SHORTCOMINGS OF RADAR SPEED MEASUREMENT

The operation of radar speed-measuring devices is explained; it is based on the Doppler principle, which relates the frequency shifts in reflected radiation to the relative velocity between the reflecting object and observer. These devices (either stationary or moving mode) should be used only in moderately heavy or light traffic. More obvious sources of error in the stationary mode (e.g. patrol car fan, citizen's band transmissions) are identified, as well as more subtle sources ("cosine effect," radar oscillator frequency outside Federal Communication Commission specifications, and equipment "convenience" options). Sources of error in the moving mode are described, including the possibilities for erroneous target speed readings in the presence of multiple moving targets. Improved calibration test procedures and electronic speedometers to measure patrol car speeds are cited as the most important ways to improve existing equipment. Other possibilities include display improvements, range controls, beam-width optimization, and frequency standardization. Efforts to develop radar equipment performance standards are described. Separate notes describe the four classes of electronic speed-measuring devices used in traffic law enforcement (electronic speedometer, Vascar, Orbis, and radar) and explain the moving mode cosine effect.