Patent GB-587351-A (GB)
Title: Improvements in or relating to radio navigation systems
IPC: G01S1/02
Filed: 1943-09-15
Abstract: 587,351. Radio navigation; valve circuits. WILLIAMS, F. C. Sept. 15, 1943, No. 15161. [Class 40 (v)] A system for radio navigation of a mobile craft comprises at least two fixed spaced transmitters which radiate characteristic signal modulation in response to interrogating signal modulation radiated by the mobile craft, which is equpped with apparatus for simultaneously indicating time intervals between transmission of interrogating signals and receipt of the response signals. In Fig. 1 spaced responding stations A, B such as those described in Specification 585,347 retransmit coded pulses signals when interrogated by the transmitter in the mobile craft C which carries, in effect, a radiolocation equipment which can measure the ranges to the responding beacons. The response radio frequency preferably differs from the interrogating frequency. Craft C may be positioned by observing the ranges from A and B or may be navigated to a fixed point by following an approach path at constant range from one beacon until a predetermined range from the second beacon is reached, Fig. 2 (not shown). Alternatively, by introducing a fixed delay at one beacon, craft may be navigated along an approach course by maintaining apparent ranges to both beacons equal. To minimise interference by spurious pulses when several craft are being navigated by the same ground beacons, deliberate wobble or jitter may be introduced into the interrogating pulse repetition frequency. In a preferred arrangement for accurate range measurement by means of cathode ray tube indicators two main time base scans C4, C5, Fig. 7c, occurring alternately are made equal to short time intervals corresponding to 150 km. and have their commencements delayed by adjustable amounts so that response signals j1, j2 lie at distances z from the trace commencements equal to the small interval occurring between the commencement of each timing cycle and the radiation of the interrogating pulse j, Fig. 7b. The delay device settings then indicate the time delays or ranges t1, t2, Fig. 7a, of the beacon responses j1, j2. The commencing portions of the traces comprise stepped regions e1 Figs. 7d and 7e, and for the purposes of more accurate setting, the stepped portions can be displayed on auxiliary high speed time bases, Figs. 7f and 7g, alongside similar lengths of trace corresponding to the true commencement of each time .period on which are displayed the transmitted pulses i so that the delay control setting may be read after accurate alignment of the transmitted and response signals. In a preferred embodiment of the equipment of the mobile craft illustrated in block schematic form in Fig. 6, the output of a crystal oscillator OA at 120 kc/s. is fed to a divider DB which provides sharp output pulses at intervals of 16.66 Ás which control a four-stage multivibrator MC producing four-phase square waves of 66.66 Ás period. These square waves are integrated in circuits D to triangular form and are fed to fixed vanes of phase shifting condenser-goniometers E, E1 One square wave from MC is applied to a distorter amplifier G which produces negative going pulses spaced by 66.66 Ás which are applied to a divider circuit F giving negative output pulses spaced by 666.6 Ás, and also to a divider H with a division ratio of about 150 : 1 but which is varied between 140 : 1 to 160 : 1 under the control of the jitter unit H1 so that irregular output pulses spaced by intervals of the order of 10 millisecs are produced which are applied to units J and K. Unit J operates as a suppressor pulse generator producing a negative square wave which is fed to units G and F to cause suspension of their operation and return of divider F to the commencement of a fresh counting cycle. Unit K provides an extended control pulse to a relaxation relay circuit L which is operated by coincidence of pulses from units K, F and G to produce positive pulses each pulse following the pulse unit H and precisely coincident with the commencement of each fresh counting cycle of unit F. Output from unit L is fed through 10 Ás delay circuit D to control the modulator MOD of the interrogating pulse transmitter Tx. This repetition frequency pulse output from unit L is also fed to a half - recurrence frequency multivibrator R, the output of which is applied through an amplifier R1 to one Y-plate of a cathode-ray tube indicator to produce displacement between alternate traces, and is also fed to a differentiating and amplifying circuit R2 which provides triggering pulses for counting circuits N, O, P and N1, 01, P1 which are fed with pulses from unit F. Units N and N1 may be set to count any number from zero to 10 following each triggering pulse and thus provide output pulses spaced from the triggering pulse by selected multiples of 666.6 Ás (corresponding to ranges of 0, 100, 200 ... 1000 krns. Similar counting circuits O, 01 when triggered by the output from counters N, N 1 count 66.66 Ás period pulse waves produced in units P, P1 from the triangular output waveformsfed from the phase shifting devices E, El. through amplifiers EA, EA1. The phase of the pulse waves counted by units 0,- O1 are continuously variable under the control of the devices E, E1 and the number of pulses counted by each circuit after triggering by units N or N1 are set by potentiometers ganged to the phase shifting devices. Circuits 0, 01 thus produce output pulses at instants after the pulse from unit L which controls the interrogating signals, which are controlled by : first, the setting of the controls of units N, N1 according to the chosen number of 100 km. steps ; secondly, according to the potentiometers ganged to the phase shifters (i.e. according to the whole number of turns of phase shifters or 10 km/s. steps) and finally in accordance with the precise setting of the phase shifters. These precisely timed pulses are fed through a mixer circuit Q to control the time base generator circuit T which produces push-pull sweep voltages for application to the X-plates of the CRT to produce the time bases corresponding to range intervals of 150 km. Due to the shift produced by circuit R the traces corresponding to channels N, O, P, and N1, O1, P1 appear in parallel separated relationship as indicated in Fig. 7e. The output from unit Q, is also fed to unit U which produces short pulses which are applied to one Y-plate to produce a step at the commencement of each trace corresponding to a range of 10 km. These step producing pulses are combined in a circuit V with signals from the receiver Rx which thus also produce deflections of the traces. To obtain the high speed time bases for accurate range measurement, switches S, S1 are reversed and the time base circuit T then produces faster time base waveforms corresponding to range intervals of 10 kms. for each input pulse. As the repetition frequency output from unit L is also applied to the time base circuit, traces are also produced commencing just prior to the triggering of the interrogating pulse transmitter. Four traces, two of which display the interrogating pulse are thus produced during each complete cycle of display and the step producing voltage for, the second and fourth traces (which display the response signals) is also fed via switch S1 to the circuit V in such a manner that reversal. of the sign of deflection is produced during the second and fourth traces to produce the display pattern indicated in Fig. 7g. DETAILED DESCRIPTION OF UNITS. Units OA, DB, MC, D and E, Fig. 9. Unit OA comprises valve VI oscillating at 120 kc/s. under the control of crystal X ; the sine wave output of 175 volts is applied via condenser C2 to the suppressor grid of valve V2 which with diodes V3 and V4 forms the divider unit DB. Valve V2 is a blocking oscillator due to the back coupling through transformer T1 and is triggered by the applied sine wave diode V3 preventing positive. excursion of the suppressor grid. The negative swing of the control grid is limited to - 50 volts by the diode V4 and the rate of charge of the grid condenser C3 towards earth from the positive supply is controlled by the variable resistance P1 so that the circuit in effect counts two input sine wave cycles. Pulsed output is taken from a third winding of transformer T and is applied to unit MC comprising valves V5 to V8 arranged as two multivibrator pairs, cross-coupling between screens and control grids being provided in addition to the coupling from anodes to control grids to accelerate the change-over action. The circuits are triggered by the pulse input applied across the common cathode resistances and each valve anode is additionally coupled to a tapping on the anode to grid coupling network of the equivalent valve in the other pair so that when each inultivibrator is triggered it prepares the other multivibrator to be triggered by the succeeding pulse. Reversal of each circuit thus occurs on alternate pulses from the valve V2 and the outputs from the anodes of valves V5 to V8 thus comprises four 90 degrees phase displaced rectangular waves of frequency 15 kc /s. A portion of the output from the anode of V5 is fed through lead. 101 to unit G, Fig. 10a and the four waves are fed through separate integrating circuits such as R16, C5 to the four fixed plates of each capacity goniometer or phase shifter E, E1, the outputs from the rotors of which are obtained from leads 102, 103. Units G and F, Fig. 10a. Unit G comprises valve V9 fed with the square wave MC on its grid through the adjustable delay network L3 which allows compensation for certain delays produced in operation of the system. The inverted wave from the anode V9 is fed through condenser C6 to the anode of diode V21 forming part of unit L and is also fed through the differentiating transformer T2 which is shunted by diode V10, whereby negative pulses are fed to trigger unit F comprising valves V11, V12, V13 connected in a