From: kolstad@cae.wisc.edu (Joel Kolstad)
Subject: Re: Can Radio Freq. Be Used To Measure Distance?
Organization: U of Wisconsin-Madison College of Engineering
Lines: 25

In article <C5v13M.C37@bcstec.ca.boeing.com> rgc3679@bcstec.ca.boeing.com (Robert G. Carpenter) writes:
>I'm wondering if it's possible to use radio waves to measure the
>distance between a transmitter(s) and receiver?

Yes, you could.

>Seems to me that you should be able to measure the signal strength
>and determine distance. This would be for short distances (2000 ft),
>and I would need to have accuracy of 6 inches, or so.

Well, letsee (whipping out HP-48SX, soon to be GX): 6 inches/3*10^8 m/s=.5
nanoseconds resolution.  Hmm.  That'll be rather difficult!

The more standard (read: better) method is to use ultrasound, generally
somewhere around 40kHz.  Sound travels a heck of a lot slower than light
(radio waves), and is therefore much easier to deal with.

>What frequencies would be best for this? Or does matter?

It might be easiest to visit a hardware store and look at the numerous
"sonic estimator" type devices that do what you want here.  Many are pretty 
cheap too -- <$30.  (In fact, for awhile the Stanley Estimator was selling
for something like $8.  That's the one I bought! :-) )

					---Joel Kolstad
