GB529320A - Television broadcast system - Google Patents

Abstract

529,320. Television. HAZELTINE CORPORATION. May 26, 1939, No. 15761. Convention date, June 9, 1938. [Class 40 (iii)] Picture signals are transmitted by amplitude modulation and synchronizing pulses by frequency modulation of the same carrier, or vice versa. In the transmitter, Fig. 1, the picture signals from a cathode-ray apparatus 10 pass through the devices 16, 17, 19, 20, 21 22 to the aerial system 23, 24, the device 19 serving to suppress one side band, and the carrier wave being produced by a master oscillator 18. Saw-tooth and flat-top synchronizing pulses are produced by devices 12, 13 ; harmonics are generated by devices 25, 26 ; and these are mixed by devices 27, 28 and serve to trigger a frequency modulating device 29, which controls a frequency changer 20 in the aerial supply system or may be made to control the master oscillator 18 directly. A timing impulse generator 15 controls the synchronizing pulse generators 12, 13, 25 26 and also a pedestal impulse generator 14 connected to the amplifier 16 for the picture-signals. In the receiver, Fig. 2, the signals received by the aerial system 50, 51 are transmitted by the devices 52, 53, 54, 55 to the cathode-ray picture reproducer 56. The signals are also by-passed through devices 60, 61 to a vacuum-tube limiter 62 where the picture signals are eliminated, then through a broadly-tuned selector circuit 63 and an amplifier 64 to a modulation converter 65, this arrangement preventing back coupling. The converter 65 is so tuned as to convert the frequency modulation into amplitude variations and these are passed through a rectifier 66 to filters 67, 68 tuned respectively in correspondence with the devices 25, 26 of the transmitter and serving to control the scanning generators 57, 58. In a modification, the frequencies to which the carrier is shifted during line-scanning and field-scanning pulses are made different, the devices from D to B, C in the receiver are then replaced by two sharply-tuned selectors 81, 82, Fig. 2b, followed by rectifiers 83, 84. In another modification the harmonic generators 25, 26 may be omitted from the transmitter, in which case the devices from A to B, C in the receiver are replaced by a duration response separator, Fig. 2a.