Correlator

(correlation-type receiver), an instrument used to measure the correlation functions of random processes. A knowledge of the correlation coefficient permits an analysis to be made of physical phenomena having probabilistic characteristics, such as the noise in radio receiving apparatus, cosmic particle showers, and biopotentials (see). When two random signals in the form of AC electrical voltages U₁(t) and U₂(t) are supplied to the inputs of a correlator, its output voltage is proportional to the cross-correlation function of these signals. If a signal U_c(t) is supplied to both inputs, the correlator measures the autocorrelation coefficient.

Electronic correlators are the most widely used. The indicator is usually a pointer-type instrument calibrated in terms of the correlation coefficient, or a cathode-ray tube. Provision is usually made for the connection to a digital or a chart recording system. Correlators are employed in radio-communication devices (to measure the transient attenuations in multi-channel systems); in radar, sonar, and radio astronomical equipment (for correlation direction finding and to improve the resolution of transmission); and in medical diagnostic equipment. The signals studied in a cross-correlation have frequencies ranging from 1 Hz to 50 MHz. Special signal-processing methods are used to raise the signal frequency factor to 500 MHz. The measuring gauge for the correlation coefficient ranges from 0.01 to 1, and the error of the correlator is between 5 and 10 percent.