I don't see how a radar unit of any type can work from the side... Like when a trooper hide in a row of trees and puts the gun on you when you go by. I think you could fight that in court because I don't think it can measure speed form the side.

 

While it is true that radar cannot detect your speed from a perfect 90 degrees out, when the cop shoots you with his a$$hole gun it is not at a true 90. 90 degrees out you have a 0 mph relative speed (ie the radar hits the car and returns each time with 0 change in time difference). The side detection on most detectors is a broader spectrum than just 90 out. For example, I don't know what parameters Valentine uses, but lets just say that your front detection covers from 315-045 degrees relative to your nose. The rear detects 135-225 degrees. That would leave 226-314 and 046-134 degrees for the side detection angles. That would allow a cop to shoot you from "the side" and you pick up the side indication on your radar detector, and unfortunately he would have enough of a doppler shift to hit you with what I call a "gotcha tax."

Hopefully this helped a little bit. I dabble in radars from time to time.

 

If a trooper only has a side look at your car, he can't be using radar to clock you. He could be using VASCAR, measuring the time it takes you to cross betwen two objects a fixed distance apart. Like DrivnXcitment said at 90 degress with radar there is no speed reading. At 45 degress he would be reading half your actual speed.

 

To be little picky, 0.707 of your actual speed.

 

Trig was always a problem for me too...

 

If that is true how does he get a true reading?

 

If we knew that, we could make ourselves millionaires by teaching people how to beat the gun. The only true way they could get speed on someone is to be directly in front of them or behind them stationary. Obviously the radar system they have takes into account the speed that the police car is traveling and adjusts for that. So who knows how they do it from angles really.

 

He doesn't get a true reading from an angle. His reading will be low, so it can't work against you.

 

If the cop is 10 feet off the roadway, and you are approaching at a distance of 200 feet, his speed reading will be in error by 4%. At an approach distance of 50 feet, the error is almost 13%. And it just gets worse the closer he is to you.

 

Do you have a reference I could study for this information? I have to go to court in the near future and would like to have as much or more knowledge on LEO radar equipment and how it works.

 

As mentioned above, the important thing is that any angular error always causes the radar to read LOWER than your actual speed. Probably you don't want to bring that up in court...

 

My problem is I wasn't speeding! I would like to educate myself on the subject.

 

amen

 

Actually when it comes to radar, while true you can't get a reading from a tangental (ie flying perpendicular to a radar) you can overcome this by using frequency diversity (a changing frequency). Also you would only be tangental to the radar for that short period that you were perfectly perpendicular to the radar. And modern radars do not use a time base system anymore, they use doppler ( which shows a change in frequency which is relative to the distance or speed). The only way you could possibly beat any type of radar is if you could prove that it wasn't absolutely you that was targeted, ie alot of traffic where you could have been mistakenly identified or if you could prove that the radar hadn't been properly calibrated or was out of calibration. When you are talking about radar you are talking about the speed of light so it doesnt take a large reading for the person to get a reading.

 

All true as stated so far. To be accurate, an adjustment must be made for the angle of approach. Highly sophisticated systems like ground based radars for air traffic control or ship based systems compute the course and speed based on positional changes over time. They must also factor in the sending unit’s speed if any.

LEO handhelds don’t have this capability. They rely on an estimate by the officer on the angle of approach and apply it to your observed speed. Weather old fashioned radar or Doppler radar, the principals are the same.

Possible reasons for miscalculation:
1. Incorrect application of the approach angle.
2. Maladjusted radar
3. Radar anomalies (eg the first returned signal is from your rear view mirror, the second from your front plate which is closer and calculates a greater speed)
4. Other vehicles near-by. (eg returned signals from 2 different cars)

Several years ago I was ticketed. I had my cruise set @ 63 in a 55 zone. Crested a hill and LEO ticketed me for 70. Went to court – explained all to the judge – they were all very polite – and questioned me on my knowledge of radar. The Judge said I could possibly be right but he found me guilty and I paid the full amount.

The best way to avoid radar is with a radar detector and lowering your “Radar Cross Section” or RCS. Without getting overly technical – the smaller area presented to the radar, the shorter the distance for detection by LOE. LEO can detect a Semi @ 2000 yds. Your wife’s Camery @ 1600 and the front or your Vette @ 600 yds. It gives you more time to see him and slow. Take off your front plate and the 600 yd detection drops to 450 yds. These numbers are not exact but a close approximation based upon data in Texas LEO radar tests.

 

Oh BTW - Good luck

 

That bites getting a ticket and not even speeding. I have found a 400 investment in an Escort radar detector has been my best friend in the world on these long straights here in Texas. It has paid for itself many times over. Not that I would ever speed.

 

The term used to describe the error involved is commonly called cosine error. It derives it's name from the way you compute the speed vector which is parallel to the direction the gun is aimed. In particular if you take the cosine of the angle between the gun direction and the vehicle velocity direction and multiply it by the vehicle speed you get what the gun will read. Since the cosine of any angle is always 1.0 or less the gun always reads lower than you were going. As an example if the gun is 90 degrees to the vehicle direction of motion the reading is 0 mph since the cosine of 90 degrees is 0.0. (don't you wish you paid attention in high school trig?)

There is a situation when you are clocked by a moving car where the radar can read higher mostly because the police car gets his own speed wrong. This is only true if the police car uses the radar to compute his own speed which is required to figure out the speed of the car he is tracking. To avoid this trouble some systems use the wheel speed i.e. speedometer reading.

Good luck explaining any of this to lawyers or the judge in court.

 

In both cases, the speed on the gun is LOWER than your actual speed.

 

All I know is my V1 has saved my a$$ a number of times