GB1448871A - Systems for distributing television programmes by cable - Google Patents

Abstract

1448871 Television distribution systems BRITISH RELAY Ltd 11 July 1974 [13 April 1973] 18038/73 Heading H4R Multiprogramme TV signals are distributed over a single cable pair or coaxial cable as suppressed carrier luminance and, if colour, suppressed carrier chrominance modulations accompanied by a pilot, the suppressed carrier frequencies being different multiples of the pilot frequency or offset from such multiples by multiples or submultiples of the frame and/or line frequency. The lowest band programme may be transmitted in known manner as the upper sideband of a 4À43 MHz carrier and two upper band programmes on carriers of 14À35 and 24À60 MHz which are 7th and 14th harmonics of a 2À05 MHz pilot. Another cable pair may use a synchronized 4À43 MHz carrier for the lower band or the 5th harmonic of the same 2À05 MHz pilot; upper band carriers being 10th and 15th harmonics. The pilots in different pairs may be offset and need not accompany the corresponding modulation carriers. This requires a phase locked loop at the receiver which could serve to synchronize the transmitter and receiver if the pilot phase or frequency is periodically altered or switched between pairs for scrambling purposes in a subscription system. The suppressed carriers are regulated at the receivers from the pilot and if necessary the frame and line information in the programmes.