Patent GB-914328-A (GB)
Title: Attachment for television receivers to be employed in subscription television systems
IPC: H04N7/16
Filed: 1959-01-01
Abstract: 914,328. Radio-receiving apparatus; radio signalling. BRITISH TELEMETER HOME VIEWING Ltd. Jan. 1, 1959 [Jan. 20, 1958], No. 46/59. Class 40 (5). [Also in Groups XXXIX and XL (b)] Relates to an attachment for a television receiver for use in a subscription system for connection between the source of programme signals and the input terminals of the receiver, which functions to convert the frequency of a selected subscription transmission to a frequency to which the receiver can respond (e.g. a spare one of the normal channel frequencies), the conversion being effected only after a coin demand, which is established by control signals in an associated channel, has been met. Provision is made to receive " banker " signals and to make a recording of coded signals identifying a programme subscribed to. The invention is described for use in a system having three subscription channels, each consisting of an audio carrier, a video carrier and a control signal carrier. In addition, a single " banker " carrier carries audio announcements concerning the subscription channels. The subscription carriers are all located in a band below that of the normal free television channels. Signals for the receiver are received over a coaxial cable network and are applied first to a network 100, Fig. 4B, which separates the free channels from the subscription channels. The free channels are applied directly to the receiver antenna input terminals via a change-over switch 101A, whilst the subscription channels are applied to a converter circuit 104, 109, 110 in which the audio and video carriers of a desired one of the three channels are selected and converted to a frequency band to which the receiver responds. The output of the converter is applied to the other side of change-over switch 101A. Switch 101A is operated by a solenoid 101, which functions as a smoothing choke in the power supply for the attachment, and is normally held in the subscription channel position. 'The H.T. supply to the local oscillator and mixer stage 109, 110 of the converter circuit is controlled by a switch PW4 which is closed only after a coin demand (see below) is satisfied. Selection of the desired channel is effected by a multiway switch 108 which also adjusts a control circuit to select the corresponding control signal carrier. In the control circuit, Fig. 4A, the three control signal carriers and the " banker " carrier, which are grouped in a band separate from the video and audio carriers, are selected by band-pass amplifier 106 and applied to a combined mixer and local oscillator stage 132. The resulting signals at reduced frequencies are then applied to two detectors. The first 134, 139 responds to the " banker " carrier and produces an output for an audio stage 142, whilst the second 138, 140 which is adjusted to the appropriate frequency by switch 108, selects the correct signal carrier. The control signal, Fig. 3, consist of a sequence of pulses repeated at 6 second intervals and made up of a ¢ second start pulse 60, a number of 1/20 second pulses 62 in accordance with the price to be paid to receive the programme, an end-of-price interval of at least ¢ second duration, and a sequence of coded pulses 0, 1, 0 &c. identifying the programme. A first output from detector 140 is applied through an integrating circuit 143 and causes a valve 142 to be cut-off whilst a control signal is being received. A second output is applied through an integrating circuit 154, 156 and causes a valve 150 to conduct only in response to a start signal. Contacts PW1 and PW2 are controlled by a coin-box mechanism (not illustrated in detail) which in its initial blank or no-price position are closed. Conduction is valve 150 operates relay 160 which at contact 160A pulses a pricing solenoid 162 and moves the coin-box mechanism from its initial position to open contacts PW1 and PW2. PW1 removes the integrating capacitors 154 and thereafter valve 150 conducts in response to each price pulse to actuate relay 160 and pulse the pricing solenoid correspondingly to create a coin demand. During this operation, the H.T. supply for valve 150 is derived from the charge in a capacitor 164 which is received at each pulse via contact 160B. The charge is dissipated during the end-of-price interval so that thereafter valve 150 cannot respond to the coded pulses. The price set in the coinbox is displayed. When the demand is met, the mechanism moves to a first paid position where contacts PW3 and PW4 are closed. The latter completes the H.T. circuit for the converter circuit as described above, and permits the programme to be received, whilst the former completes a circuit for the drive motor 172 of a magnetic tape recorder. A cam 174 on the recorder closes contact 176 which completes an anode circuit for valve 150. The valve then responds to the coded pulses and effects recording by a head 178. At the completion of recording the cam closes a contact 180 to actuate pricing solenoid 162. This moves the coin-box mechanism to a second paid position where contact PW3 opens to stop the recorder motor but contact PW4 remains closed. The apparatus remains in this position during reception of the programme. At the completion of the programme, the control signals cease. Valve 142 thereupon conducts and operates relay 144. Contacts 144A short-circuit solenoid 101 to place switch 101 in the free channel position, contacts 144B reset the coin-box mechanism to its initial position.