Patent GB-321990-A (GB)
Title: Improvements in telegraph receiving systems
Filed: 1928-08-24
Abstract: 321,990. Beatty, W. E., (Bell Telephone Laboratories, Inc.). Aug. 24, 1928 Restoring imperfect signals.-Isolated impulses lost in transmission are re-inserted at the receiver by two vibrator magnets R1, R2 which interact with one another and with pairs of distributor rings IC. RC. So long as a succession of isolated impulses of opposite sign is being transmitted, no signals reach the receiver from the cable 38, and the normal biassing voltage is applied by the battery 45 through brush RB and successive segments 1R, 2R, to the grids of the valves RT1, RT2, so as to keep the currents in the upper windings of the magnets R1, R2 at their mean value. At the same time the currents in the lower windings of these magnets, which are controlled by the valves IT1, IT2 and rings IC, remain at their mean values, for the reasons given below, so that the armatures pr1, pr2 remain in the positions to which they have been set, namely, in opposite positions, and give opposite polarities to their rings PC1, PC2, which feed alternate printing magnets 1<a>, 2a, 3<a> - - through alternate segments : the successive printing magnets consequently record a series of impulses of opposite sign. The grid-potentials of the valves IT1, IT2 are controlled as follows :-When the armatures r1, r2 are oppositely set, the middle point 32. of the potentiometer 43 is at earth potential, opposite voltages being applied to its ends from the potentiometer 23, 24, 25. When both armatures r1, r2 are to the right or to the left the point 32 becomes negative or positive as the case may be, the change being rendered more gradual by the condensers 27, 28. The potential of the point 32 determines, in conjunction with the permanently connected biassing battery 47, the grid potential of that valve IT1 or IT2 which is connected to the brush IB at the moment through a segment 1i or 2i, and the charges remain on the grids until the next passage of the brush over the appropriate contacts. If now a block of positive impulses be transmitted from the distant station, a positive signal will be received from the line 38 and will act through the brush RB and one of the valves such as RT1 upon the upper winding of one of the magnets such as R1. The current in this winding therefore increases so as to overpower that in the lower winding, and (the armatures being supposed to move in the direction of the electron current) the armature r1 and consequently pr1 will move to the left, so that positive current will now be supplied to printing ring PC1 as well as PC2. When the armature r1 moves to the left, the middle point 32 of the potentiometer 43 becomes positive, and the current through the lower winding of R1 increases; but since its effect is balanced by that of the current in the upper winding, the armature r1 remains inert in the leftward position. So long as positive signals are received from the line the armatures r2, pr2 also remain to the left and positive signals are recorded on all the printers. If the positive block signal be followed by a negative block signal the upper windings of the magnets R1, R2 cease to carry current, as negative potential is applied to their grids in succession through the brush RB; the armatures r1, r2 are therefore successively carried to the right under the influence of the lower windings, and negative signals are recorded by printing magnets of both sets. If, on the other hand, when both armatures r1, r2 are to the left the positive block signal is followed by a succession of impulses of opposite sign, beginning, for instance, on a segment 1i the currents in the upper windings of R1, R, are reduced to their mean values. The armature r1 corresponding to the segment 1i is moved to the right by the current in the lower winding; a negative impulse is recorded, and the potential of the point 32 falls to its mean value so that when the next contact 2i is reached the current in the lower winding of R2 falls to its mean value. The upper and lower windings are thus balanced, and the armature r remains set to the right. The armatures then remain oppositely set until a fresh block signal of either sign arrives. The valve currents are supplied through differential meters 83, 34. In a modification (Fig. 2, not shown) the potentiometers 23, 24, 25 and 43 and printing relays PR1, PR2 are discarded, and the armatures r1, r2 are connected to the printing rings PC1, PC2 so as to feed the printing magnets directly. These armatures and rings are also connected to alternate segments by which the solid ring IC is replaced, so that the currents in the lower or interpolating winding of the magnets R1, R2 are respectively determined by the armatures r1, r1 acting through alternate segments. Each determination lasts for the duration of two impulses, as in the arrangement shown in Fig. 1, and is such that each lower winding tends to set its ' armature opposite to the armature by which it is controlled. Type-printing telegraphs; distributor systems.- When there is an even number of channels, the printing magnets 1<a>, 2a, 3a - - , divided into group of five per channel, are connected alternately to segments arranged in two groups for co-operation with the two printing rings PC1, PC2 the polarity of whose potential is determined as described above. With an odd number of channels a larger number of printing rings and corresponding groups of magnets must be employed.