Patent GB-646355-A (GB)
Title: Improvement in indicator and/or control system
IPC: F41G3/06
Filed: 1945-04-16
Abstract: 646,355. Automatic control systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 16, 1945, No. 9520. Convention date, Nov. 29, 1941. [Class 38 (iv)] [Also in Groups XXXVIII, XL (b) and XL (c)] The phase of an electrical pulse with respect to a pair of reference waves having simultaneouslyoccurring oppositely-sloping portions is determined by mixing similar derivatives of the pulse with each of the sloping portions so that one of the resulting composite signals increases in peak amplitude and the other decreases in peak amplitude in response to changes in phase. In the invention described, the difference in the peak amplitudes of the composite signals is used to produce an error voltage for automatically maintaining the reference waves in a predetermined phase with respect to the pulse and this is applied to an automatic ranging unit in a radar system or to maintaining two rotating discs in synchronism. Radar system, Fig. 1. The output from the 819.4 kc/s. master oscillator 10 is frequency divided and shaped at 11 to produce 4.1 kc/s. timing pulses which trigger the transmitter 13 and also produce gain-control pulses which are applied to the receiver 16 to reduce the gain at the time of transmission of a pulse, the receiver gain then increasing at a rate dependent on the time constant of the gains control circuit. The output from the master oscillator 10 is also fed to the phase shifter 31 and the phase-shifted output is frequencydivided and shaped at 32 to produce a 4.1 kc/s. " reference " wave-form 33 having a flat top and sloping sides. This wave-form and the inverted wave-form 36 produced by the inverter 34 is mixed at 29 and 28 with an echo pulse 17 from the receiver and the composite waveforms y and x are applied to the grid-leakbiassed peak-rectifiers 39 and 38. Due to the long time-constant of the grid circuits, the peaks of the composite wave-forms extend into the region of positive grid voltage by constant amounts and if the pulses 17 are not located on the mid-points of the trailing edges of reference wave-forms 33 and 36, Figs. 3a and 3b (not shown), the D.C. levels of the composite wave-forms will be unequally biassed and the voltages produced by the integrating circuits 50 and 45 will be unequal. These voltages are D.C. coupled to the balanced amplifiers 52 and 51 and the difference of the outputs is applied as an error voltage to the reversible D.C. motor 66 which rotates the phase shifter 31 until the error voltage is reduced to zero. Condensers 56 and 57 are shunted across the upper and lower sections of the potential divider 48 connected across the integrated outputs of valves 38 and 39 to provide a first-derivative-of-error voltage to prevent hunting. In order to cause the control to operate on a selected echo pulse, the pulses from the receiver are applied to the mixers 28, 29 through a gate valve 21 controlled by gating pulses 24 derived from the generator 32 and the gating pulses are displayed together with all echo pulses as radial deflections on the circular time-base of a cathode-ray tube 84. The gating pulse is adjusted for coincidence with a selected echo manually by applying variable voltages of opposite polarity from the ganged potentiometers 97, 98 to the grids of the balanced amplifiers 51, 52 which are first disconnected from the rectifiers 38, 39 by means of the relay 91. If the control system is required to operate on any echo pulse, the gate switch 25 is opened by the relay 104. The amount of phase shift which is proportional to the range is indicated on dials 76, 77 geared to the motor 66 and remote indications may be transmitted by synchronous motors ; improved accuracy is obtained by performing the phase shift on a harmonic of the recurrence frequency. A suitable phase shifter is illustrated in Fig. 4 (not shown). In place of the reference waveform shown, a saw-tooth or sinusoidal waveform may be employed. Synchronizing two rotating discs, Fig. 5. The two discs 111, 112 which may be the colour filter discs at the transmitter and receiver of a colour television system are driven by the D.C. motors 113, 114 energized by batteries. Disc 111 has narrow projecting elements 117 of magnetic material which produce narrow pulses 118 in the coil 119 wound on a permanent magnet and disc 112 has wider projecting magnetic elements 123 which produce wider reference pulses 124 and these pulses are combined in the mixers 121 and 122 as described above to produce an error voltage in the circuit 116 which adds to or subtracts from the voltage from the battery 115 to maintain the discs in synchronism.