Patent GB-597114-A (GB)
Title: Improvements in radio signalling systems
IPC: H04B1/54
Filed: 1945-08-10
Abstract: 597,114. Radio signalling. GENERAL ELECTRIC CO., Ltd., and CHUBB, A. A. Aug. 10, 1945, No. 20527. [Class 40 (v)] A radio transmission system comprises two similar stations, each transmitting and receiving on the same frequency, either station being able to call the other by the automatic emission of pulses of carrier frequency alternating with receptive periods, the called station replying by a pulse of carrier which terminates the automatic emission of carrier pulses by the calling station. The operator at station A wishing to call the operator at a similar station B, lifts a micro-telephone hand set from a cradle switch, closing contacts 2, 3. This connects the microphone 1 to the transmitter, and operates relay C. Contact C1 energizes the pulsing relay chain X, Y, Z which continues to close and open in turn until the current is cut off. The operation of relay X energizes one coil of vibrator relay V through contact X2, extinguishes the " ready " lamp 6 through X4 and operates relay B through X3. Vibrator relay W continues to open and close to give a tone which is applied to the telephone 7. The receiver is muted as its H.T. supply is interrupted as contact B1 opens, and the telephone 7 is disconnected from the receiver's output, which is short circuited by contact B3. The aerial relay A is energized via contact B2, transferring the aerial to the transmitter while contact B4 completes the H.T. supply to the transmitter, which emits a burst of carrier frequency, until the re-opening of relay X restores the receiver to operation, re-lights the " ready " lamp 6 and stops the calling tone produced by relay W. This cycle of operations continues as long as the hand set is off the cradle switch 2, 3. At the called station B, the receiver is operative, but no A.V.C. potential appears at terminal 19 until a signal is received. On receipt of a call from station A, a negative potential is applied to the grid of valve V2, cutting it off and allowing anode current to flow in valve V1 and operate relay D. This operates relay G through contacts D1 and C1 and energizes the bell 4 to call the operator at B. When relays X and B at the calling station A release, the transmission ceases and relay D at station B releases, allowing relay G to release slowly, and stopping the bell 4. The operator at B when replying lifts the handset from the cradle switch, operating relay C and connecting his microphone to the transmitter. The press switch 5 is closed for a period longer than that separating two ringing periods. If switch 5 is closed while station A is not transmitting, relay G at station B is releasing slowly, so that when relay C operates, relay E is operated through contacts G1 and C1. Contact E 1 locks relay E while relay B is operated via contacts C2 and E2 and the press switch 5. The operation of relay B causes station B to transmit a carrier which is received at station A, causing relay D to operate. Relay E at station A is operated through contacts D2 and C1, de-energizing the pulsing relay chain XYZ through contact E1, which also serves to lock, relay E, and rendering relay B operable by the press switch 5 and contact E2. Conversation can now take place between the stations, each transmitting when its press-switch is closed. When the handsets are replaced on the cradle switches both microphones are removed from the circuits and relays C and E release at both stations. Instead of the operator at called station closing his press switch to reply to a call, a reply signal may be sent automatically. The circuit which operates a relay on the receipt of a carrier may be replaced by a circuit using one valve controlled by the A.V.C. potential developed by the receiver, with a relay connected in the anode circuit.