Patent GB-760482-A (GB)
Title: Improvements in and relating to radar equipment
Inventor: MILLANE MICHAEL JOHN
IPC: G01S7/14
Filed: 1953-07-22
Abstract: 760,482. Radar; cathode-ray tube oscillographs. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 22; 1954 [July 22, 1953], No. 20361/53. Class 40(7) A radar employing a P.P.I. type display is provided with means for expanding a selected sector of the field being scanned to cover a larger angular space on the display by causing the angular velocity of movement of the radial trace to be greater than the angular velocity of the aerial scanning beam. In one embodiment a rotatable aerial 20 is provided which is driven by a motor and coupled through gearing to selsyns 28 and 29. The rotor of selsyn 28 is made to rotate at the same speed as the aerial 20 whilst that of the selsyn 29 rotates at a higher speed for example 4 times as fast. For the provision of a normal P.P.I. display selsyn 28 is coupled by switch 30 to selsyn 27 which drives the rotatable scanning coil 25 of the display tube 24 in synchronism with the aerial rotation. The radial trace sweep. voltage is generated by unit 40 triggered by a pulse synchronized with the transmitter pulse and fed in at 38. Received echo signals are fed from the receiver at 45 and applied by unit 44 to intensity modulate the tube 24. To obtain the expanded sector display switch 30 is operated to connect selsyn 29 to selsyn 27 to cause angular expansion of the trace.. Switches 22 may be provided co-operating with cam 21 on the aerial drive shaft to cause the aerial to scan over the wanted sector. The wanted sector may be selected from the full display by manually positioning the bearing cursor 31 to indicate the required sector. This drives selsyn 33 which, with switch 36 closed (i.e. in the position for expanded display), drives selsyn 34 to control differential 37 to position the sector required correctly on the tube and also drives selsyn 35 to adjust the positions of operation of the limit switches. For some uses it may be desired to expand the range scale over a selected portion of the sweep. For example the radial sweep may be adjusted to represent a change in range of 1 ¢ miles and means be provided for adjusting the position of a wanted image to a point 2/3 of the way along the trace. For this purpose an adjustable range marker may be provided on the normal P.P.I. display. This can be obtained by the use of a saw-tooth generator 41 triggered by the pulse from input 38. When the saw-tooth voltage reaches a level equal to that fed in by manually adjustable potentiometer 43 comparator circuit 42 generates a marker pulse for application through amplifier 44 to the tube. On changing to expanded sector type display the switches 39 and 47 are changed over and the trigger pulse is fed to sawtooth generator 50 similar to generator 41 whose output is compared in circuit 49 with a voltage level set by potentiometer 43 and non-adjustable device 48 to represent a range value one mile less than the positioning of the adjustable range marker. When coincidence of input levels occurs in circuit 49 a pulse is generated which is applied to time base generator 40 to produce a delayed high speed radial scan representing 1¢ miles overall. The pulse from circuit 49 may also be applied to circuit 53 which provides fixed range ring producing signals to the tube over switch 52 operated synchronously with switch 47.