Patent GB-520141-A (GB)
Title: Improvements in or relating to electrical remote control systems
IPC: H03J5/14
Filed: 1938-10-10
Abstract: 520,141. Electric control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 10, 1938, No. 29367. Convention date, Oct. 9, 1937. [Class 40 (i)] [Also in Group XL] In a remote control system, the control unit includes a number of oscillators each capable of generating two different frequencies, so that in response to manual control the various frequencies may be fed singly or in combinations to the apparatus to be controlled. Figs. 1, 2 show respectively a wireless receiver and a remote control unit both of which are adapted to be plugged into the power supply lines. The receiver is controlled alternatively by local push-buttons and by signals of various frequencies transmitted by the control unit over the power lines, the generated frequencies being modulated at the frequency of the supply. Local control. To switch on the receiver, key 83 is moved to the left, closing contacts 62, 63 and 59, 64. The A.C. supply is extended to the receiver and to transformers 44, 75 and relay 73 operates momentarily to swing a lever 52 to the right-hand position in which locking, contacts 49, 50 in parallel with 62, 63 are closed. The tuning condenser 100 is driven by the motor 92 when the latter is rotated at high speed, the circuit being made over one of cams 110-113 and co-operating contacts 114-117 and a selected station button 124-129. The volume controlling potentiometer 103 is driven by the motor 92 when the latter is rotated at low speed, the circuit being made through contacts controlled by key 83 and resistance R1 or R2. To switch off the receiver, a button 179 is operated to connect up relay 72 which restores the lever 52 to the left-hand position. Remote control. The valves 230, 231 in conjunction with tuned circuits 236, 237 and 234, 235 oscillate at 300 kc., or if condensers 232, 233 are in circuit at 200 kc. The plate voltage however is derived from the A.C. supply through a transformer 238 from either end of a secondary winding 246 having the midpoint grounded. The oscillations are thus modulated at the frequency of the supply, two phases differing by 180 degrees being possible. The connection of the supply and the insertion of condensers 232, 233 is controlled by buttons 200-208. In the receiver unit, the 300 kc. oscillations are led through a tuned circuit 15, 17 to a valve 24 while the 200 kc. oscillations are led through a tuned circuit 14, 16 to a push-pull valve 23. Grid bias for both valves is obtained from the supply through the diode part of the valve 24, and a diode 20 serves to increase the sensitivity of the valve 23. The plate circuits which include relays 36, 37, 38 are fed from the A.C. supply from a secondary winding 42 of the transformer 44 having the midpoint grounded, so that the relays operate only if the modulated oscillations are in phase with the positive peaks of the supply. In addition, a cold cathode tube 6 operating in the manner described in Specification 516,648 is controlled by a circuit 9, 10 tuned to 300 kc. so that it becomes ionized if the modulated oscillations are in phase with the A.C. supply across condenser 9 and operates relay 8. The relays control the sets of contacts S8, S36-38 in such a way that the various circuits referred to in the preceding paragraph may be completed in response to appropriate signals when the buttons 200-208 are operated. Of these,' 200 serves for switching on and for increasing the volume, 204 for reducing the volume, 208 for switching off, and the remainder for station selecting. In certain cases, both the valves 230, 231 are operative to send a combination signal which connects up two of the relays 8, 36-38.