) on my map.

73,
Charles
NZ0I