Patent GB-627766-A (GB)
Title: Improved carrier wave telephone system
IPC: H04B3/54
Filed: 1947-03-05
Abstract: 627,766. Carrier transmission. WESTERN ELECTRIC CO., Inc. March 5, 1947, No. 6242. Convention date, March 9, 1946. Addition to 627,314. [Class 40 (iv)] [Also in Group XL(c)] In a carrier telephone system of the kind described in the parent Specification, each of the subscribers A, B, C ... &c. normally transmits on a carrier f<SP>2</SP> which is automatically changed to f<SP>3</SP> when a call to another subscriber in the same group is answered. Connections are set up with the help either of an operator or of automatic equipment at a central office CO. Subscriber's station. At station A, the unmodulated carrier f<SP>1</SP>,  rectified at 28, operates relay R<SP>1</SP>, followed by R<SP>2</SP>, and lights the busy lamp 35. If the handset is raised, battery is supplied from 31 and the transmitter 20 sends out a carrier f<SP>3</SP> under the control of a crystal r<SP>2</SP>. If the carrier f<SP>1</SP>  is modulated with a 20-cycle ring- ing current, the relay R<SP>1</SP> releases intermittently at 20 cycles and operates a ringer 34. If the handset is raised in answer to a code ring, R<SP>2</SP> cannot operate again and the carrier f is transmitted under control of crystal r<SP>1</SP>. A conventional dial 32 is provided for use with an automatic central office. The key 33 enables the outgoing carrier to be suppressed when listening-in. Carrier terminal station CT. The carriers f<SP>2</SP> and f<SP>3</SP>are accepted by circuits 37 and 38. Carrier f<SP>2</SP>  is rectified at 52 and operates relay R<SP>3</SP>. Relay R<SP>6</SP> follows, applies battery at 61 to send out carrier f from transmitter 45, and closes the loop 41 to the central office CO. Only if R<SP>3</SP> is already operated can carrier f rectified at 56, operate relays R<SP>4</SP> and R<SP>6</SP>. The transmitter 45 can also be shorted by ringing current on one wire of the central office line 41, which is rectified at 57 and operates relay R<SP>5</SP> to connect battery 60. Call from central office to subscriber. Ring- ing current on one wire of line 41 operates R <SP>5</SP> to start transmitter 45 (f<SP>1</SP>). The subscriber, recognizing the code ring, lifts his handset 18 and a carrier f<SP>2</SP> is sent back to CT. Speech currents pass between the subscriber and the central office over a hybrid coil 39 with a balancing network 40. Call from subscriber to central office. When the handset 18 is raised, the carrier f<SP>2</SP> is transmitted to CT, where it starts the transmitter 45 ( f<SP>1</SP>) and closes the loop 41 to signal the central office. Call between subscribers on the same carrier terminal. The calling subscriber calls the central office as described and hangs up. The wanted subscriber is called from the central office as described. When the called subscriber answers, the carrier f is transmitted from CT and operates relays R<SP>1</SP>, R<SP>2</SP> and busy-lamps 35 at all stations. When the calling subscriber lifts his handset 18, the carrier f<SP>3</SP> is transmitted as described. With relay R<SP>4</SP> operated, the hydrid coil 39 is unbalanced by the substitution of a network 44 for the network 40 and speech received in circuits 37 and 38 is returned to the line 1 over hybrid coil 39 and circuit 36.