2,204,574. subtracted from each other'and the resultant. is Ki-IE2. This subtractive resultant is that which is desired for automatic frequency control and for fiequency or phase modulation wave detection. 5, When it is desired to receive amplitude modulation, the desired resultant is El+E2. In order to obtain such tt@ resultant, -the combining system 6onsisting of switches-S and Si, tubes V and Vi and transformer T are used. Switches S and Si 10 are ganged together so that when switch S is on point #1 switch Si will be on its point #1 also and ,w,hen switch 8 is on point #2 switch Si is also on point #2, etc. Potentiometer P clivides the voltage from point "W' to a value substantially e(jual tq -15 (Ei-E2) /2. Tubes V and Vi amplify the voltages on the arins of switches S and Si, respectively, and combine them in push-pull in transformer T. This pushpullconnection ciluses the voltage fed to tube V to be subtracted from that fed to 20 tube Vi. With the switches on poin't 1, no voltage is fed - to tube V and the voltage, i(Ei-E2) /2 is fed -to tube Vi. The output voltage is then equal to, the Ooltage fed to tubi@ Vi, br (El-E2) /2 which is 25 the resultant desired for phase or frequency modulation detection when the'two diodes are fed by phase or frequency modulatibn discriminator, eir4@uits whi6h impart amplitude @ modulation envelopes of opposite phase to the two diodes.. 3( (The gain of the tubes V and VI has been disregarded for simplicity.) With the switches on point 2, the voltage Ei is applied to tube V and the yoltage (Bi-E2)i 12 to tube Vi. 7be resultant appearing in traiisformer 35 T would then be equal to Bi minus (El-E2) /2 or (Ei+E2)2. This rc-@ultant is 'the sum of the two diode voltages Instead of the difference and is that desired: for amplitude modulation output when the diode detectors are fed amplitude mod40 ulated waves by phase or frequency ipodulation discriminator circuits. The other twb positions on the 6witches, posi@ tions 3 and 4, are for obtaining the outputs of each diode separately. With the arm on point 3, 45 tube Vi Is shut off and tube V amplifies El which appears in th6 output traiisformer. With the arms-4Dn point 4, tub@6 V-@@receives the voltiige El these two inputs are combined subtractively in 50 the push-pull output transfi)rmqr, the resultant is Ri-(Ei-E2) or E2, These stu . gle outputs are used for testing pumoses ori th'e frequency and. pham modulation receivers or are used for reducing intetference. These single oiitputs'aid 55 In balancing the two filter characteristics andilso allow the choice of the futer,which gives the oids,,Interference least interference. In other w may bo- reduced by choosing the discriminator -wyaich gives minimilm output fpr the frequency -go at which the interference ocour's. For itistsnee, suppose the tvio diodes 109 I and f.10 ar6 fed by. the sloping futers haiking chaiacteristics as shown Ftt A and B of Figure 5 in a fiequency_ modulation interfer@nce has the frequ6ney receiver. If th6 65 Pi,,& reducedinterference output may be obtained by choosing that diode which 14 fed by discrim-inator.. fllter having characteristic B which h @s a rainimum c@utput At the frequeney Pi. Another instance would, be that of Pngureg 6a and 6b In 70. which the dise'rinilnator characteristi@s of a phase modulELtion receiver, which MaY also 'receive amplitude rdodulated wwve@, are'shown. ,Since either, amplitude or phase modulatiori may be received on a single Mter, when an interf@r75 ence occurs, say at the frequency Fi. the detector which is being fed by a filter circuit or discriminator having the characteristic shown in Flgure 6b, is chosen and tlmt fed by the filter or discriminator having th6 characteristic shown in Figure 6a switched off. The single sideband.effect of the discriminator circuit therefore reduces the effect of the interference. I claim.: - 1. In a system for converting phase modulation on wave energy into corresponding amplitude lo modulations, -an impedance on which said phase modulated wave energy may be Impressed, a pair of diode detectors having input electrodes and having output electrodes conneeted in series, an under,- neutra@lized crystal futer circuit, and an 15 over-neutralized crystal futer circuit comprising a single, piezo-electric crystal baving one input electrode corinected to said,impedance, and a pair of outpu@ electrodes connected to the input electrodes pt said detectors, and a connection 20 between a second point on said impedance and sat d detector inout electrodes. 2. In a system for converting phase modulations on wave energy to correspondiiig amplitude modulatioiis on wave energy" an impedance ener- 25 'gized by said phase modulated wave energy, a piezo-el6etric crystal having -a plurality of electrodes, a ffrst Mt6r circuit including ek Pair of said piezo-eleciiie electrodes couplod to said.. impeoance to be fed by wave energy therefrom, 30 a second filter circuit including a pair of the electrodes of said piezo-electric crystal couwed to said impedance to be fed by waileenergy therefrom, a detector coupled to each of said filter circuits, apd means for under-neutralizing the 35 capacity between a p@ir of . said electrodes and ovei,-neutralizing the capacity bet*een another pair 6f said electrodes. 3. In a -system for converting phase rriodulati.ons on wave energy to coiresponding amplitude 40 modulatioiis on wave energy, an impedatice energized by'said phase iftodulated wave energy, a piezo-electric crystal having a plurality of electrodes, a first filter circuit including a pair of said piezo@-electrib electrodes connected in series 45 *ith said impedance to be fed by wave energy therefrom, 'a second Mter circuit Including a pair nected in series with said impedflnee to be fed -by. wave energy therefrom, a detector having in- 50 fl put electrodes epupled to each'of said Iter circuits, an(k meons for under-neutralizing the capacity between a pair of said eiectrodes and oyer-neutralizing tiie capacity between another pair of said electrodes. 56 4. In a -iy-stem for converting phhse modulations on wave energy @o corresponding amplitude modulations and demodulating the same, an iinpedance energized 6y said phase modulated wave energy, a. detector system having input electrodes, 60 a piezo-electric crystal having a plurality of elt!ctrodes, a futer eir@uit incltidi.ng a pair of said piezo-electric electrodes coupling the input electrodes of Eiaid detect I or system to- said impedance, a. second futer including b@ Pair of the electrodes 65 of- said. piezo-electric crystal coupling other input electrodes of raid detector system to said imped ance, and means- for under-neutralwng the capacity between a pai.r of said electrodes and over-neutralizing capacity between another pair 70 of said electrodes. :5. In a system for converting phase modulati6ns on wave 6nergy to 6orresponding amplitude modulatipns and.demodulating the sanie, an lmPedance energized by said phase modulated wave and.tube Vi receives the voltage El-E2. When of the electrodes of said pie2@6-electric crystal con-

tnergy, a detector system haou Input electrodes, a piezoelectric crystal having a plumlityof electrodes.'a ifflter circuit Including a pa# of said Piezo-electric electrodes and a resistance coupling the lnpiit electrodes of &Ud detecto@.- 6ystem In shunt,to said lrdpedance, a.second fiater lncludIng a resistance and a pairof the el6etrodes of said pie@zo-electric crystal cdupling other input electrodes of said detector system in,shunt to said im1( p@6dance, and meons fot und6r-i2eutralWng the capacity between a pair of said electrodes and overneutralizing the capacity between another pair of said electrodes. 6. ]In a phase modulation receiver, a reactance On wmch phase modulated wave energy may be impressed, a piezo-electric crystal having an eleetrode connected to a point on said reactance said crystal r ha@ing. an additional pair of electrodes, 26 " pair of electron discharge devices each having a control electrode, a cathode, and an Anode, a@ connection between the cathodes of said tubes and another point on said impedance, conneetions between @@d pgir of crystal electrodes and the control grids of said tube8, reactances of 25 d@ftei@en.t ebaracter connected in shunt to the eleetrodes of said crystal, a pair of diode rectifiers each havii* Input and output electrodes, a band pass transforiner couphng the input electrodes of one of said diode rectiflers to the output elec30 trodes of on6 of said tiibes a second band pass tiransf6rmer cdnnecting the input electrodes of the@- oth6r of said diode rectifiers to the output electrodes of the other of said tubes, and a utilizatioti circuit coupled to the output electrodes of 35 said diode rectifiers. 7.1, ]In a modulated wave demodulating,and indicating system the combination of a -plurality Of filter circuits having similar but ooposed output characteristics such that 6ertain frequencie7s 4!1 with@i the band passed thereby'are exalted and others substantiahy rejected, rectifying 'meam having Inputs coupled to said fllter eircuitr. and having outputs coupled by impedances difrerentially responsive to, rectifled energy,, and means 4.-. for amplifying the potentials, In the separate, differential Impedances or the sum of the potentials in the differential Impedances or the difference of thi- potentials in the differential impedances. . 8. In a system for adapting a phase or frequency modwateci wave receiv6r of the type wherein a pair of filter circuits of opposed characteristics supply energy to detectors having output electrodes di)gerentiany coupled by a PeAr of f,5 seiies Impedances, one ternitnal of the @ series connectign of Yvhich Is connected to a point of substantially fixed potential, thO combination of a pair of ele I etron discharge devices each having an anode, a cilthode, and a co@trol@ gri . d, a c I orkC-( nection between the cathodes of said devices, and said point of substanti&Uy fixed potential, a connection'between th6 anodes of mdd devices and an indicating circuit, an impedance connecting a relatively high potential end of ea@ of said ,oh series resistances to said potat of substsmually fixed potential, . a sottch. connected to the contiol grid of each of said tubes and ioiitacts cooper4ting with said switches for ponnecting differefit points on said impedances to add contiol ,O grids. 9. In a phose or frequency or Wmplitude'niodulated wave energy receiver, a viave energy ampfff.@ing ana demodulating mftm of the heterodyne type Including a detector cooperatinjg with a To local oscillittor of, controllsble frequeiicy to produce intermecuate frequency energy. Alter eircuits of different characteristics tuned to substantmy _the. mean frequency of the Intermediate frequency resulting from beating said modulated wELve energy with4 said local oscilliitions, 5 means for impressing said intermediate frequency energy on said filter circuits, a pair of detectors having Input electrodes coupled to said fllter circuits and having output electrodes connected differentially by impedanc6s, Weans for control- 10 ling the frequency of said locil oscillatbr i@m Recordance with the potential% across said impedances, and voltage dividing meayas connected with said iMpedsCnees for supplyjng therefrom the sum of the pot6ntials produced thereacross and the 15 diff6rence,of.the potentials ptoduced thereacross. .10. In a wave energy translating system, a tunable wave responsive means with means for ii,rpressing wave energy thereon, a frequency discriminating circuit includin a piezo-electric 20 . 9 crystal having an Input electrode cotipled to said wtlve responsive means and a pair of output eleetrades, reactances shunted between saia Input electrode and each of said output electrodes to form therewith a pair Of eirctdts one of Ch 25 is effectively'capacitive and the other of which is effectively inductive with respect to the MeiLn fre(iuency of the wave energy impressed from siild means oii said crystal Input electrode, rectiliers coupled with said oi;tput electrodes for 30,. producing a ewrent componerit characteristic of the reaction of the instantanedus -mean frequency of saict- wave energy impressed on said cr@stal Input electrode and the frequency at which said circuits are normaby capacitive and Inductive re- 35 spectively, And means for tuning,said tunable wave responsive means In accordance with said current component. 11. A @ystein as recited In claim 7 wherein each of said filter. circuits h4ve, a characteristic such! 40 that the carrier ftequenc@ of said m6dulated wave Is exalted. 12. A system as recited ir, claim 7 wherein each of said fllter circuits have a characterisft@ su6h that one of said filters substantially rejects. side- 4r, band frequencies. on one side of the carriey frequency of -"Ad wavi@ energy and the other ftlter substantiwly rejects sideband frequencies on the other side of said carrier frequency. 13. In a system for demodulating wave energy 50, modulitted In amputude at signal frequency coinprising' a carrier and sideband frequencies, a &cuit having a characteristic which is reactive In the same sense with respect to a band of sideband frequencil@s lying on both sides of the frequency,,65 to wbich the circuit Is tuned, a circuit having a characteristic whi@h is reactive in the same sense, but OPP(site to: the sense of the aforesaid elicult, with respect to a band of sideband frequencies iying on both sides of the frequency to which. So the circuit is tuned, means for applying amputude modulated wave energy!Df a mean frequency substantially equal to the frequency to which said circuits are tuned to said circuits, sud detecting means coupled with said @@cuits. 14. in a Aystem for,denwodulating wave energy, inodulated In amplitude at signa@l frequency comprising a carrier and sideband frequencies, a eircidt having a characteristic which is reaeuve in the same sense wlth rewoect to a band of 7o sideband frequencies lying on both sides of the fre(luency,to which the circuit is tqngd, a circuit having-& cheracter.istic which Is tive in the same sense, but opposite to the sense of the aforesaid circuit with respect to a b.and of side- to

2,20074 band frequencies lying on both sides of the fre- of, a different type, an fmpedance@, a plurahty of quency to which the circuit is tuned, means for output terndnals, a piezoelectric crystal-having applying amputude -modulated wave energy the a plurality of electrodes, raeans for impressing carrier wave frequ6ney of which is substanti&Hy equal to the frequency, to which said circuits are tuned to wid circuits, and deteethig means coupled with said circuits.' 15. In arx amplifying system to be used to amplify potentials characteristic of signals produced 10 in series connected Impedances a terminal of one only of which is connected tb a point of substantially fted potential, a pair of electron. discharge devices having a control grid, a cathode and an anode, an output circuitconnecting the anodes and@ cathodes of said devices izx . push-pull relation, a connection between the cathodes of said devices and gaid point, of substantially fixed potential, two resistances connected between said point of substantially fixed 20 potential and different points oxi, saio imped@. ances, and switcmng means for connecting the control -grid of each of@ said devices to different points on one only of said resistances. 16.. In a system for demodulating phage or fre25 quency or aniplitude modulated wave energy, pair of rectifiers having input and outout electrodes. filter eircuits of dissimilar choracteitsties coupled to the input electrodes @of. said recti:ders, a pair of impedances connecting the output 30 electrodes of said recti:d@rs iii a circuit, means for imi)r o b@ mod@ssing modulated wave energy t ulated on said futer circuits, whereby rectified current flows in said impedances to produce therein potentials char'acteristic of the said rec3s tified current, and voltage dividing meam connected with said impedaiiees for supplying therefrom potentials which represent the diffe of the potentials produced by recti:fted in said ixhpedances and potentials which repr 40 sent the summation of the potentials produced. by rectified current in said impedances. 17. In a system for receiving ampliiude modulated wave energy and deiiiodulating the same, an impedance on which@ said wave eriergy is 45 impressed, a pair of filter circuits each having an input coupled to said impedwe and an output coupled to demodulating means, said filter circuits including a, c@rystal having three terminals one of which is coramon to said filters 50 the other two of whieh are each in a differ'ent one of said filter circuits, reactive means in shunt to electrodes of said crystal in sgad. fllter cirrwtr, for slightly dff '- neutralizing said crystal with respect to the wave energy whereby, th'e carrier 55 arxd, certain side -frequencies passed, bSr each of said futer circuits are relatively exalted and, othef side frequencies are relatively reduced. 18. In a system for converting phase modulation on wave energy into corresponding am60 plitude modulati6ns,, ali impedance, means for impres@ing phase modulated wave 6nergy on said impedance, two Pairs 6f .6utput terminals, arx under-neutralized crystal filter eireuit, an-'iover@. neutralized crystal illter ciivuit, sMd filter cir65 cuits including a singl6 piezo-electric crystal having one electrode connected to said impedance @and having two other electrodes each. conwave length modulated wave energy on said impedance, mearii coupling one- of said elec- 5 trodc's of . said L crystal to said impedance, meam coupling other of Lsaid crystal electrodes each to one of said output- terntnals to form two fater circuits between saici impedance and sglid output terminal , and means for relatively varying the 10 degree of neuirali7Ation of iho reactance between pairs of said crystal 'electrodes to thereby retatively vary the characteristics of said filter circuit& 20. In a systq;n for converting phase modu- 15 lated wave energy to c(?rresponding amplitude ralodulated wave'energy, an impedance, a plu- - rality of output a piezo-electric crystal having a means for impressing energy on. said im- 20 Pedance. means COUPling One of @said electrodes of said crystal to said impedance, means rouPling other of ald crystal electrodes-to a pair of said output terminals, means coupling a point on mAd lmpwance to anotheir of said output 25 terminals and mems for varying the degree of rieutralization of the reactance betweenpairs of sWd crystal electrodes. 21. IrA. -a -system for converting wave'length nlodulations on wave energy into modulations of So a,- different type, an impedance, a pluraii'ty of -01@ coupling tubes having input electrodes and -hav:'--- ing output eler-trodes coupled to a utiiization meanr,, mc@ans for l@npressing wave length modulated wave energy on Wd imp@dance, 4 piezo- 35 electric crystal having a PluralitY of electrodes, meam coupling one of said crystal. electrodes to said impedance, mean@; coupling other of said crYst@Ll electrodes to said coupling tub@6 in ut P electrodc-s, and@'means fot varying the degree Of' 40 neu.tralization of the reactance betvieen pairs of said crystal electrodes.' 22. In a system. for clonvert@ng phase modulated wave energy to corresponding amplitucte@ niodulated wave energy, means for reci@iving said 45 wave energk, a tunable oscillator coupled witb said last named Erlems fof beating local osciliationg with said received wave energy..-to produce coresponcung wave energy of reduced'frequency, a reactance, means for impressing said.wave en- rj, 0 ergy- of reduced frequency.o , n said reactance, a piezo-electric crystal having an input electrode and a Dair of output electrodes, meails coupling said crystal input electrod e to said reactaxice, a rectifier system having an Input circuit and an r, r, OlitOut cireldt including impedance, a circuit 'Coupling one of the output -electrbdes- of said crystal to the input circuit'of said,rectifier system, a circuit coupling the other of soad crystal output electrodes tO the input cireu . it of said 60 re6tifier system, a coupling between said recti' fier input circuit 96nd said reactance, variab . le reactances con@ecting -.iid reactance tc> each Of sMd crystal ontput electrgdes, and means rouPling said rectifter output circuit to said tunable 65 oscfllator to control the oscillator frequenc3@ in accordance with Potentials at the output circuit nected to an: output terminal of a different, pair of, said reetinw. of said dutput terndnals, a connection between. 93. In a system for,.Converting phase-rnc)qu70 a second point on said impedance and the re- . lated :wave energy to corresponding -amplitude 70 maining terminal of each pair Gf output termodulated Wave energy, means for receiving said minals, and a utilization circuit coupled to said wave energy, a tunable owillator coupled *ith pairs of output terminals. said last named mean@ for beating local'oscills- - 19. In a systein for converting wave length tions with -said wave @eriergy to PrGduce corre@ t5 modulations o.n wave energy into.modulations s.ponding wave enerv of reduced frequency, a 74;

9,204,574 reactmce, means for. impreming said wave energy of rediaced fiequency on sWd reactance, a piezo-electric crystal having an input electrode and a paii of outptit electrodes, means coupling said crystal input elett.rode to said reactance, a rectifier system having an input and an output ciieult, means coui)ling the output circuit of said rectifier system to a utiuzation circuit. a circuit including 6oupUng means tun@d to - sublo stantially the mean frequency of said wave energy of reduced, frequency coupling one of -the outp electrodes of said crystal to the' input eire@tt of said rectifier system,@a circuit including'a -coupling tuned to suwtantially the mean frequency of said wave energy of reduced frequency coupling the other of said crystal output electrodes to the input ci@cuit of said rectifier system...a coupling'between the Input circuit of 5 said rectifier syst6m and said 7 first reactance, variable reactances coupling said first reactance to each of 'Said crystal output electrodes, and a circuit connecting the oiitput of said rectifter system to said,tunable oscillator to control the 10 tune thereof. MURR-AY G. CROSBY.

Patented June 189 19HO 2 9 2 0 4 ; @ 7 4 .UNJTED @STATES PATENT -OFFICE,, @2,204,574 THREE ELECTRODE CRYSTAL PHASE MODULATION BECE.IVER Num,sy G- Crosby, Riv@rhead, N. Y., &Wgnor to Radio 6@;i;;Wilon of America, a corporation of Ddaware Aplffio&tion January 22, 1939, 1Serial No. 196,273 23 Clainis. (CL 25(@.-20) This disclo=e concerns phase'modulation receiversof the type which utflize over-'aiid undern@'UtraHzed crystal filter characteristics to fcirio a back-toback phase modulation detector. A three-electrode crystal holder is used, but instead Of, employing a neutralwng circuit to over- and under-neutralize the holder capacities, shunt' tuned-circuits or reactances are connerted across the holder so as to tune with the holder capacity 10 aild thereby over- or under@compensate for its effect. The futers so formed convert phase modulatims In wave energy Into corresponcling ampiitude. The receivers of this diselosure,utilize, a 6om15 bination of the principles described in my Patent #2,085,008 dated June 29, 1937, and United States applications Seiial #165,056 flled September 22, 1937, @now Pateiit #2@1156,374 dated MbLy 2, 1939;. Serial #167,344 Med October 5 1937 now Patent 20 #2,156,375 dated May 2, 1 3@; Se'rlal-@#195,041 tltd March 10, 1938; Serial #178,655 filed December 8, 1937, now Patent #21156,376 dated May 2 1939; Serial #242,469 filed November 26,@ 1938. ii@e present eircuits have. an.- advantage iii sizn'- 25 PlicitY in that a pusb-pull, t ransformer is not required to obtain neutralizing voltage. In describing my, inveiition roference wili be made to the attached drawings wherein, Flgu.res 1, 21 and 3 each show the e@sential 3o elements of converting circuits arranged in accordance with iny invention. Mgure I also shows novel amplifyi ng system to be used with the@ converting circuit and detectors to perniit the, reception of phase 6r frequency or amplitude 35 MOdul@ted N'vaves in ttie dircuit witlxout revising its c6nnections; Figures 4a to 4h are iuter izzi@'eda'n'@ce characteristic reactance curves and vector diagrams of mgdulated wave components, *1,, illus . trating the 10 operation of my sygtem;'while Mgure s 5, 6a, and 6b ore fllter ch aracteristic curves used to explain the operation of all of the receivprs and in pe@rticular of the receivers when using therewith a novel signal amplifier as shown @5 in Mgure I following the differential connected detectors. The circuit of Mgure I sbows the pei-tinerit@ parts of the discriminator rircuit tor converting ase modulation intlo amplitude modulation and D f(>r obtaining autom tic fre4uency control voltage. Interftiediate freque ney energy from a superbeter,odyne receiver Is fed to the primary winding of tuned transformer 100. 'rhts transforr,aer is propefiy damped by resistances -99 and 08 and awusted by condensers,97 and 96 to fGrM a band-pass fdt@@r. The crystal 105. Is held in a crystal holder having a single input terminal IC 1 and two output terminos 002 and 103. T-he Input terminal is connected to the high potential side of the tuned tmnsforiner 100 and the two out- ;5 put terminals are connected to the plates 114 and @1 16 of diodes 109 and 010. Tuned circuits 104, I oo,,and 107, 106%are connected between the common inpat terminal and tbe'two output termt-' nals, , The resonant frecluencies of these tuned 10 circ uits are adjusted to be.a.-little above and a little below the resonant frequeney of the crystal I 05. This slight off -tuning producel an Inductive rea ctance In one case and a capacitive reactance in the other'case. Hence the effect will bi@ the .1 r) som e iLs though a cap@xity were across one of the sets of crystal terminals and an inducta@nce acr oss the @other set. Tiiis arrangement catises the formation of two crystal Mters having overand under-neutralized aharacteristies respective- 20 IY. Thus, tuned circuit 104, 000 inight be tuned cap acitive to'present an under-neutralized cht@racte ristic such as shown at Plgure 4a between tran sformer 100 and diode 109, and tuned circuit 107, 108 might be tuned inductiv6 to iiresent an 25 ove r-neiitralized filter characteristic such as sho wn at Flgure 4e between transformer 000 and diod e II 0. These two chara;eteiisties convert the pha se modulation Into: aMpJitude rnodulatiom i@ri th@ 180' phase relation between the amplitude 30 env elopes. Consequeritly, the push-pull corineetioki of diode resistors I I I and II 2 will add or aid the phase modulations and oppose and substan@ tiall y cancel amplitude modulatiom present on the.originalphase'mc)dulatedwave. Byvirtueof art the fact that one of the filter characteristics has a rejection point at a frequency lower than the carrier frequency and the other filter has a rejection ppint at a frequency higher th n the caxrier freque ncy, when the mean frequency of the wave @ene rgy shifts slgwly a differentialvoltage is avail- 40 able aerm resist(>rs III and II 2 @shunters by bypass condensers I II and I IS to control the grid of a reactance tube modwator which tunes a frequenc y-changir@g heterodyne oscillator in'the eir- 46 cuits prior to transformer 100. Tho- time contiol circuit Rc pre.vents this frequency contr6l 'circui t from, responding to signal modulations on the wave. The detected plime modulation appea ring across resistors II# and 092 is fed 50 to.an audio@ frequency amplifler 120 foi subsequent utilization. The audio frequency amplifier may be a simple tube amplifler where phase modulation only Is to b@e received. Iri case phase or amplitude modulated wave$ are to be received jo

2 the amplhler shown in Figure I and deserbed -in detail hereinafti@r may be used. In tile circuit of Flgure 2 in order to simplify the description the radio frequency ' amplifier d automatic frequency 6 heterodyne receiver an control circuits halve been@omitted. These circuit@ may be of any type stibh as shown in Flgure 1. The circuits of Fligure 1 ma:y. be added to the circuits of Figure 2 as indicated in the draw10 ings I)y connecting the elements not shown to points' 2, 4, and 6. In the circuit @ of Flgure 2 the ;;ame principles are applied exe6pt that single, reactane-es 106 and I 01 take the place of the tuned circuits of 15 the prior figure connected acro ss the dr-ystal holder terminals and diode-driver amplifier tubes 109' and 110' having their grids 113, 115 and cathodes 6onnected to the crystal output eletirodes are excited by the filtered energy and are 20 used to feed the two filtered energies to the diodes 109 and II 0. Tuned bandpass rtransformers 128 and 130, having - their primaries shunted' by damping resistances 125 and 127 couple the anodes and cathodes of the driver tubes 10.9' and 25 1 1 O' to the diode plates I 1 4 an I 1 6. The terminals of the diode outpiit impedances I I I and 112 may be connected to the input electrodes of any audio f requency amplifier tube supplying a utilization means or directly to a utilization 3o means.. If desired, the impedances I I I ond II 2 may be connected to an amplifier as illtistkated in Fligure 1. - The rectangle 120 of the figure r6presents the simple amplifier mentioned above b,nd also represents aii amplifier as illustrated in 35 Flgiire 1. Th,e operation of this circuit in othe"r ri@Apects is the same as that of @Figure 1. In the cireiiit of 14gure 3 a discriminator is shown which utilizes a shunt connected crystal in the manner of the discriminators described in 40 my application #167,344 flled October 5, 1937, now Patent #2,156,375 dated May 2, 1939. In'termediate frequency. energy Is fed to tuned transformer 1001 and through isolating resistors 200 and-201 to the two terminals of the rryst@Ll 41; holder 102' and 103'. The common terminal 101' of the crystal holder is connected to the low siae of the tuned iransformer. Reactances Xi and X2 would be either an inductance and a capacity or two tuned circuits. These reactances 5( are adjusted so that one forms a capacitive action across the ers'stat holder and the other an inductive action. The output of the two filters is taken from terminals 102, and 1031 and fed to the grids 113 and 115 of diode-driver tubes 109' 55 and 1101 'such as are used ip 24gure 2. The other features of this circuit are the same I as those of E4gure I and Mgure 2. In the operation of the receiver. of Flgures 1, 2, and 3 t,*Q futer characterlstics are produced to 60 be led to the two diode detectors -1 09 an.d II 0. The energies fed from the crystal output terminals 102 and 103 t6 ampli:fter and coupling'tubes 1091 and 1101 of Mgures 2 and 3, or directly to diode rectifters .109 and I 10 of Plgure 1, are over05 or under-neutralized crystal energy and have characteristics as shown in Flgures 4a and 4e. This energy appears in transformers i28 and 130 Of Mgures 2 and 3 and on the diode.electrades of Mgure 1. The characteristic of 'the energy present on the Input electrodes of l'OS bf Figure I 7o and in, say transformer 128 . of lmgures 2 and 3, Is as sh6wn @i lmgure 4a being derived from a futer 2,204,574 actance at Xi of Figure 3 or 164 and I$$ of Ingure 1. This is obtained by adjusting the said elements of the respective figures so -that the reactanioe across the crystal. holder is capacitive for the case of the series connecteet crystals of Flg- .5 @inductive for the case i)f the ures 1 and 2 and ghunt connected crystals of Flgure 3. The characteristic of the energy say in transformer 130 of Plgures 2 and 3, or @n the electrodes of diode I I 0 of Flgure 1 is as shown in Flgure 4e, this en-' 10 ergy being passed by filters which are over-neutrahzed by adjusting the elements 107 and. 108 of Flgure 1 or 107 of Flgure 2 so that the crystal holder has an iriductive 'reactance ai sub@tantially the carrier frequency, and adjusting the, 15 reactance X2 of Mgure. 3 so that the crystal holder has a capacitive reactance. In the case of the shunt connected crystal, -the under-neutralized characteristic I is given by ingure 4e and Its reactance characteristic As given by Flgure 4b. 20 That is, in the case of the shunt connected filter the low Impedance point on the reactance curye (where the line crosses the X axis) coincides with th6 rejection point on the output chELracteristi ' c. Also, the high impedance point on the reac- 25 tande curve coincides with the carrier frequency. This is o@posite to the case of the series connected filter in which the under7neutralized chara . cteristic is given by Figure 4a its reactance curve is given by 4b, the zero react@nce curve coincides 30 with the rarrier frequency, and the maximum impedance point coincides with the rejection point. The reason for this difference between the shunt- and series-cormected fnters is the fact. 3r' that with the series conne etion the crystal aJloNVs more or less energy to flow according to its impedance, while with the shunt connection, since the &op across the crystal is utilized, the output' voltage is pr(jportional to.thecrystal impedance. 40 . In the case of Flgure 4b a negative reactance is present o:n bgth sides of the caxrier frequency, that is, the circuit would be capacitive on both sides of th6 carrier except for the very short interval near t;he, carrier frequency. .5ince the re- 45 actilnee is capacitive In the frequency region in which the. side bands are disposed and is resistive at the carrierfrequenenp, the phase of the side bands WiU be shifted 90' with respect to the carrier. In Figure 4c the carrier and side bands c;f 50 a phase modulated wave are shown. The carrier is marke(i C, the upper side band U and the lower side band L. The positive direction of rotation is taken as counter-clockwise and the directions of rotation of the side bands with respect to the 55 carrier are indicated by arrgws attached to the side band vectors. Side bands of an order greatected due to their small er than I has been negi amplitude and for simplici ty of explanation. V,7hen the phase modulated wave of Figure 4c 60 ii passed to the crystal having the characteristic of Figure 4a and the reactance characteristic of Fligu re 4b the side bands are swfted 900 with respect to the carrier so that the side band relation 65 shown in Fligure 4d Is effected. With the rela-. tion of Fligitie 4d between the carrier and sidebands, the wave is an amplitude modulated wave. and is suitable for detection in diode 109 or for amplification in - IGO, and detection in diode 119. There would. also be an attenuation of the side brnds which Is not shown tii Figure 4d. This of the under-neutralized type such as is obtained cOnversiOn Of the PhRm modulated wave as of by under-neutrahzing the holder electrodes. 101 4c to an amplitude modulated wave as of 4d takms and 182 b@ mftns of I Os of lmgure 2 or -the replace In 10 1, 102, 1@3L .a3id 1$5, =d the WnV"ted 11

2,204,874 6nergy appears on the diode cathode or' grid of the diode driver tube 198'. The energy Preseiat In III', 193, 117, and It$ of Mgure I and of the same elements and transformers 139@ of Figures 2 and 3 is pwwd by,and Is a chara,L*teristic of energy In a fflter baving an over-neutralized charact"tic and having an input-output characteristic as shown In Pigure 4e, and having a reactanee characte#stic as I 0 shown In Ingure 4f. Thus, thi reactance of this last filter is positive or Inductive on bot.h sides of the carrl6r frequen 6y except for a short Interval near the carrier frequency. CoinMuently, the side bands are shtfted 90' in Phase'bY this luter 15 also but in an opposite direction@to, the shift produc'ed by fllters having the characteristics shown in Flgure 4a.. Hence, the phase,modulated wave as shown in Flgure 4g Is converted to the alilpliIn Plgti 4h. tude modulated wave as shown re 20 Ftom an examination,of Mgure 4d and Engure 4h, it can'be seen that the si4e bands ate approaching -cancellation 6f the carrier in Flgure 4d and are approaching aiding the carrier in Figure 4h. 7bus, the envelope of the @amplitude 25 modulations produced by the two fllters ha,.,inkr characteristics as shown above are 1800 aport and their detected output must be combined, in 8@ push-pull or serips combiiiation to reproduce the converted modulations. This combination Is ef-@ 30 fected in the diode circuits of all of the figures ,by grounding the cathode of one of the diodes, say I 19, and making the cathode of the other diode, say 189, the high Potential side of the output, circuit. s6 Unwanted amplitude mddulations'on the wave received, which are not converted to phase modulations by the actibn of the @Mters as described herein and In my United Sfates Patent #2,085,008 dgted June 29., 1937, have the same or substan40 tially the same effect on the energies passed by both futers and consequently due th the phase displaced combination of the detected energies cancel each other more or less complei6ly. The unwanted A . mplitude modulations which are con45 verted to characteristic phase modulations have - As stated above, the phase modulations on the wave are, In the fflter circuits, converted to corresponding amplitude modulati(>ns of opposed enso velopes and rectifled In the diodes 109 and I A$ so that a difference potential appears across the resistances III and 112 characteristic of the sig-@. nal which n@ay be utilized in any manner. An additional feature of this application is the proljg vision of a novel differential diode combining amplifier which arhpliflesvariatiorts in potential In the differential detectors characteristic of the phase modulations oii the wave and also characteri,stic of ttie amplitude modulations On- wave e* energy, passed through the conversion circuit, thereby adapting the receiver to the recleption of amputude,modulated wave energy. Mc)re specifically, this 4pplication. also concerns an amplifier for combining the outi)uts of differ65 entially connected diodes such as III vjid 1.10 of Figures 1, 2, and 3 In a manner such that el.ther the differential output or a parallelcombination of the outpuo may be utfli7,ed without disturbing the connections of the diode resistors. 7bur,,,the, 70 amplifler is applicable to phase,and frequency modulated wave receivers and amputude modulated wave receivers. , This ampuffer 'also has additional aes and features which wnl appear from the description thereof which will now be, rg given. no effect on the diocie d6tectors, I in fr'L-quency and phase modulation receivers In wwch a frequency or phase discriminat6r feeds diode d6tectors,, the di6de detect.ors must be connected differentially so that automatic frequency control -inay be taken from the combination 6f 5 the diode voltages. - This differential connection is effected as shown 'in Flgures 1, 2, and 3 by grounding the ce&thode of one of the diode detectors, such as for example, tube II 0, and niaking the.cathode of th& other dii)de detector such as for'example, tube 109, a high potential poiat. This effectively reverses the voltage across one diode resistor.with respect-to that on the othet go that the two diodo voltages oppose and the only output that Is obtalned is that due to the differ- 15 ence between the tw6 diode voltages. This differential output Is desired for the automptic frequencv conti@611ing potentials, supplied in this particular and Is' also destred:t6'r the cystem to RC, frequency and phase modul@tion outljut. How- go ever, when it is desired to re6eive amplitude modulation on the safiie recolvers, a parallel conneetiori of the diode resistors Is necessary for Prop& operation although thti differential connection is nece%sary if automatic frequency control voltage -25 is obtained from the same diode resi4tors. By the use of the audio amplifter of ngur6 I sknd proper adjustment of the degree of offn6utralization of the crystal ffltem the present-receivers may be tuned to receive either phase or am7 so plitude modulation. lhave found that by adjusting the crystal fllt&rs so that one has a very, small amount of negative reactance across the hqlder and the other a very smaitamount of. p6dtive reactance, a single sideband effect is obtained U as shown In P16res 6a and'66. , With thi crystals almost neuttalized In this way the output on the side of the carrier frequency, which does not ha@ve the rejection point Is higher than the output on the side hgv_ing the rejection poinl Conse-@ 40 quently, one of the filters exalts the carrier and selects the lower sidebitnd ancl the other exalts the carrier and select@s, the upper sideband. Hence, in accordance with the principles descril-ood In my United Stat-es Pt@ient #2,114,335,1 dated 45 April 10, 1938, these two fflter outpum may be detected and combined differentially to receive phase modulation and In parallel to receive amplitude modulation. However, in the circuits of Mgures 1, 2, and P, the detectom are connected bo differentially,in order that automatic frequency control energy may be ob4ined from - them. Hence, the novel combining amplifier of Mgure I is required. With the. ainpliller such as is about to be de- 65 scri bed here, a means is provided which allows the, amplitude modul6tion output to be obtained fro m the differentiallv connected diodes. Whffe, the same differential connections are supplying the automatic frequency control voltagm used in 60 tbis e receivers@ it will be understood that this nen y, ampufter circuit is to be used with any phase or frequency or amplitude modulated wave receiv er wherein differential output effect is uwized whe n phase or frequency modulation is bdm re- 65 ceiv ed and f6r frequency control PurPoses. ' The circuit of, Flgdre I shows the combining amp lifier, connected to the differentiany connected diod es at points o--4--b. D iodes 199 and Oil are differentiaby connected with the diode resistor 7o I 1 2@ of diode I I 0 grounded at the cathode connee tion and with the diode resiat6r- I I I of diode 169 mad e I-,Jgh potential at the cathode connection. This combines the voltages Et and E: w-bibb ap,- pear across the diode resistors so that they are