Patent GB-844842-A (GB)
Title: Radio indication of bearing
Inventor: SAGE MORLEY WILLIAM
IPC: G01S1/02
Filed: 1955-04-20
Abstract: 844,842. Radio navigation; automatic phase control systems; pulse shaping circuits. MURPHY RADIO Ltd. July 20, 1956 [April 20, 1955], No. 11456/55. Classes 40(5), 40(6) and 40(7). In a mobile radio receiver adapted to determine its bearing relative to a beacon transmitting pulse signals, a local oscillator is automatically phase cocked to selected received pulses by deriving from each cycle of the local oscillation two pushpull bi-polar waveforms, one only shown in Fig. 2 C, and combining with said waveforms the selected pulse signal D to give two resultant waveforms E and F whose negative portions are selected, smoothed, and combined differentially to give a D.C. even signal which is applied to control the frequency of the oscillator. The invention is described as applied to a beacon system in which:-(1) Fig. 1, reference pulses of constant recurrence frequency are transmitted from a fixed omni-directional aerial and bearing pulses of the same recurrence frequency are transmitted from a rotating narrowbeam aerial, the bearing pulses being delayed relative to the reference pulses by a varying amount proportional to the instantaneous bearing of the rotating aerial; alternatively the reference pulses could be transmitted by the rotating aerial; the reference and bearing pulses may be separated at the mobile receiver by amplitude discrimination, (2) Fig. 3, pulse pairs are transmitted by a wide-beam aerial, e.g. candioid radiation pattern, which is rotated at 30 c/s. and the recurrence frequency of the pulse pairs is modulated at 30 c/s. in synchronism with the aerial rotation so that at the mobile receiver the received pulses are amplitude modulated at 30 c/s. due to the rotation of the beacon aerial, the phase difference between said amplitude modulation and the frequency modulation of the pulse recurrence frequency being indicative of the bearing. The invention is also applicable to rotating narrow-beam systems in which the pulse recurrence frequency is varied with the aerial rotation and to rotating wide-beam aerial systems in which the reference signal is provided by time modulation of pulses transmitted from a fixed aerial. The beacon may also comprise a transponder for use in a secondary pulse radar system in which case the reply signal may be constituted by either the bearing or reference pulses or by an additional pulse signal transmitted by a fixed aerial system; in the latter case the reply signals are preferably suppressed during transmission of the bearing pulse signals. FIRST EMBODIMENT, FIGS. 1 & 2 Automatic synchronization of blocking oscillator 1, Fig. 1, by positive reference pulses D, Fig. 2. The negative sawtooth ouput B, Fig. 2 from the cathode of the blocking oscillator 1 is coupled to the suppressor and control grids of a pentode 3, the RC circuits 2, 5 and 2, 4 being such that the time constant of the suppressor grid circuit is twice that of the control grid circuit. The resultant waveform C, Fig. 2, at the screen grid of the pentode 3 is applied, to the grid of a triode 12 which is cathode-coupled to an earthed-grid triode 13 and positive reference pulses D are invented by a transformer 17 and applied to the cathode circuit of triodes 12 and 13. The negative portion of the resultant output waveforms E and F from the anodes of triodes 12 and 13 are selected by diodes 25, 24, smoothed by circuits 27, 26 and applied to a differential amplifier 28, 29 to give a D.C. error signal dependent on any displacement of the pulse D from its position relative to waveforms E and F as shown in Fig. 2; this error signal is applied to the grid of the blocking oscillator 1 to control its frequency. Measuring time interval between reference pulse D and the succeeding bearing pulse. The received bearing pulses are applied to two pentode gates 44, 45 which are gated on respectively by a narrow pulse and by a long pulse of duration equal to twice that of the narrow gate pulse. These gating pulses are derived from the screen grid and anode of a pentode pulse generator 46, the output from a delay phantastron 47 triggered by the output from the pentode 3 being applied to the suppressor and control grids of the pentode 46. The gate valves 44, 45 feed through transformers 48, 49 and diodes 51, 52 to the grid of an integrator valve 53 controlling the delay of phantastron 47, the transformer ratios being such that there is twice as much output from the diode 51 as from the diode 52 within the duration of the narrow gate pulse so that the outputs from the gates 44: 45 are equal when the bearing pulse is symmetrical with respect to the trailing edge of the narrow gate pulse, and the system operates automatically to establish this condition. The control voltage applied to the phantastron 47 from the integrator 53 is proportional to the required bearing which is displayed by a pointer 62 controlled by a servo comprising a potentiometer 58 and a motor 59 actuated by relays H and K controlled by a polarized relay G (contacts Gl) connected between the anodes of a differential amplifier 56, 57 having as inputs the phantastron control voltage and the voltage from the potentiometer 58. In the absence of any output from the wide gate 45 for a predetermined period, e.g. 10 secs, a relay M (contacts Ml) operates to connect the grid of the integrator 53 via the contacts N1 of a reversing relay N to a positive or negative bias voltage to vary the delay of the gating pulses cyclically between limits controlled by the reversing relay N which is actuated by an output from the integrator 53. When an output is obtained from the wide gate 45, this output is integrated by a valve 63 and de-energizes the relay M. The duration of the gating pulses is increased during search; this is effected by returning the suppressor and control grids of the gate pulse generator 46 to the anode of the integrator 63. In order to increase the accuracy of the bearing determination, a second set of bearing pulses of different duration may be transmitted by the rotating beam at the beacon, the maximum variation of the second bearing pulses corresponding to a 36 degree change in bearing. In this case a second potentiometer 58 is provided and the ratio of the gearing 61 is selectable, the coarse or fine indication being selectively displayed under the control of a relay actuated by a pulse width discriminator. Ambiguity at the bearing, e.g. mouth, at which the delay of the bearing pulse changes abruptly is avoided by ranging the delay over a range 0 degrees - x degrees to 360 degrees + x degrees and suppressing the bearing pulse during the remaining portions of the rotation periods preceding and succeeding the period in which the delay is varied continuously. SECOND EMBODIMENT, FIG. 3. In this embodiment the second pulse of each received pulse pair is selected by a pulse spacing discriminator 71, 72 and applied to synchronize the local oscillator 1 by means of a control circuit 2-29 corresponding to that shown in Fig. 1. The time constant of the synchronizing loop 2-29 is such that the synchronizing action can follow the 30 c/s modulation of the pulse recurrence frequency which therefore appears as a 30 c/s ripple in the output of valve 28 which is selected as the reference signal by an amplifier 83 and filter 84. The second pulse of each received pulse pair is also selected by a gate 73 controlled by a gate pulse generator 74 controlled by the local oscillator 1 and the output from the gate 73 is peak rectified at 75, amplified at 76 and smoothed in a filter circuit, the resultant 30 c/s amplitude modulation component due to the rotation of the beacon aerial being selected by an amplifier 77 and filter 78 and compared in phase with the 30 c/s reference signal from the amplifier 83 by means of a servo phase meter comprising a phase shifter 86, servo motor 91, rectifier 81, 89 and discriminator 82.