Patent GB-594239-A (GB)
Title: Improved device for measuring the relative speed of two objects, such as a vessel or aircraft and target
IPC: G01S13/58
Filed: 1945-03-12
Abstract: 594,239. Radiolocation ; valve circuits. WESTERN ELECTRIC CO., Inc. March 12, 1945, No. 6206. Convention date, March 21, 1944. [Class 40 (v)] The relative speed of two objects such as an aircraft and a target or the ground, is determined by a pulse radar system, located on one object, in which a voltage which changes substantially linearly with time and at a much lower rate than the range sweep voltage is so adjusted that the instants of equality of the two voltages coincide with the receipt of successive echoes from the target, the rate of change of the second voltage being a measure of the relative speed of the two objects. The pulse radar system 1, of Fig. 1, is controlled from a recurrence-frequency pulse source 14, a B-type display being produced on the cathode-ray tube indicator 3, the horizontal deflecting coils HDC of which are energized by a rotary potentiometer 22. A time base generator 24 controlled by the pulse generator 14 and producing negative and positive 100Á see square waves to control the range sweep generator 50 and a pedestal pulse upon which the range sweep voltage is raised, comprises a biassed multivibrator, Fig. 2 (not shown), a condenser resistance filter being provided to remove distortion of the trailing edge of the negative output wave. The range sweep generator, Fig. 3, comprises a normally conducting valve V3 fed from the battery 31. via the potential divider 59, 60 resistor 58 and the diode V5. The 100Ásec negative pulse applied to terminal C2 cuts off the valve and permits a positive sweep voltage to be produced by the charging of condenser C and trimming condensers 69, 70. This sweep voltage of about 100 volts amplitude is superimposed upon the pedestal voltage fed via terminal B2 and appears at the cathode of valve V4 (terminal D1) which acts as an amplifier linearising the trace by feedback. The linearity of the sweep is further increased by the integrating circuit R<1>,C<1>. The range sweep voltage is fed, when, switch S (Fig. 1) is in the upper position, to the vertical sweep amplifier 200 to produce the range traces on the C.R. tube and is also fed together with the output from slow rate sweep generator 80 to the range differential amplifier 110. This unit 110 produces an output pulse when the rising voltage of each 100 Ásec range -sweep equals the output voltage of the rate sweep generator. This pulse is mixed with the received echo signal in amplifier 140, Fig. 6 (not shown), and is fed via video amplifier 170 to intensity modulate the C.R. tube indicator. Amplifier 170 is also fed with an unblanking pulse from the vertical sweep circuits 200 and may also be fed with suitably derived voltages to blank the oscilloscope trace during certain portions of the cycle of rotation of the antenna. The pulse from the range differential amplifier, occuring on each range scan, produces a range marking line RL on the B-type display and .the rate sweep generator is so adjusted that this marker intersects the echo signal as shown in Fig. 9A. With switch 8 in the lower position the vertical sweep on the C.R. tube is arranged to occupy 11 Á secs and commences at the instant of the output pulse from the range differential amplifier. Due to the delay network 250 the echo and range mark then appear on the indicator displaced from the end of the trace as indicated in Fig. 9B (not shown) and are stationary when the rate sweep generator is correctly adjusted for the relative speed of the target. The rate sweep generator, Fig. 4 comprises a valve V6 with a feed-back condenser C<11> coupled from anode to grid via the direct coupled amplifier V7 and cathode follower V8. The grid is connected to an adjustable positive voltage from potential divider 81 via a high resistance 85. When switch S<1> is in the upper position condenser C<11> is charged up through resistor 108 to about 195 volts as batteries 31 and 105 are in opposition, this voltage appearing also across resistor 103 and the voltage regulator tube V9. The output voltage on terminal F1 is then set by tap 109 to equality with the range sweep voltage at any desired instant during the 100 Ásec interval. When switch S<1> (corresponding to S of Fig. 1) is reversed the condenser C" discharges linearly at an adjustable rate which causes the output voltage to fall from 200 to 100 volts approximately in a time interval varying from varying .from 1¢ to 6 minutes, and causes the range mark to move slowly over the range sweep. The rate of discharge of C" is adjusted by tap 82 on potential divider 81 so that the range mark remains coincident with the target echo displayed on the 11 Ásec sweep (Fig. 9B, not shown), the setting of tap 82 indicating the relative target speed. The range differential amplifier Fig. 5 (not shown) comprises two valves coupled by a common cathode load comprising a constantcurrent valve. To one of the two valves the falling rate sweep voltage is applied while the other is fed via a cathode follower with the range sweep voltage. A positive output pulse is obtained at the anode of this second valve commencing at the moment of equality of the two sweep voltages and continuing to the end of the. 100 Á sec range sweep interval.