We had a successful practice Monday evening (5/6/19). After Imre and I set the transmitter on the side of a steep re-entrant, Ruth and David joined us in a walk around the transmitter that went through a large re-entrant and over and behind a ridge. The goal was to gain some experience determining which signals were pointing toward the transmitter and which weren’t. What was particularly enlightening was having the four of us standing just a few meters apart and getting very different signal bearings. Because we marked the location of the transmitter on our maps we knew which signals were reflections. We didn’t figure out a great way to distinguish the correct signal, but the most successful technique was keeping track of the various signal bearings and choosing the bearing that came up over and over again. The reflections didn’t tend to come from the same location as one moved – even just a few meters. Next in line was walking toward the signal – the accurate signal was more consistent as you walked toward it than the reflections. One surprise was that using the polarized characstic of the signal was less effective than we expected. While the correct signal almost always quieted when the antenna was rotated vertically many of the reflections behaved similarly. We confirmed the general knowledge that until you get quite close to the transmitter, you can never be 100% sure that you have a correct 2m signal bearing. As you collect more information you improve the probability that you are correct, but until the gain is down to 1 or 2 and it is screaming, you are never 100% sure.

The next time we do this two of us will each put out a transmitter. That way we can do a reflection analysis on the transmitter we have marked on the map and in addition have a chance to analyze the signal and find the one at the unknown location.

Advance notice of this practice was sent out on the BOK ARDF list. If you didn’t get a notice, and would like to be added to the list, just send a comment to this article and I will add you to the list so you can get future notices

Filed under: Radio Orienteering by Joseph