So… I lost my quad again. I lost video during aerobatic flight, lost track of my orientation, and ended up crashing, apparently in a wooded area at the far end of the park. You can watch the crash video here.
I walked to about where I thought it should be but I couldn’t hear the lost model buzzer, so I resorted to direction-finding my quad using a directional video antenna. Since this is a useful technique, which has saved me from completely losing a quad on two occasions, and simplified the search on several more, I thought I should share it.
Here is a picture of my Quanum V2 goggles. I have a diversity receiver, the excellent Boscam FR632, with the usual combination of an omni-directional antenna and a directional antenna. In my case the directional antenna is an Aomway 11 dBi helical antenna rather than the usual patch. The reason I chose a helical is that it’s quite simple to make a helical that performs well, and the manufacturing tolerances aren’t stringent, while it is actually quite difficult to make a circularly polarized patch antenna with decent performance. The helical antenna has a more tightly focused pattern than a patch, which is not ideal for general flying, but perfect for finding lost quads! I don’t know how well this technique would work with a patch antenna – it may be worth getting a helical antenna just for lost model finding duties.
First, if you are using a diversity receiver, remove all but the directional antenna since the omni will just confuse things. If you are using a receiver with only an omni antenna, then you can replace it with a directional antenna for the search. I strongly recommend that you have a narrow beam directional antenna available for such an emergency, even if you don’t use it while flying. For less than US$ 15 it’s cheap insurance – mine has so far saved me at least a hundred times as much in replacement costs.
Then stand in the vicinity of where you think the quad went down and turn slowly in a circle while watching the video screen. I don’t actually wear the goggles for this, as I want to be able to monitor my orientation as I turn, and also not to fall over. If the quad is some distance away, or its video antenna is obstructed, then you may not see a picture – it may just be a slight change in the way the background noise looks when you are pointing in a particular direction. This is an indication that the quad probably lies in the direction where the background noise looks different. Of course other RF sources can give the same effect, so you may need to try from several different starting positions until you find one that leads you to your model.
As you get closer, you should start to see a picture. As the signal gets stronger, it may become harder to tell precisely which is the best direction, as you may get a good picture over a considerable portion of your circle. In this case, find the “edges” of the good picture zone – for example, the two points in the circle where the picture changes from colour to black and white – and the direction to the quad is most likely in the middle between these “edge” points.
As you get even close and the signal becomes quite strong, you will find that you get video all the way around the circle. In this case it can be helpful to find the direction with the weakest signal, and then go in the opposite direction.
Using this method I quite quickly located the likely position of the quad. It was out of view behind the hedge of a private property bordering the park, about 50m from where I had started searching for it. When I listened at the hedge, I could just barely hear the lost model buzzer beeping, and was able to retrieve it. Had I been relying on my eyesight and the lost model buzzer alone, I probably would have lost it forever. I was just fortunate that the battery had remained connected to power the video transmitter.