Patent GB-258691-A (GB)
Title: Wired broadcasting system
IPC: H04H20/76
Filed: 1925-07-02
Abstract: 258,691. Western Electric Co., Ltd., (Western Electric Co., Inc). July 2, 1925. Systems for transmitting music, theatrical performances, and news.-Subscribers connected to a central station, such as a telephone exchange. are able to control apparatus at the central station for selecting different programmes. The distribution from the central station may be in high or low frequency form and may be over telephone lines or special lines. Four systems are described. First system, Fig. 1 (Low-frequency transmission over special line). The line L is normally connected to the programme trunk Ta. By moving a switch S the subscriber can connect ground, direct or through a resistance, over a simplex circuit to relays 3, 4. Relay 4 is marginal, so that either the relay 3 alone or both relays can be energized, and thereby energize relay 2 or 1 to connect the programme trunk Tb or Tc. Whenever a programme trunk is not connected to the line L it is bridged by an equivalent resistance Ra, Rb, or Rc. Second system, Fig. 2 (High-frequency transmission over telephone line). The line L is normally connected over a high-frequency path 11 to the programme trunk Ta. By momentarily pressing a key C or B the b side of the line is grounded directly or through resistances 60, 61 and a differential relay DR is energized alone or together with a marginal relay MR, whereby a circuit is closed through the upper windings of relays 1, 2 alone or in series with a high-resistance relay 62. Relay 1 is marginal, so that both the relays 1, 2 or only the relay 2 is energized and the line L is connected to the program trunk Tc or Tb. The relays 1, 2, which are slow to release, lock over their lower windings when the subscriber lets up the key. The relay 62 can be energized to unlock the relays 1. 2 and thereby restore connection with the trunk Ta by momentarily pressing key A, which bridges resistance 61 across the line to energize relay LR but not DR or MR. The resistance of relay 62 prevents the call lamp 35 from glowing, whereas in the case of a telephone call from the subscriber the relay MR is energized along with LR and short-circuits 62. A telephone call can be set up without interrupting the broadcast service. The subscriber's high-frequency receiving set comprises a detector DD, amplifiers AD, AA and a loud-speaker LS. The valve AA is supplied from alternating current mains 43 through a rectifier RR and includes in its plate circuit a relay 50 controlling the filament circuits of the valves DD, AD. Third system, Fig 3. (Low-frequency transmission over telephone line). In this system the subscriber operates a step-by-step switch DS by means of a dial impulse-transmitter 24 to connect any of the program trunks A - - H to his line L through a transformer 20 and back contacts of his cut-off relay CO. When the dial is operated, an offnormal contact 29 energizes relays 23, SR over the b side of the line. Relay SR energizes a slow-to-release relay 27, which energizes a slow-topull-up relay 28, ,and a circuit is momentarily closed for magnet RM to restore the switch DS from its previous position to normal. Interruptions at the contact 32 then control relay SR and magnet SM to step the switch DS to the wanted program, and finally the opening of the off-normal contact 29 results in the de-energization of relays SR, 27, 28. Meanwhile relay 23, which connects up the loud speaker LS, has locked itself over its right-hand winding, the resistance of which is too high for the, relays LR, SR to be energized. To discontinue the program, the subscriber unlocks relay 23 by opening a contact 31. A telephone call from the exchange unlocks relay 23 by energizing a. sleeve relay 30, which energizes relay CO to disconnect the line L from the transformer 20 and to connect it to the jack multiples, but when the conversation is finished the subscriber can re-establish the previous broadcast connection by momentarily closing contact 33 to reenergize relay 23. The subscriber originates a telephone call by removing his receiver from the switch-hook 10, which unlocks relay 23 and lights the call lamp 35 by energizing relays LR and SR. Since both these relays are energized no circuit is closed for relay 27. Fourth system, Fig. 4. High-frequency transmission over telephone, line). The selecting arrangements are similar to those of Fig. 3, but since telephony and broadcast reception may proceed simultaneously the relay 23, Fig. 3, is omitted and the switch DS is permanently associated with the line L through a high-frequency path.