GB562915A - Improvements in or relating to radio transmission systems - Google Patents

Abstract

562,915. Multiplex wireless signalling. BEATTY, W. A. Oct. 16, 1942, No. 14540. [Class 40 (v)] In a multiplex system using polarisation methods for separating the respective channels, residual interference between the channels is eliminated or reduced by adding on any particular channel a fraction of the signals on the other channels, such addition being in anti-phase and effected at the transmitting station or at the receiving station. The channels may be distinguished by the direction of polarization of the transmitted waves, a number of dipoles being set up in the same vertical plane but at different inclinations ; and anti-phase signals corresponding to the signals on channels B, C, &c, may be superposed on channel A in addition to the true signal to be transmitted on that channel. If these antiphase signals are of correct amplitude, the signal received on channel A is free of interference from channels B, C, &c. In a modified arrangement, only the true signals are transmitted on their respective channels, and the signals received on the respective channels are mixed in such proportions that a true signal without interference is derived for each channel. The Specification gives details as to the proportion in which the signals received on the respective channels are mixed with each other. When the signals are conveyed in the form of time-modulated pulses, the mixing may be performed at the pulse stages of the transmitter or receiver. The system may be used for simultaneous transmission of sound and vision signals on the same frequency spectrum, the vision signals being sent in the normal manner as amplitude modulation with interposed synchronizing signals, and the sound signals as time-modulated pulses. Horizontal and vertical polarization are used for the respective transmissions, and anti-phase sound signals are introduced into the vision transmission. Preferably, the pulse frequency is equal to, or a multiple of, the line synchronizing frequency, and the fixed edges of the time-modulated pulses coincide with the line signals.