Patent GB-997839-A (GB)
Title: Improvements in or relating to radar training apparatus
Inventor: FRANKLIN KENNETH VINCENT
IPC: G06G7/78
Filed: 1962-06-27
Abstract: 997,839. Radar simulators. COMMUNICATIONS PATENTS Ltd. June 27, 1962, No. 24608/62. Heading H4D. Radar simulating apparatus comprises means, generating in sequence, signals corresponding to the co-ordinates, relative to a datum point, of each of a plurality of simulated observed craft, means generating in sequence, range control signals/for each craft, having maximum values corresponding to the maximum range of observation of the respective craft, and means comparing co-ordinate signals and range control signals of each craft and controlling gating means, such that only craft with simulated positions within their corresponding observation range are displayed by display means. In Fig. 1, craft 1 and craft 2 potentiometers 12 and 13 are connected in parallel across a D.C. source 10, together with an " Own " craft potentiometer 14. The wipers of the three potentiometers are positioned by respective shafts 12<SP>1</SP>, 13<SP>1</SP> and 14<SP>1</SP> to tap off voltages representing the N-S coordinates of the three craft relative to a common datum point. The wipers of the craft 1 and craft 2 potentiometers are cyclically earthed through switch 18, provided with a centre contact rotated by motor 21 via gears 22, whilst the " Own " Craft wiper is connected to one input terminal of an amplifier 23, having its other input terminal earthed. The amplifier output at terminal 23<SP>1</SP> and applied to the y plates of C.R.T. 25, thus represents the N-S or yr co-ordinates of the two craft in turn relative to the " Own " Craft. E-W or xr relative co-ordinates are similarly provided at terminal 24<SP>1</SP> and fed to the C.R.T. x plates. To ensure that only simulated craft are displayed having ranges within the required limits, " bright up " pulses, generated by monostable unit 28 triggered by rotating switch 26, rotated in synchronism with switches 18 and 19 are applied to the C.R.T. control grid through an AND gate 29, having its other input fed from a range system fed in turn with co-ordinate signals from terminals 23<SP>1</SP> and 24<SP>1</SP> and comprising the range control signal producing means and the comparing means of the opening statement. The range control signal circuit, Fig. 2, comprises means 46, generating quadrature signals E sin wt and E cos wt through potentiometers 43 and 42 respectively. The maximum value Rm of the range control signals for each craft is the product of two constants, Fo, or " Own " Craft constant and Fc, a Craft 1 on Craft 2 constant. Equal signals are tapped off these two potentiometers by wipers controlled by an Fo setting shaft 40. The Fo signals are passed to the rotary contacts of switches 48 and 47, having Craft 1F potentiometers 45 and 44 connected to their first contacts and Craft 2 Fc potentiometer (not shown) connected to their second contacts. The wipers of Fc potentiometers 45 and 44, controlled by Fc setting shaft 41, are similarly connected to the first contacts of rotary switches 50 and 49, the centre contacts of which, rotating in synchronism with switches 18 and 19, pick off signals representing Rm sin wt and Rm cos w. respectively for each craft. These two signals are fed to symmetrical amplifiers 52 and 51, yielding signals at their output terminals 52<SP>1</SP>, 52<SP>11</SP>, 511 and sill, representing Rm sin wt, - Rm sin wt, Rm cos #t and - Rm cos #t, respectively. These signals are respectively fed to comparators 65, 64, 61 and 60 of the range limiting system of Fig. 3. Comparator 61 is also fed with the Yr co-ordinate signal from terminal 23<SP>1</SP>. Similarly the Yr co-ordinate signal is added to the - Rm cos wt signal at the input of comparator 60, the Xr co-ordinate signal from terminal 24<SP>1</SP> is added to the + Rm sin wt signal at the input of comparator 65 and to the - Rm sin #t signal at the input of comparator 64. Comparators 60, 61, 64 and 65 each comprise a double triode having a common cathode resistance, one grid connected to ground and with the input signals fed to the other grid. The potentials of the anodes of the double triode thus charge in opposite senses when a signal is applied to the input grid. Each anode is connected to a separate amplifier chain, comprising a triode amplifier and a cathode follower circuit. The amplification of the double triode is such that a slight signal on the input grid cuts off or saturates the triode amplifiers. Each comparator is therefore provided with two outputs one of which provides a pulse output following the combined potential at the comparator input and the other of which provides a pulse output opposing the said input. The outputs from comparators 60 and 64 which follow the input are chosen, whilst the outputs from comparators 61 and 65 which oppose the input are chosen. When, for example, a positive Yr co-ordinate signal is at terminal 23<SP>1</SP>, the combined input to comparator 61 is mostly positive excepting for a small negative section having a width representing the duration for which the signal Rm cos wt was greater than the amplitude of the co-ordinate signal. The output of comparator 61 will give a corresponding positive pulse of like width, which is passed via negative pulse blocking diode 69 to the grid of an " OR " triode 72. A similar positive pulse will be produced from comparator 60 when a negative Yr co-ordinate signal is present. Comparator 64 similarly produces a positive pulse with a negative Xr co-ordinate signal and comparator 65 produces a positive pulse with a positive Xr co-ordinate signal. The pulses passing to the grids of triodes 72 and 77 therefore have widths representing the time during which, Rm cos wt > Yr and Rm sin wt # Xr. The outputs of " OR " gates 68 and 73 are as shown in Fig. 4 then, If the pulses overlap then ty > tx, or The pulses will therefore only overlap when the distance between the distant craft and the " Own " Craft, is less than the maximum observational range Rm. The outputs from gates 68 and 73 are therefore fed to an "AND" gate 78, which only develops a signal across the output resistance 82 when the output pulses overlap. The output signal from gate 78 is differentiated and detected at 85, and the resulting positive spike is fed to trigger a bistable circuit 84. With no signal from gate 78 valve 88 is normally kept cut off by a succession of pulses from the wiper of switch 26, Fig. 1. A pulse from circuit 85, however, switches the bistable circuit over such that valve 88<SP>1</SP> is now cut off and a positive potential can be taken from the anode thereof and applied, via a neon 99 and a cathode follower valve 98, to one input of an " AND " gate 29. The other input of gate 29 is fed with a signal from switch 26, delayed by means 28 by an amount sufficient to give the rest of the circuit time to settle down. Simultaneous reception of signals at the two inputs of the gate 29 produces an output signal from the gate, which is fed to brighten up the C.R.T. beam and display the corresponding craft. Alternatively, since the width of the amount of overlap of the outputs from gates 68 and 73 represents the range of the craft, the output of gate 78 may be integrated, and the resulting signal used to control the brightness of the C.R.T. display. This produces dimutation of the display with increasing distance. Both methods of display may be combined to provide progressive dimutation of response after a predetermined initial range value has been exceeded.