A rotating antenna transmits RF pulses at defined intervals. The greater the echo delay from a particular object in space, the farther from the display center its point appears. The maximum range of a UHF or microwave radar system depends on the height of the antenna above average terrain, the topography of the surface in the region, the atmospheric conditions in the region, and in some cases the level of radio background noise. Radar is known to the general public for its use by law enforcement in determining the speeds of motor vehicles. This type of radar does not display the exact position of an object, but determines its radial speed vector from the Doppler effect .
Radar detectors are illegal in some states.
The Weather Service uses so-called Doppler radar to determine not only the positions and extent of storm systems, but wind patterns and velocities aloft. The ionosphere refracts HF waves, allowing much greater system range than is possible with radar at UHF or microwave frequencies. During the 1970s and early 1980s, the signals from these systems became infamous because of the interference they caused.