ABSTRACT
The first intercity links for television signals were coaxial cables, which were installed by the GPO (General Post Office) from London to Birmingham, then on to Manchester, and from London to Cardiff, between 1950 and 1952. A special 1-inch diameter coaxial cable was used for the London to Birmingham circuit, whereas standard 3/8-inch telephony coaxial cables were used for the other two circuits. Repeaters were installed every 12 miles for the 1-inch coaxial cable, and every 4 miles for the 3/8-inch coaxial cables, to equalise and amplify the signals. In the case of the 1-inch coaxial cable, the 405-line video signal was amplitude modulated on a 6.12 MHz carrier. This occupied a bandwidth of 3–7 MHz, using a partially suppressed upper sideband. The 3/8-inch coaxial cables utilised amplitude modulation of a 1MHz carrier, which occupied a bandwidth of 500 kHz–4.5 MHz, using a partially suppressed lower sideband.
