Patent GB-202294-A (GB)
Title: Improvements in radio broadcasting systems
IPC: H04H60/04
Filed: 1923-07-20
Abstract: 202,294. Western Electric Co., Ltd., (Assignees of Ryan, F. M.). Aug. 14, 1922, [Convention date]. Thermionic amplifiers, generators, and modulating systems; measuring and testing apparatus. -A studio A containing the microphone transmitter 4 is preferably located at a distance from the radio transmitting installation proper. The latter is contained in a separate " radio " room and comprises a multi-stage audio-frequency amplifier (panel B), a constant-current modulator M and thermionic generator O (panel C), an automatically operated " send-receive " switch (panel D), and control switches and apparatus together with a second alternative microphone transmitter 9 (panel E). The circuit arrangements provide means of communication between the studio and " radio " room, and also a control sytem divided between the studio and radioroom attendants. The operations are so interlocked that the various parts all function in proper sequence, and indicating-devices are provided to indicate automatically the conditions of the various circuits. Principal circuits. Speech currents are fed from the microphones 9 or 4, according as the switch 8 is in the upper or lower position, to the audio-frequency amplifiers 10, 11, 12. Filament current is fed to the valves 10 and 11 in series, and the valve 12 in parallel, from a battery 13, whilst a battery 28 supplies plate voltage to all three valves, a switch H, I, J, K and a potentiometer 32 providing a separate adjustment for the voltage of the last amplifier 12. The battery 13 also supplies the microphones 4, 9 through resistances 27, 20, choke coil 26, and conductors 21, 22, 23. The output from the amplifier 12 is fed to the input of a thermionic amplifier L under the control of a relay 44. The amplified currents next pass to a constant-current modulator similar to that described in Specification 133,366, comprising two electron discharge tubes 62, arranged in parallel, and are then impressed upon a radiofrequency generator O. This consists of two tubes 50 back-coupled through the coils 53, 59 and condenser 60. A condenser 52 shunting the plate coils 53, prevents the absorption of power by interior oscillations. The modulated radio currents are fed to the aerial 57 through the coils 53, 55. Filament current is fed in parallel to the tubes on the panel C from a generator GA, whilst a generator GB provides plate voltage. The plate-supply circuit, comprises resistances 67, 68 by means of which the grids of the amplifier L. modulator M, and oscillator O are maintained at such a negative potential that very little space current can pass until the resistance 68 is shortcircuited by a time-relay 82 connected across the generator GA. This can only occur when the switch on panel D is in the " send " position and the normally-open contacts 84 are closed. Operation. The closure of switch 91 closes the contacts of the relay 92 so as to excite the relays 93, 93 from the generator GA. This opens the ccntacts 89, 90 and closes the contacts 94, 95, throwing the aerial into the " send " position. At the same time the contact 84 is closed in readiness for the time relay 82 to short-circuit the grid-stabilizing resistance 68. The switch 91, when closed, also lights a lamp 100 in the studio, and prepares a circuit for the energization of the inter-amplifier relay 44. If the switch 8 is in the upper position, the circuit of the relay 44 is completed through a switch 105 to earth and back to the grounded positive pole of the battery 13. With the switch 8 in the lower position the relay circuit comprises the lamp 101, relay 102, and switch 103. The output from the panel B can therefore only be impressed upon the tubes of the panel C through the relay 44 so long as the switch 91 is closed, and the radio transmitter is consequently functioning and connected to the aerial 57. Indicating and control means. The closure of the switch 103 in the studio is indicated by the lighting of a lamp 101 in the " radio " room E. Simultaneously the lamp 106 is lit up through the relay 102 from battery 13. A buzzer 107 may also be energized through a push-button 108. The lamp 100 automatically indicates that the panel C is functioning with the switch 8 in the upper position; the microphone 9 comes into use and control of broadcasting operations is then in the hands of the attendant at the switch 105. Ammeters 200, 201 indicate the space-currents flowing through the modulator M and oscillator 0 respectively; the ammeter 203 measures the grid current of the oscillator, and the ammeter 202 the aerial current. A loud speaker 98 enables the input across the transformer 73 to be monitored. In a modified circuit arrangement, the triple-pole double-throw switch 8 is replaced by a two position switch, the loud speaker 98 may be connected at will either to the input of the radio transmitter or to a monitoring radio receiver, and hand telephone sets, call-lamps, and buzzers are provided for the purpose of intercommunication between the studio and radio room.