Abonnements-Fernsehanlage

摘要

784,108. Television. ZENITH RADIO CORPORATION. Sept. 29, 1955 [Oct. 21, 1954; Dec. 31, 1954], No. 27727/55. Class 40 (3). In subscription television systems in which a coding signal, which operates means to code the video signal at the transmitter and uncode it at the receiver, is transmitted in scrambled form and unscrambled at the receiver, a further signal is derived from the coding apparatus, in both the transmitter and receiver, and applied to effect further modification of the coding. As shown in Fig. 1, a signal from camera 10 is coded in unit 12 by signals from a multivibrator unit 57, 58, 59. The latter is driven by impulses from the synchronizing signal generator 19, which are stepped down in a blocking oscillator 30. Code signal bursts, produced by a generator 29, follow various paths chosen by a multiple switch arrangement 27 to control unit 57, 58, 59. The bursts are also connected through a different pattern of paths to a second multivibrator 571, 581, 591, which operates a gating circuit 46 in a further path from switch bank 27. The further signal mentioned above is thus produced and led to oscillator 30 rendering it ineffective at certain of its normal operating conditions and thus superimposing a further pattern of operation on the coder 12. The receiver shown in Fig. 6 includes a decoding unit 140. The code signal bursts pass along conductor 191 to a gating circuit 159 operated by a unit 160 driven by the field sweep components. Unit 160 also transmits blanking signals via unit 161 to the cathode-ray tube. 141 to ensure complete blanking of the code signal bursts. The unit 159 is connected by a line C to switches 27 and multivibrators 57, 58, 59 and 571, 581, 591 similar to those in the transmitter and these are conected to the decoder 140. In modifications the gating circuit 46 may be operated from the output of multivibrator 57, 58, 59, or from the coder 12 itself, multivibrator 57, 581, 591 being then omitted. In a further modification the gating circuit 46 is altered to a selector and either diverts a control pulse to the blocking oscillator 30 or turns it into the multivibrator 57, 58, 59.