Feb. 18, 1947. A. M. SKELLETT 2,415,855 RANGE INDICATOR Filed July 26, 1944

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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. The transmitter may comprise, for example, duce a positive square-topped pulse 6 at the a high voltage rectifier of any suitable form which plate of the left half of the tube, which pulse, as Supplies about 12,000 volts direct current to a 40 shown in Fig. 2, is applied to the control grid of Suitable charging circuit or element capable of the tube W2 through the coupling condenser 27. producing a still higher voltage. After the charg The control or first grid of the tube V2 is con ing voltage builds up to about 21,000 volts, any nected to ground through the leak resistor 28 suitable rotary Spark gap discharges the capaci while the cathode is connected to ground through tor in the charging circuit. This discharge takes 45 the resistor 29 and the by-pass condenser 30, place in about one microsecond and causes a mag The common terminal of the elements 29 and 30 netron Oscillator in the transmitter to oscillate is connected to the suppressor or third grid which for this brief period and send short pulses of is connected to a point 3 on the potentiometer radio frequency energy through a T-R box to comprising the resistors 32, 33, 34, 35 and 36 con 50 nected between the terminal 23 and ground. By transmit to an antenna f2 which, for example, way of example the point 3 on this potentiometer includes a wave guide and a parabolic reflector. has a potential of about 53 volts positive with re Any Suitable antenna may be used. Radiations spect to ground. The screen or second grid of from the antenna strike one or more objects and the tube V2 is connected to a point 37 on this produce reflections or echoes therefrom which potentiometer which has a potential of about 150 are received by the antenna f2 and transmitted volts. The anode of the tube V2 is connected to through the T-R box to the receiver 3. The the positive terminal 23 through the resistor 38 T-R box can be of any desirable type, for ex and through the coupling condenser 39 to the ample that employing a Western Electric Com cathode of the triode W3. Negative echo pulses pany 709-A tube in a resonant cavity. This tube 60 62 from the receiver 3 are applied to the cathode is filled with an ionizable gas and has a small of the tube W2 through the coupling condenser gap therein. During reception of the low voltages 40. Due to the positive potential applied to the of the received energy, the gas is not ionized, the Cathode of the tube W2 from the point 3 on the cavity is tuned to resonance and the received potentiometer, the tube V2 is normally biased energy is applied to the receiver 3. During the 65 well below cut-off to such an extent that the con emission of a transmitted or radiated pulse from trol grid is approximately at cut-off potential the transmitter 0, the voltage due to the pulse When the range gate pulse 6 from the tube W is ionizes the gas thus detuning the cavity and sub applied to the control grid of the tube W2. The Stantially preventing the energy of the pulse from negative echo pulses from the receiver 3 thus reaching the receiver 3. 70 get through the amplifier mixer tube V2 only In the receiver 3 the received waves are when there is an overlap or coincidence in time heterodyned to a convenient intermediate fre of an echo pulse 62 and a range gate pulse 6. quency and these intermediate frequency waves When the tubes V2 and W3 are not passing cur are amplified, detected and applied to the range rent the coupling condenser 39 has a potential of indicator circuit 4 with such polarity that the 75 approximately 250 volts at its left-hand terminal 2,415,855 5 q 6 A and one of approximately 18 volts positive at range unit pulse a positive square-topped pulse its right-hand terminal B since this terminal is 6 in the output circuit thereof in a manner well connected to a point 4 on the potentiometer known. The pulse 6 is called a range gate pulse having this potential through the large re and is applied to the control grid of the tube W2. sistor 42. 5 It is to be understood that the time of each range The control grid of the tube V3 is placed at gate pulse 6 with respect to the corresponding ground potential while the anode is connected to radiated pulse from the transmitter is determined the point 37 of the potentiometer which is sub by the setting of the dials in the range unit 5 stantially 150 volts positive with respect to ground. and can be varied at will by turning the dials on The tube W3 acts as a rectifier and amplifier of the } {} the range unit. When the time of the range gate pulses produced in the output of the tube V2 and pulse 6 from the tube W overlaps the time of Serves with the condenser 39 and the resistor 42 as an echo pulse 62 from the receiver 3, the tube a peak voltmeter to produce a direct voltage repre W2, as pointed out above, conducts and causes the sentative of the amplitude of the output pulses potential of the terminal A of the condenser 39 produced at the anode of the tube W2. This di to drop suddenly from a value of about 250 volts rect voltage is applied to the control grid 50 of to a much lower value. Terminal B of the con the tube V4 which by way of example is a 6E5 denser 39, which has previously been at a po tube (frequently called a "magic eye' indicating tential of about 18 volts due to the fact that the tube) of the electron ray type. This tube com tube V3 is not conducting, follows this potential prises a first part comprising a triode or direct variation and its potential also swings in the Current amplifier including a cathode 5, the negative direction. The potential of the cathode control grid 50 and an anode 62 and a second of the tube W3, which is directly connected to the part comprising a continuation 53 of the cath terminal B of the condenser 39, also swings in a ode 5, a shadow casting or control electrode 54 negative direction and the tube V3 thereby con and a fluorescent screen or target 55. An end-on ducts current producing a flow of current through view of the target 55 is shown in Fig. 3. A tube the resistor 42 and varying the charge on the of this type is shown on page 30 of the booklet condenser. 39. At the termination of the echo, entitled "RCA Receiving Tube Manual' (1940). the cathode of the tube V3 and hence the grid 50 The target 55 is connected directly to the positive of the tube W4 is driven in a positive direction terminal 23 and through a resistor 56 to the anode due to the anode returning to its maximum volt 52 and the shadow casting electrode 54 which are age and to this charge variation, thus opening up electrically connected together. The target 55 the dark area of the screen 55. When the grid attracts electrons from the cathode 53 when the 50 of the tube V4 is negative with respect to the grid 50 is above its cut-off potential. When the cathode 5 thereof, the pattern of the tube screen electrons strike the target they produce a glow is a single bright line (the “magic eye' is just on the fluorescent coating thereof. Under these "overclosed”), but when the grid 50 swings in a conditions the target appears as a ring of light. positive direction, due to the coincidence of the The ray control electrode 54 mounted between range gate 6 and an echo pulse 62, the pattern the cathode and target is at a less positive po Opens up to a dark Sector about 90 to 100 degrees tential than the target when electrons are flowing 40 wide as shown by the shaded area in Fig. 3. As due to the potential drop in the resistor 56, and the coupling condenser 39 discharges through the hence electrons flowing to the target are repelled large resistor. 42 with a time constant consider by the electrostatic field between these electrodes ably longer than the pulse interval, the dark and do not reach that portion of the target be sector of the electron ray tube W4 remains open hind the electrode 54. Because the target does to a width proportional to the amplitude of the not glow where it is shielded from electrons, the echo as long as the coincidence of echo and gate control electrode 54 casts a shadow on the glowing is maintained. The action of the tube W3 in con target. The extent of this shadow varies from junction with the coupling condenser 39 and the approximately 90 degrees to 100 degrees of the resistor 42 is similar to that of a peak vacuum target when the control electrode is much more 50 tube voltmeter. The tube W3, being a triode, also negative than the target to substantially 0 de Serves to amplify the pulses in the output of the grees when the control electrode is at approxi tube W2. The potential of the cathode of the mately the same potential as the target. When tube V3 and hence of the grid 50 of the tube V4 the voltage of the grid 50 changes in the positive is a direct voltage substantially representative of direction, the plate current increases and the 55 the amplitude of the pulses produced at the plate potential of the control electrode 54 goes down of the tube W2 and hence of the echo pulses 62. because of the increased drop across the resistor By turning the dials on the range unit 5 to vary 56 and hence the shadow angle widens. When the spacing of the range gate pulses 6 produced the potential of the grid 50 changes in the nega in the output of the tube W with respect to the tive direction, the shadow angle narrows. 60 transmitted pulses radiated from the antenna 2, The operation of the circuit shown in Fig. 2 a survey may be made of all of the echoes being in the System of Fig. 1 will now be described. received, each echo being indicated by a pattern Radio frequency pulses of short duration are like that shown in Fig. 3. A reading of the range transmitted from the antenna, 2 and received by unit dial when such a pattern is produced gives the receiver "3 in the manner described above 65 with precision the range to the target. By way and negative echo pulses 62, such as those shown of example in a system of the type disclosed ac in Fig. 2, are applied to the cathode of the tube curacies of the order of two yards in 15,000 have W2. There may be one or more of these echo been obtained. pulses following each pulse radiated from the an While the invention has been shown and de tenna, 2, depending on the number of objects 70 scribed in connection with a pulse actuated object producing reflections within the range of the locator and distance measuring System, it will be equipment. For simplicity in the drawings, how obvious that the principles and apparatus are ever, only one negative echo 62 has been shown applicable to other pulse actuated systems in Fig. 2. Negative range unit pulses are ap wherein it is desired to indicate the coincidence plied to the multivibrator W to produce for each in time of two pulses. Moreover, it is obvious 2,415,855 7 8 that certain elements of the system described casting electrode which is connected to have its above can have uses other than in indicating potential varied as the intensity of such stream systems. is varied to thereby change the area of the The circuit constants of an operative form of shadow pattern on the screen, and means for the invention have been indicated on the draw applying said direct voltage to said Control elec ing but it is to be understood that the invention trode to produce a pattern on the Screen which is is not limited to the use of these specific Circuit of much larger area than is the pattern thereon constants as a change of one or more of the when said pulses are not applied to said elec variables of the system may necessitate a change trode. r of the circuit constants in a manner understood O 4. A device adapted to have applied thereto a by all those skilled in the art. first series of pulses and a second Series of pulses, What is claimed is: the individual ones of which are time spaced 1. A device adapted to have applied thereto a from corresponding pulses of the first Series by first series of pulses and a second series of pulses, substantially equal periods, and to give an indi the individual ones of which are time Spaced 5 cation of the duration of said periods comprising from corresponding pulses of the first series by means for forming a third Series of voltage varia substantially equal periods, and to give an indi tions time spaced like the first Series but in cation of the duration of said periods compris which the individual ones are displaced by a con ing means for forming a third series of Voltage trollable and measurable period of time from variations time spaced like the first Series but 20 corresponding pulses of the first series, a space in which the individual ones are displaced by current device to which pulses in the second and a controllable and measurable period of time third series are applied and being normally cut from corresponding pulses of the first series, a off to such an extent that it becomes conducting space current device to which pulses in the second to produce an output pulse only when a pulse of and third series are applied and being normally 25 the second series overlaps in time a pulse of the cut off to Such an extent that it becomes Conduct third series, means for producing a direct voltage ing to produce an output pulse only when a pulse from the pulses in the output of such space cur of the Second Series overlaps in time a pulse of rent device, and means for indicating said direct the third Series, means for producing a direct voltage, said means for producing a direct volt voltage from the pulses in the Output of such 30 age Comprising a condenser, a Vacuum tube and space current device, and means for indicating a resistor connected to function as a peak vacuum said direct Voltage. tube voltmeter, the time constant of said con 2. A device adapted to have applied thereto a denser and resistor being considerably longer first series of pulses and a Second Series of pulses, than the time between pulses in said first series. the individual ones of which are time spaced from 35 5. A device adapted to have applied thereto a corresponding pulses of the first series by sub first series of pulses and a second series of pulses, stantially equal periods, and to give an indication the individual ones of which are time spaced from of the duration of said periods comprising means corresponding pulses of the first series by Sub for forming a third series of voltage variations Stantially equal periods, and to give an indi time spaced like the first series but in which the 40 cation of the duration of said periods compris individual ones are displaced by a controllable ing means for forming a third series of voltage and measurable period of time from correspond variations time spaced like the first series but ing pulses of the first series, a space current de in which the individual ones are displaced by a vice to which pulses in the Second and third series controllable and measurable period of time from are applied and being normally cut off to such corresponding pulses of the first Series, a space an extent that it becomes conducting to produce current device to which pulses in the second an output pulse only when a pulse of the second and third series are applied and being normally series overlaps in time a pulse of the third Series, cut off to such an extent that it becomes con means for producing a direct voltage from the ducting to produce an output pulse only when a pulses in the output of such space current device, 50 pulse of the Second Series overlaps in time a and means for indicating said direct voltage, said pulse of the third series, means for producing last-mentioned means including an electron ray a direct voltage from the pulses in the output device. of Such Space current device, and means for 3. A device adapted to have applied thereto a indicating Said direct Woltage, said means for first series of pulses and a second series of pulses, 55 producing a direct voltage comprising a con the individual ones of which are time spaced from denser, a resistor and a vacuum tube compris corresponding pulses of the first series by sub ing an anode, a cathode and a control element stantially equal periods, and to give an indication connected to function as a peak vacuum tube of the duration of said periods Comprising means voltmeter, said condenser being connected be for forming a third series of voltage variations 60 tween the output circuit of said space current time spaced like the first Series but in which the device and the cathode of Said vacuum tube, and individual ones are displaced by a controllable Said resistor being connected between the Cath and measurable period of time from correspond ode of said vacuum tube and a point of fixed ing pulses of the first series, a space current de potential. % vice to which pulses in the Second and third 65 6. Circuit means adapted to have applied there series are applied and being normally cut off to to a series of pulses and to produce in the out Such an extent that it becomes conducting to put thereof an undulating direct potential, com produce an output pulse only when a pulse of prising a condenser, a resistor, a source of fixed the second Series overlaps in time a pulse of the potential, a Space current device comprising an third series, means for producing a direct voltage 70 anode, a cathode and a control element, a series from the pulses in the output of Such space cur circuit including said condenser, said resistor and rent device, an electron ray indicating device of said source of fixed potential and in which series the type comprising means for generating a circuit the condenser and resistor have a con stream of electrons, a control electrode, a fluo mon terminal which is connected to said cathode rescent target for said electrons, and a shadow 75 and said source of fixed potential has its posi 2,415,855 O tive terminal connected to the terminal of said ating a stream of electrons, a control electrode, resistor remote from said common terminal, a fluorescent target for said electrons, and a means connecting said control element to the shadow casting electrode which is connected to negative terminal of said source of fixed poten have its potential varied as the intensity of said: tial, means placing the anode at a fixed poten stream is varied to thereby change the area of tial positive with respect to the positive pole of the shadow pattern On the screen, means for said source of fixed potential, said potentials applying a series of pulses to Said control elec being Such that in the absence of pulses said trode, each of said pulses having a very short Space current device is cut off, and means apply duration compared to the time interval between ing said series of pulses to said series circuit and O pulses, and means responsive to each pulse in through said condenser to said cathode to drive the series for generating and applying to said said cathode in a negative direction to thereby control electrode a voltage during at least a por make the space current device conducting where tion of the interval between successive pulses by said condenser has its state of charge varied whereby the pattern On said Screen which Would by the flow of current through said resistor have been produced by Said pulses alone is made caused by the conduction of Said Space current more distinct. device, which state of charge is again varied by ALBERT M. SKELLETT. leakage through said resistor in the interval be tween pulses, said condenser and resistor hav REFERENCES CITED 8. ing a time constant which is considerably longer 20 The following references are of record in the than the interval between pulses whereby an file of this patent undulating direct potential is produced acroSS said resistor. UNITED STATES PATENTS 7. In combination, an electron ray indicating Number Name Date device of the type comprising means for gener 25 1924,174. Wolf------Aug. 29, 1933 Disclaimer 2,415,855.-Albert M. Skelett, Madison, N. J. RANGE INDICAToR. Patent dated Feb.Laboratories, 18, 1947. Incorporated. Disclaimer filed Mar. 3, 1950, by the assignee, Bell Telephone Hereby enters this disclaimer to claims 1 and 4 of said patent. Official Gazette April 4, 1950.

Disclaimer 2,415,855. Albert M. Skellett, Madison, N. J. RANGE INDICATOR. Patent dated Feb.Laboratories, 18, 1947. Incorporated. Disclaimer filed Mar. 3, 1950, by the assignee, Bell Telephone Hereby enters this disclaimer to claims 1 and 4 of said patent. Official Gazette April 4, 1950.)