Preface
This is an older article based on information available at the time. I have edited it "lightly" and updated some of the links, but be aware that the information is not necessarily up-to-date or complete. As with everything on this site, it is presented "for your information" only. For further information see the RCGroups threads, Finding a lost model and The Planelocator thread. Also note that, according to the Communications Specialists web site, The PT-1B transmitter is "temporarily" unavailable as of 11-22-06. Check the Planelocator web site for more details. You may also want to have a look at the Walston Retrieval Systems site.
I continue to use this system and have been pleased with how easy it is to use. I have not, unfortunately or fortunately depending on how you look at it, actually needed to use it. (One pilot did report needing it on The Planelocator thread.) However, my testing has convinced me it should work if required (see below).
Introduction
AP pilots tend to fly higher and "further out" (and in more, um, "interesting" locations) than your average Sunday pilot. An alarming number of pilots on the Aerial Photography forum have reported losing their aircraft, after losing control and having them come down who-knows-where. After temporarily losing my own plane in a bean field, I decided I needed an upgrade to my Lost Model Alarm (LMA). I investigating both an audible LMA, and some DIY RF (radio frequency) solutions. However, my knowledge of RF (both technical and regulatory) is somewhat limited and I didn't want to spend a lot of time learning the ins and outs, getting a HAM license etc.
In the thread Lost Models... what do we really need?, Vince53 suggested the planelocator. While I thought this was a little on the expensive side, it seemed to be what I was looking for, and it didn't seem like anything cheaper might come along any time soon. So I ordered it.
I have been using the system for about two years now. Unfortunately (or fortunately, depending on how you look at it), I have not actually had occasion to use it to find a lost plane. So what you are reading below is based on my testing only, not on "real world" experience in finding a lost plane.
First Looks
From first impressions, unpacking the box, was very impressed. The receiver looks very well made and rugged. The instruction manual (which you can view on-line if you're interested) is very clear and well illustrated. They supply you with everything you need and then some. They throw in three rubber caps to cover over the battery in the transmitter, three extra transmitter antenna wires of varying lengths, scads of extra nuts and lock washers (to hold the antenna wires on the transmitter), and even a nut driver!
The receiver itself is a rugged-looking aluminum box, with a BNC connector on the top for the "rubber duck" and directional antennas (both included). The included 9V battery fits in a clever little tray on the bottom. The transmitter is very small and light, and they supply two batteries (supposed to last 30 days of continuous use). The on-board weight breaks down like this:
| Transmitter | 3.8 g | |
| Battery | 2.9 g | |
| Antenna wire & connectors | 0.6 g | |
| Rubber cap | 1.0 g | |
| Total | 8.3 g |
Note that the rubber cap is optional, but probably advisable, especially if you're flying over a swamp!
Attached is a photo of what comes in the box if you order just the receiver and one transmitter. I actually ordered two transmitters and a sheet of extra batteries (not shown).
| A | - | Directional antenna |
| B | - | Receiver |
| C | - | Instruction manual |
| D | - | Non-directional "rubber duck" antenna |
| E | - | Transmitter with 4" antenna wire installed |
| F | - | Extra (longer) antenna wires (three) |
| G | - | Batteries (two) |
| H | - | Rubber caps |
| I | - | Extra nuts and lock washers (lots!) |
| J | - | Nut driver |
From first impressions, this seems like a very solid, well-made and professional product.
First test, July 24, 2005
This first test was just to see how effectively I could locate the transmitter, without worrying too much about how "good" at test it was in the sense of being a fair approximation of the kind of search I'd be up against in a "real" lost-model situation.
I asked my wife to hide the transmitter near a country road, but left it up to her where along the road that would be. The logic was that, usually when a plane goes down, you have a bearing on it when last seen, and can be fairly sure it is near a line drawn from your pilot station to the last sighting. (This, obviously, wouldn't work if the plane were lost in a cloud.)
For a bit of visibility, I placed the transmitter in an empty margarine tub. My wife dropped me at a corner left to hide the transmitter. After about 20 minutes, she returned and the search was on.
When I first powered up the receiver, I couldn't get a signal at all. (Looking at a map later, I saw it was at least 1.5 miles from the hidden transmitter, so this is hardly surprising.) I got in the car and drove along the road, leaving the receiver on. After a time, the receiver started picking up the signal. I don't remember exactly when I first noticed it, but I don't think it was more than about 500 ft. from where the TX was hidden. This will bear further investigation, as the range is supposed to be a mile. However, they do mention that the range is considerably diminished inside a vehicle. I plan to do some more testing to see exactly what the range is.
After driving for a short while the signal began getting weaker again and I pulled over to the side of the road and continued on foot. I made a "360" and determined that the signal was greatest back the way we'd come so I proceeded up the road in that direction. I began walking up the road and observed that the signal was getting noticeably louder. Several times I stopped to do a 360. Most of the time this indicated I should proceed the way I was going, however, at one point the signal direction seemed to be off to the side of the road. I debated what to do at that point, thinking that the TX was hidden off the side of the road at that point. However, I decided to keep walking back on the road just to see if I could "triangulate" the TX location a bit better. As I continued to walk, however, the signal got louder still and no longer indicated it was off to the side.
A little ways further, there was a parking area for a nature trail. As I passed it, the signal seemed the loudest I'd heard yet, and diminished as I walked past it. A 360 at that point indicated that the signal was coming from opposite the parking area. A trail lead off on the other side of the road and I proceeded down that.
The signal continued to get louder, and at one point I had to switch from "long" to "medium" range on the receiver to avoid overloading it. I actually narrowed down the location of the TX to within about 10 feet or so fairly quickly, but took another 5 or 10 minutes to actually locate the TX in the underbrush. At less than 20 ft. or so, the receiver seemed to get confused about the directionality. After going back and forth within five or ten feet or the TX, I eventually found it. My wife had done a pretty good job of hiding it!
Conclusions - first test
Generally, I am pleased that the TX was located fairly quickly. I don't know that it wasn't a 100% fair test as I knew it was hidden fairly close to the road and/or an accessible trail. However, the exercise did point out a few interesting aspects.
- The direction at which the signal is loudest is generally fairly accurate, but at times can be off by as much as 90 degrees. I would conclude therefore that any particular reading should not be considered necessarily very accurate, and one should take a number of readings at a number of locations when determining direction.
- Signal strength proved to be a fairly good indication of the distance to the target. The "art" of RDF (Radio Direction Finding) seems to consist of combining indications from both the direction and signal strength data, taken at a number of locations.
- Close-in work (less that about 20 ft.) tends to be a bit troublesome. This should generally not cause problems -- if you are within 20 ft. of your model you should be able to see it! However, the inclusion of an audible alarm is probably of some utility. It should shorten the time to locate the model after one gets to within about 100 ft. or so.
- More tests will be necessary to determine the outside range. I don't remember well enough when the signal first appeared, and at any rate it was within a vehicle, so this information would not be conclusive anyway.
Second test, July 31, 2005
The purpose of this test was establish range information for this system, i.e. how far away from a lost model one would have to be to lose the signal entirely, and how effectively one could locate the model if a weak signal could be received.
I placed the transmitter, with the little 4" antenna that comes attached, on a rock about 12" off the ground. I turned on the receiver and began driving. By 0.2 km (kilometer = 0.62 mile) the signal in the car was very faint, and by 0.5 km it was lost. Out of the car, the signal was somewhat better, however by 0.7 km, I could not pick up a signal.
This was rather disappointing, to say the least. They say the range is over a mile. It still works well if you can get within about ½ km, but there are situations where that might be a problem. I started thinking seriously about taking them up on their 30-day no-questions-asked return policy.
As mentioned, the receiver comes with a 4" antenna (just a piece of stiff wire) attached. They also supply three other antenna wires in (roughly) 8", 12" and 18" lengths. So thinking I might get better range with the longer antenna, I put the 18" wire on the transmitter.
The difference was apparent right away. The signal even in the car persisted for over a km. The range out of the car was way up. The signal remained usable up to about 2 km (over a mile). At that distance, I had to listen carefully to hear the signal, but it was enough to give a direction.
I did not have enough time to test the intermediate antenna lengths. Given the results of this test, I think I'll be using the longest wire at all times. I may even run some tests with even longer wires to see if I can boost the range even more.
Here is a chart made from my field notes. The Distance, Signal, Meter and Dir. refer to observations made out of the car with the ignition off. In car was in the car while driving (slowly!). Distance is in kilometers, with miles in parentheses. The meter on the receiver has 10 divisions, and the Meter column is the meter deflection for each "blip" from the transmitter, with the meter at about half-scale. The Dir. column is how accurate the directionality information was.
4" antenna |
||||
| Distance km (mile) |
Signal | Meter | Dir. | In car |
| 0.5 (0.31) | faint | 1 | good | no |
| 0.6 (0.37) | barely audible | no | good | no |
| 0.7 (0.43) | nothing | no | no | no |
| 18" antenna | ||||
| Distance km (mile) | Signal | Meter | Dir. | In car |
| 0.5 (0.31) | clear | >10 | good | clear |
| 1.0 (0.62) | clear, a bit faint | 4 | fair | faint |
| 1.5 (0.93) | faint | ½ | good | no |
| 2.0 (1.24) | faint | slight | good | no |
| 2.5 (1.55) | nothing | no | no | no |
Some other interesting observations:
The range in the car was much reduced compared to the range outside the car. Even when I got a signal in the car, I could not get any reliable direction information. I found I got the best directionality by moving away from the car (turned off) and holding the antenna pointed directly away from my body, then making a full circle. I found it also important try the antenna both horizontal and vertical as that could make quite a difference in the signal strength.
I found both the audio and the meter to be useful. When the signal was very weak, there was no meter deflection, but I could pick up changes in signal strength by listening to the sound. In stronger signal situations, the meter gives a good indication of the exactly direction where the signal is strongest.
The "rubber duck" antenna, as suggested in the instructions, can be used for "close-in" locating. It is not directional, so you don't have any direction information, but I found the signal strength to be a fairly accurate indication of the distance to the target. This worked well even in the car, where the direction information was scattered.
Conclusions - second test
- Size matters. The short antenna is to my mind almost useless. Range with the longer antenna is over a mile.
- Directionality remains surprisingly good, even in very faint signal situations. If you can get a signal at all, you should probably have your plane found in short order.
- Signal in a vehicle is much reduced, and the directionality is scrambled. The best approach is to turn off the car, get out and do a "360" with the antenna pointed away from you.
- For "close-in" work, distance-to-target (signal strength) can be used reliably, as well as directionality.
I would conclude therefore, based on these tests, that with the 18" transmitter antenna, this system should be sufficient to locate your lost plane under almost any conceivable circumstance. If you have maintained visual contact until the plane goes down over the horizon, you should have a good enough idea where it came to rest to be able to locate it in short order. In situations where it's location is not as well known (if the plane is lost in a cloud and never seen again for instance), I would think a systematic search should be able to put you within range of your plane eventually. If you get any signal at all, you can get pretty good direction information from it, and from there you're pretty much home free.
All my AP missions from here on in will have one of these on board!
Further reading
See the planelocator web site.
Also, here is a partial list of "lost model" (and solution) threads on the RCGroups forums.