Patent GB-907714-A (GB)
Title: Synchronizing system for recurrent pulses
IPC: H03L7/00
Filed: 1958-11-18
Abstract: 907,714. Pulse radar; automatic phase-control systems. HOLLANDSE SIGNAALAPPARATEN N.V. Nov. 18, 1958 [Nov. 19, 1957], No. 37064/58. Classes 40 (5) and 40 (7). Relates to an automatic ranging pulse radar system in which a first pair of contiguous narrow gating pulses, Figs. 3, D, and 4, G, are automatically maintained symmetrically coincident relative to an echo pulse by means of a quick-acting long-range electronic servo system comprising a double-gate discriminator 201, 202, 205 and electronic integrator 210 and a second pair of contiguous narrow gating pulses are automatically maintained in a similar relationship with the echo pulse by means of a slower-acting but more accurate short-range electro-mechanical servo system comprising a double gate discriminator 155, 157, 158 and modulator 234, 235, each servo system being effective only if the echo pulse overlaps at least one of the associated gating pulses. According to the present invention the electronically-controlled gating pulses are automatically and rapidly brought into approximate coincidence with the echo pulse by disconnecting the electronic integrator 210 fromthedouble-gatediscriminator 201, 202, 205 and connecting it to the output from an auxiliary discriminator which produces a D.C. control voltage whose polarity depends on whether the echo pulse occurs earlier or later than the narrow gating pulses. When coincidence is attained relays A225 and B226 are automatically actuated causing (1) the electronic integrator to be re-connected to the double-gate discriminator to provide normal electronic tracking and (2) the auxiliary discriminator to provide a D.C. control voltage of polarity dependent on the relative position of the electronically and electro-mechanically controlled gating pulses, said control voltage being applied to the modulator 234, 235 of the electromechanical servo to bring the electro-mechanically controlled gating pulses into approximate coincidence with the electronically-controlled gating pulses; when this is attained a relay C151 operates automatically to disconnect the auxiliary discriminator and connect the double-gate discriminator 155, 157, 158 to the modulator 234, 235 to provide normal electro-mechanical tracking. If the echo fades and does not reappear within a predetermined memory period determined by the operating time of the relay A225 then the system is restored to its initial condition in readiness for manual initiation of the automatic search. Means are also provided for unlocking the gating pulses from a particular echo and for manual adjustment of the electronically or electro-mechanically controlled gating pulses; in the latter case the auxiliary discriminator is used to synchronize the elec- Ironically-controlled gating pulses with the electro-mechanically controlled gating pulses. Auxiliary discriminator. First embodiment.-As shown, the auxiliary discriminator comprises a cathode follower 219 to which is applied (1) the echo pulses (when used for synchronizing the electronically controlled gating pulses with the echo) and (2) a positive pulse, Fig. 3C, whose leading and trailing edges are coincident respectively with the transmitter sync. pulse and the leading edge of the first electronically-controlled gating pulse, the cathode-follower 219 being biased so that it is rendered conductive only by coincident input pulses to give a smoothed positive D.C. voltage across a capacitor 220 which is applied to a differential amplifier 221, 222 coupled to a cathode follower 224 which produces a positive D.C. control voltage if the shaped echo pulse VP, Fig. 3D and E, is earlier than the first electronically-controlled gating pulse and a negative D.C. control voltage if the echo pulse VP<SP>1</SP> is later than the first electronically-controlled gating pulse or if no echo pulse is received. In a modification (not shown) the variable duration positive pulse, Fig. 3C, applied to the cathode follower 219 is replaced by a negative pulse of fixed duration greater than the maximum echo time t but less than (p - t) where p is the pulse recurrence period, the leading edge of the negative pulse being coincident with the leading edge of the first electronically-controlled gating pulse. In the above forms of auxiliary discriminator the functions of the echo and first electronicallycontrolled gating pulse may be interchanged, e.g. in the embodiment shown the variable duration positive pulse, Fig. 3C, may be terminated by the echo pulse and the first gating pulse applied to the cathode follower 219. Second embodiment.-In this embodiment (not shown) a pulse is initiated by each first electronically-controlled gating pulse and is terminated by each echo pulse so that the duration of the resultant pulse is either shorter than or much greater than the maximum echo time t according to whether the echo is later than or earlier than the first electronically-controlled gating pulse. The average voltage of the resultant pulse train is thus less than or greater than a predetermined level and may be applied to a differential amplifier similar to 221, 222 to give a corresponding error voltage. Third embodiment.-In this embodiment the echo pulse EP, Fig. 4, is applied in parallel to two auxiliary gates, one of which is opened by the sync pulse, Fig. 4F, and closed by the gating pulses, Fig. 4G, as shown in Fig. 4J, the other gate being opened by the gating pulses and closed by the succeeding sync. pulse, as shown in Fig. 4K, and the outputs from the two auxiliary gates being applied to a differential amplifier to give a corresponding error voltage. Detailed operation. The contacts a211 &c., b135 &c., c230 &c. and e239 &c. of the relays A225, B226, E212 and C151 are shown in the drawings in positions corresponding to the de-energized state of their respective relays. Normal tracking (all relay contacts in positions shown).-The electronically-controlled gating pulses are generated by applying a transmitter sync. pulse over leads 145, 144 to a monostable trigger circuit 120, 124, 126 giving negative and positive pulse outputs from the anodes of valve 124 and valve 126, respectively, the negative pulse being integrated in a bootstrap integrator 103, 107 to give a positive sawtooth, Fig. 3B, which is applied together with the D.C. range control voltage, Fig. 3B, from the electronic Miller integrator 210 to an amplitude comparator 108, 109, 111 to give a variably-delayed short negative pulse which is applied to the grid of valve 124 to terminate the pulse outputs from the trigger circuit 120, 124, 126. The positive pulse output, Fig. 3C, from valve 126 is applied through a cathode-follower 131 to the cathodefollower 219 of the auxiliary discriminator described above and a short positive pulse derived from the trailing edge of the variable-duration positive pulse, Fig. 3C, by a differentiating circuit 128, 113 and inverter 114 is applied (1) over a lead 115 to the C.R.T. range display, and (2) to the first gating pulse generator 116 whose output is applied to the first gate 201 and to the second gating pulse generator 117 whose output is applied to the second gate 202. The video echo pulses are applied in parallel to the gates 201, 202 over a lead 200 and the negative integrated outputs from the gate are applied (1) to a differential amplifier 205 whose error output is integrated in the Miller integrator 210 to give the positive D.C. range control voltage, Fig. 3B, and (2) through rectifiers 203, 204 to a biased cathode-follower 215 producing a negative output of amplitude proportional to the amplitude proportional to the amplitude of the echo signal coinciding with both of the narrow gating pulses which is applied (1) over a lead 216 to the A.G.C. and other control circuits (e.g. for automatic direction-finding); and (2) to cut off valve 218 and maintain relay A225 de-energized. The electro-mechanical range servo comprises corresponding first and second gating pulse generators 153, 154 and gates 157, 155 and a differential amplifier 158 whose output is applied in push-pull to the modulator 234, 235 feeding the amplifier 241 of a servomotor 245 which controls the position of a potentiometer 244, the first gating pulse generator 153 being triggered by a transmitter sync. pulse delayed by a variable delay circuit 152 controlled by the potentiometer 244. Automatic search.-If the electronically-controlled gating pulses are not coincident with an echo, the valve 218 will be conductive, thereby energizing the relay A225 to close contact a211 and move the change-over contacts a228, a229 from their positions as shown. The search is initiated by closing a push-button 227 to energize the relay B226, thereby (1) applying echo video pulses from a lead 134 to the cathodefollower 219 of the auxiliary discriminator via the contact b135 and a limiter 139, and (2) applying the output from the cathode follower 224 of the auxiliary discriminator to the electronic integrator 210 via the contact e209. When the electronically-controlled gating pulses are coincident with an echo pulse, the valve 218 is cut off, thereby de-energizing the relay A225 to (1) change contacts a228, a229 back to their positions as shown, and (2) to open contact a211, thereby de-energizing the relay B226 to (1) reconnect the integrator 210 to the differential amplifier 205 via the contact b208 and (2) apply the second electro - mechanically controlled gating pulse to the auxiliary discriminator via the contact b135. The output from the auxiliary discriminator is applied to one input of the modulator 234, 235 via the contact c230 of the normally-energized relay C151 (the other input to the modulator being earthed via the contact c231) to drive the servomotor 243 until the electronically and electro-mechanicallycontrolled second gating pulses applied to the anode and grid of a valve 148 are coincident. When this occurs the valve 148 becomes