RF gurus! Triganulating position of transmitters

Ahoy there.

The other day I decided I wanted to work out where a Wireless Access point was, that had been bugging me. A friends family had been complaining that it was messing with their phones (not sure how likley that really is, but hey, its an excuse).

Anyway, I pulled out an OS map, stuck my pen down a few times and said "I'm going there". I then took out my laptop, went to each point, logged and averaged signal strength at each point. I then did a bit of guestimating and converted Signal to Noise ratio to an approximate distance. I then took the map back out, picked the 3 highest signals and then drew a circle around each.

I then looked for where they crossed and said "It's there". As a matter of fact I was about a house out.

Tell me, somebody, how wrong this method is. Tell me I need more complicated equipment than a built in wireless card (omnidirectional antenna), a map and a notepad.

I had another idea that if you had 2 laptops with directional antenna, and you went to predetermined points, and did a 360 scan, take the bearing of the highest signal and then draw a line on the map for each point, and where they cross is the location of the WAP.

Again, tell me how wrong this method is. Please. It must be wrong. I know its crude (not properly taking into account LoS or anything like that), but tell me that its wrong.

 

Goldy, here in the US we have what’s called, Citizen Band Radio, they were a fad in the 70’s…there’s still a few in every town, and even here in town…….we had a club, that would play a game, find the rabbit……..on person in their car would speak for 15 seconds every 3-5 min. and the others would use their signal strength meter, and drive around the town to find the rabbit………..and that with a 360 degree antenna…….if you have a directional antenna it would be even easier……..wobbles

 

Standard procedure for locating a transmitter is to use a very directional antenna. Nail down the direction from your location and draw a line on a map to match it. Move to a second location away from that line, take another reading, and draw that line. Where the 2 lines cross will be the transmitter, within the limits you're able to judge with your antenna.

But as Wobbles noted, location by signal strength is doable, just takes more times and more readings. May be complicated by terrain that interferes with your reception, or by other noise sources that adds to your signal-to-noise ratio in your case, but is doable with enouth samples.

 

Both R.F. signal strength or direction are valid. Usually, all you need to do is measure angle A. measure angle B, find the intersecting lines, as was said. You can do a third measurement of angle as a double check if you want. It's simplicity itself in its basic form. Signals are often garbled, weak, ambiguous and numerous other factors, though.

 

Hmm, so I wasn't far off then? Hummm! Interesting...