Patent GB-174312-A (GB)
Title: Improvements in or relating to electric high-frequency signalling
IPC: H04J9/00
Filed: 1920-07-09
Abstract: 174,312. Day, A. van T. Jan. 25, 1919, [Convention date]. Multiplex signalling.-In a method of multiplex carrier-wave signalling, two signals are transmitted on separately modulated, phasedifferentiated components of the same frequency. At the receiving station, local currents are maintained in continuously effective co-operation with the received waves as described in Specification 148,380. In the receiving system shown in Fig. 5, the generator 22 produces a wave differing in frequency from the received carrier wave, so as to produce a beat frequency through a detector 676 and transformer 679 for driving the synchroncus motor 686. Oscillations from source 22 in quadrature phase relation in the transformers 671, 672 produce beat currents in quadrature with each other in the audio transformers 677, 678. These beat currents produce in the field coils 683, 684 a rotary field having the same angular velocity as the motor 686, so that the two coils 685, 708 rotated by the motor will maintain a, fixed angular relation to the rotating field. One coil, say 685, is arranged with the field axis continually passing through the coil axis, so that this coil will be affected by changes in the strength of the field but not by slight angular variations of the rotary field axis with respect to the coil axis. The coil 685 will thus produce in the telephone 712 voice currents resulting from strength modulations in the received carrier waves. The other coil 708 is arranged in the mean plane of the rotary field so that it will not be affected by changes in field strength, but will respond to angular variations or oscillations of the rotary field. Fig. 6 shows a transmitting system, in which the microphone 691 varies the field of a generator 693, thus varying the strength of the emitted waves, whereas a microphone 688 varies the permeability of the iron cores of an inductance bridge 695 in series with the generator, thereby varying the phase of the carrier wave without varying its strength. Additional multiplex telegraphy may be effected by generators 731, 732 having different frequencies which are superposed on the transmitter circuits for modulating the carrier wave from the generator 693, these frequencies being tuned out of the telephones 711, 712, Fig. 5 and selectively affecting tuned receivers 743, 744. The phase multiplexing receiving apparatus can be adjusted with respect to distinct modulation components having the same frequencies and different phases, and having their individual strengths independently varied by the independent transmitters. Fig. 7 shows a system of this kind in which the sending generators 718, 719 produce synchronous components in quadrature with each other, and having their strengths modulated by the microphones 716, 717, or by modulating generators 735, 736, 737, 738 of different frequencies. Alternatively, the sending generators 718, 719 may be controlled by microphones 722, 725 arranged as indicated, so that microphone 722 will modulate the strength of the resultant carrier wave without changing its phase, whereas the microphone 725 causes a phase libration of the carrier wave without varying its strength. Modulating generators 739, 740, 741, 742 may be arranged as shown. In a modified receiving system shown in Fig. 4, the carrier wave coacts with a local generator 22 and a duplex valve detector 634 to produce a beat current to drive a synchronous motor 637, as in Fig. 5, so as to generate oscillations strictly synchronous with the carrier wave, these oscillations and the modulated carrier wave being impressed upon a duplex valve detector 646. The resultant telephonic currents are amplified and purified at 648, 649, 650. By adjusting the rotary field coils 640, 641, the phase of the local current may be made such that it effectively coacts with one modulation component but not the other. The receiving apparatus may be duplicated more or less completely, the second apparatus co-operating with the other modulation component. In the system shown in Fig. 2, a duplex valve amplifier 575 is used to supply synchronous local waves to the detector 591. Although the aerial is tuned to a frequency slightly different from that of the carrier wave, for the purpose of reducing interference, the secondary circuit 574 is tuned to the carrier wave and the valve amplifier 575 has retroactive connections 576 so as to produce in transformer 579 currents of carrier frequency, the circuits being highly resonant to the constant component of the carrier wave, while tending to suppress its modulations and waves due to atmospherics. These currents of carrier frequency are amplified at 580, 585, purified by filtering circuits, and finally led by transformer 589 to the grids of the duplex rectifier 591, to which are also led the modulated waves from the transformer 590. The audio transformer 592 is connected as before through amplifiers 596, 597 and filtering circuits 593, 594 to the telephone 18. The relative phase of the local current is adjusted by inductance 586 or condenser 587, so as to make the detector effectively coact with one modulation component only, more or less of the apparatus being duplicated and adjusted to respond to the other component. In the system shown in Fig. 1, the received waves and the local currents from the generator 510 (maintained in synchronism with the received waves, as previously described) are led to the duplex valve rectifier 531, the currents from which are led through the audio transformer 518 to a duplex amplifier 532, an artificial loaded line 529, a second duplex valve amplifier 533, and a second loaded line 537 to a telephone 538. In the case of telegraphy, the carrier wave may have a frequency between that of the local generator and the natural frequency of the aerial, and the heterodyne beat waves may be raised above the audible frequency, the disturbing waves due to atmospherics having a still higher frequency, so that they may be suppressed in the artificial lines 529, 537. When the signalling beat wave is thus raised above the audible limit, it constitutes a secondary telephonic carrier wave, and may be passed through amplifiers and filtering circuits to suppress disturbing components to a non-polarized receiver 735, or it may be applied to the grid circuit of a duplex valve rectifier 629, the plate circuits of which are connected through a transformer, the secondary of which is connected to one diagonal of a bridge, of which one pair of arms are ohmic resistances and the other arms comprise inductance and capacity, the telephone 633 being connected across the other diagonal of the bridge. For multiplexing, the apparatus shown in Fig. 1 may be duplicated, the synchronous local generators being adjusted in phase so that each set responds to one phase component but not to the other. The system shown in Fig. 1 may also be used in another way since the secondary or sub-carrier wave is characterized by all the phase components and strength modulations of the received carrier wave. Thus the sub-carrier wave received at the point 735, say, will include a constant component and two modulation components in quadrature, which may be selectively received by any of the means already described. The Specification as open to 'inspection under Sect. 91 (3) (a) states that the frequencies of the modulating generators 735, 736, Fig. 7, may be high enough to act as carrier waves for additional telephonic communications, microphones varying the field strengths of these generators. The apparatus shown in Fig. 4 may be used as follows :-The two quadraphase modulation components of the carrier wave may be transmitted from the coupling 606 through a resonance bridge like 650 to two detectors like 646. The bridge is tuned to the carrier wave and transmits only its modulation components to the detectors, each of which is unresponsive to that modulation component which is impressed on its grids in quadrature with the local current. When the system shown in Fig. 1 is used for multiplexing, the entire apparatus shown in Fig. 2 could be duplicated, both aerials being connected in parallel between the wires conveying the subcarrier waves to the point 735, Fig. 1. The connections of the, detector to the aerial and to the local source may be transposed; thus in Fig. 2 the transformers 589, 590 may be interchanged. When the aerial is mistuned to reduce atmospherics. as previously described, a single aerial may receive two carrier wave trains, one above and one below the aerial frequency. In the system shown in Fig. 3 (Cancelled), in which simultaneous transmission and reception occur, the aerial 605 is tuned to the frequency of the transmitting generator 608 and mistuned to the frequency of the received carrier wave. Instead. of maintaining the local wave in exact synschronism with the carrier wave, the local wave, produced by a generator 22, is divided into two phases in quadrature, which are supplied to the grids of two duplex valves 601, the received waves being led to the grids in parallel as in the systems previously described. As the phase of the local wave varies in relation to the phase of the received waves, one or other of the valves will be effective, each producing its effect in one of the two telephones 18 mounted on a common head-piece, or in the magnets 623 acting on a common diaphragm 624. The magnets 623 may be used as the rotary field coils in the system shown in Fig. 5. The apparatus shown in Fig. 3 will receive a signal transmitted on a carrier wave of zero mean value, without a constant component. Such a wave may be produced by the arrangement shown in Fig. 7 if the fields of the generators 718, 719 are maintained at zero mean strength by having the coil 720 balanced by the coil 729 and the coil 721 balanced by the coil 730. This subject-matter does not appear in the Specification as accepted.