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From: gfv@homxc.UUCP (G.VALVO)
Newsgroups: sci.electronics,misc.misc,misc.wanted
Subject: Re: Measuring distance using lasers  (followup)
Message-ID: <4154@homxc.UUCP>
Date: 10 Nov 88 14:13:24 GMT
References: <122@ericom.ericsson.se>
Organization: AT&T Bell Laboratories, Holmdel
Lines: 23

In article <122@ericom.ericsson.se>, etxbrfa@kklm01.ericsson.se writes:
> It seems as many people out there are interested in laser-rangefinders.
> I got lots of answers to my question earlier, and I've done the homework
> for this time. Now for todays questions.
> 
> If the beam is modulated with a frequency of, say, 10MHz (30 meters), how
> can I electronically measure the phase difference between outgoing signal
> and reflex. If I use an oscilloscope, it's easy to se how many millimeters
> the reflex is from the output and multiplying that with the timebase gives
> the time. (And from that ofcource the distance.) But how can this be done
> electronically? I suppose the solution is't that difficult, but at least
> I don't know how to do it.


I don't know if it's actually done this way, but phase comparitors are
very common electronic components.  They are required for phase locked loops.
A (double) balanced mixer will work.  The output (after low pass filtering)
will be a DC voltage proportional to the phase difference.  They
key is being able to perform a nonlinear operation.



				Greg