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Speed Guns

Digital radar, lasers and candid cameras make life hard for traffic scofflaws.

February 01, 2002  |  by Carl Fors


More innovative speed enforcement technologies have appeared in the last five years than in the previous two decades. Law enforcement agencies can now pick and choose from a bewildering buffet of high-tech devices, including digital radar, lasers and cameras, and all of them make using older analog radar guns as quaint as listening to AM radio or still using film in a camera.

Digital Radar

Smaller and with increased targeting range and accuracy that results in better tracking history and conviction rates, digital radar is so advanced that comparing it to analog is like comparing a slide rule to a calculator.

Digital radar guns measure speed based on a 12-inch travel distance of target vehicles, compared to 10 to 15 car lengths used by analog guns. What that means is target speeds with digital are immediate and can be recorded at great distances, up to two miles. The increased range provides improved tracking history and better evidence against the violator.

In addition to the increased range of digital radar, there are several other reasons why this equipment results in more sustainable citations. For example, digital circuitry of antennas and counting units virtually eliminate radio frequency interference (RFI), a long-time nemesis of analog radar. New two-piece digital radar guns also help to end the problem of shadowing.

Shadowing, as any state trooper knows, occurs when moving radar's low Doppler locks on to a large moving object-like an 18-wheeler-instead of the road surface in front of his or her patrol car to compute patrol speed. This incorrectly adds to the actual speed of an approaching target vehicle in the opposite lane, and many an officer has lost in court when knowledgeable defense council discovers shadowing.

Two-piece digital radar guns-like Kustom Signals Inc.'s Golden Eagle and Applied Concept Inc.'s DSR-offer speedometer interfaces to eliminate shadowing. The VSS (vehicle speed sensor) signal of the patrol car is fed into the radar gun providing accurate patrol speed not dependent on the radar's low Doppler. Goodbye shadowing.

Ka Band

Stalker Radar (a brand of Applied Concepts Inc.) pioneered digital development of Ka band (33.4-36 GHz) radar, but since the first Stalker Ka units hit the market, all radar gun makers have started offering Ka band models. Ka band offers distinct advantages compared to X (10.525 GHz) and K band (24.150 GHz).

The first major advantage of Ka is smaller beam divergence. A typical Ka beam diverges to 79 feet at 500 feet, compared to X band, 157 feet and K band, 104. This means there are fewer target vehicles in the beam and the reading is more precise.

Ka band also allows changing of frequencies within the band. For example, the MPH Bee III transmits at 33.8 GHz, Kustom Signal's Golden Eagle, at 35.5 GHz, Stalker DSR at 34.7 GHz, Decatur Genesis II at 35.5 GHz, and Lockheed Martin's photo system at 34.6 GHz. The difference in frequencies between these commonly used devices is bad news for the owners of radar detectors, because older radar detectors can't sweep the entire Ka band.

Another detector defeating feature for Ka band radar, POP mode, is available from MPH Industries on the Bee III moving radar. POP mode transmits for less than one-tenth of a second, and this extremely short transmission is outside of the sweep rate of radar detectors. However, it's important to note that POP mode can only be used from a stationary position and it can't be locked.

Speed Measurement Laboratories Inc. tested the POP mode against all new and many older radar detectors last October. Not one detector saw the MPH Bee III POP mode. However, MPH cautions in its manual, "Citations should not be issued based solely on information derived from the POP burst since there is no tracking history developed. If the speed is a violation, the radar must be allowed to enter the continuous transmit mode so that the tracking history may be developed."

Fast Vehicle Mode

Older, analog radar guns always display the strongest reflected signal. This creates great frustration when you are locked on to an approaching 18-wheeler in a group of oncoming vehicles that includes a speed demon sports car. You see the Mustang going 80 mph, but the radar gun shows 53 mph because it's reading the 18-wheeler.

One solution to this problem is Fast Vehicle Mode (FVM), a technology first introduced by Kustom Signals. Digital radar guns that feature FVM display the fastest vehicle in a group of approaching vehicles, not just the most reflective target.

Digital guns with FVM have three display windows with the "Fast" target vehicle speed appearing in the middle window.  In the stationary, directional mode, these radar guns also look for and display fastest target vehicle speeds in the middle window.

Direction Sensing Radar

When operated in stationary mode, older radar guns are bi-directional in  speed reporting, showing the speeds of vehicles approaching and those going away. Bi-directional reporting is the bane of a traffic officer's existence and many convictions are lost because testifying officers cannot confirm the identity of the target vehicle.

Applied Concepts introduced the first direction sensing radar (MPH Industries calls it Automatic Same Direction) in 1998 to solve this problem. Operated in the stationary position, Applied Concepts' DSR-equipped radar guns (and guns with similar systems from other manufacturers) show speeds in only one direction, selected by the officer, thereby eliminating target vehicle confusion. This is digitally accomplished by the radar's ability to measure "compressed/upshifted"  reflected signals, i..e. higher Doppler shift frequencies of vehicles approaching and "stretched/downshifted" lower Doppler shift frequencies of vehicles receding.

CONTINUED: Speed Guns «   Page 1 of 2   »

Tags: Radar, Catching Speeders, LIDAR, Radar and Laser Enforcement

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