A method for accurate receiver tuning and precise measurement of the carrier frequency of voice-modulated, suppressed-carrier, single-sideband radio signals

Abstract

A well known problem associated with suppressed-carrier single sideband (SSP) communications is the difficulty of accurately tuning a receiver to the suppressed-carrier frequency of the transmitter is this frequency is not known a priori at the receiver. Although it is possible to tune a receiver to within 20 to 30 Hz of the correct frequency by tuning for the most natural voice timbre (in the case of radiotelephone voice transmissions), this is an unacceptably subjective and inexact method to use in signal and frequency monitoring applications. This report describes an aural-visual method of tuning a SSB receive to within 3 Hz of the suppressed-carrier frequency of a SSB voice signal containing no discernible carrier. This tuning method supplements the familiar aural technique (tuning for most natural voice quality) with a visual oscilloscope display which facilitates an order of magnitude improvement in the accuracy of frequency measurement compared with aural tuning alone. A theoretical analysis is presented which shows that SSB speech signals contain information sufficient to determine the suppressed-carrier frequency. Also described are experiments which were conducted to indicate the effectiveness of this tuning method in determining the carrier frequency of SSB signals when the SSB message is human speech. It is suggested that this technique may find application in the domestic and international monitoring services.