GB555212A - Improvements in modulated carrier-wave communication systems - Google Patents

Abstract

555,212. Wireless signalling ; television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 9, 1942, No. 1708. Convention date, Feb. 7, 1941. [Classes 40 (iii) and 40 (v)J To avoid distortion in television and picture transmission due to the reception of indirect or reflected waves, the carrier frequency is charged periodically by synchronizing signals at the end of each line, or each frame or at the end of a determined number of lines or frames ; the frequency change being of such amount that the signals over the direct or desired path combine in their effect, while those over the indirect or undesired path do not so combine. With interlaced scanning, an odd number of lines is used, and the frequency change is made at the end of each line, so that the same line on successive frames is sent at different frequencies. When only one indirect or reflected path is in question, the two adjacent frequencies are so selected that the difference in length between the direct and indirect paths represents one half the mean wave-length, or an odd multiple thereof. Four carrier frequencies may be used in turn in such an order that changes from one frequency to the next adjacent frequency are avoided as far as possible. As shown, television signals applied at 1, 3 are amplified at 5 and modulate the radio transmitter 7. The synchronizing signals are separated at 9 and applied to a tripping-device I giving a rectangular output wave which changes the carrier frequency periodically. The rectangular wave may be derived from an oscillator which synchronizes the saw-tooth scanning wave. Specifications 402,629 and 474,682 ; and U.S.A. Specification 2,000,685 are referred to.