And a $80 GPS puck giving meter position accuracy is too expensive for him??

What is your time worth? Do you have the deep pockets needed to pay for
certification of your system since it is unlikely they would work
out to 2km in any license free band/power? FRS radios are probably close, but
they are not licensed for use with any antenna other than
the one they come with. But you are not prevented from strapping one to
a tower to increase it's range. Some even have subaudible tones to open
the squelch, and which might be usable for phase measurement to get distance
if hacked up to a high, inaudible frequency (as suggested in an earlier post).

See also 'radio altimeter' for ranging methods using frequency chirps.

There are also a couple of patents on using existing radio stations
to navigate by looking at multiple carrier phase relationships, and
comparing them to a 'reference' station log (which you would send
to your rover).

Do let us know what you finally work out.

Robert

Dave Tweed wrote:
>
> 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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