GB1150301A - Improvements in or relating to Radio Transmission Systems. - Google Patents

Abstract

1,150,301. Radio signalling. E. BORRESEN. 30 June, 1966 [3 July, 1965], No. 29346/66. Heading H4L. In a radio transmission system at least one information or calling signal and one auxiliary frequency are transmitted and at the receiver the auxiliary frequency is used for detecting the information or calling signal. In a receiver, Fig. 1, for a selective calling system, a signal consisting of an auxiliary frequency a and a band K comprising four calling frequencies is frequency-changed via circuits 1 to 7 and the auxiliary frequency and calling frequencies are selected by filters 10, 8, respectively. The outputs of filters 10, 8 are amplified and supplied to a demodulator 12, the resulting difference frequencies being selected by respective filters 13, rectified and supplied to a decoding unit 15, which applies an audible or visible signal when a correct code combination is received. A transmitter for generating the required signals by frequency-changing is described, Fig. 2 (not shown). In further arrangements in which a central station cooperates with a plurality of substations single sideband speech modulated signals are transmitted, and at a substation the received auxiliary frequency is used to demodulate the signals and also to produce the substation transmitting carrier frequency. The auxiliary frequency is not transmitted by the substations but is combined with the received signals at the central station.