Patent GB-604608-A (GB)
Title: Improvements in or relating to radio echo systems
IPC: G01S13/66
Filed: 1945-10-03
Abstract: 604,608. Automatic control systems for alignment. WILLIAMS, F. C. Oct. 3, 1945, No. 25768. [Class 38 (iv)] [Also in Groups XXXVIII and XL (c)] A radio echo apparatus is maintained trained on a target by causing the echo to maintain a locally-generated strobe in coincidence therewith and utilising only echoes occurring within the strobe periods for automatic training. General description.-The invention is described with reference to an aircraft having scanning radio mirror units SP, SS, Fig. 1, on the port and starboard wings respectively and adapted to be. switched from non-automatic to automatic operation. The mirror SP includes an eccentrically rotating transmitting aerial. The two units when operating non- automatically are adapted to scan overlapping areas from 70 degrees to port and 70 degrees to starboard and from 6 degrees below horizontal to 14 degrees above horizontal. , Any echo appears as a bright spot on a cathode-ray tube RAR, whose vertical distance from the bottom of the trace indicates range and whose horizontal position from the centre line of the tube represents bearing. The aircraft course is altered to bring a selected echo within the area scanned by the port scanner SP. At this point the starboard mirror is switched-out and if necessary an " inching " switch used to bring the selected echo on to the screen of the cathode-ray tube. The representation on the tube RAR is then changed to give range only, i.e. the echo appears as a vertical line whose horizontal distance from a strobe marker line represents range ; bearing and elevation are given by a second tube RAL. The strobe marker line is then advanced to coincide with the selected echo and the apparatus is then switched for automatic maintenance of training, the mirror following the selected target whose bearing and elevation are depicted on tube RAL. Automatic operation.-Pulses from a generator MVO are supplied through HFU to a rotating transmitting aerial and reflected echoes received on SP vary rhythmically according as the target is off centre of the mirror SP. These echoes are applied over HFU to the intermediate frequency amplifier IFU which is rendered inoperative during the periods of pulse transmission by valve V10 and after amplification, detection and restoration of direct current are applied over OFV2 to a strobing unit SU which is caused to generate a pulse coincident in time with the selected echoes. This pulse is used to isolate the selected echo which is applied to valve V11 in IFU for automatic gain control and to a distributer RSW which runs synchronously with the rotating aerial of SP. The distributer charges condensers RC7 ... 10 in accordance with quadrantal echo strengths so as to energize valves RV1 ... RV4 to operate elevation and azimuth motors ELM, AZM controlling the orientation of the mirror SP, so that the mirror SP is trained to receive equal strength echoes. Variometers VUA, VUE are fed from an oscillator VO and have their rotors moved in accordance with the azimuth and elevation of the mirror SP to provide potentials for application to cathode ray tube RAL so that the trace is a line whose angle indicates bearings. To avoid the 180 degree uncertainty, the oscillator output VO is applied over a delay network PL including rectifiers W to the suppressor grid of valve VB to pass pulses in the anode circuit corresponding to negative halfcycles of the oscillations from VO ; these pulses are differentiated by elements VC24 and VR72 to produce a short positive pulse causing VVII to conduct, so that the cathoderay in tube RAL is cut-off except for the short period in each cycle when VV11 conducts. Oscillations from VO are maintained of constant amplitude by diode VV9 determining the grid bias of VB so that an increase in amplitude of the oscillations from VO will cause anode current of VB to rise and the consequent fall in screen voltage of VB and VO will reduce the amplitude of the oscillations of VO. Operation of strobe unit.-The transmitted pulse is applied over STP, Fig. 1, to valve SV7, Fig. 4, to initiate a cycle in which a pulse is developed in the screen grid circuit at a time determined by the anode potential of SV7. This pulse is applied to SV9 and delay networks SDL1, SDL2 to produce pulses of, e.g. 3Ás and 1.5Ás duration applied respectively to valves SV1 and SV3. Echoes from IFU, Fig. 1, are applied over OFV2, Figs. 1 and 4, to the anode of SVI, Fig. 4, so that only that echo occurring within the pulse period of 3Ás is passed over RSO and SAGC for application to the distributer RSW, Fig. 1, and the gain control valve AGC, Fig. 1. The echoes are also applied from OFV2 to the anode of valve SV3, Fig. 4, which is "gated " by the pulse of 1.5Ás duration so that its anode potential varies according to whether the echo selected by SV1 lies within or without the pulse of 1.5Ás duration and is at a datum level when the echo lies equally within and without the pulse of 1.5Ás duration. This varying anode potential is applied over integrating valves SV4, SV5 to the cathode of diode SV6 to control the anode potential of SV7 and thus control the time of initiation of the pulses of 3Ás and 1.5Ás generated by SV7, SV8 and SV9. Stabilisation of supply voltages is obtained by the use of valve SV10 having condenser SC10 for instantaneous feed-back.