US2440301A - Signal reproducing system - Google Patents

Description

April 27, 1948. J, SHARPE SIGNAL REPRODUCING SYSTEM Filed Nov. l, 1945 INVENTOR.

JACK SHAR PE,

ATTO RN Patented pr. 27, i948 SIGNAL REPRODUCING SYSTEM .lack Sharpe, Wembley, England Application November 1, 1945, Serial No. 626,117 In Great Britain November 1, 1944 13 Claims. l

Thisinventon relates, in general, to signalreproducing systems. It is especially directed to systems for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at the same repetition frequency throughout the same time interval. The invention, while subject to a variety of applications, particularly suited for use in a radio-locating systemand will be described in detail in that connection.

One prior radio-locating system of the type under consideration comprises a-directional transmitting and receiving system for exploring or searching an area in space to derive an output signal in the event that one or more reflecting objects are within the space scanned. The searching process entails scanning the space in question with signal energy in a uniform scanning pattern and at fixed scanning frequencies. The scanning may be similar to that well 'understood from television practice wherein an area is scanned in a plurality of elds each of which includes a relatively large number of scanning lines. The output signal, denoting the presence of a refiecting object in the scanned space, constitutes a reiiection of the transmitted energy occasioned by the reilecting object and intercepted by the receiving component of the system. This output signal is applied to a cathode-ray indicating device which is controlled to scan a target, such as a picture-reproducing screen of the `fluorescent type, in synchronism with the scanning of the explored space. The applied signal modulates the cathode-ray beam to establish on the target an indication of the position of the reflecting object in the scanned space.

'When a stationary object is encountered, repeated eld scanning of the explored spaceover a given time interval produces one related output signal occurring at a constant repetition frequency-corresponding to the field-scanning frequency. ,This signal establishes repeated indications in theisame partA of the target of the indicating-device from which an observer is able to discern the stationary object. However, a relatively fast-moving object in the explored space causes a vdifferent or second output signal to be obtained i from f the receiver. recursat a varying frequency determined by the speed of movement of the object with relation to tbe scanning times. It controls the indicating device toiestablish indications on different parts of its target during succeeding field scans from-which VThe second signal 2 an observer may detect the presence of the moving object.

lil

Arrangements of the type described have proved to be satisfactory but are subject to the limitation Athat they require prolonged observation of the target of the indicating device to distinguish stationary and moving objects in the explored space. This is so because the target picture is composed of the same colors in each case and differentiation of stationary and moving objects is based upon the movement of a portion ofthe picture in repeated field scans. In some installations, where it is desired to distinguish between moving and stationary objects at a glance at the picture pattern, this limitation may be objectionable.

Another radio locator forms the subject matter of copending application-Serial No 626,148, filed November l, 1945, in the names of Leslie C. Jesty et al., and assigned to the same assignee as the present invention. This other arrangementv includes a signal-reproducing system havingluorescent means adapted to emit visible light of one color when repeatedly excited a predetermined plurality of times but adapted to emit visible light of a contrasting color when excited for a lesser number of times. It has the advantage of displaying stationary or relatively slow-moving refleeting objects in one color while indicating fastmoving objects in a different color. Such a system requires repeated scanning of an area inspace for at least the aforementioned predetermined plurality of times to produce a multicolor picture pattern. In some installations it may be desirable to obtain such a multicolor picture pattern more quickly.

It is an object of the present inventiori, there fore, to provide a signal-reproducing system which substantially avoids the aforementioned limitations of the described arrangements.

It is another object of the invention to provide an improved system for reproducing and distinguishing between two signals, one of which recurs at a substantially constant repetition frequency in a given time interval while the other does not recur at the same repetition frequency throughout the same time interval.

It is a specific object of the invention to provide animproved signal-reproducing system especially suited for application to radio-locating systems and adaptedy quickly to distinguish between stationary and moving objects or between relatively slow-moving and relatively fast-moving objects. y

In accordance with the invention, a system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at the same repetition frequency throughout the same time interval comprises fluorescent signalreproducing means. The signal-reproducing means is adapted to emit visible light of one predominant color when excited for a given eX- citation period with incident energy within a iirst amplitude range or when repeatedly excited at the aforesaid repetition frequencyfor a certain number of such given excitation periods with incident energy within a second and lower amplitude range. It is also adapted to emit visible light of a contrasting color when excited for a lesser number of such excitation periods with incident energy within the second amplitude range. The system has means for effectively scanning the signal-reproducing means at the aforesaid repetition frequency during the above-mentioned time interval with excitation energy representing the lrst and second signals. The scanning process is such as to excite elemental areas of the signal-reproducing means in any one scanning cycle for an interval at least equalto the `aforesaid given ,excitation period. Means are also provided for adjusting the ampli'- tude levels of the excitation energy during one scanning cycle within the given time interval to values within the first-mentioned amplitude range and during another scanning cycle within this given time interval to values Within the second-mentioned or lower amplitude range.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed o-ut in the appended claims.

In thedrawing, Fig. 1 is a schematic representation of a radio-locating system embodying the present invention in one form; and Figs. 2a and 2b areV views of one component of the Fig. 1 arrangement.

Referring now more particularly to Fig. 1, there is represented a radio locator including a signalreproducing system in accordance with the instantrinvention. The locator arrangement, as illustrated, includes a space-scanning and reflected-signal-receiving system lil represented in block form. There is associated with unit IU a directive transmitting antenna system which, in order to simplify the drawing, is represented by a dipole antenna l i and a parabolic reflector lla. A receiving antenna system, having similar directive properties, is also associated with unit l and is indicated by a dipole l2 and a parabolic reflector lEa. An ultra-,short-wave signal generator is included in unit iii for energizing antenna Il. The generator usually operates in thc ultra-short-wave range since short-wave signals are most easily directed and most readily reflected by reflecting objects. Unit I@ also has suitable means for controlling antenna system H so that the directed signal energy transmitted thereby scans a portion of space in a series of fields of parallel lines at constant line-scanning and held-scanning frequencies. The scanning elements additionally control antenna I2 in synchronisrn with the transmitting antenna to intercept reiiections of the transmitted signal energy which may be caused by reilecting objects positioned within the scanned space.

A synchronous dei'iecting-signal generator 13 is coupled to unit i8, as indicated by construction lines ll and l5 extending between parts a and b of unit it and parts c and d of unit I3. Where the space scanning effected by unit it is in the form of a series of fields of parallel lines, unit i3 includes elements for generating two delecting signals. These deiiecting signals may be termed the lineand field-scanning signals. The intercoupling of units iii and I3 is such that the lineand held-scanning signals generated are synchronized with and correspond to the line and eld scanning, respectively, of antenna systems l l and l2. This interconnection varies with the type of apparatus utilized in units It and i3. Where antenna systems ll and l2 are mechanically controlled to accomplish desired lineand held-scanning functions, the interconnection may be mechanical and the synchronous generator may be mechanically controlled in synchronism with the antenna scanning. On the other hand, for electrical control of the scanning operations of the antenna systems, generator i3 may produce deflecting signals applied through the connection ld and i5 to control the antenna systems in synchronism with the generated signals.

A suitable arrangement for elements Iii-l5, inclusive, is illustrated in United States Letters Patent 2,231,929, issued February 13, 1941, to Joseph Lyman. In the reference patent, space scanning is accomplished by a pair of transmitting antennas. One antenna radiates a vertical ribbon of signal energy which is swept horizontally at a desired field-scanning frequency. The other transmits a horizontal ribbon of signal energy which is swept vertically at a line-scanning frequency, thirty or more times that of the iield scanning. A corresponding pair of directive receiving antennas are provided, each moving synchronously with one of the transmitting antennas. The scanning for all antennas is accomplished by mechanically driving a parabolic reflector associated with each. The receiver coupled to the receiving antennas includes an. amplitude-delayed detector which produces an output signal only during time intervals when reflected signal energy is received concurrently by each cf the receiving antennas. The synchronous deectin'g-signal generator 0f the reference patent includes a pair of adjustable resistor arrangements for producing lineand iieldscanning signals synchronized with the corresponding components of the space scanning. The adjustable element of one resistor is driven with the line-scanning antennas, while the adjustable element of the other is driven with the eldscanning antennas. To this end, a mechanical interconnection is provided between the antennas and the adjustable elements of the resistors.

The radio locator of Fig. l of the present invention further includes a system for reproducing and distinguishing between a rst periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at this same repetition frequency throughout the same time interval. This system comprises uorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy within a iirst amplitude range or when repeatedly excited at the aforesaid repetition frequency for a certain number of such given excitation periods with incident energy within a second and lower amplitude range. It is also adapted to emit visible light of a contrasting color when 5; excited for'rar'lesser number-,of tim'esiwitrrincident\y energy.- withinithe 'loweramplitudefrange.'V

Moreispeci'cally,'the signalereproducing meansr comprises .a uorescent screen' constitutingxthe target :areaof-'a cathode'fray tube'.2. Thescreenrthefampn'en- AdjpstaniegtapsgssrandAu'of the.` potential-dividing; resistor.' are associated'Y with' includes afglass 'carrierl l :andsuperposed uores:n cent '5. portions or." layerss. adapted.' to emit visible light of contrasting colors. The rst layer.` 22f fluoresces fully. When excitedifor ffa'given' excita.-

tiOIl fperiodrwithpenergy Within arstlamplitude lolplitudef'rangefand 'during anotherscanning' cyclerange. It has. an afterglow'. period, longwith'refA erence tozthe :period corresponding: to' the repeti'- tiorrfrequen'cy'of the repeating signal to 'befreproducedso 'that v'recurrent v'excitationrfat 'this' fre+ quency' produces.; cumulative iuorescent effects. It has-2' an excitation i bui'l'd-upperiod such that substantial'uorescence is also obtained .when the layerris'repeatedlyexcited a certain'num'ber'of' times; dene'd'more particularly hereinafter; with' incident errergytW-ithin: a second.' butzlower amiplitud'erange.V The .secondflayer 23:-'has an' afterglow period less thambut preferablyalm'ostequal to; the 'period tof the applied' repeating; signal.

It has an `excitation'build-up characteristicsnch that 'substantial fluorescence is obtainedwvhen: it is excitedfor alesser number cf times but, pref.-V erably,r when excited for only a 'single one4 of 'theaforementioned;'given` excitation period-s withrinfcident energywithin either thel rst or second' amplitude rangesreferred to. layers, preferably,- has excitation andA afterglow characteristics/such thatthe ratesl of build-un of .fluorescence'and .decay of afterglow; vary with the-intensity ofe thegcxcitation energygappliedthereto; Layer 22 is substantially;- transparent to ythe-light vemitted by layer 23, enabling the-- fluorescence of eachto be viewed-'from -af single I side of screen' 2l'. Additionally, 1ayr-23=hasenorgy-translating properties` such'i that.A incidentf energy applied thereto is partially; `translated Vto the. alternate layer, permitting thecexcitation of both-from the opposite fside 'of the-'composite screen structure. The method `offabricating this screen, aswell assuitable fluorescent materials Which 'may be included therein, is given hereinafter.

The signabreproducing'system `under consider'- ation has means for effectively scanning. the'- screen-.oi tube Ztl-at the repetition frequency of the Yilrst-ment-ioneel..periodic signal' with excita.- tion energyin such ainanneras toexcite ele-- mentall areas of each layer or portion.of. the screen in any one scanning cycle for anv intervalat least equal to the given excitation period.

thel screen is illustrated as the targeaarea of cathode-ray tube- 20,'fthe exciting means includes a conventional electrode system for producinga5 cathode-ray beam but a potential source 2? normally biases `the tube to .cutoii Apainof-hor-izc-ntal deflecting plates 3'and 3! are-*coupledy to one output circuit of-unit I3 for deecting the' beam .of cathode-ray l tribe 26 in' a'horizonta-ll direction synchronously with the horizontal Vertical deecting thati'unit I B7. repeatedly'. scanszan areatinispace scanning antenna of unit IQ.- platesSZ and 33 are coupled to a second output circuit of unit I3 to deflect the -cathode-raybeam synchronously With the Vertical-scanning antenna of unit I 0.-

The` beam of 'tube-'may becontrolled-:by 'lo tainedfrom :the receiver1portion'of'unit .|0. Itv

brilliancy-control.electrode 35.- The signal-outputv of the receiver' portion ofunit mais appliedfto thiselectrode toV overcome the tubev bias ando supply beam energyy modulated in-.accordance" with and representing .the signal outputthereon 75? through affcondenseraandca; Variablefgain''am-y plifier-312 A potentialfdividingz resistor '38 'is 'proa vided for." controlling: thengain'; characteristic i of commutator .'meansr 4| yfoi-adjustingv the amplitudes-'levels of*y the.' beamzenergy. ofy 'tube' "20 during .1

to ,--values'l .Within a.' second; and lower amplitude ranger Commutatorrll-l `is ,shown inblock form,I partially brokemaway: to reveaLsegments-GZ and- 43'. connected'. in.; circuit; with: taps- 39- and 1 do through".coaoperating brushes; M and d5; respectivelyi.

Plannviewsf ot.segments=4'21" andvd3 r areA represented :irri-Figs: 2a: and 2b, respectively The vfor- `erihas onequadrant:ll2a'ofjconductive-material .and a remaining'section'AZb ofzinsulatingmaterial'. The latter. hasa' quadrant lbof insulating materialand; the' remalnderfllSa'r'is of conductive material.;` Both.'are-"secureditoa shaft llxandfso.v

oriented'thatf'sections 42a' and 45h are viii-axial valignment.' The segments :are-'connected through shaft it-'in'. circuit '.with. a slip; ring: .4l and 'co-'01-v eratingrbrush; 148; A :coupling: indicatedvby'. con struction 'linesall 'and .5 'l extending between parts i a andzhofmnit 'I li'andparts'e andff of commutator.- Each otr these 300138,'. providesrsaA driving. connectionforshaft 45:.

This finterconnection,4 .Where-tthefspacescanning arrangement. Yis :in- 'the form tof .ithe'V above-'identi'ed patent; comprises la :mechanical linkage: :for`v rotating thezcommutator in' synchronismwith the'.' 35 i mld-scanning: processi'. Withf theiparticular: seg;

ment .construction;illustrated; the' coupling.- in' Y cludes'V a i stepzrdowrr.; gear trainf (not shown) to driver the; commutatorr at'. onefiourth ther iield= scanning frequency;

Intiadjnsting;v the?. describedz radio locator,- tap;

391s 'set tozestablishsuch azhigh gainfoiamplier f' 3 l f that .signals applied; v'therethrough :to n control:` electrode'z 35: with'. this amplication produce'- av beamiintensitysin'tube ZUWithini'a 'high' amplitude 4;,-range,'.eifectiVertoa-excite both 'layers .ot screen.:

2 ["-23jto substantiallyefull' iiuorescence irrav single tofestablisira reduced amplier gain'sozthatsig'- the` screenrtosubstantial uorescence' in. a'lrsingle Let it zb'e .assumedfthatlayers :.22 fandif'23 'oi the' referred'to in the preceding paragraphe.. Since"55;screen'emit green'andre'dlight,respectively; that layer 22.2has'abuild-uplfperiodlgfor 'intensities A of the cathode-ray beam. Within the. reduced amiplitudetran'ge such' :as .torrequire repeated: excita.-4

tion during at least fiveconsecutive fieldzscan's'to'v l 69 g attain:substantialnuorescerrce; and that `.layer x23; produces" substantial'ly.- ful'lfluorescence". int'. re-

sponseltor'each ireldxscanfothe'cathodefray beam;

even thoserinzwhich': the beam intensity :is 'withinthe"reduced' ainp'litudfrange.' Further. assume duringga: timev interval in; which` both a. stationary and av relatively'ffastmoving. reectingiobject are included'.withinarthefscannedrspace.- For the assumed conditions.' avcomposite output vsignalis obincludes. a` rst Aperiodic signal; repeating. at the eldfl-scanningz frequency; and'. occurring rduringr that 'portion of. each'v .eldi scan :'when. the trans-f' Y mitted energygis :incident zupon; thestationaryr reiieotin'gr object;- The!v composite signal alsocin'e cludes a second signal which does not repeat at the field-scanning frequency because the position of a fast-moving object in the scanned space changes materially from one eld scan to the next. The receiver output signal is translated through amplifier 31 to brilliancy-control electrode 35, producing in tube 20 a modulated cathode-ray beam representing both the first and second signals. The deflecting elements 3D3l and 32-33, under the control of synchronous generator I3, scan screen 2l-23 with the modulated cathode-ray beam in synchronism with the space scanning, exciting elemental areas thereof in any one scanning cycle for an interval determined by the physical length of the scanning spot divided by the rate of passage of the spot across an elemental area. The beam-scanning function traces a picture pattern on the screen depicting the positions of both reflecting objects in the scanned space in the following manner.

Consider that commutator segment 62 controls the gain level of amplifier 3l during the first fieldscanning period. In this operating interval the beam of tube 2i) has amplitude values within a high range. It excites portions of the screen 21-'23 corresponding to the positions of the reflecting objects in the scanned space. In View of the high beam intensity the resulting picture pattern is predominantly green, the characteristic color of layer 22 which has the longer afterglow and hence the slower rate of decay of fluorescence. For the neXt three succeeding scanning intervals commutator segment d3 causes amplifier 31 to have a reduced gain, resulting in a beam intensity of amplitude levels in a lower range of values. In each of these three succeeding scans the rst signal, representing the stationary object, partially restores the decaying fluorescence of that part of layer 22 which designates this object, thereby to maintain the representation of the stationary object in green light. However, the second signal, representing the fast-moving object, excites different parts of the screen in each of the three scans under consideration. In general, it excites parts of the screen that have not previously been excited and because of the reduced beam intensity produces a traveling light spot of red color, characteristic of layer 23 which alone is energized to substantial fluorescence in a single scan by the beam of reduced intensity.

In still further field-scanning intervals, the excitation of the screen is cyclically varied by commutator lll, as described above. That is, in one eld scan all reflecting objects are displayed predominantly in a green color pattern and in the next three succeeding scans the stationary object is continuously shown in a green color while the representations of fast-moving objects fade away from green and appear in red. Thus, by observation of the screen the presence of stationary and relatively fast-moving objects may be discerned and distinguished. Where a relatively slow-moving object is in the scanned space, the related signal component of the composite output signal of unit l' occurs at approximately the eldscanning frequency and produces a substantially green indication of this object on the screen.

It will be apparent that the commutator segments of unit #ll may be proportioned in any desired manner. The illustration of Figs. 2a and 2b is given only by way of example. In the limiting case these segments have equal conductive and insulating portions. When so constructed and rotated at half the field frequency, they cause the beam of tube 2B to have values within high- 8 and low-amplitude ranges in alternate Ileldscaning intervals. For such operation, stationary objects are again displayed in green light but fast-moving objects are designated by alternate red and green light spots, traversing the screen at a rate governed by the speed of movement of the moving object within the scannedA space.

In constructing fluorescent screens of the type provided for tube 2li, it is not necessary that the several layers be entirely discrete. One may merge into the other but it is preferable that there be a preponderance of one fluorescent mixture emitting light of a desired color on one surface of each layer. For example, a preponderance of one material should be provided at the face of layer 22 adjacent carrier 2| and a preponderance of the other at the face of layer 23 closest to the cathode of the electron-gun structure, Either or both layers may be composed of a mixture of two or more fluorescent compounds to obtain a desired visible color.

A screen of the type discussed above may be fabricated in the following manner. A first layer of fluorescent powder is dusted upon the glass carrier which is previously covered with a thin binder layer consisting of a solution of phosphoric acid in acetone, The thickness of this layer is arranged in accordance with a desired per cent. optical transmission thickness. An optical transmission thickness of given percentage means that this percentage of a normally incident beam of parallel light rays penetrates the layer. The second layer may be applied by spraying over the first layer a dilute solution of potassium silicate and thereafter depositing a second fluorescent powder with a dry powder spray to the desired optical thickness. Succeeding layers, if utilized, may be applied in the same way as the second. The screen in one form may include, as layer 22, green iluorescing calcium-magnesium tungstate activated with uranium and having an optical transmission thickness of 30 per cent. Its layer 23 may include red fluorescing calcium phosphate activated with samarium and having an optical transmission thickness of 55 per cent. Other suitable screen compositions are recited in the above-mentioned copending application of Jesty et al. The arrangement of the copending application is generally similar to that here described and, for the most part, corresponding components thereof are identiiled by the same reference characters. It will be apparent that the screen constructions of the other application are suitable for use in the reproducing system forming the subject matter of the present invention.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiilcations as fall within the true spirit and scope ofthe invention.

What is claimed is:

1. A system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, fluorescent signal-reproducing means adapted to emit visible light of one predominant colorwhen Lexcited for a given excitation period with incident energy within a first amplitude range or when repeatedly excited. atsaid repetition frequency for a certain number of saidfgiven excitation periods with incident energy within a second lower amplitude range but adapted toy emit visible light of a contrasting color when excited'for 'a lesser number of said excitations periods with incident energy within said second amplitude.

range, means for effectively scanning said signalreproducing means at said repetitionfrequency during said time interval with excitation energy representing said `first and second signals so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to-said rgiven excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle within said given time interval to values within said first amplitude range and during another scanning cycle Within said given time interval tovalues withinsaid second amplitude range.

2. A system for reproducing and distinguishing between a first periodic signal which recu-rs ata substantially constant repetition frequency in a given time interval and a second signal Awhich does not recur at said repetition frequency throughout said time interval comprising, fiuorescent signal-reproducing means adapted to emit visible light of one color when excitedl for a Vgiven excitation period with incident energy within a first amplitude range or when repeatedly excited at said repetition frequencyfor a certain number of said given excitation periodsv with incident energy within a second lower amplitude range but adapted to emit visible light of acontrasting color when excited by incident energy within said second amplitude range for only said given excitation period, means 'for eiectively scanning said signal-reproducing means at said repetition frequency during said time interval with excitation energy'representing said firstand second signals so as to excite `elemental areas thereof in any one scanning cycle for an interval at least equal to said 'given excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle Within said given time interval'to values within said first amplitude range and during Vanother scanning cycle within said given time interval to values within said second-amplitude range.

3. A system for reproducingand distinguishing between a first periodic signal which recurs at a substantially constant'repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising; a fluorescent screen adapted to emit visible light'ofone predominant color when excited for agiven excitation period with incident energy within a-rst amplitude range or when repeatedly 'excited at said repetition frequency for a certain number of said given excitation periods with incident-energy within a second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods withincident energywithin said second amplitude range, means for effectively scanning said screen at said repetition frequency during said time interval with excitation energy representing said rst and second signals --soas to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting theamplitude :levels of' said excitation energyduryiing one f scanning x cycle within :said given @time interval to values nwithin said rst. amplitude range -andiduringnanother scanning: cycle within said :.givenf time interval .to values within *said l second amplitude range.

4. Y-A system for reproducing .andy distinguishing i between a: rst. :periodic signal' which recurs'- at va substantially Vconstant repetition frequencyrin: .a

given time interval :and-i a Vsecond signal which does not Vv'recur .zat said repetition 'frequency throughout said vtime interval comprising, signalvreproducingY means including. first .and second Ailuorescent `gportions, :said *first portion .being adapted to emit visible `light of one coloriwhen excited for` al. given excitation period with incident 'energy within `a :'first. i amplitude rangeor when repeatedly 'excited -at said repetition fre- -quency'fora certain number of saidgiven excitationi'periods with incident energy Within-asecond lower amplitude rangeasaid second portionbeing adaptedto emit visible light .of va contrasting color when excited 'for' a. lesser. number .of said excitation periods with incidentY energy Within saidsecond amplitude range, meansfor effectively scanning said signal-reproducing .means at saidrepetition frequency during said time interval with excitation energy representing said first and=.second signalsso-,as to'excite elemental areas ,of'each of said portions thereof :in anyone scanning cycle for an 'interval` at least equal to'said given excitation period, vand means for adjusting the amplitude levels-0f. said excitation energy 'during .one

yscanning cycle within said given time interval to values Within said first amplitude range andfduring anotherscanning cycle within said given time interval .to values Withinsaid second .amplitude range.

5. A: system for reproducing anddistinguishing between a first periodic signal Which recurs at: a substantially constant repetition frequency inra given time interval and a second signal .which does vnot recur at said repetition frequency throughout said time interval comprising, -a

' screen including rst and second superposed fiuorescent portions, said first portion being adapted .to emit visible vlight of one color whenyexcited for a given excitation period with incidentV energy within a first amplitude range or when repeatedly excited at said repetition frequency for a-certain number of said given excitation periodswith incident energywithin a second loweramplitude range, saidsecond portion being adapted to=emit visible light ofy a contrasting color when excited for a-lesser number of said excitation periodswith incident energy within said secondamplitude range, one-ofsaid portions -being substantially transparent Ito the .light emitted .by the other, means for effectively scanning said screen at said repetition frequency during said time interval with excitation energy representing said vfirst and second signals so-as vto excite elemental areas of each of-said portions thereofin any one-scanning cycle for an interval at leastequal to said given` excitation period,-and means for adjusting the amplitude levels of said excitation energy during one scanning cycle Within said given time interval to values within said first `amplitude range and duringanother scanning cycle Within said given time-interval to values within said second. amplitude range.

6. -A system for reproducing and distinguishing between aV first periodic signal which recursat a substantially constant repetition frequency in a given time interval and a second signal which 11 does not recur at said repetition frequency throughout said time interval comprising, a screen including first and second superposed fiuorescent portions, said first portion being adapted to emit visible light of one color when excited for a given excitation period with incident energy within a first amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with in- .cident energy within a second lower amplitude range, said second portion being adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, one of said portions having energy-translating properties such that the excitation 'of said one portion causes excitation of the other, means for effectively scanning said one portion of said screen at said repetition frequency during said time interval with excitation energy representing said first and second signals so as to excite elemental areas of each of said portions thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle within said given time interval to values Within said first amplitude range and during another scanning cycle within said given time interval to values within said second amplitude range.

'7. A system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, a screen including nrst and second superposed fluorescent portions individually having excitation and afterglow characteristics such that the rates of build-up of fluorescence and decay of afterglow vary with the intensity of the excitation energy, said first portion being adapted to emit visible light of one color when excited for a given excitation period with incidentV energy within a rst amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with incident energy Within a second lower amplitude range, said second portion being adapted to emitl visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range and having energy-translating properties such that the excitation thereof causes excitation of said rst portion, means for effectively scanning said second portion of said screen at said repetition frequency during said time interval with excitation energy representing said first and second signals so as to excite elemental areas of each of said portions thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle Within said given time interval to values within said first amplitude range and during another scanning cycle Within said given time :interval to values within said second amplitude range.

8. A system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, signalreproducing means including a first fiuorescent portion having an afterglow long with reference to the period of said repetition frequency and a second fluorescent portion having an afterglow approximately equal to the period of said repetition frequency, said first portion being adapted to emit visible light of one color when excited for a given excitation period with incident energy within a rst amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with incident energy within a second lower amplitude range, said second portion being adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, means for effectively Y scanning said signal-reproducing means at said repetition frequency during said time interval with excitation energy representing said first and second signals so as to excite elemental areas of each of said portions thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle within said given time interval to values within said first amplitude range and during another scanning cycle within said given time interval to values Within said second amplitude range.

9. A system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, fluorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy Within a rst amplitude range or when repeatedly excited aty said repetition frequency for a certain number of said given excitation periods with incident energy within a second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, means for effectively scanning said signal-reproducing means at said repetition frequency during said time interval With excitation energy representing said first and second signals so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting the amplitude levels of said excitation energy during one scanning cycle within said given time interval to values within said rst amplitude range and during a predetermined number of succeeding scanning cycles Within said given time interval to values within said second amplitude range.

l0. A system for reproducing and distinguishing between a first periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, fluorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy Within a first amplitude range or when repeatedly excited at said repetition frequency for a certain num-ber of said given excitation periods with incident energy within a second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, means for producing a modulated cathode-ray beam representing rst and second signals and for scanning said signalreproducing means with said beam at said repetition frequency during said time interval so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for adjusting the amplitude levels of said cathode-ray beam during one scanning cycle Within said given time interval to values within said first amplitude range during another scanning cycle vthin said given time interval to values within said second amplitude range.

11. A system for reproducing distinguish'- ing between a rst periodic signal which recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, liuorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy within a iirst amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with incident energy within a .second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, an electrode system for producing a cathode-ray beam, means including a variable-gain ampliier for applying said iirst and second signals to said electrode system to modulate said beam in accordance therewith, means for scanning said signal-reproducing means at said repetition frequency during said time interval with said beam so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for controlling the gain characteristic or said ampliiier to adjust the amplitude levels of said cathode-ray beam during one scanning cycle within said given time interval to values within said first amplitude range and during another scanning cycle within said given time interval to values within said second amplitude range.

l2. A system for reproducing and distinguishing between a first periodic signal which' recurs at a substantially constant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, iluorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy within a first amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with incident energy within a second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, an electrode system for producing a cathode-ray beam, means including a variable-gain amplifier for applying said first and second signals to said electrode system to modulate said beam in accordance therewith, means for scanning said signal-reproducing means at said repetition frequency during said time interval with said beam so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and commutator means for controlling the gain characteristic of said amplifier to adjust the amplitude levels of said cathode-ray beam during one scanning cycle within said given time interval to values Within said first amplitude range and during another scanning cycle within said given time interval to values within said second amplitude range.

13. A system for reproducing and distinguishing between a iirst periodic signal which recurs at a substantially Iconstant repetition frequency in a given time interval and a second signal which does not recur at said repetition frequency throughout said time interval comprising, lluorescent signal-reproducing means adapted to emit visible light of one predominant color when excited for a given excitation period with incident energy within a first amplitude range or when repeatedly excited at said repetition frequency for a certain number of said given excitation periods with incident energy within a second lower amplitude range but adapted to emit visible light of a contrasting color when excited for a lesser number of said excitation periods with incident energy within said second amplitude range, means for effectively scanning said signalreproducing means at said repetition frequency during said time interval with excitation energy representing said first and second signals so as to excite elemental areas thereof in any one scanning cycle for an interval at least equal to said given excitation period, and means for cyclically adjusting the amplitude levels of said excitation energy to values within said rst amplitude range during at least one scanning cycle within said given time interval and to Values within said second amplitude range during at least one succeeding scanning cycle within said given time interval.

JACK SHARPE.

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