| 摘要 |
939,293. Intercommunication systems. STANDARD TELEPHONES & CABLES Ltd. March 25, 1960 [March 26, 1959], No. 10601/60. Class 40 (4). In a substation equipped for " hands-free " loud-speaker and microphone operation using transmit and receive amplifiers, the depression of a push-button key enables the exchange line to be held and an interim conversation to take place with a secretary or the like over two oneway microphone-amplifier-loud-speaker links. On the restoration of the push button key the original conversation over the exchange line may be continued. The embodiment described includes two keys K1 and K2, the contacts of K1 being shown in the normal condition and those of K2 in the operated condition. With K1 and K2 both normal the telephone set 3 is connected to the exchange line 1, 2 and may operate as a normal set. Depression of key K1 switches the line to the hybrid 4, incoming currents from line being amplified at 6 and applied to the loudspeaker 8, while outgoing speech currents from the microphone 7 are amplified at 5 and applied via the hybrid 4 to the line. To speak with the secretary, keys K1 and K2 are depressed whereupon the output of amplifier 5 is switched to the secretary's loud-speaker 9, and her microphone is connected to the input of amplifier 6. the exchange line being held by the loop presented by the line input winding of the hybrid 4. The closure of contacts g of K2 sets the gain of amplifier 6 at a predetermined value. |
