Patent GB-477175-A (GB)
Title: Improvements in or relating to radio communication systems
IPC: H04B1/38
Filed: 1936-07-17
Abstract: 477,175. Wireless transmitting and receiving systems. STANDARD TELEPHONES & CABLES, Ltd. July 17, 1936, No. 19890. Convention date, Sept. 26, 1935. [Class 40 (v)] A combined radio receiver and transmitter for two-way operation at a plurality of frequencies comprises a selector switch control mechanism for selectively connecting one of the transmitter tuning-units and for supplying highvoltage power, relay means normally rendering the transmitter inoperative, and a timecontrolled relay energized by the selector or by return to normal condition of the relay means and operative a predetermined time after its energization, to release the selector and disconnect the transmitter. The transmitter is prepared for transmitting on a chosen wave-length by dialling at 620 or 680, Fig. 6, thereby closing the selected tuned circuits of the oscillator and amplifiers and connecting up the various supply voltages. Initially, however, operation is prevented by earthing the anode of the oscillator valve 613 through a relay winding 607, and the contacts of a relay 313, Fig. 3. Relay 607 closes its contact and energizes a time-controlled slowrelease relay 625 which operates after an interval of say 1 to 15 minutes to shut down the transmitter if no modulating tone or speech is applied in this interval. The modulationis applied over an amplifier 309, 310, Fig. 3 to the modulator valve 532, Fig. 5, and also to control valves 323, 324, Fig. 3, to energize the relay 313, thereby removing the earth connection of the oscillator anode, and de-energizing the relays 607, 625. When the modulation ceases, relays 607, 625 are again energized, and provided no further modulation is applied in the meantime the relay 625 operates after the time interval to disconnect the tuning circuits and to interrupt the plate supply at a relay. Thereupon a slow-release relay is energized and operates after another interval to disconnect the cathodeheating circuits of the transmitter. Hangover relay 314, Fig. 3, delays the earthing of the oscillator anode for a short time after cessation of signal, and relay 315 disables the receiver, Fig. 1, for a further short period. During normal transmission, the receiver is disabled by a relay 122, which renders inoperative an output circuit of the receiver, the relay 122 being polarized over a series circuit containing the winding of the relay 313 and the discharge path of the control valve 324. If the transmitter has been prepared but no signals are being transmitted the relay 122 is only weakly polarized, and a received signal acts through the diode-triode valve 123 to operate the relay 122, thus disabling the transmitter and connecting up the receiver. If, however, signals are being transmitted, the relay 122 is strongly polarized and received signals are ineffective. During the hangover period after a transmission, the relay 315 is effective to polarize the relay 122 strongly, and to render received signals ineffective. Additional relays 109, 110, 111 are operated by the high current resulting from the low impedance of the valve 324, when signals are being transmitted or have just ceased, the relay 109 earthing the receiver aerial 101, the relay 110 disabling the frequencychanger 103, while relay 111 opens its contact to give zero transmission through the balanced circuit 114 between the detector 107 and the amplifier 108. The transmitter, Figs. 5 and 6, comprises a number of superposed chassis each carrying the apparatus pertaining to a corresponding valve stage. The lowermost carries a number of frequency-determining crystals 611 and a number of tuning-coils 612, any one of which may be associated with the oscillator valve 613 by operating the selecting switches 602, 608. Two amplifying stages 512, 522 with similar switch selection are superposed, followed by a modulating stage 532 and an output stage 542. Operation at any particular frequency is effected by raising the corresponding vertical rod 605 which actuates all the relevant switches by bell cranks 608. Each rod 605 rests on an arm 652 which is clutched to its shaft by a lever 650 when the corresponding magnet 603 is energized. This is effected by the arm 644 of a selector switch which is advanced to the selected position by the alternative dialling switches 620 or 680. The shaft is then rocked by the energization of the solenoid 604, through the intermediary of a relay 624. As the rod 605 lifts, a switch operated by a further arm 653 opens the circuit of the magnet 603. The several crystals 611 are kept at constant temperatures by heaters 615 intermittently energized by thermostatic switches in the circuits of relays 617. As a relay armature pulls up it closes the circuit of a motor 690 through a rotating arm 695 geared to the motor. The motor and the arm rotate, breaking the motor circuit and stopping the arm on the next contact so that the motor will start again when the relay releases its armature, and the arm will move forward to similar further contacts associated with the next crystal. As the motor rotates, lamps 691, 692 connected in parallel with it, light up, thus indicating correct operation of the heaters. If one heater is defective, the arm 695 is arrested in a position which indicates which heater is at fault. The apparatus may also operate as a telegraph transmitter using a simple carrier wave, or a tone-modulated wave. The respective functionings may be under the control of relays, or they may be automatically brought into operation, when predetermined numbers are dialled, by particular contacts on the selector 642. The tone-frequency is generated by a valve oscillator, and a control key is provided which in one position connects the oscillator output to the input of the speech amplifiers through a Morse key, so that a keyed tone replaces speech. In the other position of the control key, the input circuit of the second speech amplifier is shorted at the upper contact of a relay 312, but the tone passes through the rectifying control valves 323, 324 and energizes the relay 313 to interrupt the unmodulated carrier. The hangover relay 314 is shorted at the lower contact of the relay 312. The radio telephone system may be connected to any one of a series of four-wire subscribers' extensions under the control of keys. When one of these keys is " up ", the operator and the subscriber are connected, and when " down " the subscriber is connected for twoway communication by radio. Lamp indicators enable the subscriber to call the operator. An alternative system is also described employing two-wire subscribers' extensions. The operator's microphone and telephone are arranged under the control of a key which in one position connects them to the radio system. In a mid-position the operator may listen for incoming calls, and in a third position he hears the received signal as heard by the connected subscriber.