US1986812A - Detector - Google Patents

Description

Jan. 8, 1935.`

MHA/s HARRIS DETECTOR Filed May 27 1950 Egg@ INVENTOR WILLIAM A. HARRlS ATTORN EY Patented 8, 35 u ,E55 `-l-rilENT1,0F-FICE N u William gli; Harris, fa'idubc, .NQ 1J., assigmir to "ofi Delaware i f commonly called platedete'ction;utilizes the curvature of ,the plate current-gridfvoltage"characteristic curve to effect reetication or detection, the circuit being substantially the same" `as would be used with 'thefsame electrondis'chargetube as an amplierexcept that` a greaterl negative grid bias is re 1uire"d."`l fflyin the past Abecause of `its `g'f'reater sensitivity; especially fork the relativelyismall inputs heretof fore available; 1 ""But rwith vrecent developments -in radio frequencyamplification,` and the present advantages of reduced audio Aa,`mpliiication in min l. `imizinghurn`in alternating eurrenthoperated vradio receivers, efiicient-detectioni of muchl'arger inputs is urgently needed? `Tomeet this needg l plate detection has been used, this r'nethod"being moresensitive for largef` inputs than `for "sm'all inputs, `the reversebeing"` true `of the heretofore known t forms of Agrid detection. Y I-Iowever, plate detection at its best, relatively 'insensitive com#` pared with grid detectio'nof small in'putQl v Itis, therefore, highly desirable to provide anv improved. method of operating an electronjdil` charge tube for` grid detection of "large inp" As, such that greater sensitivity and nriaxinnunY audio frequency output'may be :obtained `than vvithany methodfof obtaining such improvedfloperation ivm `te most Clearly; Seifen-,n following; ltrier general description oftheprocess of griddetecf-f" tion, which Will show the rcause of the insensitivity forllargeinput of-` theusual lforrns` voffgrid de'- tectors.'` l i` 1 j I When anaudio frequency rmodulatedu'radio fre@ quency voltageof D pressed onthe gridof `theusual form of'grid. de -Qr tector, grid current `flovvs,andbecausefonthe curvature ofthe grid current-grid voltage' char,-

acteristic curve, rectification takesplaceand this current has both radio `frequencyand audio frequericy components.

tionA or `detection of the `impressed `signal .modul` Grid detection has been I usedfalmo-st eiielfusive i heretoforeknovvnv form ofgrid ,detection 'Ifh sufficient magnitude is i These* components of grid current, now-ing `through the externalgrid circuit impedance, produce voltages at thegrid equal 4to the product of current and impedance, These voltagesas VWellfas the voltage originally impressedA on'the grid all `affect the plate current f5 1n accordance with theplate currentgrid voltage characteristic of Athe tube, and if the resultant i 4'instantaneous"plate current varies overa non-` linear'portion of that characteristic curve, further rectification, i. e., plate detection occurs.

If this plate detection occurs4 at the lowerbend in thelv plate `current-grid voltage characteristic eurveuas lis usuallythe case, the resulting audio i frequency component of plate current is opposed in 'i phase to the `audio f frequency component' of 15` plate` currentprodu'ced by `amplification without detection 1in the plate circuit of theaudio frequency component of grid voltage produced by the grid detection.` This opposing andghence `undesirablasplate,detection effect is negligible' with small inputssuch as have `heretofore been used Withfgrid' detector circuits. But, if it is attempted to use the Amethod of grid detection with increasinglylarger inputs, it isfound that this plate detection effect increases in magnitude and importance, 4resulting in a greater decrease in sensitivity or efficiency,` until a point is reached beyondvvhich an inerease in input causes an actual reduction in audio frequency output` i 1` AThus, Lthe maximum u audio" frequency `output obtainable."from` `a grid `detector Vis ordinarily limited bythe peak value` of fthe `instantaneous alternating` plate current, since this determines the magnitudeoftthe opposing and undesired plate` detectiorn` Vlith,` the `1,lsual'-g`rid detector 35 circuit this .peakvalue of the instantaneous alternating plate current is much larger than the peak .vvaluei pf` the audio -frequency component of plate current,since a largem radio frequency component i'sAfp-roducedbygtheradio frequency Aconiponent of grid flvoltage. The maximum audio frequency output obtainable from' a 'given electron discharge `asa grid detector is therefore considerably 1 i less than would be obtainable fromthe same tube used as an audio frequency amplifier. j

lt-follows then, that if theflow of radio fre-` queney eurrentinthe plate circuit ofthe detector tubefwere suppressed, a; considerably greater audidfrequency output could beobtained with a given input.` The factorz limiting the maximum audio frequency outputvvould then be `the distor tion of the audio frequency output analogous to `that `vvhich would` occurif the saine tubelwere used as an audigojfrequency amplifier. Concisely statedfa grid detector combines the functions of detection in the grid circuit, with audio frequency ampiication, and although the useful effects of the impressed radio frequency voltage stop with the production of the audio frequency voltage at A lo ' ponent in the detector anode circuit may be Sub:

stantially reduced, or suppressed, by producing a high frequency voltage at one cf the electrcdes of Vsuch a magnitude and phase with respect to theV high frequency voltage on the control electrode of the detector, as to partiallyor completely;

compensate for the latter, thereby obtaining a considerably greater audio output for a given signal vinput .than has heretofore been secured with detectors. Itis, therefore, one of the mainfobjects of my present invention to provide preventitive means, forfreducingor eliminating the eifect of the radio frequency component of grid voltage on the plate current of an electron discharge tube .used for grid de tecticn.

YAfurth'er important object of the invention is to reduce or suppress radio frequency components o f plate ci'irrent.` Y

`Another importantobject of my present invention is to provide a method of, and means for, op-` y f erating an electron discharge 'tube as a detector of signal'rnodulated radio frequency energy, vand particularlyas a grid leak detector, .which'consists in employing,- in'addition to the usual anode, cathode and control electrode, an auxiliary electrode,` and prDducing on the latterra radio frequency voltage of such magnitude v.and phase, as to substantially balance out'theeiect ofthe conrtrol electrode radi() frequency voltage on the anode current, thereby increasing the audiooutput of the detector. y y Another object of the invention is to provide a method of, and means for, vemploying Van electron discharge tube, the latter having at least an anode, cathode, and control electrode, as a de tectorofsignal modulated radio frequencyvoltagesof large magnitudes,l which consists l inem#` ploying the radio frequency component ofthe sig-v n al 'input to produce a radio frequency' vcltage' of such magnitude and'phase as to suppress or tector anode circuit. VAnother object of the invention is to provide means for detecting signal modulated radio v'frequency energy, the means comprising an electron reduce the radio frequency componentin vthe dedischarge tube having besides the usual anode,

cathode, and control electrode, one orirnore aux-2 iliary electrodes, at least one yof the latterbein'g utilized :to suppress or reduce the flow o f radio vfrr'eduenc'z'y currentin the detector" anode circuit, thereby increasing the flow of audio frequency Still another object of the invention is to pro-v lvide a methodMand meansfor, operating atriode, tetrodeora pentode as a power'detector of signal vmodulated radio `frequencyy voltages of large igna'gnitudes.y y Stilll other objects of the invention Yare to improvegenerally the efiiciency of lthe electron discharge tube, as the triode, tetrode orfpentode, used as ,a detector, and to, additionally, provide adetectorof ,the grid -leak type which is net only reliable and einci'ent in operation but possesses greater sensitivity and maximum audio frequency output, and is economically introduced in a receiving circuit.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the inventionitself, however, as to both its organization and method o f operation willibestbe'understood by reference tothe following description taken connection with the drawing in which I have 'indicated diagrammatically several circuit organizations whereby my invention may be carvried into effect. l Y

'Inftheldrawing Fig. 1 diagrammatically shows a receiving circuit embodying one form of the invention, Figs; i2 to 5 inclusive show modified forms of the invention,

Figj shows the invention embodied in still anotherform, Y, o

I'discloses another ,modification of the invention.

.Referring to the accompanying drawing in which like characters Qf reference indicate the Same Aalenarnia in the different eures, :there is shown in Fig 1 a receiving circuit comprising means for collecting signal modulated radio frequency energy, auch as a grounded .antenna cir-` cuit, A, the latter being coupled, as at M, to a radio .frequencyampliiier vconsisting of one, or more stages of amnlieatan. arranged in any we llgknown manner. The output circuit of the amplifier is coupled, as at ,Mito the input circuit o f anelectron discharge tube 1.

vlI Yhe tube 1, and its associated circuits, are arranged toVV operate as adetector of the amplified radio frequency energy, the specific type o f ,de- 'section -employed inthe circuit shown in Fig. l, being of the so-called grid leak type of detection. The latter detectionis secured by connecting a capacity 3 in serieswith the control electrode 4 of the :tube 1 and connecting a `leak resistance 5 betweenthecontrol .electrcde 4 andthe cathode 6, This type of ,detection is-well known to those skilledin the art, and need not ,be explained any further `in great detail. The `.tube 1 is preferably ofthe-screen grid type, .the :tube including a screen element 7, the anode of `the tube receiving potentialfrom asource B through a resistor 8,

resistor 5 is connected, the said point being also l connectelsto the positive terminal of the source B thTgQl/lgll `a, xed capacity 9. Positive potential is applied to the screen element '7 from thesource B, crany other source .cf positive potential, through an element 10 possessing a high impedance to radio frequency current, and shown herein as a radio frequency choke. The low potential end fQralternating l`current of the choke 10 is con- I-.leltedto the'v negative .terminal of the source B tlrugh a ,by-pass capacity 11. The rectified cutput of the detector tube 1 is transmitted, by means of the resistance-capacity coupling, which includes the resistor 8 anda capacity 12, to the input .terminalsof .an audio system, the latter beingforexample Aan audio amplifier comprising one o r. more stagesof amplification, or any other system adaptedto utilize the rectified output of the` detector 1.

,Y The radio frequency choke 10 is inserted in series Awith .the s creenelement '7, to reduce, or

l 1,986,812 eliminate; the effect ofzthe iradio'frequency com-l ponenti off theacontrolfelectrde voltage; on 1 the ancideg:current,` thus? permitting a larger audio currentriny the s ancdecircuit" of thev detector tube 1". 1,2. If the voltageV on thecc`introl electrode 4 `is considered as-composed of a radio frequency vand an audio frequencyzcomponentfit will `be seen i that withrespectto the` audio'componentfythe tube lbehaves` asl `an ordinary screen` grid amplier, miviewpffthe `fact thatthe impedance betweenrftheiscreenelement '7` and ,the cathode .is

` i low to audioyfrequenoies. 1 n E.;sI-Iowever;` the screen-element awhigh impedanceto radio'frequencies this Abe- 'ing dueto the insertion of the choke "10min the `have screen circuit, p thus resulting inta" variation of screen element potentiaLat radio frequency, this variation beingf wholly,`or partially/put offphase with ,the radio. frequencyrvoltage 4on .the.,;control electrode e. ,w Accordingly, Lthere. results ,la substantial decrease in the radio frequency` come ponentf of anode current owinggthrough th anode :circuit of the detector tubel. i

While the presence of high impedance to radio Xfrequencies'in the `screen `element circuit will cause `reaction between the screen element cirf cuit` andthe `control electrode circuit, such .re-

` action, may be rendered innocuous by any of the methods ordinarilyemployed in radio frequency n ampliersnsuch methodsgbeing` welljknown to n those 'skilled in the art. As a matter of fact, this Y reaction between the controlelectrode and screen clement-circuitsmay "be usedt'to advantage to increase themsensitivitypof the circuit, thereby 1 providing,` factya regenerative detector.

While-the tube 1 lliaisbeen `shownas a screen grid tube, itis to be rclearlyunderstood` that `this typeof tube neednot be necessarilyused for the success ofi the-present invention. i WhenI a screen `griettube? is utilized, the, current .inwthe anode circuit, of any` frequencypcanfbe limited to a small 1value, nbyfemploying in theqscreen grid cireuit,;a circuit elementA having highimpedance tothe frequency* desired to be limited. j From another pointofyview, 'although notnecessarily the `only explanation possible, the explanation for .this phenomenon vmay,.befbased uponjthefact thatcurrent tends toflowl inthe screenfgridcircuit in phase Withwtheanode"current*or 180` out of phase `with the controlelectrodevoltage.`

f vWhen a high impedance is inserted in 'the screen grid circuit, this current produces a volt-- age out of phase withthecontrol electrode'volta age, and therefore,` tending to fbalancefout' the effect` ofthecontrol electrode voltage` 'onthe anode,` current.` `It, is `obvious thattthe samecffect maybcsecured by impressing the required volt-'- 'agefupon the screenelement from anyJother sourcel V n f Y t H It `'is tobe clearly understoodthat the amplifier preceding the grid leak detector adapted to impress: voltages upon`^ the control f gridlf'circuit of the detector of such `magnitude` that, without the` inclusion of the 'present inventionplate de tection attains proportions such that anincrea'se i iniinput tothe 'detector causes an actual reducplaterectification` Y j I Forex'ample-` while. I have shown in Fig. Ilthe required high impedance inthe screen grid cir-f` cuit obtained Vbyfmeans `ofza` :radio frequency choke,` in` Figi 2there `is shown a method of obe. taining the required high impedance in the screen grid: circuit .by `disposing Y. a' vtuned circuit insereswiththe screen: element 6. This' tuned i circuit consists. of` a' Variable capacity 13 t connected between the high` potential ,terminal of the "choke .10: andwthe. negativev terminal of the source B. `The tuned circuit A13, 10 offers a high impedance to the flow ofradio frequencycurrent inuthe screen zgri'dcircuit, and,l moreover the phase `of `the resultant vvoltage `of the screen grid may be adjusted accurately by virtue ofthe 4adjustabilityo-ff the variable.capa`cityjl3.`

y i In Fig.' there is shown .still another method fora'ccomplishing the resultfsecured-in theforms shown fin Figs.11 and 2, by the use: of `inductive coupling betweenrthe anode circuit` of the de` tectorgtube 1 andthe screen .element circuit. By coupling the" screen element `6: to` the anode,V

through 1a radio frequency transformer, or other l coupling system, compensation -forpthe radioifrequencycomponent of: anode `current can be secured.'` `The coupling consists? :of f the radio--`fre quency coil l0 inserted. in thescreen element 6,

and asecond radio frequency coil 14 connected in series between the` anode of the tube `and the resistor fA by-passcapacity `l5 ,is connected between thefhigh potentiallterminal of the resistor and the` negative `terminal of the source B.

- In this form` of compensation, as inthe forms hereinbeforedescribed a radiofrequency voltage is'caused to "appear on ithe screen element of the tube `1 "of sucha magnitude and phase as toipartiallypor completely, `compensate for the effect of the -radiofrequencycomponentj of controlwelectrode voltage on` the radio frequency componentr'of, anode current; It will be observed that `inr'Fig. 3,;the radio frequency vcomponent existing` in theanode circuit, is employed for producing theA compensating, or neutralizing; voltage ron; the screen element, thereby' offering another mode of securing the rrequired campen Still another` modev of -suppressing `theradio frequency component 4offcurre'nt in `the detector anode circuit,`;,1(which` is applicable to either simple triode or screen grid detectors,l see Figs.` 7

high impedance being a radio `frequency choke lfinconnectedin series with thevanode,` a fixed capacity 15,l being connectedv between thejnega-` tiveterminal ofthe source B `and the choke 10'. A by-pass fixed capacity `16,` is, also,'connccted and'` 4 respectively);` is ,to employ ahigh imped- `ance in the anode` circuit ofthe detector, the

between one end of the resistor and the negal tive terminal of the source-15? i 1 jlnthis modification the radio frequencygchoke coil inthe plate circuit ofthe detector` tube prevents-the flow .ofvradio-frequency currentsto the plate of the tube. 1 -By preventing the flow of the radio frequency current componentin the fplate 'circuit of the detectortube the detector overloading which 'occurs with increased signal input is effectively* prevented;` 'andi the f relation between 'detectorl output'energy and signal input energy becomes substantially linearefor signals! of increased intensity. explained heretofore substantially linear operation in ra' grid leak detector for signals of" intensity above the normal `overloadingpoint can be prevented only by mini-` mizing, orgeliminating, the condition conducive to anoderectifcation. The effect. Oflthezradio l lo flo

. rents. in the anode circuit.

frequency chokein the vexternal plate .circuit-fof themodication, illustrated in Fig. 'l'.for example,

is tozsubstantially prevent .radiojfrequency currents `from Viowingv to .the .plate .and through the plate circuit. i. At this point, it may be .-observedthat the limitation in audio output due .to radio frequency .current. in the :anode .circuit maybe explained by noting .thatrecticationoccurs in rboth the .anode and grid circuitsy .ofa .detector tube, and Ythat these .two .effects are iin -phase opposition relation. Hence, `'by preventing `the condition Vconducive .to anode rectification (bias detection) the maximum audio .output is increased; and, incidentally, the sensitivity. l j

In Fig. 5, `thereis shownstill another modifica- I tion ,of the invention, .theanode .circuit :of the detector .tubeillincluding .this form, ,a variable capacity 13 and an inductance 10'., the .capacity being connectedbetween the anode and .theinegative terminaly of -thesource.B.` v.A fixed .by-pass capacity 17 is also connected from the. choke 10 to lthe negative terminal .of .the source B. In this'instance, ithetuning ofthe anode .circuit pery mits accurate adjustment ofthe magnitude and phase .of `the Limpedance .to Iradio frequencycuriArrelectron discharge tube of the -pentode type readily lends itself vto..powergridrleak .detection when it .embodies any @of the arrangements, eX- plained hereinbefore, for` suppressing radio frequency currentin the anode circuit.-` The pentode tube construction `is Well known to those skilled in the art, and need only be described by reference to Fig. 6, as including beside the usual control electrode, `cathode and anode, a screenelement 30 and an auxiliary electrode-31, the latter being disposed vbetween lthe anode and screen element, and connected to the midpoint of the cath-ode.

rThe .element 30 receives potential from the sourceB, through a radio frequency choke 10, as shownin connection with thedetector tube in Fig; 1. A by-pass vcapacity 24 is shunted across the source 'B. As already explained, the high impedance 1.0 functions to produce the balancing radio frequency voltage. A pentode tube serves ras-a'detector-amplifier in this Way,v and' can be directlyconnected toa speaker, vor the like.

While I have indicated and'describecl several systems for carrying myinvention into effect, it Will'be apparent tol one skilled in the a-'rt rthat my vinvent-ion is by no means `limited to the particular .organizations shoWnvand-described, but

that many modifications in the circuita'rrangements, as Well as in the apparatus'employed, may be made Without departing from the scope of my inventionv asset forth inthe appended claims.

What I claim is; f- Y i l 1. A method of operating-lan electron discharge tube; provided-W-ith a cathode, anode andfgrid electrode,y asapower.'letecto'r of the gridreetiiication-type, which consists in impressing' signal modulated radio frequency. energy -ioff relatively high intensity upon the ygrid electrode of the tube, maintaining av substantially linear yrelation betweenfthe detector output energy and the signal input energy up lto -said high intensityby establishing in the external anodecircuitof said tube a :Oatl'i'l of r high impedance' to 'the l130W of radiofre- 'quencyi current, and impressing the output'energy ofthe said detector upon a maensfforrenderiiig saidsignalsdiscernible.' Y 'Y 2. '.In'combination, 'means' for collecting, and

.amplifying to a high level modulated'radio frequency Yenergy;means for.detectilig'said amplified .energyicompri'si'ng an electron/discharge :tube provided .witna cathode, anode, .control .electrode andza screen element', the tube input circuit beingarranged for gridldetection, and .means-disposed in the screen `element circuit offering a'high the'screen jelementscircuitl and anode circuit of v the '.tube for .substantially `.diminishing fthe flow of radio frequency current `in theanode Acircuit of` .the 'tube and increasing :the i10W frequency outputfthereof.v v

4. In combination lin acombined detector and amplier circuit-an electron discharge tube vprovided with a cathode, a single anode, control electrode, ascreen element, and an additional electrode at .cathode potential, .the tube input circuit being arranged forgriddetectiomand means in the screen elementcircuit for substantially reducing the flow of :radio frequency current in the anode `circuit .and increasing the low frequency output of `the detector.

5. 'A method of -operating a grid leak detector including a .screen'electrode'with -radio frequency signal" inputs of an` intensi-ty normally resulting in a decrease in the audio Ifrequency output of the detector which consists in collecting such signals, amplifying the collected signals to said intensity, impressing the amplified signals `on the control grid `circuit of the detector, and simultaneously producing aradio frequency voltage in the screen electrode circuit of .thedetector of a magnitude and phase sulcient to substantially suppress the radio frequency component of signal current in the detector anode circuit and` thereby prevent said detector audio output decrease.

16. .Incombination; means for collecting, and amplifyingfto a high 'level modulated radio frequency energy, means 'for detecting Isaid amplified energy comprising an electron discharge tube provided'with a cathode,..anode, control electrode and a .screen element, .the tube input circuit being` arranged for griddetection, and means disposed in the screenxelement .circuit offering a high impedance .to .the flovv of radio frequency current inv .thepanodecircuit of the tube thereby increasingthefaudio frequency output thereof, said last mentioned means consisting of .a resonant circuit.

17..In ,cgmbination, means for collecting, and amplifying to a high level modulated radio frequencyenergm-Ymea-ns'vfor detecting said amplified energy.V comprising an electron discharge tube provided ,with a cathode, anode, control electrode anda screenjelemenhthe tube inputy circuit being arrangedfor gridgdetection, and means disposed `gin-the screen element circuit offering a high impedance to the now of radio frequency current oin the `anode .circuit of. the tube thereby increasing the audio frequency output thereof, said last. mentioned means consisting of a resonant circuit including a variable condenser.

" 8; In combination, :means for collecting, and amplifying to a high level modulated radio frequency energy, means'fo'r detecting said amplified energy Vcomprising `-anlelectron discharge tube provided with a cathode, anode, .control'electrode "ing arranged for grid detection, and `rneans in- Cil cluding a tuned circuit disposed in the anode cir- -cuit offering a high impedance to the ow of radio frequency current in the anode circuit of the tube thereby increasing the audio frequency out- Y put thereof. i

` 9; In combination Witlia detector 'stage ofthe y 3 A grid rectification type, a source of signal energy Varying in intensity over a wide range,"an audio frequency load circuit, said stage includinga tube and at least one positive cold electrode, a conneotion from the positive electroder to said load y circuit, and means connected to the positive electrode circuit for substantially suppressing the radio frequency component in said load circuit whereby the detected output energy of said stage is substantially linearly related to the signal input energy over said range. y i WILLIAM A. HARRIS.

`'provided with a cathode, a signal cold electrode,

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