GB516630A - Improvements relating to carrier wave transmission systems - Google Patents

Abstract

516,630. Multiplex wireless signalling ; television. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. July 1, 1938, No. 19573. [Classes 40 (iii) and 40 (v)] Stereoscopic or two-colour television 'signals are transmitted by modulating the two signals on separate carriers of the same frequency dephased by 90‹. Carrier oscillations generated by valve V1 are transmitted to modulating valve V2, where one signal is impressed upon them from transformer T1. Modulated carrier is passed to the output tuned circuit TC3. Carrier is also modulated with the second signal from transformer T2 in the carrier suppression modulator V3, V4, the sidebands only passing to the output circuit TC3. The tuned circuits TC2, TC4, which are coupled to the oscillator circuit TC1, are de-tuned above and below resonance to produce the 90‹ dephasing between the carriers supplied to the two modulators. In Fig. 2 (not shown) both modulators are of the carrier suppression type, and an adjustable amount of carrier of one phase is fed to the output circuit via a separate amplifying valve. At the receiver the signals are obtained by demodulation with a carrier of correct phase. After amplification and frequency-changing of the sidebands and carrier in the receiver, Fig. 3 (not shown), the carrier is separated by a " crystal gate," and after further amplification is split into two 90‹ dephased components for application to two separate heterodyne demodulators. The demodulating carrier at the receiver may be obtained from a local oscillator, and automatic frequency-control may be applied to the receiver. Specification 457,485 is referred to.