Join Date: Jan 2010
Location: Chattanooga, TN
Thanked 45 Times in 39 Posts
Just to clear things up - The cop was not using a radar gun. He had a radar unit mounted in his back window. Had he been using a gun he would be accurate with a proper tune of about +-1mph. The units mounted in the vehicle are accurate to a certain point. But if you are going to court to try and convince the judge that you were only speeding 10mph over the speed limit then you'll probably look like a dumbass.
(Q)What is the "Cosine Effect"?
(A)The Cosine Effect is a radar measured speed error due to the angle between the radar and target vehicle or object.
(Q)How does the Cosine Effect influence measured speed?
(A)The Cosine Effect causes a stationary radar to measure speeds low, the greater the angle the lower the measured speed. Moving mode radar may measure target speed HIGH in some situations.
(Q)Which angle is the Cosine Effect angle?
(A)The Cosine Effect angle (from the target vehicle's point of view) is the angle between the direction of the target vehicle and the radar. If the target vehicle is traveling directly toward (or away) from the radar, the Cosine Effect angle is 0 degrees (no error).
(Q)How large or small is the Cosine Effect error?
(A)The greater the angle, the greater the error. The error is a function of the cosine of the angle, thus Cosine Effect error. Measured speed = actual speed multiplied by the cosine of the angle.
So after using simple math calculations, the angle of 24 ft by 100 ft away came to 13.5 degrees. According to your explanation of the cosine effect error: 75 = x * cos13.5 therefore x (my actual speed) is closer to 77 mph? SO, you're saying the radar error is to my disadvantage?
you guys are misinterpreting what I mean by resolution. OP said there was a car NEXT to him. I am not saying anything about angle of incidence changing the doppler effect, nor am I saying to check his calibration, because there is no way it is out, I am saying with the beam spread, there isn't a way for him to definitively say that the reflected waves were not off of the car in the closer lane.
I agree with you. But I think Selkie is just explaining that there is also another added factor: the distance I was away from the car (perpendicularly) that changes things.
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