Patent GB-764733-A (GB)
Title: Distance measuring systems of the pulse radar type
Inventor: LEWINSTEIN MARCUS
IPC: G01S13/70
Filed: 1955-03-10
Abstract: 764,733. Pulse radar; electric-discharge tube circuits. SPERRY CORPORATION. March 10, 1955, No. 7051/55. Classes 40(6) and 40(7) In a pulse radar two contiguous shortduration early and late gate pulses M and N, Fig. 2, are oscillated between the centre and the trailing edge of long-duration gate pulse D whose timing is adjusted manually until a desired echo pulse is coincident with its second half and when the early gate M coincides with the echo the short gates M and N stop oscillating and return gradually to the centre of the long gate D whose timing is now controlled auomatically to maintain the short gates M and N symmetrical with respect to the echo. The oscillation of the gate pulses M and N is controlled electronically by a range sawtooth sweep generator and the timing of the gate pulse D is controlled by a motor which may also be coupled to a computer; thus a rapid search is obtained without requiring a corresponding rapid motion of the motor. General operation. As shown in Figs. 1 and 2, 3,400 c/s trigger pulse B, Fig. 2, for the transmitter 1 and the deflection circuit 9 of the C.R.T. 7 are derived in generator 5 from a 81.94 Kc/s sinusoidal output A from a crystal oscillator 11. Another output from generator 5 is applied through the variable-duration pulse generator 13 to trigger a monostable flip-flop 17 producing the long-duration gate pulse D which is applied to a coincidence circuit 25 together with a squared wave train F derived in 21 from another output from oscillator 11 and applied thereto through phase shifter 19 which is ganged with delay device 13 that the relative timing of waveforms D and F is constant. The output G from coincidence circuit 25 is differentiated at 27 and the positive peak of the resultant waveform H triggers a mono-stable generator 29 giving a sawtooth output I which is clipped in 31 at a level determined by the instantaneous amplitude of a sawtooth waveform (period=1 sec.) applied thereto from generator 43. The output J from clipper 31 is differentiated successively at 33 and and 35 and the positive peak of the resultant waveform L triggers the early gate pulse generator 39 whose 1/8 Á.s. output M is applied to coincidence circuits 45, 46 and 50 and through a 1/8 Á.s. delay line 51 to give the late gate pulse N which is ,applied to coincidence circuit 53. The long gate pulse D from 17 is differentiated at 49 and applied to coincidence circuit 50 together with the early gate M from generator 39, and the output 50 terminates the sweep output from generator 43 when the early gate M coincides with the trailing edge of the long gate D. The output from receiver 3 is applied to C.R.T. 7 and to coincidence circuits 45, 53 and 46. When an echo pulse coincides with the early gate pulse M the resultant output from coincidence circuit 46 operates switch 47 to terminate the sweep of generator 43 and gradually reduce its output voltage to zero and the resultant outputs from coincidence circuits 45 and 53 produce in balanced detector 55 a control voltage which is applied through switch 59 to actuate servomotor 57 controlling phase shifter 19 and delay device 13 to maintain the early and late gate pulses M and N symmetrical with respect to the echo. If the echo fades the sweep generator 43 starts to operate again causing the short gates to search until the echo re-appears. During the initial setting of gate pulse D the motor 57 is connected through switch 59 to a manually controlled voltage source 61. Valve circuits. The circuits of components 27, 29, 31, 33, 35, 37, 39, 43, 46, 47, 49 and 50 are shown in Fig. 3. The recurrent sawtooth output I, Fig. 2, from generator 29 is applied to the anode of a diode 71a and a sawtooth wave of much longer recurrence period from generator 43 is applied to the cathode of diode 71a via a cathode follower 73 so that only the portion J of sawtooth I which is of greater amplitude than the voltage of the cathode of diode 71a appears at said cathode. Diode 71b maintains sawtooth I positive relative to earth and triode 77 maintains the voltage at the anode of diode 71a equal to the voltage at its cathode when the grid of triode 73 is at earth potential. The clipped output J from diode 71a is differentiated by capacitor 79 and resistor 81, inverted in the lefthand side of double triode 83, differentiated again in the grid circuit of the righthand side of valve 83 and the resultant positive pulse L applied to trigger a double-triode blocking oscillator 39 which produces the early gate pulse M delayed relative to the start of sawtooth I by an amount proportional to the instantaneous amplitude of the voltage output from generator 43. Generator 43 comprises a thyratron 187 in parallel with a capacitor 93 connected in series with resistors 91 and 89. In the absence of echo pulses, thyratron 187 is triggered by circuit 50 each time the early gate pulse M reaches the trailing edge of the long duration gate pulse D but when the early gate pulse M coincides with an echo, the resultant negative pulses from gate circuit 46 are inverted by triode 113 and rectified by diodeconnected triode 109 giving a negative voltage which is applied via filter 107 to cut off valve 105 thereby making valve 103 conductive to discharge capacitor 93 and so return the narrow gate pulses M and N to the middle of the long gate pulse D.