Rob Stockley <robstockley@MOWGLI.NET.NZ> wrote:
> I like the idea of building a UHF transponder/beacon set. The unit sends
> a unique pulse train then listens for a reply. The beacon receives and
> decodes the pulse train, waits a preset time, then replys. The unit
> receives the reply and calculates distance from the signal's time of
> flight. Jittering the PRF and range gating would improve signal to
> noise.

You've just described DME (distance-measuring equipment) as used on
aircraft almost exactly. See
   http://www.acay.com.au/~willt/yssy/enthus/whatis/vordme.html

You might be able to pick up some used equipment and modify its frequencies
and power levels to suit your project.

To address a point that another responder brought up, there are ways to
achieve high precision in time while still using narrowband signals.
For example, look up "chirp radar" on Google.

-- Dave Tweed

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