GB562794A - Apparatus for reducing echo effects in picture transmission systems - Google Patents

Abstract

562,794. Television. PHILCO RADIO & TELEVISION CORPORATION. Jan. 12, 1943, No. 558. Convention date, March 19, 1942. [Classes 40 (iii) and 40 (v)] In a radio television system of the kind employing different carrier frequencies for the vision and the synchronizing signals, distortion of the received picture due to delayed reception of the synchronizing signals over a path involving reflection is substantially eliminated by proper choice of the difference between the two carrier frequencies. The echo signals give rise to alternate dark and light patches in each line of the picture as indicated in Fig. 3, and these may be caused to cancel each other out by choosing the carrier difference an odd multiple of half the line or frame frequency. In Fig. 4, the carrier generator 19 for the vision signal, and the carrier generator 20 for the synchronizing signals are alternately switched to the amplifier 22 by valves V1, V2 oppositely triggered by the synchronizing signals from the source 26. The carriers may be multiplied in frequency at 22 and are then 'amplitudemodulated by both vision and synchronizing signals supplied from 26, the modulated carriers passing to the aerial A through an amplifier 24 and side-band filter 25. The line synchronizing signal is fed from its source 26 to a frequency halver or divider 33, and thence to a multiplier 34 raising the frequency to an odd multiple, which is fed to the generator 20 to create therein a carrier frequency differing from the vision carrier frequency by an odd multiple of half the line frequency. Specification 562,707 is referred to.