GB1478960A - Method and apparatus for effecting digital signalling over television signal channels - Google Patents

Abstract

1478960 Data transmission; PSK systems; television COMMUNICATIONS PATENTS Ltd 26 July 1974 [17 Aug 1973] 38926/73 Headings H4P and H4F A method of digital signalling over a television channel comprises phase shift keying the television carrier wave at line scanning frequency rate and determining at a receiver the phase of the carrier wave during each line relative to a datum and extracting a corresponding digital signal. In the embodiment described the keyed carrier is either in phase or anti-phase with an arbitrary datum in accordance with information to be signalled. Preferably the presence of line synchronizing signals are determined in order that phase shift may be imparted at a determined time relative to each scanning line. A high frequency modulated carrier wave television signal in a wired broadcasting system is sent to line through a PSK arrangement 1. Television signals also pass through a demodulator 4 and sync. pulse separator 5 and applied to a timing device 6 controlling a gate 8 which monitors the passage of digital information applied to terminals 9. By gating data signals, phase shifts are arranged to occur when they are least likely to produce any visible or other disturbing effects on television receivers. A preferred time is to effect shifting either during the back porch or line sync. pulses. At the receiver (Fig. 2 not shown) the transmitted signal is amplified at 11 and passes to parallel circuits, a demodulator (12) from which video synchronizing and display circuits are derived to a receiver 13, and also to a phase locked loop (14) which also in known manner, is arranged to detect phase shifts which control data utilizing circuits (15). By utilizing each line it is stated that data may be signalled at a higher speed than former systems. For example, with 625 or 525 line standards, data may be transmitted at a rate of over 15kb/s.