Patent GB-191125-A (GB)
Title: Improvements in and relating to wireless signalling receiving systems
IPC: H01Q11/02
Filed: 1921-09-30
Abstract: 191,125. British Thomson - Houston Co., Ltd., (General Electric Co.). Sept. 30, 1921. Aerials and like receiving conductors; multiplex and directive signalling: atmospherics and undesired signals, eliminating.-Horizontal directional aerials of the type described in Specification 175,315 are adapted for the simultaneous reception of a number of signals of different wavelengths. In order to neutralize the effect of strays, or of imperfect balance for desired signals of widely different wave-length, or of undesired signals coming from the wrong direction, means are provided for impressing upon each separate detecting-circuit current derived from another point in the aerial and adjusted so as to have the proper intensity and phase to neutralise the disturbing factors. As shown in Fig. 1, the signals are received at the end of the aerial 1, 2 opposite to that carrying maximum signalling-current, the aerial itself acting as a transmission line through a transformer 6, 7 from the end 3 of maximum current to the receiving end 4. The aerial comprises goniometer coils 8, 9, a grounding-resistance 5 of a value equal to the surge impedance of the aerial, and the primary windings of two intensity couplers 19, 20. Owing to the wind-point connections at 7 and 10, no current will flow through the ground connection at 4 from the desired signal impulses flowing in the aerial. Undesired signals may, however, flow through the branch 4, and these are transferred through the couplings 19, 21 and 20, 22 and are adjusted through phase rotators 23, 24, located in the tuned input circuits of the separate detecting-devices 17, 18 so as to balance the same disturbance factors transferred from the coils 8, 9 to the coupled coils 11, 12. In order to avoid the reaction effect of the coils 19, 20 these may be taken out of the ground branch 4 and replaced by an electron discharge device, the grid circuit of which is connected directly across the resistance 5. As shown in Fig. 4, the receivers 17, 18 are located at an intermediate point of the aerial, the desired signals flowing through a primary winding 29 branched across the aerial. The balancing currents are applied through couplings 19, 21 and 20, 22 in the output circuit of an amplifier connected across a choke coil 32 is a ground branch 20 connected to the mid-point 31 of the coil 29. As shown in Fig. 1, an artificial transmission line made up of series inductance 25 and shunt capacities 26 and closed by a surge impedance resistance 27 is coupled to a coil 23 included in the ground branch 3. Neutralizing-currents are impressed upon the input circuits of the amplifiers 11, 12, 13, the output circuits of which are respectively coupled to detectors 20, 21, and 22. The phase of the neutralizing-current is adjusted by means of the tappings 28, 29, 30 and its intensity by means of potentiometers 31, 32, 33. The winding 23 is shunted by a variable resistance 34, and the resistance 4 is adjusted to approximately the surge impedance of the aerial for different frequencies. The amplifiers 11, 12, 13 may be replaced by intensity couplers having high impedance windings so as to constitute only a small load on the transmission line.