Dec, 17, 1946. ` - A. V. BEDFORD 2,412,669 PULSE-ECHO POSITION INDICATOR Filed June 1_9, 1942 NN ‘ 2 Sheets--Sheet l Dec. 17, 1946. A. v. BEDFORD PULSE-ECHO POSITION INDICATOR _ Filed June 19, 1942 2,412,669 ` Patented Dec. 17, 1946 2,412,669 unirse > 2,412,669 PULSE-nono POSITION mDIcA'roR Alda V. Bedford, Collingswood, N. J., assignor to Radio Corporation of. America, a- corporation of Delaware Application June 19, 1942, Serial No. 447,630 5 Claims. (Cl. 250,-1) My invention relates to pulse-echo position in-V dicating systems and particularly to systems adapted to convey the position information to a remote point or central station. The invention is- hereinafter described as applied to a position indication system in which a directive transmit ting antenna is rotated horizontally to sweep a radio beam through a horizontal plane while puls ing the beam. The radio pulse is reflected if it strikes an airplane or the like. The reiiected pulse is picked up by a receiver located near the pulse transmitter and the distance of the re 'a rates being 30 per second and 600 per second,` respectively, in the example described below. The `signal for pulsing or modulating the cathode ray of the indicator tube at the remote sta tion (this signal corresponding to the reflected pulses applied to the indicator tube at the trans mitter) is obtained by applying the >received re flected pulses to a second cathode ray tube at the transmitter to store them on a fluorescent screen and by deflecting the cathode ray of this tube circularly at the pulse rate. The result ing stored pulse at a point on the circular trace is scanned _by a single aperture disc rotating at flecting object is determined by the time elapsed the low-frequency radial-deflection rate employed between transmission and reception of the pulse._ The direction of the reflecting object is deter 15 at the remote indicator tube. When the scan ning disc aperture comes opposite the light spot mined also by employing at the receiver a_ cath on the circular trace, a pulse of light is trans ode ray indicator tube in `,which the cathode ray mitted to a photoelectric cell to produce a cor- . is rotated in synchronism with the rotation of responding electrical pulse. These pulses may be the transmitting antenna and is swept radially 20 transmitted over an ordinary wire line to the cath ode ray tube indicator at the remote station since It may be desirable to install a plurality of their repetitionrrate in the example assumed is stations of the above-described type spaced apart 30 per second instead of 600 per second as at the proper distance to give protection over a the transmitter station with a corresponding re large geographical area. In that case it may be desirable to convey the information from all 25 duction in the frequency band.' In another embodiment of the invention, the pulse-echo stations to a central station where frequency reduction is obtained by employing a one person has before him a view of all the posi to establish a distance coordinate. - tion-indicating views or patterns that are present ` ' cathode ray storage tube in place of the scan ning disc and by scanning circularly the storage at the individual stations. A diñiculty in doing this is that such information ordinarily occupies 30 tube. The pulse signal is stored on a mosaic by ' a fairly wide frequency band, from 600 to 60,000 cycles per second, for example. 'I'his band is too wide for transmission over the usual tele phone,`telegraph or other wire line. An object of the present invention is to pro 35 means of a cathode ray that is deflected at the high-frequency rate,v such as 600 per second. It is taken oiï the mosaic by means of a cathode ray that is deiiected at the low-frequency rate, such as 30 per second. The invention will> be better understood from the following description taken in connection with the accompanying drawings in which Fig. 1 enough to permit transmission of the position is a diagram of a pulse-echo position indicator indication information over a wire line to a cen 40 system embodying the invention, and Fig. 2 is a tral station. . di-agram of another embodiment of the inven Another object of the invention is to provide an vide a method of and means for reducing the above-mentioned frequency band, preferably improved method of and means for conveying information from a radio pulse-echo position in tion. Like parts in the two figures are indicated _by similar reference numerals. . Referring to Fig. 1, a radio transmitter I0 is "Another object of my invention is to reduce 45 keyed at the rate ,of 600 pulses per second, for the amplitude of the noise in the signal of reduced . example, to radiate pulses of very short dura frequency as compared with the original signal. tion from a suitable directive antenna II. An tenna Il may be la dipole in a parabolic reflector In one embodiment of my invention the posi I2 or it may be of any other suitable design. It tlon indication at .the remote station appears on a cathode ray tube provided with a deflecting is rotated at 10 rotations per minute, for example, in a horizontal plane about a vertical shaft I3. yoke that is rotated in synchronism with the The shaft I3 is- driven by a synchronous motor rotation of the transmitter antenna. ' The radial ldeflection produced by this yoke is at a lowy fre I4 through a gear box I6, the mechanical cou dicator to a remote point. quency rate as compared with the rate at the pling being indicated by the broken lines. The indicator tube .located at> thetransmltter; these 55 ' motor i4 is connected to a (iO-cycle power line 2,412,669 4 I5. Suitable pulse-keying means I1 is driven 4by a synchronizing-pulse generator I8. The receiver I6, which is located in the vicinity of the transmitter, responds to the reflected pulses of carrier-wave frequency, demodulates them, and applies them to the control electrode of a cathode-ray indicator tube 2| having a fluores cent screen 22. Tube 2| is provided with a rotat . circular deflection. In order to direct light from the spot 35‘ to a photoelectric cell 43, two mirrors 44 and 46 are mounted on the disc 42, one opposite the disc aperture and the other at the disc axis. A lens system 41 in front of the disc aperture images the light spot 35 thereon. Counterbal ancing means for the disc is shown at 40. The disc 42 is> rotated at a comparatively low speed. able dei'lecting yoke 23 of the magnetic type which may be a submultiple ofthe pulse rate. havingfslip rings 24 and 26 which are connected 10 this being 30 rotations per second in the example through brushes to a. sawtooth generator 2l. The illustrated whereby the frequency band is reduced yoke 23 is rotated synchronously with the antenna to 3%00 or 1750 of the original band width. It may rotation by means of gears 28 and 29 mechani be driven through a gear box 5| by the syn cally coupled to the gear box I8. chronous motor I4. The pulse output of the ’ The sawtooth generator 21 is synchronized with 15 photoelectric cell 43 is amplified by an amplifier the radio-pulse transmission by means of pulses 52 and transmitted over a wireline to the central from the synchronizing generator _| 8 supplied station. _ over a conductor 3|. T_he deiìecting wave ap-~ plied to the yoke 23 contains a direct current com At the central station there is a cathode ray indicator tube 54 which, like the tube 2|, is pro ponent such that the deflection of the cathode ray 20 vided with a rotatable deñecting yoke 56 that is is from the center of screen 22 toward the circum rotated in synchronism with the antenna rotation. ference. Since the cathode-ray tube 2| is biased This may be done by a synchronous motor 51 that is supplied with power from the same 60 cycle to beam-current cutod in the absence of a re ceived pulse, or at least to less than maximum line l5 that supplies power to the motor |4. A beam current, a luminous 'spot appears on the 25 sawtooth deñecting wave recurring 30 times per screen 22 upon the reception of a pulse. This second is produced in the yoke 56 by a sawtooth. spot has a circumferential position depending Wave generator 6| to deñect the cathode beam radially. The generator 6| is held in fixed time relation to the pulse transmission by connecting position (distance from center of screen) depend 30 lit to the 60-cycle power line I6 through a phase l upon the direction of the reflecting object from the rotating 'transmitter antenna and has a radial ing upon the distance of said object from the transmitter antenna. shifter 62. It will be understood' that at the in dicator tubes 2| and 54 the sawtcoth sweep is so If an attempt were made to transmit the re phased with respect to the transmitter pulse that iiected pulse, which recurs at 600 timesV per sec the deflection starts from the center of the ond, to a remote station over an ordinary wire 35 iiuorescent screen at the instant the pulse is line it would be found that the fidelity of trans transmitted. The fluorescent screen of the tube mission would be very poor as the telephone line 54 is indicated at 63.' « would not transmit the required frequency band. The persistence of fluorescence of the screen 68 ' Therefore, I have provided means for reducing. and the screen 22 of tube 2i should be several the frequency. band required whereby informa 40 seconds, preferably six seconds' where the yoke tion sent over a telephone line to a central station will give on the indicator tube an acceptable in dication of the position of the airplane or other rotates 10 R. P. M. or once in 6 seconds. The persistence of fluorescence of the screen 30 of the tube 32 should be at least 1,600 second (the time of one circular deflection) and preferably is about The frequency-band reducing means comprises 45 ¿so second in the example shown for good signal a cathode ray tube 32 having a fluorescent screen to noise ratio. The iiuorescence decays gradually, 8U. Circular deñection of the cathode ray is as is well known, but a satisfactory screenA is one provided by means of two pairs of deiiecting coils in which the light falls to one-half maximum in 33 and 34 positioned at right angles to each other. tensity in 1%@ second. reiiecting object. Coils 33 and 34 are supplied, from a suitable 50 From the foregoing it Will be apparent that the ' source 36, with sine wave current having a fre pulse produced in the photoelectric cell 43 occurs qency of 600 cycles per second, the current in at a time following the instant of pulse trans coils 34 being shifted 90 degrees with respect to mission which is measured by time taken for the that in coils 33, by means of a phase shifter 3l. disc aperture to rotate from the “O-delay” posi The GOO-cycle sine wave current is synchronous 55 tion indicated on the screen 30 to the position of with the keying pulses. In the example shown it is produced by supplying the 60G-cycle pulses from the synchronizing pulse generator I8 over the spot of light 35.` 'I'hus the 30-cycle pulses sent over the wire line to the central station have a time delay with respect to the instant of pulse a conductor 38 to the sine-wave source 36. The transmission that corresponds accurately to the source A36 may be simply a circuit tuned to 600 60 delay between pulse transmission and pulse re cycles per second. The tuned circuit converts the ception at receiver I9. `'I'he radial position in pulses into sine waves which may be amplified or dication on' the indicator >tube 54 will be the the pulses may be amplified before conversion. ' same as on the indicator tube 2|. 'I‘he tube 32 may be (but is not necessarily) In Fig. 2 the frequency band reduction is ob biased to beam cutoff so that a spot of light 35 65 tained by means of a cathode-ray storage tube appears on -the screen 30 whenv a reflected pulse 66 of the general type shown in Schroter Patent is applied to the control electrode of tube 32 over 2,175,573, issued October 10. 1939. The specific a conductor 4|. This light spot appears at a tube construction illustrated- is the same as‘that point on the path of circular deflection indicated shown in Beers Patent 2,273,172, issued February by the dotted circular trace and at a position 70 17, 1942.- The tube 66 is a double-tube construc- . determined by the time that the reíiected pulse tion in which a-highly evacuated envelope con appears upon the control electrode. tains oppositely-disposed electron guns, each of A rotatable disc 42 having a single aperture which may be of conventional construction in which preferably is a radial slit is located opposite cluding the usual cathode control electrode, ñrst the screen 30, and centered with respect t0 thel 75 Vanode and second anode. ' asiaeco , _ mosaic lindicated at 1l and collecting electrodes transmission which time> depends upon the po sition of the stored pulse on the mosaic li. yringswhereby they may collect secondary elec trons from the mosaic 1| without being struck the ray is unblocked or modulated to produce a yspot of light at a distance from said center which ‘.The tube includes the so-called double-sided 12 and 3 on opposite sides thereof. The collect ing electrodes 12 and 18 may be in the form of by the electron beams as the mosaic is-scanned. Therefore, as the cathode ray oi’ tube dt is de ilected outwardly from the center or screen B3. "represents ‘the distance of the reflecting airplane several well-known constructions. For example, or the like from the rotating antenna Il. The direction of the reflecting object from the an 28, 1934, in the name of Leslie E.' Flory and as Fig. 1.v The double-sided mosaic screen 1i may be any of it may be constructed in accordance with the 10 tenna Il -is shown by the circumferential posi _tion ofthe lightspot Just as in the system of teachings 'of Patent No. 2 045.984, filed February . It may be noted that, in addition to reducing the frequency band, the use of my invention lm - Preferably the mosaic 1| is operated slightly positive with respect to the second anode. In the 15 proves the signal to noise ratio since the reflect ed pulses occur and are stored in a deñnite phase example illustrated. the mosaic is connected to relation whereas noise pulses occur in a random ground while the second anodes are 25 volts nega time relation. tive and the other electron gun electrodes are op I claim ’as my invention: v „ erated at suitable negative potentials with re 1. In a radio system, means for transmitting spect to ground, as indicated. Specific voltages pulses to an object whereby they are reflected are given on the drawings merely by way of ex from said object, said pulses recurring at a cer ample. tain rate, means for receiving said reflected The cathode ray in the left hand section of pulses in the region of the transmitting means, tube 56 is deflected along a line on the mosaic 1I signed to Radio Corporation of America. at the rate of 600 deñections per second by means there being a certain time interval between the instant of transmission _of a pulse and the re ception of said pulse, means for converting said reflected pulses to pulses which recur at a sub multiple frequency of said certain rate with each line on the mosaic at the rate of 30 deñections per second by means of deñecting coils 18 con 30 pulse of said submultiple frequency occurring at nected to a sawtooth generator 19 which may be a certain time interval following a time reference synchronized from the power line l5. ^ instant, said last-mentioned time interval being ' 'I'he collecting electrode 12, which may be con equal to said submultiple times said first-men nected to ground through a resistor 1d, functions _ tioned time interval, a cathode ray indicator tube as the input control electrode and is connected to having a'beam control element, means for ap the output circuit of 4the receiver I9 through a plying said submultiple pulses to said control ele conductor 10. The collector electrode 13, which ment, and means for deilecting the cathode ray may be connected to ground through a resistor of said indicator tube at said submultiple fre 18, functions as the signal output electrode to quency with the start of each deflection begin supply the signal of reduced band width to the 40 ning at said time reference instant. wireline through an ampliñer 15. 2. In a radio system, means for transmitting The operation of the- delay tube SS is substan pulses to an object whereby they are reñected ` tially as follows: Simultaneously with the scan from said object, said pulses recurring at a cer-' ning of the mosaic 1_l by the electron beam_ ro tain rate, means `for receiving said reflected 45 duced in the left hand portion of the tube` the pulses in the region of the transmitting means, received reflected pulse is supplied over the con there being a certain time interval between said , ductor -10 and is impressed upon the electrode 12 transmission and reception, a cathode ray tube to vary its potential in accordance with said pulse having a storage screen and means for directing whereby the individual capacity elements of the a mosaic acquire electrostatic charges in accord 50 cathode ray against said screen, means for de flecting the cathode ray along said screen at said ance with the amplitude of the applied signal. It certain rate, means for modulating said cathode will be understood that the capacity elements of ray by said reflected pulses whereby an image the mosaic 1| acquire different charges in this of defiecting coils 11 connected to the sawtooth generator 21. The cathode ray in the right hand section of tube 65 is deflected along this same manner because the electrode 12 collects more or less secondary electrons from them depending“ thereof is stored on said screen, means for scan ning said screen at a frequency lower than said certain rate, and means for simultaneously tak ing signals off said screen Vat said lower frequency to produce pulses at said lower rate, a cathodev ray and may be taken oil` at any time by causing the indicator tube having a beam control element, electron beam produced in the right hand end means for applying said pulses occurring at the of the tube to scan the other side of the mosaic 60 lower rate to saidcontrol element, and means for 1|. As this other side of the mosaic 1| is scanned, deflecting the cathode ray of said indicator tube secondary electrons are released from the mosaic at said lower frequency. ~ and collected by the electrode 13 whereby the 3. A system for reducing the frequency band _pulse signal appears across the resistor 16. It required to transmit the information contained will be understood that this output signal is pro in a wave consisting of electrical pulses recurring duced because the number of secondary electrons upon its potential. . _ Thus a pulse signal is stored on the mosaic 1i . going from a picture or capacity element of the , periodically at a certain rate each of which occurs mosaic 1I to the-.collectorv electrode 13 depends upon the potential difference between them, this depending upon the charge of the individual pic reference pulse, said system comprising a cathode at a certain time after the occurrence of a time ray tube having a fluorescent screen which has a certain persistence of fluorescence, means for modulating the cathode ray of said tube by said first pulses, means for deflecting said cathode ray parent that pulses are supplied to the telephone at said certain rate whereby there is stored on line which recur 30 times per second and which occur at a time following the instant of pulse 75 said screen an image of said iirst pulses with said ture or capacity element. _ From the foregoing description it will be ap image spaced from a time reference point by an. - amount determined by said deiiection rate, opti cal means i‘or scanning the image on said screen at a lower rate than said certain rate, and means for simultaneously taking signals ofi.' said screen at said lower scanning rate for converting said stored image to pulses recurring at said lower object, means for transmitting pulses to sam ola»-4 ject from a rotating directional antenna whereby they are reñected from said object, said pulses recurring at a certain pulse repetition rate, means in the region of the transmitting meansl for receiving said reñected pulses, there being a certain time interval between said transmission and reception, a cathode-ray tube having a stor rate. 4. In a system for indicating the position of age screen and means for directing a cathode ray g an object, means for transmitting pulses to said 10 against said screen, means for modulating said object from a. rotating directional antenna whereby they are reflected'irom said object, said pulses recurring at a certain pulse repetition rate, cathode ray oi.' said tube by said received pulses. means for deflecting said cathode ray at said pulse repetition rate whereby there is stored on means in the region of the transmitting means said screen .an image ot said received pulses with for receiving said reflected pulses, there being a 15 said image spaced from a time reference point by certain time interval between the instant of an amount that is a function of said certain time transmission of a pulse and the~ reception of said interval, means for scanning said time reference pulse, means for converting said reñected4 pulses point and the image on said screen at a lower to pulses which recur at a lower rate than said scanning rate than said pulse repetition rate, and certain pulse repetition rate with each pulse oi 20 means for simultaneously taking signal on said said lower rate occurring at a time interval fol screen at said lower scanning rate for converting lowing a time reference instant which interval said stored image to pulses recurring at said lower is equal to the ratio of said certain pulse repeti rate, a cathode ray indicator tube, means for ap- ' tion rate to said lower rate times said ñrst time plying the pulses occurring at said lower rate to interval, a cathode ray tube including electron 25 said tube to modulate said beam, means for radi beam producing means, means for applying said ally deiìecting the electron beam of said indi lower rate pulses to said tube to modulate said cator tube, means for rotating the plane of said beam, means for radially deñectin‘g the electron radial deflection in synchronism with the rotation beam of said tube, means for rotating the plane of said antenna, and means for producing said of said radial deflection in synchronism with the so radial deñection at said lower scanning rate with rotation of said antenna, and means for produc the deiìection from center starting substantially ing said radial deñection at said lower rate with at the instant of scanning said time reference the deiiection from center starting substantially point. at said time referenceinstant. ` ' 5. In a system for indicating the position oi’ an 35 ALDA V. BEJDBI’ORD.