Patent GB-633762-A (GB)
Title: Improvements in radio navigation systems
IPC: G01S1/20
Filed: 1946-04-23
Abstract: 633,762. Radio navigation; pulse and saw-tooth generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 23, 1946, No. 12285. Convention date, April 20, 1945. Addition to 633,547. [Classes 40 (vi) and 40 (vii)] Relates to receiver means for measuring the time interval between the pulses received from two spaced stations A and B in a pulse hyperbolic navigation system as claimed in the parent Specification in which A and B pulses are displayed on a cathode-ray tube in two parallel traces produced by a deflecting wave having two parts of similar shape, the pulses being aligned by adjusting the starting time of the second part of the wave and means being provided for applying timing markers to the traces. According to the present invention, means are provided for producing an additional twopart deflecting wave, the initial portions of the two parts having comparatively steep gradually-decreasing slopes which may be applied to the cathode-ray tube in place of the first deflecting wave to produce two fast parallel traces, each part of each first and second wave starting contemporaneously. Method of operation, Figs. 6, 7, 8, 10, 11 and 12. The indicator is provided with a multi - bank five - position selector switch and in position one the received A and B pulses are displayed on two vertically-displaced sequentially-produced slow time-bases ab and cd, Fig. 6, the total period of which is equal to the recurrence period of'the received pulses (40,000 Ás as shown). Both traces sweep from left to right and the time of changeover from trace ab to trace cd is variable so that cd is increased as ab decreases. The two traces are first made of equal duration and the two pulses are then drifted on to the lower trace ab and adjusted so that one pulse, the B pulse, is at the beginning of the trace. The relative trace duration is then adjusted so that the A pulse appears at the beginning of the upper trace cd, Fig. 7, and the selector switch is turned to position two, which expands the first 1,400 Ás of each trace exponentially to produce traces fg and hi, Fig. 8. The two pulses are roughly aligned by further adjustment of the relative duration of the slow traces and are then shifted to the more expanded left-hand ends of the traces, Fig. 9 (not shown), which are then superimposed by switching to position three, to facilitate accurate alignment of the leading edges of the pulses, Fig. 10; for the last operation, the amplitudes of the two pulses are equalized by a differential gain control. The selector switch is now turned to position four, which reintroduces the slow time-bases together with 1,000 Ás timing pulses and the end 20,000 Ás portion of the trace cd is blanked out, Fig. 11, so that the duration of the remaining portion cd<1> gives the required time interval to the nearest 1,000 Ás. The fractional part is determined by expanding the left-hand portions of each trace in position five of the selector switch which also applies 10, 50, 100 and 500 Ás timing pulses as shown in Fig. 12. The required interval is the duration of the upper trace up to the first 1,000 Ás marker z, but since the commencement of the trace is not well defined, the second 50 Ás marker on the lower trace is taken as a reference mark and the interval is then obtained by counting the marks between the 1,000 Ás marker z and the 50 Ás reference mark and adding 100 Ás. General description of the system, Figs. 1 and 13. The timing of the various waveforms applied to the indicator is controlled by a 100 kc/s. crystal-controlled oscillator 10, the output from which is successively divided in frequency by the factors 1, 5, 2, 5, 2, 5 and 4 in the blocking oscillators 12, 15, 16, 33, 52, 56 and 59 to produce pulses with recurrence periods of 10, 50, 100, 500, 1,000, 5,000 and 20,000 Ás respectively. The output from the divider 59 is applied through a limiter 60 to trigger an Eccles-Jordan oscillator 65 (i.e. a multivibrator with two stable states) giving a waveform C which is applied to trigger a multivibrator 101 giving a waveform F. The timing of the trailing edge of the negative portion of this waveform may be varied by the control 1021 and a further fine adjustment is provided by the control 106<1> on the delay circuit 106. The waveforms C and F are differentiated at 107 and 108 respectively to give waveforms E and G and the resultant positive pulses are selected, shaped and inverted at 110 to give negative pulses (waveform H) which are applied to cut-off the valve 116 in the fast time-base generator circuit 111. The inverted H wave at the anode of valve 116 is differentiated by the CR circuit 121, 122 and the positive peaks of the resultant waveform J trigger the slow time-base generator 115, the outputs I and K from the two timebase generators being applied through section 123 of the selector switch and through the pushpull amplifier 124 to the X plates 128 of the cathode-ray tube 129 so that the slow time-base is applied in positions one and four of the switch and the fast time-base in positions two, three and five. The slow time-base traces are vertically separated by applying a wave-form M from the delay circuit 106 to the upper Y plate 168 of the cathode-ray tube via positions one or four of switch 171 and the inverter valve 170. In order to separate the fast time-base traces in positions two and five of the selector switch, a waveform L from the oscillator 65 is delayed at 177 to give waveform D<1> and an inverted wave D from the push-pull amplifier 181 is applied to the upper Y plate of the indicator via positions two and five of switch 171, the connection to position five being via potentiometer 187 so that the separation may be adjusted. The received pulses A and Bare amplified and detected in the receiver 161-164 and the negative output pulses are applied to the lower Y plate of the cathode-ray tube; in positions four and five of switch 248, the IF stage 162 is biassed off by the negative voltage source 252, and in positions two and three the gain of the two pulses may be differentially controlled as in the parent Specification. Negative 10 Ás and 50Ás timing pulses from the dividers 12 and 15 are applied through the phase inverters 80 and 190 to the lower Y plate to give downward timing markers which are present on all the traces but are only distinguishable on the fast traces. 1,000 Ás pulses from the divider 52 are applied to the upper Y plate in position four of switch 171 and timing pulses for the fast time-bases are applied to the upper Y plate in position five of switch 171 through the valves 178 and 179 which are rendered operative by the waveforms D<1> and D respectively so that the outputs from the two valves are applied to the upper and lower fast traces respectively. As shown, 50 Ás and 500 Ás upward markers are applied to the lower trace and 100 Ás and 1,000 Ás upward markers are applied to the upper; to facilitate counting the 100 Ás markers on the upper trace, 500 Ás pulses of opposite polarity are applied so that the amplitude of every fifth 100 Ás marker is reduced. The end 20,000 Ás portion d<1>d of the slow trace cd is blanked out in position four of the selector switch by applying the waveform L from the oscillator 65 through switch 221 to the grid 227 of the cathode-ray tube and a blanking wave for the fast time-bases is obtained by applying the inverted H waveform at the anode of valve 116 to positions two, three and five of switch 221; a D.C. restoration diode 224 is provided to render the brilliance level controlled by the potentiometer 229 independent of the blanking waveform. Separate horizontal shift circuits 236, 237 and 239, 241 are provided for the slow and fast time-bases and since the amplitude of the slow sweep voltage K is greater than that of the fast sweep I, the bias on valve 146 of the push-pull amplifier 124 is increased in positions one and four of switch 157. In order to vary the recurrence frequency to select different pairs of stations, the recurrence period of the output pulses from divider 59 is reduced in steps of 50 Ás by means of the ganged switches 64 and 67 which feed the output from divider 59 back to dividers 16 and 33 respectively so that for odd positions of switch 64, divider 16 is triggered one pulse earlier and divider 33 is triggered one, two and three pulses earlier when switch 67 is in positions 2 and 3, 4 and 5, 6 and 7 respectively ; since the recurrence frequency of the output pulses from divider 59 is effectively halved by the oscillator 65, the recurrence periods thus selected are (40,000 - 100n) Ás, where n is an integer. The feed-back operation may be checked in position five of the selector switch by counting the number of 50 Ás markers on the lower trace from the reference marker to the first 500 Ás marker, there being eight for position 0 of the switches 64 and 67, seven for position 1 &c. Further groups of stations may operate with basic recurrence periods of 30,000 Ás or 50,000 Ás and to receive these the division factor of divider 59 is changed to three or five. The received pulses are drifted slowly along the traces by adjusting the frequency of the crystal oscillator 10 by means of the control 11; a more rapid drift to the right is produced by feeding the output from divider 59 back to divider 33 through switch 96 causing it to trigger earlier and a more rapid drift to the left is produced by applying the wave H through switch 253 to block oscillator 12 during the negative portions of the waveform, thereby causing oscillator 15 to run unlocked and increasing the average recurrence period. Fast time-base generator, Fig. 3. The fast time-base sweep voltage, Fig. 14 (not shown), is produced by adding two exponentially decaying voltages of different time constants so that the resultant voltage initially decays very rapidly, then less rapidly, and this is obtained by connecting two parallel RC circuits 131, 133 and 132, 134 in series in the