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From: andyw@aspen32.cray.com (Andy Warner)
Newsgroups: sci.electronics
Subject: Re: measuring vehicle speed
Message-ID: <110139.19717@timbuk.cray.com>
Date: 28 Jun 91 17:17:17 GMT
Followup-To: sci.electronics
Distribution: na
Organization: Cray Research, Inc (People who make computers out of ECL).
Lines: 27



A little while ago (ie long enough that it's expired from our
nntp server), someone posted an idea for bouncing radio off the
road under a car and figuring out how fast you were going
from testing which antenna from an array gave the best signal.

Someone tell me this was a joke, please.

How far is the car going to move in the time it takes for the signal
to bounce back, at say 60MPH ..

Well my rough calculations say about .. 2nS (assuming a 50cm path,
s = 3x10^8 m/sec - rough, but the right order of magnitude).
So how far does your average 60MPH Subaru move in 2nS ?

Roughly 0.000006 cm.

I think the engineering tolerances might be a little tight here..

Now, I could have the wrong end of the stick here, but I don't
think so.

--
andyw.	(W0/G1XRL)

andyw@aspen.cray.com	Andy Warner, Cray Research, Inc.	(612) 683-5835