Importance

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Abstract

In a communications-receiving system for demodulating phase-coded signals and displaying the resultant information on a cathode-ray tube (CRT), an information code is modulated on a carrier by shifting the phase of the carrier by an integral multiple of predetermined phase step. At the receiver a locally generated reference signal is compared with received pulses to ascertain their phase offsets. The resulting demodulated information is presented in a CRT display that indicates not only the received information but also, by the slope of bright dots, the frequency difference between the local reference and the signal, so that frequency drift can be corrected. The CRT's horizontal sweep represents time and the vertical sweep represents phase angle. The start of each vertical sweep is synchronized with zero-crossings of the locally generated reference signal. The intensity of the CRT beam is controlled by the message. The vertical position of bright message spots therefore indicates the phase difference between the received signal carrier and the locally generated reference signal at the instant of a zero-crossing.

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First Claim