Teensy wireless: measuring distance of a sent radio frequency?

[eskaygeebee]

First post for me, but I've been using teensy boards for about a year now. Totally in love with the compactness and malleability of 'em <3

Hey there, ya'll!

So, would it be possible to use virtualwire (http://www.pjrc.com/teensy/td_libs_VirtualWire.html) to measure the distance a radio frequency travels?

I would be using two teensy boards, one to send the frequency and one to receive it. Basically, I need to measure the distance the frequency travels so I can measure how near or far the sending teensy chip is. Speed, and accuracy are of the essence, it's not for anything too long range, maybe just a distance of about 20 feet.

Any thoughts?

 

[mlu]

This is not practically possible, remember that radio waves travel with the speed of light, more than 980 000 000 ft per second.
To measure a distance with an accuracy of 1 feet, you must measure the time of flight for the radio wave with
an error smaller than 1ns. The Teensy3 has cycle time of 10.4 ns if it is clocked at 96MHz. So the accuracy must be
better than 1/10 of a Teensy3 instruction cycle.

Detecting the exact start of the transmission and the reception is almost impossible unless you use very special equipment,
it takes some time for the carrier wave to build up when transmitting and also for the receiver to detect the radio wave.
These errors will distance measurement very imprecise.

It is possible to measure changes in distance by exactly measuring the phase change between a received radio wave and a reference
oscillator, but that needs special equipment like Software-Defined radio receivers and cost a much bigger chunk of money.

 

[stevech]

Time difference of arrival systems are common but expensive. They require 2+ receivers with a common time reference accurate to a few nanosec.

Can't be done on a low budget.
Some vendors that do this are Ekahau, Time Domain. They help track, e.g., wheeled equipment in a hospital.