Patent GB-317523-A (GB)
Title: Improvements in or relating to high frequency signalling systems
IPC: H04B3/03
Filed: 1928-05-18
Abstract: 317,523. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). May 18, 1928. Directive signalling; undesired signals, eliminating. - Transformer systems, particularly in tended for use in wireless reception, with wave antennµ, are so designed that the phase shift in one transformer, or series of transformers, bears a desired relation to the phase shift in another set of transformers, with the result that interfering signals can be balanced out. Fig. 1 shows the system applied to a broadside array of three wave antennµ A, B, C, of the type described in Specification 207,536. Desired signals arriving from the right in the figure, produce currents in the parallel antennµ wires A which flow to earth through the primary coil of the reflection transformer 1 and induce a current in the loop circuit A which is transferred through the signal transformer 2 to the output circuit 2<1>. Undesired signals coming from other directions also produce a current in the compensating transformer 3 and its output circuit 3<1>. To enable the interference signals to be balanced out, the transformers are so designed that the phase shift produced by transformers 1, 2 jointly is the same as that produced by transformer 3; or alternatively the phase shifts, may differ from each other but the difference should be such a function of the frequency that it may be compensated for by ordinary phase-shifting devices. The complete system comprises three such wave antennµ A, B, C, and the three signal output currents in the circuits 2', 5<1>, 8<1> are combined together in two stages by means of compound transformers B31 and B33. The circuits 2<1>, 8<1> feed through transformers 10, 14 the input coils 16, 17 of the compound transformer B31, and the output from this is combined with currents from the circuit 5<1> in the compound transformer B33. The interference-compensating currents arising in the transformers 3; 6, 9 is similarly combined in two stages by the compound transformers B32, B34. The resultant signal currents and the resultant compensating currents are jointly impressed on a further compound transformer B35, the interference being balanced out and the pure desired signals transferred to the receiver 40. Owing to the geographical separation of the antennµ, the lines 2<1>, 3<1>, 8<1>, 9<1> may be longer than the lines 5<1>, 6<1>, and the difference in phase shift thus produced may be compensated by introducing further transformers 26, 27 and phase-shifters PS-61 and PS-62 in the circuits fed by the short lines 5', 6<1>. Artificial lines AL-51, AL-52, and AL-55 are employed for adjusting the amplitude of the input to the following transformers 20, 23, 25, and a final phase-shifter PS-65 is interposed before the transformer 24. Each compound transformer comprises, as shown in Fig. 2, a pair of cores carrying input coils W1, W2 and secondary coils W3 - - W6. The secondary coils W3, W4 are connected in series to the output line 40<1>, and the secondary coils W5, W6 are connected in series to a balancing network N35. The directions of winding of the coils are such that for input currents in phase the effects add in the output circuit and neutralize in the balancing network. The two input currents do not react on each other. Waves from the chanels 2<1>, 5<1>, 8<1> are added cumulatively in the transformers B31, B33, and interference-compensating waves are similarly added in the transformers B32, B34. The input to the transformer 25 is equal in amplitude and opposite in phase to the interference component present with the signals in the input to transformer 2 ; consequently the interference is neutralized in the receiver 40.