Patent GB-516993-A (GB)
Title: Improvements in or relating to broadcast diffusion systems
IPC: H04H20/81
Filed: 1938-07-15
Abstract: 516,993. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. July 15, 1938, No. 21095. [Class 40 (iv)] In a system in which a telephone subscriber can select a desired programme by means associated with his line circuit, this means is controlled by temporarily employed apparatus which is reached over the ordinary switch train, e.g., a particular level of the first or second selectors, and responds to dialled impulses. In the system described there are four programmes and the programme selecting switch takes a number of steps complementary to the digit dialled with respect to 6. The programme circuit is of low impedance to prevent interference between the lines using it. When the line is looped through the transmitter the programme circuit is disconnected and subscribers are thus unable to interfere deliberately with their ordinary instruments. Selecting and setting control apparatus. The call is extended by an ordinary line-switch S and by one or more group selectors (not shown) to the circuit shown in Fig. 2, in which line and release relays A, B pull up and also the first relay CA of a series of counting relays CA.. CG. The first impulse received energizes C which remains up throughout the digit and at the end of the impulse CB pulls up, locks and arranges for the release of CA by the second iinpulse, if any. Similarly CC pulls up at the end of this impulse and CB falls at the beginning of the third. CD pulls up at the end of this impulse and CO falls, re-energizing CA at thebeginning of the fourth. At the end of this impulse, CB is re-operated. Four is the maximum number that should be dialled, but if a fifth is received CA is released at the beginning of such impulse, CB, CD remaining locked up and causing CG to pull up and lock at the end. Any impulses received subsequently are without effect. Controlling programme switch. At the end of the digit the relapse of C, if an obtainable number has been dialled, energizes CE which sends back ringing tone to warn the subscriber to switch on his amplifier. This breaks the loop and relays A,B fall back, the other relays being held by CE. The relapse of C also acts on the counting relays like the beginning of a new impulse, releasing CA in the case of digit 1, CB in the case of digit 2, and so on. On the relapse of B, SS connects the impulse relay A to flicker earth on wire. 11. Relay A on its first response re-operates B and on falling again re-operates C. - Its next operation energizes CF, which locks, connects booster battery to the private wire, and causes the next relapse of A to release CE to terminate the booster impulse. Relay BK in the line circuit responds to the impulse, connects the stepping magnet of the programme switch to flicker earth synchronous with that controlling the impulse relay and holds after thetermination of the impulse over off-normal springs N3. The next operation of A completes the impulse to the counting relays which was begun by the relapse of C. Thus as the switch takes its second step, the counting relays receive the first impulse additional to those dialled. When the chain has received a total of 5 impulses, CG pulls up and shunts out B. SS in the control circuit and K, BK in the line circuit are thus released and the programme switch is stopped. The control circuit is thus'restored to common use and the subscriber is connected to the desired programme circuit, all individual and common relays being de-energized. Unobtainable numbers. If the subscriber energizes CG prematurely by dialling 5 or more, the relapse of C at the end of the digit connects up N.U. tone. Telephone calls during programme reception. Switching off-the amplifier produces no effect at the exchange, but when the line is looped by the removal of the telephone instrument to answer or originate a call, relay BR pulls up and homes the programme switch and the circuit then behaves like an ordinary one. Modifications suggested but not described in detail. In systems using booster metering an alternating current signal may be used for starting the programme switch. The programme switch may be such as to require two digits to set it, corresponding modification being made in the control circuit. Applications of rectifier. Rectifier MRA polarizes the right-hand winding of BK. Rectifier MRB prevents a ground connection which is provided to keep the circuit guarded while the armatures of CE are between their contacts from short-circuiting the booster battery.