GB180683A - Improvements in and relating to wireless signalling systems - Google Patents

Abstract

180,683. British Thomson - Houston Co., Ltd., (Assignees of Beverage, H. H.). May 25, 1921, [Convention date]. Aerials; undesired signals, eliminating.-Relates to aperiodic receiving-aerials of the kind described in Specification 175,315 comprising two long parallel conductors 1, 2 grounded at the ends 3 and 4, whereby an initial selection is made between signal energy passing through the ether in one direction and signal energy travelling in the opposite direction, and consists in means for eliminating interference between the desired signals and signals travelling in the same direction and of approximately the same wave-length. Signal energy travelling in the direction from 3 to 4 would normally create a maximum effect in the aerial at the end 4, but as the coil 7 is grounded at its mid-point, such signals will not affect the receiver 10. On the other hand, signal energy in the opposite direction would give rise to a maximum effect at the end 3, and might ncrmally be received there. In order however to retain the receiving-apparatus at the end 4, whilst receiving desired signals culminating at the end 3, the mid-point of the coil 6 is grounded through a coil 5 which then acts as a primary to induce the current discharge through the coil 6 as a secondary, back into the conductors 1, 2 along which the signalling currents flow in opposite directions so as to have a cumulative effect across the coil 7 and its secondary 8 of the receiver 10. An adjustable resistance 9 prevents reflection of the currents from the ground point 4. In order to eliminate interference from signal-energy flowing in the same direction as the desired signals, one or more circuits 12, 13 tuned to the undesired signal-frequency are inserted in shunt to the primary 7, as shown in Fig. 1, so as to offer a path of low impedance to such signals and divert them from the receiver 10. Fig. 3 shows equivalent interference shunts arranged in bridge formation. The arms 19, 20 are each made up of two parallel shunts 21, 22 tuned, say, one above and the other below the desired signals, so that the points 25 and 26 are equipotential for such undesired frequencies which do not therefore affect the receiver 10, whereas the bridge is unbalanced for the desired signals. By choosing suitable constants, the resultant impedance of the shunts 21, 22 may be made individually inductive and capacitive with respect to the desired signals, and may then be mutually tuned so as to form a substantially infinite impedance trap for that frequency, the result being the same as though the desired currents were impressed upon the receiving-apparatus solely through the resistances 23, 24.