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4%. 44 Patented Feb Feb. 18, 1947. A. M. SKELLETT 2,415,855 RANGE INDICATOR Filed July 26, 1944 A3 rawsurrea AaAMEWOca? off7 (P/G 2) WVEWTOR a- A.MSEZLA-77 4%. 44 Patented Feb. 18, 1947 2,415,855 UNITED STATES PATENT office 2,415,855 RANGE ENDICATOR Albert M. Skellett, Madison, N.J., assignor to Bell Telephone Laboratories, Encorporated, New York, N.Y., a corporation of New York Application July 26, 1944, Serial No. 546,630 Claims. (C. 6-15) 2 This invention relates primarily to object locat unit is a measure of the distance to the target ing and distance measuring systems of the pulse producing this echo. This arrangement, however, reflection type and more particularly to a circuit is subject to a number of disadvantages. The for producing a distinctive visible indication area on the screen of the cathode ray tube that when a pulse produced by reflection from a tar is used for the indication of the particular echo get is in Synchronous relationship with a pulse which is being aligned with the marker pulse is produced a controllable and measurable length of not over a square centimeter or two and to pro time after the radiated pulse producing the re duce this the cathode-ray tube is usually accom flection. panied by a power supply which produces thou The invention is particularly applicable to and O sands of volts and by sweep and other, cathode will be described by way of example in connec ray tube auxiliary circuits. The present inven tion with a pulse reflection type system employ tion, in One of its primary aspects, is concerned ing radio Waves, commonly called a radar System, with the provision of a precision range measuring but it is applicable as well to pulse reflection sys equipment which does not require a cathode-ray tens employing other types of waves, as, for ex 5 Oscilloscope and its accompanying auxiliary, ap anple, Sound ranging systems employing com paratus and circuits. pressional sound waves. In certain of its aspects It is an object of this invention to provide the invention is not limited to use with object novel pulse-actuated means for indicating the locating distance measuring systems as will be presence of an object and for measuring the dis apparent from the accompanying description and 20 tance thereto. appended claims. It is another object of this invention to pro A radar System usually includes a transmitting vide a precision range measuring equipment uti device adapted to emit radio frequency pulses lizing a relatively small number of circuit ele of very short duration (called “transmitted' or ments. "radiated' pulses) at frequent intervals, a re 25 It is another object of this invention to pro ceiving device at the same location for picking vide a novel pulse-actuated object locating and up and detecting reflection or echo pulses which distance measuring system utilizing a simple in are reflected from objects or targets on which dicating device for indicating the coincidence of the radiated or transmitted pulses impinge, and an echo pulse and of a pulse produced a meas a suitable indicator such as a cathode-ray oscillo 30 urable and controllable period of time after each Scope having its sweep synchronized with the radiated pulse producing the echo. period of the radiated pulses for causing images In accordance with One embodiment of the of the detected echoes in the order of their recep invention shown by Way of example for purposes tion to be displayed along a time axis on the fluo of illustration there is provided a simple range rescent screen thereof so as to provide a meas 35 indicator circuit comprising an electron ray in ure of the time interval elapsing between the dicating tube (frequently called a “magic eye' emission of each radiated pulse and the reception tube) and three other tubes which is intended to of a corresponding echo at the observation point. be used with a range unit of the type which is The elapsed interval is proportional to the dis disclosed in an application of I. A. Meacham, tance to the object causing the echo and may be 40 Serial No. 491,791, filed June 22, 1943, or in an translated into distance units. In one known type article entitled "The SCR-584 radar' in the Feb of radar System, there is provided a variable de ruary 1946 issue of "Electronics' beginning on lay unit (called hereinafter a "range unit') for page 110, for example. A negative pulse produced producing a pulse a variable and controllable in by the range unit is applied to the first tube in terval of time after each radiated or transmitted 45 the range indicator circuit which comprises a pulse and this range unit pulse (or another pulse double triode the two portions of which are con produced therefron) is applied to the same set nected as a multivibrator to produce a positive of deflecting elements to which the echo pulses Square-topped gate pulse which is applied to the are applied to produce a marker pulse on the control grid of a mixer tube to the Cathode of fluorescent screen adjacent a small portion of the 50 which is applied the video signal. This tube is trace of the video signal (comprising the echo normally biased well below cut-off so that the pulses). By varying the time delay of the range grid is approximately at Cut-Off potential when unit output pulse until the marker pulse over the range gate pulse is applied thereto. Thus, an laps or coincides in time with an echo pulse, the echo plulse in the video signal passes through the delay indicated on the range dials of the range 55 mixer tube only when there is an overlap in time 2,415,856 3 4. of the range gate pulse and an echo in the video echo pulses are in a negative direction. The cir signals. The mixer tube output signals are ap cult 4 will be described more fully below. plied to a peak voltmeter to form a direct volt Pulse energy from the transmitter 0, which is age representative of the amplitude of the pulses. in the nature of a synchronizing pulse, controls This direct voltage is applied to the control grid the range unit 5 which is essentially a variable of a "magic eye' indicator tube. When the range delay bircuit or unit which produces a pulse, for gate pulse coincides in time with an echo pulse, example in the negative sense, of predetermined the pattern on the fluorescent screen of the in duration and a controllable period of time after dicator tube is a large dark area about 90 to lo the initiation of the pulse from the transmitter degrees wide but when the gate pulse does not 0 f0, which is in the same position as, or slightly loincide with an echo pulse, the pattern is a after the radiated pulse. A suitable range unit thin bright line. By turning the range dial on is disclosed in the L. A. Meacham application or the range unit, a survey of all the echoes being in the "Electronics' article mentioned above. received can be made and the ranges of the Varl The output pulse from the range unit 5 com ous targets causing the echoes can be read on 5 prises, as shown in Fig. 2, a sharp negative pulse. the range dial. 60 which is applied to the tube V in the range The invention will be more readily understood indicator circuit shown in that figure. by referring to the following description taken in The tube V comprises a double triode such connection with the accompanying drawing form as a 6SN7 tube. The range unit pulse is applied ing a part thereof in which: 20 to the control grid of the left half of this tube Fig. 1 is a schematic block diagram of a radar through the coupling condenser 20 while a leak system employing a novel range indicator circuit resistor 2 is connected between the grid and ir accordance with this invention; cathode of this half of the tube. The cathode of Fig. 2 is a circuit diagram of the range indi the left half is also connected to the cathode of the cator circuit; and 25 right half and both cathodes are connected to Fig. 3 shows the pattern on the fuorescent ground through the resistor 22. The anodes of screen of the magic eye indicator tube when an the left and right halves of the tube W are con echo pulse and a gate pulse coincide in time. nected to the positive terminal 23 of a source of Referring more particularly to the drawing, direct voltage of, for example, 250 volts through Fig. 1 shows by way of example for illustrative 30 anode resistors 24 and 25, respectively. The purposes, a radar system utilizing a simplified anode of the left half of the tube W is connected range indicator circuit. Fig. 1 is a single line to the control grid of the right half through a block diagram to show the relationship of the coupling condenser 28 while the anode of the various major elements of the system and is not right half is connected to the control grid of the intended to be a circuit diagram. In the arrange left half through the resistor 47 and the coupling ment of Fig. 1, an ultra-high frequency pulse condenser 20. The two halves of the tube V are modulated wave is produced in the transmitter thus cross-connected as a multivibrator to pro O.
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