GB606145A - Improvements in or relating to television systems - Google Patents

Abstract

606,145. Transmission systems. RUDKIN, E. P. Nov. 21, 1945, No. 31425. [Class 40 (iv)] [Also in Group XL (b)] In order to avoid the use of an ultra-high frequency carrier in a television system employing video signals covering a wide frequency band, e.g. up to 20 mc/s. the video signal band is split up into a plurality of sub-bands which are used to modulate separate adjacent carriers, each carrier being amplitude-modulated by one sub-band and frequency or phase-modulated by another. The video signals are developed in the iconoscope 1 to which line and frame frequency signals are applied from the generators 8 and 9 which are synchronized by the master oscillator 10. The output from the oscillator 10 is suitably frequency-changed at 11 and used to synchronize the oscillators 02, 03 ... O10. The video signals which in the example described cover a band of 0-20 mc/s. are separated into bands 0.2 mc/s., 2.4 mc/s., ... , 18-20 mc/s. by the filters F1, F2 ... F10 respectively. The outputs from the filters F2 ... F10 are heterodyned in units C2 ... C10 with the outputs of the oscillators 02 ... O10 which are such that the output of each of these units lies in the band 0-2 mc/s. as does the output from F1. Carrier frequency sources R1 ... R5 are provided, operating on adjacent frequencies and are frequency-modulated by the output signals from F1, C3, C5, C7, C9 respectively and amplitude-modulated by the signals from C2, C4, C6, C8, C10 respectively. The outputs obtained from the modulators M1 ... M10 are fed to the transmitting aerial system. At the receiver, the ten channels are separated out by conventional means and the video-frequency sub-bands in the range 0-2 mc/s are heterodyned back to their original frequency bands by means of oscillators synchronized from the received line and frame synchronizing signals. The heterodyning oscillations may alternatively be transmitted to the receiver upon a separate carrier ; if they are harmonically related a single synchronising modulation is sufficient.