Patent GB-630367-A (GB)
Title: Improvements in or relating to wireless signalling systems
IPC: G01S1/24
Filed: 1945-06-14
Abstract: 630,367. Automatic phase control systems. WILLIAMS, F. C. June 14, 1945, No. 15186. [Class 38 (iv)] [Also in Group XL (c)] In a radio navigation system groups of pulse signals of constant pulse recurrence frequency are radiated in regular order from two or more spaced aerials. Where two aerials are used the system defines a course line to or from the beacon whereas if three or more aerials are in operation the bearing of the beacon may be determined on the craft. In each case the phase relationship at the pulse recurrence frequency of the pulses in the respective pulse groups is determined at the receiver. A preferred beacon station comprises a pulse transmitter cyclically connected by lines of equal length to respective ones of three omnidirectional aerials A, B, C, located at the corners of a right-angled isosceles triangle, the order of energization being A,B, A,C, A,B, and so on. The pulse repetition frequency may be 5 Kc/s. and the groups consist of 25 pulses. To synchronize the receiver the back edge of the pulses may be width-modulated with the aerial switching frequency and superimposed on this modulation a communication channel for speech or morse may also be provided. At the distant craft Mc there will be a change of phase between the pulses of groups received from the A and B aerials proportional to l cos #, and between those received from A and C proportional to l sin #. On the craft pulses are received by receiver 14 (Fig. 2) and a 5/Á sec. pulse is generated in response to the first “/Á sec. only, of the incoming pulse by unit 15. An A.V.C. circuit 16 controls the gain of the receiver and is arranged to be quick-acting. A free-running oscillator 17 having a natural frequency equal to the pulse recurrence frequency is arranged to have its frequency varied byŒ 1 per cent by a reactance valve unit 18 controlled by a sawtooth sweep unit 19 having a period of a few seconds. Oscillator 17 controls the strobe generator 20 which provides 10/Á sec. pulses in timed relation with each oscillator; these are fed back to gate the 5/Á. sec. pulse generator 15. normally held inoperative except during the anticipated arrival times of pulses. The 10/Á sec. pulses are also applied to sweep unit 19 where, when these are in chosen relation with the 5/Á sec. pulses from unit 15 also applied thereunto, the sweeping action is stopped and the oscillator 17 maintained at the chosen frequency. When there is a discontinuity in the phasing of the incoming pulses owing to aerial switching at the transmitter, the oscillator 17 alters its frequency for a short time until the integral of the change of frequency equals 'the phase shift; it does this under the influence of the sweep unit 19 which accordingly passes pulses proportional to l cos #, - l cos #, l sin #, - l sin 0, to the reactance unit at each successive discontinuity. These pulses are also amplified and applied to a sine-cosine potentiometer 22 from which two outputs proportional respectively to the sine and cosine of the angle # of the potentiometer setting are made available; these outputs are applied to a switching unit 23 controlled by the switching frequency derived in unit 25 from the pulse width modulation. It is arranged that only outputs proportional to - sin # cos # and cos 0 sin # are selected and applied to centre zero meter 24 whose indication is thus proportional to sin (# - #) and will be zero when # = # or #+180 degrees so that by adjusting the potentiometer for zero reading the required bearing angle may be read off on its scale. The communication channel is fed through filters 26 and amplifier 27 to reproducer 28. The switching unit 23 may either employ valve switching, or for fairly slow rates of aerial switching, mechanically-operated relays, Figs. 5 and 11 (not shown). A number of ground beacon stations can be worked on a common radio frequency but at different pulse recurrence frequencies and power can be saved in the receiver by applying H.T. supply only during the 10/Á sec. strobe pulse, a suitable circuit arrangement for this is given in Fig. 10 (not shown). The oscillator, sweep, reactance, and strobe units. Valve V8 is the sweep valve and is used as a saw-tooth generator, at the start of the cycle its anode is at a voltage determined by R5, R6 and R7 and the control and suppressor grids have been biassed by the connection of R10 to - 150 volts by relay RL1 which has just been de-energized and connects R10 to earth. Current flows through R8 and the control grid potential rises causing the anode voltage to fall, the fall being linearized by C3, C4 and R9. At the end of the run-down period, the screen current increases and RL1 energizes, connecting R10 to - 150 volts and causing cut-off conditions in the valve which eventually release the relay and re-commence the cycle. The sawtooth output is applied to reactance valve V7 which acts as a variable capacitance in shunt with the tuned circuit L1, C1, of oscillator V6a and causes the frequency to vary by 1 per cent either side of the nominal pulse recurrence frequency. The cathode output of the oscillator valve is shaped to form positive pulses of 20/Á sec. duration. These are applied to the grid of V6b through network C8 and R16 and the negative edge of each pulse serves to cut off V6b and thus generate a 10/Á sec. strobe pulse at the anode which are fed through t6 to t2 (Fig. 3) and also through an integrating network to V9a. V10a is normally cut off except when 5/Á sec. signal pulses from unit 15 (Fig. 2) are applied to its grid, then current normally flows through V9b until the integrated strobe pulse (a saw-tooth wave) applied to V9a reaches a value at which there is a changeover. If this changeover from V9a to V9b occurs in the centre of the 5/Á sec. signal pulse the output of T1 through reversed diodes D8 and D9 comprises two pulses of equal magnitude flowing in opposite directions. However, if the signal pulse and the integrated strobe pulse are not exactly synchronized there will be a resultant output from the reversed diodes fed to the sweep unit circuit in such a way as to bring the oscillator back into coincidence. In fact when overlap occurs between the strobe and signal pulses the sweep circuit is prevented from sweeping by a small output from the reversed diodes and therefore the stable synchronized position is with the changeover between the two halves of V9 slightly displaced from the centre of the 5/Á sec. signal pulse. When there is a phase change in the received pulses the balance of the circuit will be upset and there will be a control voltage generated changing the oscillator frequency until the new pulse group is synchronized; this control voltage is also fed to the sine-cosine potentiometer. Specifications 581,602, [Group XL], 581,603; 605,053, [Group XL (c)], 615,416; 630,421, [Group XL (c)], 630,422 and 630,423, [Group XL (c)], are referred to.