> Date:          Fri, 19 Jun 1998 13:34:54 +0200
> From:          Pavel Korensky <pavelk@DATOR3.ANET.CZ>
> Subject:       Length measurement (Was 4GHz PIC)

> >  Okay here is why I am looking to get a 1nanosecond clock pulse. My
> application
> >is to measure the distance between 2 unknown points ( at most being
> 500-600 yards
> >apart) using a two-way (round trip) ranging principle based on point
> source radio
> >systems. This is basically how I want it to work. Transceiver 1 transmits a
> >signal(pulses), the signal is received at transceiver 2, and after a fixed
> known
> >delay , it is re-transmitted back to transceiver 1, is received by
> transceiver
> >1`s receiver and input to a ranging circuit. The ranging circuit measures
> the time
> >difference between the original transmission time and the time of
> reception (less
>
> >the known fixed delay) , which would be a direct measure of the two-way
> distance
> >when multiplied by the speed of light.This is the problem, the speed of light
> >travels at 186,000 miles per second.That translates into roughly
> 98,208,000 feet
> >per second. For an accurate measurement I would need an oscillator( I
> guess out of
> >the question with a pic) that would supply my ranging circuit with a time
> period
> >that would translate into approximately 1nanosecond per foot. I would like
> to use
> >a PIC to do all the conversions( time to feet and/or yards) and drive an LCD
> >display. Any help will be greatly appreciated.
> >
> >Dominic
> >

Are the points line of sight?
If so you could use laser ranging. A pulse of laser light is sent out
to a retro-refelector which returns it to a CCD sensor. The CDD has a
Pockels cell shutter which is opened after a short period, for a
fixed short period. The amount of the laser pulse reaching the CCD
determines the charge accumulated by the CCD. The charge accumulated
is dependant on the distance traveled by the laser pulse and the
apperture period of the shutter. The charge is read by an A-D
converter, and can then be processed by whatever digital system you
want.

Fast timing is still required for the shutter delays but you could
probably use lumped constant delay lines.

I have seen a version of what is described above on display at
Salford university (a laser ranging camera), so there are going to be
patent, copyright and IPR issues here.

If you are using radio have you considered the multipath problems
causing skewing of the received signals?
______________________________________________________________________

A conclusion is simply the point where you got tired of thinking.


Phone +44 (0)161 275 4094

Jason.Bent@man.ac.uk

I am a technician in the Dept. of Physics & Astronomy
at Manchester University