Continuous Wave (CW) radars may use Linear Frequency Modulation (LFM) waveforms so that both range and Doppler information can be measured. In practical CW radars, the LFM waveform cannot be continually changed in one direction, and thus periodicity in the modulation is normally utilized. CW radars do not have to use LFM waveforms in order to obtain good range measurements. Multiple frequency schemes allow CW radars to compute very adequate range measurements, without using frequency modulation. Radar systems employ low, medium, and high Pulse Repetition Frequency (PRF) schemes. Low PRF waveforms can provide accurate, long, unambiguous range measurements, but exert severe Doppler ambiguities. Pulsed radars transmit and receive a train of amplitude modulated pulses. Range is extracted from the two-way time delay between a transmitted and received pulse. Pulse Doppler radars utilize high PRFs to increase the average transmitted power and rely on the target's Doppler frequency for detection.