From: dtmedin@catbyte.b30.ingr.com (Dave Medin)
Subject: Re: Police radar....Just how does it work??
Reply-To: dtmedin@catbyte.b30.ingr.com
Organization: Intergraph Corporation, Huntsville AL
Lines: 35

In article <1993Apr2.182216.28603@walter.bellcore.com>, deaddio@ski.bellcore.com (Michael DeAddio) writes:

|> |> Question 2:
|> |> 
|> |> 	If I am right about the doppler(if I spell it different every time,
|> |> maybe one will be right) effect, how does the radar get an accurate reading
|> |> when the car containing it is moving??  It would seem to me ( for all thats
|> |> worth) that it would need to be calibrated with the speedometer of the car
|> |> containing it??  I am fairly sure this isn't the case, so whats the deal??
|> 
|> Essentially, this is actually how it is done.  The radar gun is tied into
|> the speedometer of the car.

No, it is independent of the speedometer. The gun processes two doppler
returns--the speed of the car relative to the pavement and the speed
of the target, taking the difference between the two. Some guns with
a "moving mode" actually have a split beam with one beam aimed
preferentially at the pavement.

Car and Driver had a good article on traffic radar, but it was back in
1985. I used its contents and references to defend myself against a bogus
radar-measured ticket. It detailed "moving mode," which is easier to
defend against because of the increased amount of variables.

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