US2451005A - Cathode-ray storage tube apparatus and method of operation - Google Patents

Description

Oct.

Filed Aug. 30, 1946 P. K. WEIMER ETAL CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION 6 Sheets-Sheet 1 Oct. l2,

Filed Aug.

TRA Ns. I Ifp uz 6E 1948. P. K. wElMER ETAL 2,451,005

CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION 30, 1946 6 Sheets-Sheet 2 Rec. El' g TRM/s Rfc, fifa/sf WFM/1.55 I/Pz/Lsf I I L/GH 7' PULSE l I l 2L I scfPff/v Porn/TML 7M l Jamin aap/N6 2m scm/uws IRv/NG WULFF A T TOR/VE Y Y Oct. 12, 1948. P. K. WEIMER ETAL (CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION 6 Sheets-Sheet -3 asm oscopf ELAN/'50 LIGHT Arm/'mfr Oct. 12, 1948. P. K. wElMER Erm. 2,451,005

CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION Filed Aug. 30, 1946 6 Sheets-Sheet 5 /MAGE ORTH/CO/V FOR TIME DEX 7G/VAL //V 7' RGDUCED U JCREEA/ PULSE F11/sf I IPUTOW/V I mlm-@FF I 55AM Guxme-Nr I /3/ I--I (//vpur .WGA/,4.4) |/\/I I /32 I l I I I (33 |V I r/Mf POTENTIAL 0F 2 I-z----I l /36 ,vorf/vT/AL'MFT a/v GLASS TARGET FOR TARGET Br 1:1.' suiv (BEFORE SCA/v) RE Tuk/v 55AM (our/ur S16/VAL) 1N VEN TOR. PAUL A. WE/MEE' VLAD/M/R A. Z WOR YK /N da ATTUR/VEY K. wl-:IMER er AL 2,451,005 AY STORAGE TUBE APPARATUS @cte P.

cA'rHonE-R AND METHOD or' OPERATION Filed Aug. so, 1946 e sheets-sheet 6 PULJL SQUARE PULSE E' GLA/MA1 R WAVE- i SOURCE j GIA/5R47' "5) /2/ y L53 56/ REVERS/N6 U5) r "N L 4 VL AMP. :LJ-11144 m r 61 "7 l, AMR r\f S16/VAL? 36N DEFL. INPUT c/RcU/ V will 46 2/ /34 54) n.9` :aU/veraf LIGHT PULSE OUTPUT L\ AMR P- AMP s/GNAL INPUT URV/N6 WoLFF atented Oct. 12, 19

CATHGDE-RAY STORAGE TUBE APPARATUS AND METHOD F OPERATION Paul K. Weimer and Vladimir K. Zworykin, Princeton, and Irving Wolil, Manasquan, N. J., assignors to Radio Corporation of America, a

corporation of Delaware Application August 30, 1946, Serial No. 694,042

1s claims. 1

Our invention relates to cathode ray storage tube apparatus and particularly to methods of and means for utilizing such apparatus for ground clutter reduction in radar systems, for delaying signals, etc.

The invention will be described with particular reference to the use of a television pick-up tube of the type known as the Image Orthicon especially as applied to a radar system for distinguishing between stationary and moving objects. One of the diiliculties in detecting aircraft approaching a radar station, particularly if the aircraft is at a low altitude, is that the signal reflected from the ground or from buildings or hills obscures the signal reflected from the aircraft. Such obscurlng signals are referred to as ground clutter. Similarly, signal reflected from an aircraft flying through a regionfilled with floating metal foil or the like may be obscured by reflections from the metal foil.

One of the objects of the present invention is to provide an improved method of and means for distinguishing between signals reflected from stationary or substantially stationary objects and signals reflected from moving objects.

A further object of the invention is to provide .an improved method of and means for reducing the amount of ground clutter or the like in a radar picture.

A still further object of the invention is to provide an improved method of and means for utilizing a cathode ray storage tube of the low-velocity-beam double-sided-mosaic type for distinguishing between signals reflected from stationary objects and signals reected from moving objects.

.A still further lobject of the invention is to provide an improved method of and means for utilizing a cathode ray storage tube of the low-velocity-beam double-sided-mosaic type for delaying signals.

Y A still further object of the invention is to provide an improved method of and means for indicat-.ing any difference in signals that occur in succession.

According to one preferred embodiment of the invention, a cathode ray storage tube of the Image Orthicon type is employed in combination with a. pulse-echo radar system of the coherent pulse type. By utilizing a'coherent pulse system the phase of the carrier wave of the ref'lected pulse may be compared with a carrier wave of fixed phase so that any change in phase due to motion of the reflecting object may be detected. Thus, there may -be supplied to the 2 storage tube a received signal that remains the same for successive received pulses if the pulses are reilected from a stationary object but which is dlerent for each received pulse if the reilecting object is moving. The storage tube is employed for comparing the successive signals and is so operated that there is signal output only if successive signals are unlike.

In this embodiment of the invention for distinguishing between stationary and moving objects, the successive signals from the radar receiver or mixer are applied to a storage tube electrode so that one signal puts a charge pattern on the storage plate or target as itis scanned by an electron beam. If the next successive signal (produced by the next reflected pulse) is the same there will be no output signal but if it is different there will be an output signal or pulse indicating reilection from a moving-object. At the end of the second signal (and the second electron beam scan) light is flashed on the photocathode of the storage tube to bring the tube back to its initial operating condition.

The invention will be better Iunderstood from the following description taken in connection with the accompanying drawing in which Figure l is a block and circuit diagram showing one embodiment of the invention as applied to a pulse-echo radar system of the coherent pulse type wherein the signa-ls are impressed upon a mesh screen electrode of the storage tube,

Figure 1A is a view illustrating a modiilcation of the circuit shown in Fig. 1 wherein the signals are impressed upon the cathode of the storage tube,

Figure 2 is a group of graphs that illustrate the operation of the apparatus of Fig; 1 when successive receivedsignals are alike.

Figure 3 is a group of graphs that illustrate the operation of the apparatus of Fig. 1 when successive received signals are dilerent as when reflected from a moving object,

Figure 4 is a block and circuit diagram of an embodiment of the invention wherein the received signal is applied to a control electrode of the storage tube to modulate the electron beam of the storage tube instead of being applied to a screen adjacent to the target plate as in Fig. l or to the cathode as in Fig. 1A,

Figure 5 is a group of graphs that illustrate the operation of the apparatus of Fig. 4,

Figure 6 is a group of graphs that illustrate the use of the invention for delaying a signal where the signal is applied to the screen adjacent to the target plate,

Figure 7 is a group oi graphs that illustrate the use of the invention i'or delaying a signal when the signal is applied to the electron beam modulating electrode, and

Figures 8 and 9 are block and circuit diagrams illustrating apparatus for delaying a signal in the way illustrated in Figs. 6 and '7, respectively.

In the several figures similar parts and similar graphs are indicated by similar reference characters.

Referring to Fig. 1, the radar system includes a radio pulse transmitter which comprises an oscillator I acting as a source of radio frequency energy and a power amplifier II which is pulse Y modulated by means of periodically recurring pulses supplied from a pulse generator I2 through a suitable modulating circuit I3. As inthe usual pulse-echo systems, the resulting radio pulses radiated from the transmitter antenna i6 are of short duration compared with the period be-V tween successive pulses.

Pulses reflected from an object are picked up by a receiving antenna I1 and supplied to a mixer I8 which may be the same as the first detector or converted tube of a superheterodyne receiver. However, the local oscillator signal supplied to the mixer I 8 is obtained from the R.F. source I0 and is of the same'frequency as Athe carrier wave of the received signal.

The output signal of the mixer I8 depends upon the phase relation of the received carrier wave signal with respect to the R.F. signal supplied from the source I0 to the mixer. This output signal is the same for successive received pulses of R.F. signal so long as this phaserelation is unchanged, as when the signal is reilected from stationaryobiects. However, if the reecting object is moving, the said phase relation is continuously changing and the mixer output signal is dierent for each received pulse.

In order to detect a changing signal and separate it from any unchanging signal, a cathode ray storage tube 2| is employed. The specific storage tube shown is the well known Image Orthicon which comprises a double-sided mosaic or target plate 22 on which signal is stored, a mesh screen electrode 23 close to the target plate 22, and a photoelectric cathode 24 on'the large end of the tube envelope. The tube 2l further comprises an electron gun at the other end of the tube envelope which comprises a cathode 26, a control electrode 21. and a ilrst anode 28. A storage tube of the Image Orthicon type is described in application Serial No. 554,494, led September 16, 1944 in the name of Paul K. Weimer, and `which is now U. S. Patent 2,433,941, issued Jan. 6, 1948.

The storage tube 2| is also provided with a w coating 29 that is held at a potential less than that of the anode 28 and is further provided with a ringelectrode 3| that is at ground potential. An external focusing coil 22 is provided. Thus, a low velocity electron scanning beam is directed against the target plate 22. The electron beam may be aligned by an alignment coil. It is caused to scan the target plate 22 by means of a deilecting yoke 24 which is supplied with sawtooth current from a de ilection circuit 36. If desired. spiral scanning may be employed instead of sawtooth scanning.

The particular tube 2| being described by way of example is of the same design as the Image Orthicon employed for television pickup and, therefore, includes ring electrodes 21. and 2l for imaging the electrons from the photoelectric cathode 24 upon the target plate 22. This imaging of the electrons is caused by the electrostatic neld resulting from the ring electron arrangement 31, 28 and by the electromagnetic ileld of the focusing coil 32. Buch imaging is not essential for the use or the storage tube 2| in the present invention as electrons from the cathode 24 are utilized only to bring the target plate 22 to the potential of the screen 22 periodically as explained hereinafter.

In operation, as the scanning 4beam moves across the target plate 22 the `number oi velectrons in the return beam depends upon the potential4 of the target plate. Iithe scanning beam strikesa spot on target 22 that at maximum positive potential, there will be a minimum lnum-- ber oi electronsin the return beam. The return beam releases secondary electrons from the end plate of the anode 2B and these electrons are directed, by means of a persuader ring electrode '39, into a three-stage electron multiplier 4I, 42, 43. The'electrons from the last stage strike a secondary electron emitting plate 44 and the resulting electrons goy to a screen electrode 4l whereby the output signal may be taken oir an output resistor 41.

The storage screen'or target plate 22 needv not be described in detail. However, it may be mentioned that a preferred target plate 22 is made of very thin glass, the glass being so thin that elemental areas of thel glass hold a charge for the desired length of time. Such a target plate is described in application Serial No. 631,441. illed November 28, 1941 in the name of Albert Rose as a continuation oi lSerial No. 357,543, iiled September 20, 1940. now abandoned.

Referring more particularly to the circuit connections for the system o! Fig. 1, the signal trom 'the mixer Il is supplied through an .amplifier 40. over a conductor 48 and through a blocking capacitor 49 to the screen electrode -23 of the storage tube 2|. A steady bias voltage is applied to the electrode 23 through a resistor 5I. Also. a square wave bias voltage 52 is applied from a square wave generator 52 through a coupling capacitor` 50 to the electrode 23. The square wave generator 53 is synchronized with the modulating pulse generator I2. The deiiection circuit 36 is likewise synchronized with the generator I2.

At the endof every second scan of the scanning beam a pulse of light is llashed upon the photoelectric cathodel 24 whereby electrons from cathode 24 bring the target plate 22 to the potential of the screen electrode 23 because of the capacity between the plate 22 and lthe screen 23. The light pulse may .be obtained from any suitable source 54- which isvenergized from an electrical pulse'source il. The pulse source S3 is operated in synchronism with the modulating pulse generator I2. v.

The output signal ofthe storage tube 2| is taken oi! the resistor 4l and supplied through a blocking capacitor 51 to an amplifier Il. The amplified signal is supplied fromamplier vto thevertical deiiecting plates of avcathode ray oscilloscope 59.

The horizontal deiiecting plates of the oscilloscope 59 have a sawtooth voltage wave applied to them from a deecting circuit Sito deilect the electron beam of the oscilloscope along a time the oscilloscope Il appears on the phosphores' cent screen (not shown) of the tube 59 unless a blanking voltage is being applied to the oscilloscope control grid 62.

In the system illustrated, the square wave generator 53 supplies a square wave blanking voltage to the oscilloscope grid 62 through an ampliiler B3 with the wave of the correct polarity to block the electron beam of the tube 59 during the first scan, i. e., during the scan immediately following the pulse of light from source 54.

Figs. 2 and 3 illustrate the operation of the system shown in Fig. 1. Referring first to Fig. 2, the top graph represents the radio pulses radiated from the transmitter antenna i6 and (in dotted line) the said pulses received at the receiving antenna I1 after reflection from an object which, in the presen-t instance, is assumed to be stationary. The graph 6B represents the sawtooth current that iiows through the storage tube deiiecting yoke 34 to produce the first scan and the second scan of 'the target plate 22 by the scanning beam.

The graph 61 represents the light pulses that are produced at the end of the second scan and before the start of the first scan so that the capacity elements of the target plate 22 are brought to a predetermined potential (1 volt in the present example) at the end of each cycleaof operation.

The rectangular wave biasing voltage 52 of one volt peak-to-peak swings the mesh screen electrode 23 first one-half volt below its 11/2 volt fixed bias to one volt and then one-half volt above its xed bias to two volts through the al.- ternating-current connection 50. This shift in the potential of screen 23 will be seen by comparing the starting points of the graphs 1la and 12a.

'I'he graph B8 represents the sawtooth voltage applied to the horizontal deflecting plates of the oscilloscope 59.

The graphs 1| and 12 represent the signals from the mixer I8 during Ithe occurrence of the received reflected pulses. The signals 1| and 12 are alsoA shown expanded in order to illustrate the operation of the storage tu-be more clearly.

The graphs 1| a and 12a show how the potential of the screen 23 varies with the applied signai and bias. The graphs 1lb and 12b show that the glass target plate 22 varies in potential the same as the screen 23, this being due to the close spacing of the target plate 22 and the screen 23. Since the potential of the gun cathode is fixed at ground, -this target plate potential is also theV voltage difference between the target plate and the cathode.

During the first scan, as the scanning beam moves along the target pla-te from capacity element to capacity element the said capacity elements are being varied in potential by the screen 23 as shown at 1lb. The capacityv elements that are the more positive at the time the scanning beam strikes them will receivethe more electrons from the beam, its velocity being so low that the ratio of primary electrons to secondary electrons is greater than unity. As a result, at the end of the first scan the charges on said scanned elements are represented by the dotted-line graph 13.

During the second scan, as the scanning beam again moves over said capacity elements the target plate is being varied in potential the same as before .by the signal on the screen 23, this target plate variation being represented at 12b. It

resented by graphs 12b and 13 are identical except that they are of opposite polarity. Therefore. the net potential variation in said capacity elements as the beam scans along them is a zero variation as represented by the horizontal line 14. Thus, there is no'varlation in the number of beam electrons deposited on the target plate and so as indicated at 1-6 there is no variation in lthe return beam. This means that the signal output at the output resistor 41 is zero and that no Vindication will be produced on the screen of the oscilloscope 59 by the signals reflected by the stationary object. Preferably, the output signal indicated at 11 that is produ-ced during the first scan is prevented from appearing on the os- 'cllloscope screen by blocking the oscilloscope scanning beam during the presence Aof the signal.

When a radio pulse is reflected from a moving object a signal will appear on the. oscilloscope screen. The operation of the storage tube in this case is shown in' Fig. 3. Here the signals supplied from the mixer I8 during the first and second scan-s are represented by the graphs 8| and 82, respectively. Since the reected pulses producing these signals are from a moving object such as an aircraft, the two signals are unlike for reasons previously explained.

The potential of screen 23 is varied during lthe 'two scans as shown at 8|a and 82a. 'I'he target plate is correspondingly varied in potential as shown at 8|b and 82h. The potential left on the target plate at the end of the first scan is indicated at 83. The net instantaneous potentials on the capacity elements as they -are scanned the second time is shown by the graph 84. The

resulting output signal is indicated by -the graph 86. As previously stated, the signal output produced during the first scan as indicated at 81 is prevented from appearing on the oscilloscope by the blanking voltage from amplifier 6 3.

From the foregoing it will be seen that the system of Fig. 1 will produce an indication only when lthe reflection is from a moving object. More generally stated, the system distinguishes between successive like signals and successive unlike signais.

As shown in Fig. 1A, the signals from the mixer I8 may be applied to the cathode 2E of the storage tube 2| by way of a lead 0| and an input resistor 92 that is connected between the cathode and'ground. Likewise, the square wave biasing voltage may be applied to the cathode 26 by way of a lead 93 and the lead 9|. The operation is the same as when the voltage variation between l cathode and target plate is obtained by applying signal to the mesh screen 23.

Fig. 4 shows an embodiment of the invention Where. instead 0f Varying the voltage difference between cathode and target plate, the number of electrons in the scanning beam is Varied. This modulation of the beam is produced by applying will be seen that as a result of the signals 1| and a lead |04 to the amplifiers 40 and |02 to block amplifier |02 during the rst scan and Ito block amplier 4 0 during the second scan. Thus. as shown in Fig. 5, the scanning beam current is graph I 06.

During the second scan the signal passes through the reversing amplier |32 and the scanning beam is modulated as shown byY graph |01 of Fig. 5. 1n the example illustrated the vilrst and second signals are unlike since it is assumed that the pulses are reflected from a moving object.

At the start of the cycle of operation the targexl plate 2l is at two volts potential'as shown by the graph 408, this lbeing the xed bias on the mesh screen 23. During the iirst scan -the number of electrons deposited on the successive capacity elements struck by the scanning beam is las repre.. sented by the graph |09.` The resulting charge on said elements at the end of the rst scanis shown 1 by the graph I I; the greaterA the 'number of elec#v trons deposited, the more negative the charge.

-At the start of the second scan the-beam current is increased bythe squarev wave voltage sup- -plied over a conductor I2 to thecontrol electrode 21 so that signal variations in either direction may be detected. More specifically', vthe beam current is increased to a valueat thestart of the second scan such that there are alwaysmore than enough electrons to bring the target plate to cath` ode potential. As the beam scans the target elements (which are charged as shown at lli) it v elements to cathode potential and also upon' thenumber of electrons in the scanning beam.

The number of electrons deposited during the second scan to bring the target plate to cathode potential is shown by the graph H2. It will be.

apparent that where the elements lof the-target plate are most negative they take a minimum4 number of electrons to bring them to ground potential. If the scanning beam contains `a reduced H3 to the amplifier IIS sov that signal is applied to the storage tube screen 23 during the first scan of the target plate 22 but not during the second scan. Also. square wave voltage from the generator 53 is applied over conductors lll and Ill to the output amplliler 58 so that it is blocked during the iirst scan but passes signal during the second scan.

'In Fig. 8, the graph. |2| represents the signal applied to screen electrode 23 during the rst scan. The resulting target plate potential variation is shown by graph |22. The return beam or outputsignal, represented by graph |23, is not passedby the amplier I3. During'the second sc'an the potential of the screen 23 is held at a steady bias voltage as shown at |24. Due to the charges left on the target plate by the nrst scan, yas shown at |23, the second scan produces the delayed output signal represented at |21.

l signal during the rst scan but not during the second scan as indicated by the graphs |3| and |32 of Fig. 7. During the first scan the target plate 22 remains at the screen potential of two volts as shown by graph |33 and the number of electrons l deposited during this scan is shown by graph |34.

yThere is no output signal during the v:ilrst scan but sinc'e there may be a certain amount of noise signal it may be desirable to block the output amplier 58 during this period.

During the second scan the charges leftvon the target plate elements by the first scan, as shown at |38, cause a corresponding variation in the' electrons deposited during the second scan as shown at |31. TheV resulting return beam or delay output signal is shown at |33.

We claim as our invention: v

1. The method ofoperating a cathode ray storlage tubeof the type having a targe't plate comnumber of electrons when it strikes these most negative elements, the number of return electrons will increase less than they otherwise would or will not increase at all. In the example shown, the rst part of the second signal is the same as the first part of the rst signal so that the return beam indicated at I3 is unchanged at rst. How

Aprising capacity storage elements which comprisesvarying the potential of said target plate with reference to a fixed potential by a ilrst signal as an 4electron beam scans capacity elements of said target plate, varying the potential of said iula't'ed'` to` produce an -output signal only it said In the circuit of Fig. 4 the function of the light and circuit diagram of Fig. 8, the storage tube 2| l may |be employed for delaying a signal. In Fig. 8 the signal to be delayed is supplied through an amplifier H6 and through a coupling capacitor ||1 to the screen electrode 23. A square rwave voltage from the generator 53 is supplied over a conductor H3 and through a reversing amplifier two signals are unlike. 4 I

- 2. The method of operating a cathode ray storage tube ot the'type having atarget plate comprising capacity Astorage elements which comprises storing a first signal Von said target plate as an electron beam scans capacity elements of said target plate, varying the potential of said target vplate with reference to a ilxed potential by a second `signal as said electron beam again scans said charged capacity elements whereby the return beam from said target plate is signal modulated to produce an output Signal only if said two signals are unlike, said capacity elements y `capacity element of` said mosaic when it is scanned by said beam is a function of said mosaic potential, means for causing said beam to scan said mosaic once while a signa`l is varying the potential of said mosaic for causing the capacity elements of the mosaic which are thus scanned to acquire charges in accordance with the potential variations of the mosaic with reference to said fixed potential, means for causing said beam to scan said once-scanned elements a second time while an applied signal is again varying the potential of said mosaic with reference to said xed potential whereby if the two signals are alike the voltage difference between the xed potential point and successive scarmed capacity elements is constant during said second scanning so that there is no signal output.

4. In combination, a cathode ray tube having a mosaic that functions to store signals applied thereto, means for directing a beam of electrons against said mosaic, means for varying the potential of said mosaic with respect to a fixed reference potential and in accordance with an applied signal whereby the charge acquiredby a capacity element of said mosaic when it is scanned by said beam is a function of said mosaic potential, means for causing said beam to scan said mosaic once while a signal is varying the potential of said mosaic for causing the capacity elements of the mosaic which are thus scanned to acquire charges in accordance with the potential variations of the mosaic with reference to said i'lxed potential, means for causing said beam to scan said oncescanned elements a second time while an applied signal is again varying the potential of said .mosaic with reference to said fixed potential whereby a signal output is obtained from the return beam only if there is a difference in said two applied signals, said mosaic being brought to a predetermined potential before the next cycle of operation.

5. The method of operating a cathode ray storage tube having a target plate comprising capacity storage elements and having an electron gun which comprises causing a low velocity electron beam from said gun to scan capacity elements of said target plate a iirst time and a second time, causing said electron beam to charge said scanned capacity elements at least during the rst scan in accordance with a signal applied to said storage tube whereby the return beam from said target plate is signal modulated during the second scan unless a signal like the rst signal is applied to said tube during the second scan, returning the capacity elements of said target Plate to a predetermined potential at the end of the second scan, and repeating the cycle of operation.

6. In combination, a cathode ray storage tube having a target plate comprising capacity storage elements and having an electron gun, means for causing a low velocity electron beam from said gun to scan capacity elements of said target plate a first time and a second time, means for causing said electron beam to charge said scanned capacity elements at least during the ilrst scan in accordance with a signal applied to said storage tube whereby the return beam from said target plate is signal modulated during the second scan unless a signal like the rst signal is applied to said tube during the second scan, and means for returning the capacity elements of said target plate to a predetermined potential at the end of the second scan and before the cycle of operation is repeated.

7. The invention according to claim 6 wherein said last means comprises a photoelectric cath- 0de positioned to release electrons toward said target plate, and further comprising means for flashing light upon said photoelectric cathode at the end of the second scan and before the cycle of operation is repeated whereby electrons fall upon said target plate to return it to said predetermined potential.

8. In combination, a cathode ray tube having a. double-sided mosaic that functions to store signals vapplied thereto, means for directing a beam of low velocity electrons against said mosaic, a fine mesh screen positioned close to said mosaic in capacitive relation thereto whereby the charge acquired by a capacity element of said mosaic when it is scanned by said beam is a function of the potential of said mesh screen and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously causing the capacity elements of the mosaicwhich are scanned thereby to acquire charges in accordance with the variations of a signal applied to said tube, means for causing said beam to scan said once-scanned elements a second time while a signal is again being applied to said tube whereby a signal output is obtained from the return beam only if there is a difference in said two applied signals, and means for bringing said mosaic to the bias potential of said mesh screen at the end of said second scan and before the next first scan begins.

9. In combination, a cathode ray tube having a double-sided mosaic that functions to store signals applied thereto, means including an electron gun for directing a beam of low velocity electrons against said mosaic, said electron gun including a cathode, a fine mesh screen positioned close to said mosaic in capacitive relation thereto whereby the charge acquired by a capacity element of said mosaic when it is scanned by said beam is a function oi the potential difference of said mesh screen and said cathode and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously varying the voltage difference between said mesh screen and cathode in accordance with a signal for causing the capacity elements of the mosaic which are scanned by said beam to acquire charges in accordance with the variations of sai-d signal, means for causing said beam to scan said once-scanned elements a. second time while a signal is again varying said voltage difference whereby av signal output is obtained from the return beam only if there is a difference in said two applied signals, and means for bringing said mosaic to the bias potential of said mesh screen at the end of said second scan and before the next first scan begins.

10. In combination, a cathode ray tube having a double-sided mosaic that functions to store signals applied thereto, means including an electron gun for directing a beam of low velocity electrons against said mosaic, said electron gun including a cathode, a fine mesh screen posi tioned close to said mosaic in capacitive relation thereto whereby the charge acquired by a capacity element of said mosaic when it is scanned by said beam is a function of the potential diierence of said mesh screen and said cathode and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously varying the voltage difference between ysaid mesh screen and cathode in accordance with a signal for causing the capacity elements of the mosaic which are scanned by said beam to acquire charges in ac- :,ssnoos cordance with the variations of said signal, means for causing said beam to scan said oncescanned elements a second time while a signal is again varying said voltage diercnce whereby a signal output is obtained from the return beam only if there is a difference in said two applied signals, and means for bringing said mosaic to the bias potential of said mesh screen at the end of said second scan and before the next rst scan begins, said last means comprising a photoelectric cathode and means for projecting a pulse of light thereupon between the end of the second scan and the beginning of the following first scan.

1l. The method of operating al cathode ray storage tube having a target plate comprising capacity storage elements and having an electron gun that includes acatho'de which comprises storing a first signal on said target plate as a low velocity electron beam from said gun scans capacity elements of said target plate, varying the voltage difference between said cathode and said target plate by a second signal as said electron beam again scans said capacity elements whereby the return beam from said target plate is signal modulated only if said two signals are unlike, returning the capacity elements of said target plate to afpredetermined potential at the end of the second scan, and repeating the cycle of operation.

12. In combination, a cathode ray storage tube having a target plate comprising capacity storage elements and having an electron gun that includes a cathode, means for storing a rst signal on said target plate as a low velocity electron beam from said gun scans capacity elements of said target plate, means for varying the voltage dinerence between said cathode and said target plate by a second signal as said electron beam again scans said capacity elements whereby the return beam from said target plate is signal modulated only if said two signals are unlike, and means for returning the capacity elements of said target plate to a predetermined potential at the end of the second scan and before the cycle of operation is repeated.

screen, means for causing said beam to scanv said once-scanned elements a second' time while ,Y

a signal is again being applied to said mesh screen whereby a signal output is obtained from the return beam only if there is a diiierence in a double-sided mosaic that functions to store` signals applied thereto, means for directing a beam of low velocity electrons against said mosa- 13. vThe method of operating a cathode ray f storage tube of the lowrvelocity beam type having a target plate comprising capacity storage elements which comprises storing a vilrst signal on said target plate as a 'low 'velocity electronl beam scans capacity. elements .of said target plate, varying the potential of said target plate by a second signal assaid electron beam vagain scans said capacity elements whereby the return beam from saidtar'get. plate is signal modulated only if said two signals are unlike, returning the vcapacity elements of said target plate to a pre--l determined potential at the end of the second scan, and repeating the cycle of operation.

14. In combination, a cathode ray vtube having a double-sided mosaic that functions to store signals applied thereto, meansfor directing a beam of low velocity .electrons against said mosaic, a une mesh screen positioned' close to said mosaicjin capacitive relation thereto whereby the charge4 acquired by a capacity element of said mosaic when it is scanned by said beam is a function of the potential of said mesh screen and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously causing the capacity elements of the mosaic which. are scanned thereby to acquire charges in accordance with the variations of a signal appliedto said mesh ic, a ilne mesh screen positioned close to said mosaic in capacitive relation thereto whereby the charge acquired by a capacity element of said mosaic when it is scanned by said beam is a function of the potential of said mesh screen and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously causing the capacity elements of the mosaic which are scanned thereby to acquire charges in accordance with the variations of a signal applied to said mesh screen, means for causing said beam to scan said once-scanned elements a second time while a signal is again being applied to said mesh screen whereby a signal output is obtained from the return beam only if there is a dii'i'erence in said two applied signais, and means for bringing said mosaic to the lbias potential of said mesh screen at the end of said second scan and before the next first scan begins, said last means comprising a photoelectric cathode positioned to release electrons toward said target plate and means for projecting a pulse of light thereupon between the end of the second scan and the beginning of the following first scan.

16. In combination, a cathode ray tube having a double-sided mosaic that functions to store signals applied thereto, means including a beam intensity control electrode for directing a beam oi' low velocity electrons against said mosaic, a ilne mesh screen positioned close to said mosaic in capacitive relation thereto wherey the charge acquired by a capacity element of said mosaic whenit is scanned by said beam is a function of the potential of said mesh screen and of the number of electrons in said beam, means for causing said beam to scan said mosaic once and for simultaneously causing the capacity elements of the mosaic which are scanned thereby to acquire charges in accordance with the variations of a signal applied to said control electrode with a certain polarity, meansv for causing said beam to scan said once-scanned elements la second time while a signal is again being applied to'said control .electrode with the opposite polarity whereby e a signal output is obtained from the return beam v said capacity elements whereby the return beam from said target plate is modulated in accordance with said stored signal to produce a delayed signal. returning the capacity elements ofsaid tar- 13 get plate to a, predetermined potential at the end of the second scan, and repeating the cycle of operation.

18. The method of operating a cathode ray storage tube having a target plate comprising capacity storage elements and having an electron gun which comprises storing a signal on said target plate only While a 10W velocity electron beam from said gun scans capacity elements of said target plate duringa, rst scan, again scanning said capacity elements whereby the return beam from said target plate is modulated in accordance with said stored signal to produce a delayed signal, projecting electrons upon the capacity elements of said target plate to bring them to a. predetermined potential at the end of the second scan,y and repeating the cycle of operation.

PAUL K. WEIMER. VLADIMIR. K. ZWORYKIN. IRVING WOLFF.

No references cited.

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