[time-nuts] position determination over short distance

[Rick Harold]

All,

I'm planning doing some experiments in distance measurement.  They don't
deal with atomic time directly but with extreme short periods of time.

I need to determine the position of a instrument with a 1mm accuracy or
less.
The instrument is not connected to a mechanical device but is separate &
independent.
The surface which the instrument is positioned on is close to the size of a
11"x11" square.

I thought of using 1 RF transmitters (not sure of freq) on bottom of the
device near the surface.
The surface would have RF receivers on 3 or 4 edges/corners to receive the
signal.

If each of the receivers positions are known and they then send a signal to
a central circuit (again known positions) how can I differentiate the time
of arrival
at the central location?  Does anybody know of a circuit/chip or system
which would determine the time 'difference'.
Obviously this is used to triangulate the position of the instrument.
Light travels 1 mm in ~3.3 picoseconds so I would suspect the differentiator
would have to have that or better resolution.
It could also use some proportional method to extrapolate the position since
the surface has a fixed size.

Any ideas/thoughts?

Thanks in advance.

Rick Harold