Patent GB-630094-A (GB)
Title: Improvements in or relating to signalling systems
IPC: H03M1/00
Filed: 1947-05-02
Abstract: 630,094. Secret transmission. WESTERN ELECTRIC CO., Inc. May 2, 1947, Nos. 11871 and 11872. Convention dates, Sept. 16, 1944, and May 10, 1945. [Class 40 (iv)] [Also in Group XL (c)] A signal transmission system comprises means for determining at regular intervals the amplitude of a signal wave and means for transmitting series of time-spaced pulses comprising a permutation code group, each series representing one of said amplitudes. As described each pulse of each series represents a different fraction of a maximum amplitude of the signal wave, and those pulses are selected for transmission which together represent the determined amplitude of the wave. At the . receiver, each series of pulses produce a single pulse of amplitude corresponding to the sum of those amplitudes which the individual pulses of the series represent, and the succession of single pulses thus produced comprises the reconstituted signal wave. The equipment at one terminal station using one embodiment of the invention, Fig. 1, comprises for one transmission channel, a source of complex wave signals 120, which may be a microphone. The source 120 is connected, through terminal equipment 121, to a sampling circuit 122 which feeds a coding circuit 123 producing pulses which are fed through amplifier 124 to the line 6. A master oscillator 10 sends a synchronizing wave over a second line 5 and controls the coding equipment. The latter comprises a controlled oscillator 110 feeding a control pulse generator 111, the output of which, after a suitable delay in circuit 112, is fed to a stepwave generator 114 and a code element timing circuit 113, the outputs of both of which are fed to the coding circuit 123. The circuits 10 and 110 ... 114 are common to all the transmission channels, another of which is fed from signal source 130 and uses a radio link 7 instead of a line such as 6. The transmitting channel outputs are monitored by circuits 125, 135 feeding signal reproducers 126, 136 respectively. A receiving equipment comprises the line 9 feeding pulses to amplifier 143, through a delay circuit 144, and thence to decoder 142, terminal equipment 141 and signal reproducer 140. A monitoring circuit 145 is provided for the station attendant. The radio channel 11 feeds similar equipment provided with signal reproducer 150. The pulse decoders are connected also to the common stepwave generator 114 and control pulse generator 111. The detailed circuits of a transmitting station are shown in Figs. 3 to 7 and of a receiving station in Figs. 8 to 10. Pulse generator, Fig.5.-The control oscillator 525 is connected to the master oscillator 510 which also feeds a synchronizing wave over line 580 to the receiver. The output from oscillator 525 synchronizes a multivibrator 511 producing square waves which are fed through a condenser-resistance combination 512, 513 to produce pulses of predetermined duration. These pulses are clipped by valves 514 ... 516 to produce rectangular pulses at the grid of the power output valve 517, positive pulses 521 being derived from its cathode load 519 and delayed negative pulses 523 from network 522 fed from its anode circuit. The frequency of these pulses may be 8000 per second for example. Code element timing circuit, Fig. 3.-The negative pulses from the pulse generator, after inversion in valve 310, shock excite the resonant circuit 312, 313 in the cathode lead of the lefthand triode of valve 311 to produce a train of slightly over six oscillations 1106, Fig. 11, before the arrival of the next exciting pulse. The oscillatory voltage is fed to the cathodefollower right-hand triode of valve 311 and thence to squarer and output valves 319 ... 321 producing wave 1107, Fig. 11. This square wave is differentiated in circuit 332, 334 to produce short negative and positive pulses 1108, 1109, Fig. 11, which are applied to the right-hand triode of valve 327. Step-wave generator, Fig. 3.-The synchronizing pulse from valve 310 is also applied to the grids of the two triodes of valve 323 to discharge condenser 330 and charge condenser 325. The discharging resistance 324 of condenser 325 is arranged to reduce the potential on 325 to one half of its initial value during each interval between the pulses 1109, curve 1113, Fig. 11. This potential is applied to the grid of the lefthand triode of valve 327 and, when the pulses 1109 appear on the grid of the other triode 327, the potential is repeated to the grid of the lefthand triode of valve 329, thereby adding an increment of charge to condenser 330. Thus a stepped potential wave-form 1114, Fig. 11, appears across condenser 330. This waveform is inverted, in the right-hand triode 329 and applied to the cathode follower power output triodes in valve 331. Coding complex wave-form, Figs. 4 and 7.- The complex wave-form to be transmitted is applied from the microphone 410, for example, and terminal equipment 411 to the grid of the left-hand triode of valve 412. The synchronizing pulse after inversion in valve 428 is applied to the anode of the same triode 412 which produces an output pulse proportional in amplitude to the complex wave-form amplitude at that time and charges condenser 413 to a corresponding potential through the righthand triode of 412 to which it is fed. The potential of condenser 413 is repeated through valves 419, 422 and to the anode of valve 423 which has an anode resistance 430 common also to valve 424. The grid of 424 is fed with the inverted stepped wave-form 1115, Fig. 11, from the anode of the right-hand triode of valve 329, Fig. 3. The combined output potential across the common load 430 is fed to valve 710 and comprises the wave 1218, Fig. 12, for one amplitude of the complex waveform. This wave 1218 is the sum of waves 1216, 1217 due to the anode currents in valves 424, 423 respectively referred to an arbitrary zero axis 1220. The grid bias of valve 710 is set at a value corresponding to axis 1219 so that the valve conducts only during positive grid voltage excursions such as 1230, 1232. The resultant pulses 1221, 1223, 1225, 1226 from valve 710 are passed through limiting amplifiers 711, 712, 714 to the screen grid of valve 715. The control grid of valve 715 responds to the positive timing pulses 1108, Fig. 11, applied from valve 321, Fig. 3, and when pulses are applied simultaneously to both grids, they are passed on through limiting amplifiers 716 ... 720 to the outgoing line 780, and to valve 620, Fig. 6, which repeats them to valves 611 and 417. Valve 417 is provided to reduce the charge on condenser 413 whenever a code pulse is transmitted to the line, and by a fraction corresponding to the amplitude of the stepped wave at this time, curve 1237, Fig. 12. For this purpose the code pulses are applied from valve 620 to the control grid of valve 417 and the stepped wave from valve 331 to its screen grid. Decoding the received pulse groups, Figs. 9 and 10.-The control wave from the transmitter is fed to a control oscillator at the receiver which feeds a synchronizing pulse generator of the type shown in Fig. 5. This produces positive and delayed negative synchronizing pulses 1305, 1304, Fig. 13, respectively. The negative pulses after amplification in valve 910, Fig. 9, are fed to the code element timing pulse generator comprising valves 911, 919 ... 921, the operation of which is the same as that of generator 311, 319 ... 321, Fig. 3. The output pulses are shown at 1308, 1309, Fig. 13. The stepped wave generator comprises valves 930, 935, 940, valve 930 becoming conductive during the application of a delayed positive synchronizing pulse to its grids to charge condensers 931, 932. The resistance 943 discharges condenser 931 to one half of its initial potential in each interval between successive pulses, curve 1313, Fig. 13. Valve 935 discharges condenser 932 each time a positive synchronizing pulse is applied to its control grid, and by an amount depending on the potential of its screen grid which is coupled to condenser 931. Condenser 932 is thus discharged in steps, curve 1314, Fig. 13, and the stepped potential wave-form is repeated by valve 940 to subsequent circuits. When a synchronizing pulse is applied to the left-hand triode of valve 1010, condenser 1014 is charged and is partially discharged each time a code pulse is received over channel 780, delay circuit 1030 and repeater valve 1018. The discharging valve 1011 has the received pulses applied to its control grid and the step wave 1314 from valve 940 to its screen grid so that the amount of charge removed from condenser 1014 is controlled by the step wave amplitude at the times when the code pulses are received. The potential of condenser 1014 is repeated by the right-hand triode of valve 1010 to the screen grid of valve 1012 to control the amplitude of output pulses from this valve occurring when a synchronizing pulse is applied to its control grid. The filter 1026 removes the 8000-cycle component from the amplitudemodulated output pulses which after amplification in valve 1013 are fed through a low-pass filter 1017 to the terminal equipment 1015 and signal reproducer 1016. Monitoring equipments, Figs. 6 and 10.-The monitoring equipment at the transmitter, Fig. 6, comprises a circuit similar to the decoding circuit comprising valves 1010 ... 1012 and 1018, Fig. 10. An alternative decoding circuit for monitoring purposes comprises valves 1019, 1020. Each received code pulse applied to the control grid of valve 1019 produces an output pulse, the amplitude of which is controlled by the step-wave applied to the screen grid from valve 940, Fig. 9. The output pulses are amplified in valve 1020 and passed through filter 1021 to the terminal equipment 1022 and signal reproducer 1023. In another embodiment of the invention, at the transmitter, Fig. 18, the complex wave signal M is applied to a modulator I in which local continuous oscillations from a generator