How to measure distance using radio frequency

I'd like to plot the path of several animals in an outdoor fenced area, ideally with accuracy of 12 inches or less.

  1. GPS very expensive is not accurate enough. I don't need world-wide location, but it needs to be reasonably accurate.
  2. Ultrasonic or IR are problematic as I cannot guarantee line-of-sight.
  3. Using image processing and multiple camera is a possible solution, but that seems to be problematic when there are more than one animal in the area, and how about detection at night?!

That seems to leave RF as my only option. Can you guys point me to hardware options that I can use to measure distance and eventually use several to triangulate the animals' location? Thank you in advance!

GPS very expensive is not accurate enough

How about differential GPS?

It'll be a lot cheaper than any system you can create using licenceable RF.

(FYI 1 nanosecond = 1 foot (30cm) a light speed roughly)

That seems to leave RF as my only option.

Well, then you are probably out of luck. An RF solution would much more complex and $$$ than the other methods you mention.

I’d like to plot the path of several animals in an outdoor fenced area, ideally with accuracy of 12 inches or less.

What an interesting problem! But what are these animals? Are they bigger than 12 inches themselves? Can you attach markers/transmitters to the animals? to their backs pointing up? sides pointing horizontally?

What are the other constraints? Can you mount a camera above the fenced area pointing down at the ground? Can you implant sensors/transmitters in the ground underneath the fenced area?

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There are radio techniques for doing that sort of thing, but they are very complex. I'd forget it, and try something else.

I found this X-band motion detector that maybe can suit your needs

it's not a range finder though, but maybe you can hack it into it it will at least detect motion through di-electrics

it's cheap, 14.19$USD + 2.80$USD for ship

there used to be lots of "toy" radar for measuring the speed of a baseball but they seem to have disappeared, I think they used to be found for 60$ but now I can only find one for 250$ :(

Thanks for all the responses everyone!

AWOL, differential GPS might be what I need. I will dig into that. thx!

RuggedCircuits, initially, the animals are dogs, they would wear an RF transmitter/receiver collar. Mounting overhead camera is not an option, but side cameras on the fence would be ok. Implanting sensors/transmitters on the perimeter is ok, but not all over the yard :slight_smile:

Tie each of them up to their own stake with a 12 inch lead. Problem solved (as long as you note down the position of each stake...)

What about triangulation? That's how to location a cellphone with three cellphone towers in a triangular setup. Each animal emits a different frequency and from the relative intensity on each of the three towers you can mathematically find out their location within the area. You can cut this down to two towers if they're confined to only one side of the line that links both towers.

If you could get them to bark on cue (perhaps with addressable collars) then you could triangulate the position of the sound. Of course if they all start barking in a pack, then you're back to zip.

Actually, that's not a bad idea; if you replaced barking with something else.

Perhaps a collar or harness with one or more ultrasonic transducers, that is addressable, and can output a "ping" when addressed remotely. In the "outdoor fenced area", you place a variety of "listening" stations, each one anchored to a predetermined location (via GPS); they might look something like a light pole, with the sensor (ultrasonic receiver) above (about 10-12 feet above the ground), perhaps with a reflector or something. These poles would be spaced apart in a hexagonal grid, perhaps 50-75 feet.

Your transducers would have to be powerful for the transmitter and sensitive for the receiver, but the idea would be that you would "ping" a particular collar, and the various stations near the dog/collar would each receive a pickup of varying strength; when they did, an interrupt would be triggered, and they would relay the information (strength level and reporting station number) to a central base station (likely PC-based for data storage, and mapping). Triangulation (with knowing the locations of the receiving stations) using the readings would be able to tell you the rest...

It certainly wouldn't be cheap to set up (differential GPS would probably be cheaper).


If there is a high point you can mount a webcam on it is quite easy. The different chicken can be marked with different colors so that they can easily be traced. If you also want to be able to follow them in the dark you can create simple IR packs that blink at a different speed. That is how you can seperate them.

What about just measuring strength of the signal on three towers. This should give a way to find position. Say if strength is same, the object is at the center of the triangle, if then A>B>C, then do some math with data taken from trials you can find distance, as radio signal power dissipates at distance square. That's what I was suggesting, not barking and else. I just don't know how accurate this gets especially the OP didn't point out the size of the area.