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1D@n 17, 1946. D. w, EPSTEIN -PULSE-ECHO POSITION INDICATOR Filed June 26, 1942 2,412,670 Dec. 17, 1946. D, W_ EPSTElN 2,412,670 PULSE-ECHO POS ITION INDICATOR Filed June 26, 1942 „34 2 Sheets-Sheet 2 CHW/ODL' )MY TUBE‘ 52 1G. Z. 4Z NORTH /NDlCH’í'l/VG ’ G. 36 Way/vc. PULSE I-I | EG. 4. l 'I l Fiend; , _pma . l Ij 70 /vomw fía. 6. Fie., Z FÍG.8a. _ITM ""“91 ' L _,igfJ/gggk ""ME _* .sPo'r 35 SYNC. Snnen‘tor David WEpvsteLn Gttomeg Patented Dec. 17, 1946 UNITED STATES PATENT ori-fica 2,412,670 PULSE-ECHO POSITION INDICATOR David W. Epstein, Merchantville, N. J., assignor to Radio Corporation of America, a corporation i of Delaware Application June 26, 1942, Serial No. 448,663 - 1 8 Claims. , My invention relates to pulse-echo position indi cating system and particularly to systems adapt ed to convey the position information to a re mote point or central station. It will be de scribed as applied to‘a position indication sys tem-in which a directive transmitting antenna _is rotated horizontally to sweep a radio beam > through a horizontal plane while pulsing-the beam. 'I'he radio pulse is reflected if it strikes an- airplane or the like. The reflected pulse is picked up by a receiver located near the pulse transmitter and the distance of the reflecting object is determined by the time elapsed between> transmission of the initial or time-reference pulse and receptionof the reñected pulse. The direc tion of the reilecting object is determined also by employing at the receiver a cathode ray indi cator tube in which the cathode ray is deflected » radially and at the same time, rotated in syn (Cl. Z50-1) . 2 . ‘ rate as compared with the rate at the indicator tube located at the transmitter; these rates are 30 per second and 600 per second, respectively, in the example describedl below. The signal for 5 pulsing or modulating the cathode ray of the indicator tube at the remote station (this signal corresponding to the reflected pulses applied to the indicator tube at the receiver which is usu ally located in the vicinity of the transmitter) isobtained by applying the reflected pulses to a second cathode ray tube at the transmitter to store them on a fluorescent screen and by deflect ing the cathode ray of this tube along a line trace at the pulse rate. The resulting stored pulse ap pearing at a point on the line trace is scanned by a rotating disc having radial slits which scan the line trace at the low frequency radial deflection rate employed at the remotey indicator. When a scanning disc aperture'comes opposite the light chronism with the rotation of the transmitting- 20 spot on the line trace, a pulse of light is trans mitted to a photoelectric cell to produce a cor antenna. responding electrical pulse. These pulses may It may be desirable to install a plurality of sta be transmitted .over an ordinary wire line such tions of the above described type spaced apart as a telephone line or over a narrow frequency the proper distance to give protection over a large geographical area. In that case it may be band transmitter to the cathode ray tube indi cator at the remote or central station since their desirable to convey the information from all pulse repetition rate in the example assumed is 30 per echo stations to a central station where one per second, instead of 600 per secondv as the trans son has before him a view of all the position in mitter station, with a corresponding reduction in dicating views or patterns that are present at the individual stations. A dimculty in doing this is 30 the frequency band. The invention will be better understood from that such infomation ordinarily occupies a fairly wide frequency band, from 100 to 60,000 cycles the following description taken in connection with the accompanying drawings' in which Fig. 1 is a per second, for example. This band is too wide diagram of a pulse-echo position `indicator sys for transmission over the usual telephone, tele. 35 tem embodying the invention, Fig. 2 is a view of graph or wire line. the scanning disc shown in Fig. 1,- and Figs. 3 to An object of the present invention is to pro 8a are graphs which are referred to in explain vide an improved method of and means for re ing the invention. Like parts in the figures are - ducing the above-.mentioned frequency band, pref erably enough to permit transmission of the po indicated by similar reference numerals. sition indication information over a wire line to 40 Referring to Fig. 1, a radio transmitter I0 is keyed at the rate of 600 pulses per second. for ex a central station. , ample, to radiate pulses of very short duration Another object of the invention is to provide from a suitable directive antenna Il. Antenna an improved method of and means for conveying Il may be a dipole in a parabolic reflector I2 or >information from a radio pulse-echo position in 45 it may be of any other suitable design. It is ro dicator to a remote point. _ tated at 10 rotations per minute, forexample, in A further object of the invention is to provide a horizontal plane about a vertical shaft I3. The an improved means for and method of producing shaft I3 is driven by a synchronous motor It an orienting indication in a system of the above through a gear box I6, the mechanical coupling - described type. In one embodiment of my invention the posi 50 being indicated by the broken lines. The motor I4 is connected to a 60 cycle power line I6.' Suit tion indication- at the remote station appears on a cathode ray tube provided with a defiecting yoke able pulse keying means I1 is driven by a syn chronizing pulse generator I8. that is rotated in synchronism with the rotation of the transmitter antenna.` 'I'he radial deñec The receiver I9, which is located in the vicin tion produced by this yoke is at a low frequency 65 ity of the transmitter, receives 'the reñected pulses ` ‘ 2,412,070 3 of carrier wave frequency, demodulates them, and applies them to the control electrode .of a cath ode ray indicator tube 2| having a fluorescent screen 22; Tube 2| is provided with a rotat rotated in synchronism with the antenna rota tion. This may be done by a synchronous motor 51 that is driven synchronously from the tele phone line as will be explained below. A sawtooth deilecting wave recurring 30 times per second is produced in the yoke 56 by a sawtooth wave gen erator 3| to deiiect the cathode beam radially. The generator 6I is held in ñxed time relation to able deñecting yoke 23 of the magnetic type hav ing slip rings 24 and 23 which are connected through brushes to a sawtooth generator 21. The yoke 23 is rotated synchronously with the an tenne rotation by means of gears 23 and 23 which the pulse transmission by synchronizing pulses are mechanically coupled to the gear box I3. transmitted over the wire line. It will be under The sawtooth generator 21 is synchronized with stood that atthe indicator tubes 2i and 54 the the radio pulse transmission by means of pulses sawtooth sweep is so phased with respect to the from the synchronizing ~generator I3 supplied over transmitter pulse that the deiiection starts from a conductor 3l. The deiiecting wave applied to the center of the fluorescent screen at the in the yoke 23 contains a direct current component 15 stant the pulse is transmitted. The ñuorescent such that the deñection of the cathoderay is screen of the tube 54 is indicated at 53. from the center of screen .22 toward the circum The synchronizing pulses for controlling both ference. The cathode ray tube 2| may be biased the sawtooth generator 3i and the synchronous nearly to beam current cutoii! in the absence of a motor 5l are produced at a photoelectric cell 33 received pulse or to some value less than maxi mum Ibeam current whereby a luminous spot ap pears on the screen 22 upon the reception >of a puise. This spot has a circumferential position depending upon the direction of the reiiecting object from the rotating transmitter antenna and has a radial position (distance from center of screen) depending upon the distance of the re ñecting object from the transmitter antenna. Ii an attempt were made to transmit the re 20 positioned opposite the scanning disc 42 whereby light from a source I1 falls upon the cell 83 each time a slit aperture 45 comes between the source 61 and the cell 66. A mask 65 may be provided to deiine an area of light opposite a disc aperture. - The resulting synchronizing pulses are amplified by an ampliñer 68 and are supplied to the mix ing ampliiler 50. Reference or “north indicating" pulses 'il are also produced by means of a photoelectric cell 33 ñected pulse, wnich recurs at 600 times per sec 30 and a light source 1 I positioned on opposite sides ond, to a remote station over an ordinary wire of the scanning disc 42. The pulses from the cell line, for example, it would be found that the ñ 69 are ampliiied by an ampliñer 12 and are sup delity of transmissionwould be very poor as the line would not transmit the required frequency band. Therefore, I have provided means for re plied through a biased amplifier 13 to the mixing ducing the frequency band required whereby in ampliñer 50. A mask 14 limits the area of light opposite the synchronizing slit. Fig. 2_ indicates the relative radial positions of fomation sent over a line to a central station will give on the indicator tube an acceptable indica tion of the position of the airplane or other re the photoelectric cells 43, 53 and 36 (which have been displaced toward the center of the scanning disc to avoid confusion in the drawings) and of fleeting object. 40 their associated light sources while Figs. 3 to 4 The frequency band reducing means comprises show the photoelectric cell outputs and the way a cathode ray tube 32 having a iluorescent screen in which they are mixed. The rotation yof the 30 on the enlarged end. Deflection of the cathode scanning disc 42 is in the direction indicatedr by ray is provided by means of a pair of defiecting , the arrow. At the instant the disc 42 is in the po coils 33 which are supplied with sawtooth current 45 sition illustrated, a synchronizing pulse (Fig. 3) from the sawtooth generator 21. The 600 cycle sawtooth current is synchronous with the keying pulses. ` ‘ The tube 32 is properly biased nearly to beam is being generated and a north indicating pulse (Fig. 6) has just been generated. The line trace 34 and spot 35 (Fig. 4) have already been scanned and will now be scanned again. y cutoff, for example, so that a spot of light 35 ap 50 A_S shown in Fig. 5, the synchronizing pulses are pears on the screen 30 when a reilected pulse reversed in polarity by ampliner 33 and are mixed is applied to the control electrode of tube 32 over in amplliler 50 with the signal representative of a conductor 4 I. This light spot appears at a point spot 35. Also, the reference or north indicating on the linear deflection path or trace indicated by the dotted line 34 and 'at a position determined by the time that the reñected pulse appears upon the control electrode.'- . ' pulse is combined with the signal (shown in Fig. 5) to produce the resultant signal shown in Fig. 7. This signal is sent over the wire line to the central station. . ' A rotatable disc 42 having a plurality of radial At the central station the signalis ampliiled by slit apertures 45 is located opposite the screen ampliilers ‘I1 and 13 and is applied to the control 30. In order to direct light from the spot 35 to a 60 electrode of cathode ray tube 54 with the syn photoelectric cell 43,v a lens system 41 is provided chronizing pulses of negative polarity. The same to image the light spot 35 on a disc aperture. The signal, but preferably of opposite polarity, is sup dise 42 is rotated te cause the apertures 4s to scan' plied to a synchronizing pulse separator 18 where the spot 35 at a low rate compared with the pulse by synchronizing pulses may be supplied to the ’ rate, this being 30 per second in the example il deilecting circuit 3| and to a tuned ampliiler 3l -lustrated whereby theirequency band is reduced which drlve's the motor 61. A diilïerential gear 32 yto 3%00 or 17g@ ot the original >band width. The permits phasing of the yoke 53 by turning a crank Vdisc may be driven by a motor 5I which may or 33. ‘ ' may not be synchronous. The pulse output of The north indicating pulse appears on the the photoelectric cell 43 is amplified by an ampli 70 screen of tube 54 only when the antenna il is iler 52 and transmitted through a mixing ampli pointing north (or is pointing in some other pre fier 50 and over a wire line to the central station. determined direction). This is accomplished by At the central station there is a cathode ray driving a switch 33 from the gear box I3 or from indicator tube sa which, like the tube 2|. is pro antenna shaft i3 so that the switch 33 is closed vided with a rotatable deilecting yoke 53 that is 75 only when antenna il is pointing in the desired $5,412,670 6 2. In a system for reducing the frequency band required to transmit the information contained direction. When the switch 88 closes it com pletes a circuit through a conductor 81 to unblock a relaxation oscillator much as a multivibrator in a wave consisting of periodically recurring I9 whereby multivibrator pulses 9| (Figs. B and electrical pulses each of which occurs at a certain time> after -the occurrence of a time-reference pulse, means comprising a cathode _ray tube and a screen associated therewith for storing an image 8a) are produced. When the switch 86 is closed it connects the cathode of a- multivibrator tube to ground to initiate a pulse 9|. Multivibrator 89 is adjusted so that a pulse 9| of said nrst pulses on said screen with said image which is short enough to add only one "north in spaced from a time reference point by an amount dicating” pulse 'l0 is added thereto in the biased 10 determined by sai certain time, said means in cluding deilecting m ansior producing a straight amplifier 'I3 as shown in Fig. 8. As shown in Fig. 8a, the antenna switch 86 is opened before line trace'on. said screen, and means for scanning another multivibrator pulse 9| indicated in dotted said trace at a slower rate' than that 4oi’ the iirst line in Fig. 8a can occur. As shown in Fig. 8, the ‘ ` pulses to convert said stored image to pulses re ampliñer 'I3 is biased suñlciently beyond cutoiï 15 curring at said slowerrate, said scanning means comprising a scanning disc having a plurality so that a north indicating pulse is passed to the mixing ampliñer 50 only upon the occurrence of a of radial slits therein. multivibrator pulse 8|. 3. In a radio system, means for transmitting The persistence of fluorescence of the screen 83 I' pulses to an object whereby they are reflected and of the screen 22 of tube 2i should be several from said object, said pulses lrecurring at a cer seconds, preferably six seconds where -the yoke tain rate, means for receiving said reflected rotates 10 R. P. M. (i. e., once in 6 seconds; The - persistence of fluorescence of the screen 30 of the pulses inthe region of the transmitting means, there being a certain time interval between said transmission and reception, a cathode ray tube tube I2 should be at least l/too second (the time of one deflection) and preferably is about 1/ao 25 having >a ñuorescent screen that has persistence second in the example shown for good signal of fluorescence, means for defiecting the cathode ' » to noise ratio. The fluorescence decays gradually, ray along a linear trace on said screen at said as is well known, but a satisfactory screen is one certain rate, means for modulating said cathode ray by said reñected pulses whereby an image in which the light falls to one-half maximum in ` tensity in ‘lsu second, for example. 30 thereof is stored on said'screen, means for scan From the foregoing it will be apparent that ning said screen at a lower rate than said certain the pulse produced in the photoelectric cell I3 oc rate and for simultaneously taking signal oft' said ~‘curs at a time following the instant of pulse screen at said lower rate to produce pulses at said lower rate, said last means including a scanning transmission which is measured by the time taken for a disc aperture to rotate from a “zero delay" 35 disc having a plurality of circumferentially spaced position which is at one end of the scanning apertures located to rotate the apertures'past said line 34 to the position of the spot of light 35. Thus trace to scan it lengthwise, a cathode ray indi the 30 cycle pulses sent over the line to the cen cator tube having a beam control element, meansx for applying said pulses occurring -at the lower tral station have a time delay with respect to the instant of pulse transmission that corresponds 40 rate to said control element, and means for de accurately -to the delay between pulse transmis fiecting the `cathode ray of said indicator tube at said lower frequency. sion and pulse reception at receiver i9. The ‘4.In a system for indicating the position oi’ radial position indication on the indicator tube an object, means for transmitting pulses to said M will be the same las on the indicator tube 2|.It will also be seen that the north indicating pulse 45 object from a directive rotating antenna whereby is obtained, without the use of any mechanical they are reflected from said object, said pulses connection between the rotating antenna || and ' recurring at a certain rate, means for receiving the scanning disc 42. This may be an important said reflected pulses in the region of the trans advantage as the frequencyreducing unit com mitting means, there being a certain time inter prising disc 42 may be located several hundred 50 val between said transmission and reception, a feet from the antenna. A further advantage is cathode ray tube having a storage screen, means that with the proposed reference or north indi for detlecting the cathode ray along a straight cating system the scanning disc 42 itself need line trace on said screen at said certain rate, not be held in synchronism with the rotating an means for modulating the said cathode ray by tenna. A still further advantage is that .by means said reflected pulses whereby an image thereof is of my system a very exact timing of the north in stored on said screen, means comprising a rotat able disc having circumferentiaily spaced slits for~ dicating pulse is obtained at the indicator tube scanning said trace at a lower rate than said cer 5I. . , - I claim as my invention: , tain rate andfor simultaneously taking signal' l. In a system for reducing the frequency band 60 off said screen at said lower rate to produce pulses occurring at said lower rate, a cathode ray indi~ required to transmit the infomation contained in a wave consisting of periodically recurring cator tube which contains means for generating electrical pulses each of which occurs at a certain an -electron beam, means for applying said lower time after the occurrence of a time-reference rate pulses to said- indicator tube to modulate said pulse, means comprising a cathode ray tube and beam, means for radially deiiecting the electron a fluorescent screen associated therewith forbeam of said indicator tube, means for -rotating l storing an image of said ñrst pulses on said nscreen the plane of said radial deñection in synchronism " with said image spaced from a time reference with the rotation of said antenna, and means for point by an amount determined by said certain producing said radial deilection at said lower ~time, said means including deilecting means for 70 rate with the deflection from center starting sub producing a straight line trace on said screen, stantially at the instant of a pulse transmission. and means for scanning said trace at a slower 5. In a system> for indicating the position of rate than that of the i‘irst pulses to convert said an object. means for transmitting pulsesto said stored image .to pulses recurring at said slower rate. . . obiect from a directive rotating antenna whereby /sntna-evo ' they are reflected from said object, said pulses recurring at a certain rate, means for receiv ing said reflected pulses in the region of the transmitting means, there being a certain time . 8 said renected pulses in the region of the trans mitting means, there being a certain time inter val between said transmission and reception, a l cathode ray tube having a storage screen, means interval between said transmission and reception, 5 for deilecting the cathode ray along a recurring a cathode ray tube having a storage screen, means for deflecting the cathode ray along a straight path or trace on said screen at said certain rate. means for modulating said cathode ray by said reilected pulses whereby an image thereof is line trace on said screen at said certain rate, means for modulating said cathode ray by said stored on said screen, means .comprising a ro reflected pulses whereby an image thereof is 10 tatable scanning disc having a plurality of aper stored on said screen, means comprising a rotat tures for scanning said trace at a lower rate than able disc having circumferentially spaced slits for said certain rate and for simultaneously taking signal oir said screen at said lower rate toipro certain rate and for simultaneously taking signal duce pulses occurring at said lower rate. .a cathode o1! said screen at said lower rate to produce pulses ray indicator tube which contains means for gen occurring at said lower rate, a cathode ray in erating an electron beam, means for applying dicator tube which contains means for generating said lower rate pulses to said indicator tube to an electron beam, means for applying said lower modulate said beam, means for radially deiiiecting> rate pulses to said indicator tube to modulate said the electron~ beam of said indicator tube, means beam, means for radially deflecting the electron 20 for rotating-the plane of said radial deflection in beam of said indicator tube, means for rotating synchronism with the rotation vof said antenna, the plane of said radial deflection in synchronism means for producing said radial deñection at said scanning said trace at a lower rate than said with the rotation of said antenna, means for pro ducing said radial/deflection at said lower rate lower- rate with the deflection from center start- ` ing substantially at the instant of a pulse trans with the deñection from center starting substan- 25 mission,r and means for increasing the intensity tially at the instant of a pulse transmission, and means for increasing the intensity of the indi cator tube beam momentarily in response to the of the indicator tube beam momentarily in re sponse to the rotating antenna reaching a pre determined point in its rotation, said last means including a photoelectric device and light source in its rotation. 30 for producing a reference voltage pulse in re ' 6. In a system for indicating the position of an sponse to a scanning aperture moving across the object, means for transmitting pulses to said ob path of light from said light source to said pho ject from a directive rotating antenna whereby toelectric device, a biased amplifier tube, switch they are reflected from said object, said pulses means for producing a voltage pulse in response recurring at a certain rate, means for receiving 35 to said antenna reaching said predetermined »said reflected pulses in the region of the trans point, and means for utilizing said last pulse to mitting means, there being a certain time interval unblock said biased amplifier momentarily to .between said transmission and reception, a cath pass one of said reference pulses to said indicator ode ray tube having'a fluorescent screen that has tube. ‘ ' persistence of fluorescence, means for deflecting 40 8. In a system for indicating the position oi' the cathode ray along a straight line trace on an object, means for transmitting vpulses to said said screen at said certain rate, means for mod object from a directive rotating antenna whereby ulating said cathode ray by said reflected pulses they are reflected from said object, said pulses whereby an image thereof is stored on said screen, recurring at a certain rate, means for receiving means comprising a rotatable disc having cir said reflected pulses in the region of the trans rotating antenna reaching a predetermined point cumferentially spaced slits for scanning said trace l mitting means, there being a certain time inter at a lower rate than said certain rate and for val between said transmission and reception, a simultaneously taking signal of! said screen at cathode ray tube having a storage screen, means said lower rate to produce pulses at said lower for deilecting the cathode ray along a recurring , rate, a cathode ray indicator tube which con 50 path or trace on said screen at said certain rate, tains means for generating an electron beam, means for modulating said cathode ray by said means for applying said lower rate pulses to said reflected pulses whereby an image thereof is indicator tube to modulate said beam, means for stored on said screen, means comprising a ro radially deiiecting the electron beam of said in tatable scanning disc having a plurality of aper- , dicator tube, means for rotating the plane of 55 tures for scanning said trace at a lower rate than said radial deflection in synchronism with the ro said certain rate and for simultaneously taking tation of said antenna, means for producing said signal oii' said screen at said lower rate to pro ,radial deiiection at said lower rate with the de f duce pulses occurring at said lower rate, a cath - :Election from center starting substantially at the ode ray indicator tube which contains means for instant of a pulse transmission, means including 60 generating an electron beam, means for applying a photoelectric device located adjacent to said said lower rate pulses to said indicator tube to scanning disc for producing synchronizing pulses modulate said beam, means for radially deflecting for synchronizing the deflection of said indicator the electron beam of said indicator tube, means tube, and means including a second photoelectric for rotating the plane of said radial deflection in device located adjacent to said scanning disc and 65 synchronism with the rotation of said antenna, circumferentially displaced with respect to the means for producing said radial deflection at said other photoelectric device for increasing the in lower rate with the deñection-from center start tensity of the indicator tube beam momentarily ing substantially at the instant of a pulse trans in response to the rotating antenna reaching a mission, and means for increasing the intensity predetermined point in its rotation. of the indicator tube beam momentarily in re '7. In a system for indicating the position of an sponse to the rotating antenna reaching a pre object, means for transmitting pulses to said ob determined point in its rotation, said last means ject from a directive rotating antenna whereby including photoelectric means for producing a they are reñected from said object. said pulses reference voltage pulse each time a scanning recurring at a certain rate, means for receiving 75 aperture passes a certain point, a biased ampli 2,412,670 A 9 10 fier, a. relaxation oscillator which is normally blocked and which ls adjusted to produce a volt age pulse of a duration greater than that of said reference pulse but less than the period of re currence of said reference pulses when it is un blocked, switch means for producing a Voltage pulse in response to said antenna reaching said last pulse to said relaxation oscillator to unblock it momentarily, and means for applying said ref erence pulses and said relaxation oscillator pulses in additive relation to said biased ampliñer and with such amplitudes that only the reference predetermined point, means for applying said pulse which is added to a relaxation oscillator pulse is passed by said biased ampliñer. DAVID W. EPSTEIN.