I was pulled over about a year ago and told that I was going 71 on a 55 mph highway. It was night and I happened to catch up on the highway patrolman who was going the same way that I was so he must have shot the radar out of his back window at me. What I am wondering is how does the gun figure out how fast I was going if we were both traveling in the same direction. How does the gun tell the difference between no moving and shooting, shooting at an object that is coming towards it while it is moving, and an object that is moving away from it while it is moving?
I think this may be done by using two different “guns.” I have noticed that often there is a disc-shaped or cylindrical object, often gray in color, sitting in the back window of many patrol cars. I have come to a hypothesis that this may be a radar device. As to the other part, basically how does the gun know how fast you’re going if the cop is moving, I think the gun is wired into the speedometer, so your relative speed is then either added or subtracted from the officer’s speed depending on the direction you’re traveling relative to the officer. Maybe there’s a cop on the board who give the real inside-the-cruiser story on what goes on in there with that radar gun.
Nah. I don’t know of any radar guns that are “wired into the speedometer”. Moving radar units can clock the speed of both the patrol car and the target vehicle. The computer calculates the doppler shift between vehicles and displays both speeds on the unit. Many cops have their moving radar units turned behind them to clock cars driving up behind them. Milwaukee County does this 100% of the time on our freeways.
My best advice is to go on E-bay and buy a used MOVING radar unit and play with it for awhile. Once you’ve done that you’ll be surprised at how many misconceptions you’ve had about it.