[Tee]

Originally Posted by NoLongerInRadioGuy

NEVER ONCE written a ticket to someone for going a speed of anything other than I saw on my radar or lidar.

Noticed you said "saw" and not "locked"

Maybe you didn't understand my post....That is exactly what I said- You guys tend to write the ticket, not for what was locked on the display, but for a momentary spike that you "saw", right? Fact is, those spikes can be attributed to other causes. I may not be an expert in police radar from a patrolmans point of view, but I am an expert in electronics and know quite a bit about doppler theory. Lets do a little radar 101, and you tell me if you disagree with any of this:

Basic representation. Most newer units (Stalker II) used in
our area are stationary (mounted in vehicle) of the patrol car.

A radar works by shooting radio waves, usually in the X, K or Ka band towards traffic in a large V-pattern, usually 11-24 degrees right to left. A portion of the waves reflect back to the patrol car and the space between the waves are measured for variances (doppler shift).

A tighter wavelength indicates an object moving towards the radar gun, a wider wave length indicates an object moving away from the radar gun. Likewise, the amount of the doppler shift *minus* the speed of the police car= the speed of the target vehicle.

Lidar uses a laser which is not susceptable to this large radar swath, they use a very small pinpoint pattern, similar to a pen laser would use. However they are not widely used in Western Kansas. You will see them in Wichita, though.

There are several factors that can contribute to inaccuracy of a doppler rader.
The angle of the radar gun in relationship to the target can affect accuracy. This is called the "cosine effect", because the measured speed is directly related to the cosine of the angle between the radar and target direction of travel.

Other factors include ground clutter, also known as ground echo, and most importantly, multiple targets. Beam width is probably the most notable reason for false readings. Even the narrowest of radar beams - 11 degrees - is 38 feet wide when 200 feet down the road and 57 feet wide at 300 feet away. Some radar units transmit a beam as wide as 24 degrees. By the time a radar beam is several hundred feet from a patrol car, the microwaves are blanketing an area as wide as an expressway. Unless you are alone in entire beams pattern, there is no way that a radar operator can conclusively discern your vehicle as the one on his target readout.

Even though police radar is based on the Doppler Principle, most units do not interpret the Doppler shift itself. Rather, they process the frequency of the signal and use its analog to represent target speeds. Known as phase-lock loop, or PPL, this processing can lock onto the wrong target, double or triple low speed readings, or produce "ghost" readings.

When the International Assoc of Cheif's of Police tested 24 police radar models, they found that the results showed that nearly all of the units were affected by temperature variations, five had failed accuracy tests, four had unacceptably wide beam patterns and three tended to provide inaccurate readings due to nearby police or CB radio signals.

Radio or Microwave Interference can come in a variety of forms, both natural and man-made, but they have one thing in common - they produce a false or incorrect reading on the radar unit's display. Common sources of electromagnetic interference include airport radar; microwave transmissions; transmissions of CB, ham, VHF/UHF, and cellular two-way radio/ telephones, including police and business radios; faulty sparkplug wires; mercury vapor and neon lights; high-tension powerlines; and high voltage power substations. The radio energy from these sources can overload or confuse the sensitive circuits in a radar gun.

Mechanical Interference is any moving object, other than the target vehicle, that can produce a false or incorrect radar reading. The most common sources are vibrating or rotating signs near the roadway; fan blades moving inside or outside the patrol car (air conditioner, heater, defroster or engine fan); another moving vehicle that reflects radar waves better than the target vehicle; and multiple targets in the main radar beam causing multiple reflections of nearly equal strength and making the display read, high, low, or completely blank.

Even under the very best of circumstances, and proper use and interpretation by it's operator, the very best police radar systems are listed by their own manufacturers to have an accuracy of 1-3% in stationary mode and 3-5% in moving mode. So despite what an oficer tells you, their radar systems are not infallable.