GB949055A - Improved subscription television system - Google Patents

Abstract

949,055. Television audience survey systems. RANK ORGANISATION Ltd. Aug. 25, 1961 [Aug. 25, 1960], No. 29352/60. Heading G4H. A central station A transmits interrogating signals over line 1 which also relays broadcast programmes to receiver B. The interrogating signals comprise a sequence of different frequencies modulated on a carrier which lies outside the frequency band occupied by the programme signals. Each receiver B is responsive to a selected interrogating signal, filters 8-11 setting triggers 12-15 in sequence when the appropriate interrogating sequence is received, and a pulse is transmitted back to the central station A from oscillator 16. The receivers may be scanned in order by transmitting all the possible interrogating signals one after the other. Each interrogating signal may be individual to a particular receiver or a group of receivers may respond to each interrogating signal, in which case a different characteristic delay period is associated with the different receivers in a group so that each interrogating signal gives rise to a train of response pulses, a missing response pulse indicating that the associated receiver is inoperative (switch 5 open). A survey of the different programmes being received may be obtained by using a different set of interrogating signals for each programme, or the frequency of oscillator 16 may be varied by a programme selecting switch so that the time at which a response pulse is received identifies the receiver as before, but in addition the frequency of the response pulse indicates the programme being received.