Patent GB-633767-A (GB)
Title: Improvements in radio navigation systems
IPC: G01S1/20
Filed: 1946-05-29
Abstract: 633,767. Radio navigation; sawtooth generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 29, 1946, No. 16392. Convention date, Jan. 1, 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 on 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 said wave and means being provided for applying timing markers to the traces. According to the present invention, each part of the wave has a steeply-sloping portion near to its leading edge, the slope gradually decreasing through the period of each part. As described, the A and B pulses are displayed on two vertically-displaced traces produced by the sweep voltages ab and cd, Fig. 5, F, and are aligned by adjusting the relative duration of the two traces as described in the parent Specification, the required time interval being then determined by blanking out the end 20,000 Ás part of the upper trace cd and measuring the duration of remaining portion cd<1>, Fig. 3 (not shown), by means of timing markers applied to it; alternatively, the midpoint d<1> of the deflection wave period may be indicated by a 20,000 Ás marker pulse. The above operations are facilitated by producing the traces by means of sweep voltages as shown in Fig. 7, F, so that the commencement of each trace is expanded logarithmically ; alternatively exponential expansion may be employed. General description of system, Figs. 1 and 5. Trigger pulses of recurrence period 20,000 Ás are produced by the chain of frequency dividers 13, 16, 33, 52, 56 and 59 as in the parent Specification, and the output pulses are applied through a limiter 60 to trigger an Eccles-Jordan oscillator 65 giving a wave B<1> which is differentiated at 106 and 107 to give waves C<1> and C respectively. The positive pulses of wave C<1> trigger a flip-flop 101 giving a waveform D the trailing edge of the negative portion being adjustable by control 102<1>, and the wave is differentiated at 108 giving wave E which is applied together with the wave C to the timebase generator 110 which is triggered by the positive pulses of the applied waves to give the sweep voltages F, which are applied through the push-pull amplifier 113 to the X plates of the cathode-ray tube 116. The traces are separated vertically by applying the wave D from the flip-flop 101 to the lower Y plate and the upper Y plate is connected through the switch 126b either to the pulse receiver 127 or to the mixer 129 to which the 10,100 and 1,000 Ás timing markers are applied. In the latter position of switch 126b, the wave Bl is applied through the ganged switch 126a to the grid 119 of the cathode-ray tube to blank out the last 20,000 Ás portion of the trace cd; alternatively the blanking may be omitted and an additional 20,000 Ás marker applied to the trace via the mixer 129. The gain of receiver 127 is controlled differentially by the potentiometer 172 and the recurrence period is varied by the feed-back circuit 65<1>, as described in the parent Specification. Wave-shaping circuits, Figs. 5, 6 and 7. The waveform B<1> is differentiated at 106 and 107, giving waveforms C<1> and C respectively, and the positive pulses of wave C<1> trigger the flip-flop 101 giving a waveform D, the timing of the trailing edge of the negative portion being adjusted by varying the bias potentiometer 102. The waveform D is differentiated at 108, giving a waveform E, which is applied to valve 110B of the mixer circuit 110, the waveform C being applied to the other valve 110A, and the positive pulses of the composite waveform trigger the valves 144, 146 and 156, the pulses applied to valves 144 and 146 being limited by the diode 143. The cathode circuit of each trigger valve comprises a capacitor and resistor in parallel, which is charged when the associated valve becomes conductive and which then discharges exponentially. The time constants of the three circuits are different so that three exponential waveforms x, y, z, Fig. 7, are produced and these are then mixed in a common lead 162 to give a resultant waveform F which is approximately logarithmic. According to the Specification as open to inspection under Sect. 91, each part of the deflecting wave may comprise a linear sawtooth. This subject-matter does not appear in the Specification as accepted.