Patent GB-140829-A (GB)
Title: Improvements in and relating to the use of thermionic devices in wireless and other signalling systems
IPC: H03G11/00
Filed: 1920-03-27
Abstract: 140,829. Western Electric Co., (Assignees of Arnold, H. de F.). Sept. 3, 1915, [Convention date]. Wireless telegraphy and signalling.-In an amplifying system employing thermionic devices, particularly adapted for use in wireless communication, foreign disturbances are reduced to a value not exceeding that of the signals by means of a current limiting apparatus so arranged that a definite upper limit is set upon the amount of energy communicated to the receiving circuit, while energy of a lower order is transmitted without interference. Another feature of the invention is the provision of apparatus for the purpose. of securing substantially uniform amplification of the incoming signal impulses, irrespective of their voltage, prior to their impression on the power limiting device and the receiving circuit. Referring to the diagram, power received by the antenna 1 is transferred to the circuit 5, 6, and amplified by the valve unit 7, the output circuit of which comprises inductances 13 and 17. The coil 17 has a reversible inductive connexion with the coil 5, controlled by a reversing switch 18, its function being to neutralize the coupling between the grid and plate circuits of the amplifier 7, and thus prevent free oscillation or " singing." Impulses impressed upon the coil 19 are converted to low frequency form by the rectifier unit 21, and then augmented by the low frequency amplifiers 31 and 38. Choke coils 16, 28, 35, and 42 are provided in the anode circuits of each of the valve units, and shunted by condensers 14, 24, 33, and 40 to form paths for high frequency currents. A resistance 37 of the nature of 500,000 ohms is connected in shunt with the winding 36, and by means of an adjustable contact any desired proportion of the potential drop across the resistance 37 may be applied to the grid of the valve 38, thus correspondingly varying the amplification in the output circuit. By the use of a constant resistance shunt of a value less than that between the input electrodes, uniform amplification, regardless of the voltage of the incoming impulses, is stated to be secured. This condition is attained by maintaining the grid at a negative potential by a battery 39, and thus making the grid-filament space resistance substantially infinite. The current limiting device is coupled to the last amplifying valve by a transformer 44, 45, and consists of two uni-laterally conducting thermionic elements placed in opposition to each other in a circuit. Current is supplied to the output circuits of these structures by the battery 65 connected through the coil 57 and the variable high resistance 58, to the middle point of the coil 54, which is coupled to the coil 55 forming part of the circuit of the receiver 66. Condenser 56 and the choke 57 prevent current fluctuations from the battery 65 from passing through the valves and the coil 54. The variations in the normal currents in the winding 55 are produced by the action of the grids 49 and 51, and since the tubes can conduct in one .direction only it is impossible to do more by any impulse than to decrease the current in one tube to zero. The current in the other tends to increase in aecordance with the increased potential applied to its grid, but no applied potential can cause a varying current in the winding 55 larger than the normal space current of the elements as determined by the constant source 65. This normal space current is adjusted to a value just greater than the amplitude of the signals to be received. The resistance 58 prevents serious unbalance of the currents in the halves of the winding 54. When a large electromotive force is impressed, the current through the resistance increases, but since the output source 65 remains constant, the current which can flow in the output circuit is decreased, the resistance 58 thus producing a choking effect.