Television transmission system

Abstract

In television transmitter equipment for a television transmission system having a time multiplexed signal in component form, the vision components are derived from a vision source (1), encoded in a MAC encoder (2) and the encoded vision signals are modulated in a frequency modulator (3) which also receives oscillations from an oscillator (4). The modulated output of the frequency modulator (3) is applied through a multiplexer (5) to a transmitter (6) whose modulated carrier is applied to a dish aerial (7) for transmission to a satellite. The equipment contains a number of sources (8 to 15) of sound/data information which are separated into two groups, an `A` group of sources (8 to 11) and a `B` group of sources (12 to 15). Digital signals from the `A` group sources are applied to an `A` packet multiplexer (17) where the signals are assembled packet-by-packet into a given time area at a bit rate of 10.125 MHz. Corresponding signals from the `B` group sources are applied to a `B` packet multiplexer (18) where these signals are similarly assembled into a corresponding time area at the same bit rate. The outputs of the `A` and `B` packet multiplexers (17, 18) are applied to respective inputs of a further multiplexer (19) to produce within the time area bits derived from the two packet multiplexers. This data, the appropriate line sync words from a sync word generator (21) and data from a source (23) for lines 624 and 625 of each frame are assembled in a data assembler (20) to produce the data burst containing the sound/data components for the time multiplexed signal. This is modulated in a 2-4 PSK modulator (22) and the modulated output applied to a further input of the multiplexer (5). The data burst of the signal produced may be readily separated into its two groups to produce a data burst at the lower bit rate from one group for the transmission of a time multiplexed television signal over a medium of narrow bandwidth such as a cable channel.