July 22, 1952 l., I_.KORos 2,504,533 ' AMPLITUDE MODULATION

Filed .March 8, 1949 '7 Sheets-Sheet 1

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INVENTOR

_l uw w/ßr/l' Lesli L. Korus ' 5.251116. BY n

ATTORNEY

2,604,533 July 22, 1952 L. L. KOROS

AMPLITUDE MODULATION

7 Sheets-Sheet 2 Filed March 8, 1949

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AMPLITUDE MODULATION Filed March 8, 1949 '7 Sheets-Sheet 4

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yfrequency-modulated magnetrons

Patented July 22, 1952 2,604,533

UNITED STATES PATENT-[orifice AMPLITUDE MODULATION

yLeslie L. Koros, Camden, N. J., assignor to Radio f ' ­Corporation of America, a corporation of Dela

Ware

Application March 8, 1949, Serial No. 80,241 i .

_ >32 Claims. (Cl. 178-5.8) . , . ' ,1 1

This invention relates to tion, and'more particularly-toI amplitude modu lation of transmitters., Y ' . `

An object of thisinvention is to'providel a new systemv for amplitude modulation of radiov fre quency carriers'. The system can be used at any frequency, but offers special advantages at ultra high and microwave frequencies.

' No systemr to date has been generally accepted as a .good technical means for amplitude modu lating - ultra-high-_frequency g oscillators. . The

open , the

possibility' ofA ­ building frequency-modulated transmitters. _for` ultra-highl ,.frequency, but frequency-modulated transmittersv , cannotV take over fthe wholer ~ultra-high-frç-:q_uency communi cations‘ñeld. , Frequency-modulated ultra-high-V frequency transmission can be used successfully in point-to-point ycommunication with direc tional transmitting and' receiving antennas, but inl ̀ omnidirectional or semidirectional frequency modulated >_systems heavy distortion has been ob served, caused by multipath transmission.v In vestigations to date show _that amplitude-modu lated transmission has given acceptable results in cases where frequency-modulated transmis sion producesV serious distortion. Amplitude modulated transmission is therefore highly de sirable in the ultra-high frequency, ñeld. Amplitude-modulated transmission provides ad vantages also in point-to-point >systems because it reduces the bandwidth required for communi cation.~ ' l

The foregoing and other objects of the inven tion will be best understood from the following description of some exempliñcations. thereof, ref .ference being had to the accompanying drawings, wherein:

Fig. 1 is a block diagram of one form of trans mitting system according to this invention;

Figs. 2er-2e represent the sideband frequency "distribution in the system of Fig. 1; "Figs 3 and 4 are sets of curves useful in the analysis of the invention; , " ' ' ` `

5 is a simplified block 'diagram of an other form of transmitting system according to this invention; ~ v' ^ i ` '

Figs. 6a, and 6b, together making up Fig. 6, represent the sideband frequency distribution in the system of Fig. 5;

Fig. 'I is a more detailed block diagram of the system of Fig. 5;

Figs. 8a-8c represent rthe sideband frequency distribution for a single sideband broadband transmission system according to this invention; _ ,

amplitude modula- f

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15

I 2 y < `.' ',r .

f Fig. 9_ is a block diagram of a transmitting ys_ys tem used for producing the sidebandl distribu,­ tion of Figs.,8a-8c; „ - g ' ­ ' '

Figs. ,10a-10c are curvesuseful. an aspect of this invention; Í ,Y - „ -, .,

Fig. 11 is a block> diagramioffazmodiñed ar rangement of this invention; . . , _

Fig. 12 isthe vectordiagram for the arrange

mentofFig.11; „ « Fig. 13 is a block diagram ofyet lanothermod

ifled arrangement of this invention; and Fig. 14 is the'vector diagram for the arrange

ment of Fig. 13. . , i.

` For frequencies over -500 megacycles, magne tron transmitters with absorption 'modulation

>iii explaining

» have been proposed.'~ Absorptionmodulationfin

20V

25

30

40

­ represented' in Fig. 2u..

-45

50

55

its known forms _has low efficiency, especially in services where> a vlow modulation factor is used for long periods of time. , ~ ­ Y ' , ,. .

In one form of this invention, _the’intelligence is amplitude-modulated onto a subcarrier byîa suitable, modulator. _The source vof the subcar. rier can be any kind of> radio frequency generator. The produced sidebands, with or without subcar rier, frequency-modulate . or , _phase`­` modulate ' a

magnetron, klystron or any source of radio .afre quency current at low modulation index. , 1 .. „

Now referring to Fig..1, this ñgure disclosesby means of. a block diagram­ one Yform of thefin. vention which isintended to operate for example in the 4000-megacycle band and which provides a television sound and picture. transmitting .sys tem. The video or pictureinputis amplitude modulated onto a 20-megacycle subcarrier in the video modulator unit 23, this subcarrier­ be- i ing obtained from a stable crystal-controlled _5 megacycle oscillator 24 through a frequency mul tiplier unit 25.> I The high pass filter ,26, to whichv the output

of modulator-23 is applied, suppressesone‘side band of the picture, providing in its .output a tele vision signal the sideband spectrum of which is

The 3975-megacycle magnetron 21 provides. a carrier which vmay be termed a "tree carrier,” This ‘tree carrier source is frequency-modulated at> low„modulation„in­ dex bythe output of filter 2=6, through the action of an FM beam 28 which iszproperly ̀ coupledto magnetron 21. Band pass filter 29 suppresses the carrier of source 21 and one ofthe first-order sidebands andV both second-order sidebands. One of the first-order sidebands of magnetrongZ-'l is radiated through the diplexer 30, to whichfthe .output of Vfilter 29 is supplied. The selected car rierv andV substantially only an -upper sideband

2,604,533 3

related to such carrier, represent a complete amplitude-modulated television video signal with B. carrier frequency of 3975 plus 20', or3995 mega cycles. ,

The sideband spectrum of this selected and radiated first-order sideband amplitude-modu lated video television signal is represented in Fig. 2b. being circled in such figure. Fig. 2b also indicates the frequency Vrelation and dis tribution of the video tree carrier itself, as well as one of the second-order sidebands. The high separation of about 20 mc. of the treercarriery andñrst-order sidebands makes possible an eiii cient carrier suppression by filter 29. " _ '

A stable frequency source or standardV oscilla tor 3| supplies a constant frequency of 3975 megacycles to the frequency and phase. control video unit 32. The output of source 21 is “picked up” by a connection or coupling 33 and is fed through the band pass filter 34 to the same control-unit 32.­~­ Filter »34'separatesl the tree-carrier’ frequency-off ̀ 3975Y me. from its-iside bands, this being made possible by the high sepa

l()

20

ration of about-'20 mc. ofthe tree carrierr and " first-order sidebands. Said-filter passes the car rier frequency'on to unit 32.!v A Y Y Unit 32 is 1a. discrim' ïator, andthe direct cur

rent output of this discriminator controls the FM beam V28 of magnetron 21, according to the frequency'difference between the standardoscil lator and'the'rest-frequency oflmaginetron 21, in suchl a Way as to maintain the rest or mid-fre quency of said magnetron at exactly- 39'15-f-nïie'ga cycles. l » >

>»The audio portion of theFig. l system is fin y generalV thesame as the video portion, with -th’e following differences. The audio input signal is frequency (or phaselrnod-ulated onto the 5 mc. subcarrier from source 24, in unit 35. ­ The modu lated signal is multiplied up to120‘ mc. in’multi .plier unit 36,. and this frequency-modulated 20 mc.- subcarrier, represented in Fig. 2c, isfre quency-modulated, at low modulation index,.onto the; carrierV output of a :4020 me. .“tree carrier” source' 31, .'throughthe action of an FM` beam 38v which is properly coupled to magnetronv 31. Band pass. filter 39 suppressesv the carrier .of source 31 and one of the-i'irst-or’der sidebands and both second-order sidebandS,­ as inthe video portion of the system'. The selected one'. ofthe

Y ñrst-order'sidebands is radiated through diplexer ' 30, to which the. output of ñlter' 39l is supplied. i '

The frequency distribution or sideband spec trum of. this selected. and radiated first-'order sideband frequency-modulatedY audio television signal is represented in Fig. 2d, being circled in such ñgure. Fig. 2d alsoindicates .the fre quency relation and distribution. of the sound or audio tree carrier itself, 'as well as one of the second-order sidebands. .The high separation of about ZO‘mc. of the tree carrierY and first-order s'idebands again makes possible an efficient car rier suppression Vby iilter’` 39; The audio carrier is 4020‘minus'20, or 4000 megacycles. ­ ~ The'standard frequencyV for the audio» trans

mittei?'is produced by the mixer andA band pass ñlt'erî unit 40.A The 45-megacycle output'of multi plierv 4|-, which is excited from oscillator 2'4,v is

` ~mixed with the 39.75-megacycle output of. oscil lator 3|, in unit 40, to produce the treeï carrier frequency of 4020 mc. which is applied; as one offl the inputs to the frequency andlphase Íc‘ontrol unit or discriminator unit 42. The output’ ‘of source 31 is “picked up” by a connection or cou pling 43- and is fed through thel band pass filter

25

' modulate or.y phase modulate

40

55

65

70

4 .

44 lto the control unit 42. Filter 44 separates theV tree carrier'frequency of 4020 mc. from its side bands, passing such carrier frequency on to unit 42; the band passA filter in unit 40 separates out and passes the 4020 mc. from mixer 40 to con trol unit' 42. `

The direct current output o-f discriminator 42 controls the FM beam 38 of magnetron 31, to maintain the rest or mid-frequency of said mag netron at 4020 megacycles‘. The diplexed or composite television signal is

represented in Fig. 2e. The width of band re quired for the picture» and sound together is ap proximately 5.25 megacycles, so that more effi

' cient utilizationofthe frequency spectrum avail able may be had. In Figure 1, it will be noted that two separate

sources 21 and 31 of carrier current are pro vided, the sound and picture signals separately modulating these two sources and being diplexed ontofthe same antenna. As a variation or modi fic'ation», the sound and picture (audio andvideo) signals could be diplexed-onthe same U. F. carrier if desired. In this> case, only a single U. I-I. F. carrier current sourceneed beprovided. Inanother form of this invention, the intelli

gence is amplitude-modulated«onto a subcarrier by means of a balancedY modulator. The pro duced sidebands, without subcarrier,. the sub carrier frequency itself being eliminated by. the action of the balanced modulator',v frequency

a . magnetron,

klystron, or any source of radio frequency cur rent. at low lmodulation index. First-order rfre quency or phase modulatedI sidebands are-sepa rated from the frequency-modulated carrierffby filters or by other tuned’ circuit elementsand, with aïsecond klystron or magnetron, lori any

, source of current, as e. g. a‘grid-c'ontrolled elec tronic device, a new carrier is added to these side bands.¿ The frequency'or phase-modulated side bandsproduce, with the newvcarrier, an ampli tude-modulated wave. This wave has similar properties to the output of a high-level modulated class C amplifier stage orr class B radio frequency amplifier stage with constant carrier. The system as established by this invention can

be applied to doublev sideband transmission of voice and music andv to single sideband broad channel transmission of television pictures, With out carrier control. ' The effect of adoption. of carrier control can also be produced, in the form that reduction of the inserted new c-arrier takes place by driving the energy of the same in side bands. This effect is realized by angularly modu lating the carrier with an. auxiliary frequency. The produced sidebands are suppressedY by a ñlter. , 1 _

Actually, as radio frequency current sources, at very high and ultra high frequenciesjthe magnetrons have the best en‘lciency. Therefore, the practical' circuits of ̀ this invention are` de scribed yin connection with magnetron tubes. >The_invention is not limited, however, to the use of magnetrons, nor even to very high or-ult'ra high frequencies or to microwaves. Any source of radio frequency current, describedl as- a mag netron oscillator in this disclosure, can be re placed by any kind of oscillator or excited ampli ñer. It is also possible to uset combinations of magnetrons and. grid-controlled' electronic de vices to form the wanted sources of radi'oï fre quency currents. ' `

9,604,533

T-Í'I’he amplitude'fmodulated wave Will__be 5de. scribed_by-the‘equationv .i n _ j _

Where: En, we and wi have the'same significance as in the amplitude-modulated'case, Bo,‘B1_are `Bessel functions and K represents the following '_inñnite members of the equation. These mem bers have forms similar ‘to the2nd and 3rd members but >the argument of the (1L-1') St‘mem ber is ' '

` vLuci-714111'

Fig. 3 represents for low modulation indices the Bessel functions Bo, B1, B2 and B3 versus modu lation index, mf. i . '

`( 3)

where D`=frequency deviation and

`­ _ ' fî-ëwi/Z.1r

_ Fig. 3 demonstrates that with low modulation index the, second and’third order Bessel func tions B2. and B3, and consequently the second and v‘third order sidebands, have a veryV low A'value vcompared-to B1, vwhich determines the first order 'sidebands vand to Bq, vwhich determines vthe vcar rier. - 'The members of the- K group are not to‘be ~tak‘en- into consideration, because theywill be ksuppressed in-this invention. » ` ' ‘ ’

­`Equations 1`­ and 2 show that the FM wavel has a similar structure tothe AM wave. difference ­is in the vector angles of the carrier with Vthe sidebands. The process in this inven tion‘to produce amplitude-modulated Waves is (a) to frequency modulate a carrier and to pro duce mainly only first order frequency-modu lated sidebands, (b) tosuppress the FM carrier and higher order sidebands by ñlter, and (c) to vinsert a new carriery in 0°­-180° phase‘relation to _the vector-sum of the two sidebands, or in other v\_7vords,.in phase quadrature to an ordinary FM typefcarrier. The composite of the first order vfrequerîl‘cy modulated sidebands and new carrier .represents an amplitude-modulated wave. .To »produce a good'broadband transmission, the in 'telligevx'i'ce­ must be amplitude-modulated onto a . subcarrier by abalanced modulator before effect VVi'r'i'gste'p (a). Narrowband intelligence, espe _î'ci'allyfof high frequency of the order of mega-v _’cycle's'," could befrequency-modulated without a previous amplitude­ modulation'. Several new circuitsgused in_this invention, will be described.

" " 'I_’o produce 'ñrst vorder frequency-modulated fïsidebands for double sideband communication transmission; the modulation index or the phase 4modulation in radians 4mfshould be kept pref ierably below 1.07. For broadcasttransmission m/êß. For single sideband transmission, ' an mfêlß'? could be used. This invention is not -limited to the use'of ~these values. .They repre sent only practical realizations of th‘e'modulating' ­«

The main '

v -10

25

30

40

45

50

60

70

75

4frequency-n‘iodulated tree carrier.

­-system„:aceordi'ng to .the principles _of good _engi

neerìng.' '_ , ` ` . Fig. .14 ¿demonstrates-_the ñrstí order .sideband

productionî if _,thelï‘carrierî is, modulated ̀ loyftwo frequencies ’at the' same` timer.' fïnzdoublesf side",`­À band transmission, the; two .,-Ír' quenciesaretlie two _sidebands fs-i-fi» and .fs-'Íi.'f;­­".[‘heV production `of ythefìrstbrder sidebandsfollows the îBoXBîi .Bessel function: ; Buandf _B1-„are the; valuesbee longing _to ¿the same modulation „_index. VGener, va-rlly,¿if two' vsignalsfn and fiziare-modulating‘the -samexFM carrier, the ñrstïorder sidebands ‘of fiz are produced according Vtothe product; I.

be reduced by the factorgof‘fBo. , k1 To simplify. this description, :numerical values

.are ,chosen ­for Athe carrier vand. for 1 the module., `¿tior1„b_and„_ although _this invention is not neces sarily/limited -tou’the use of these values._ j'I_‘he carrier­ frequency can bey selectedin a rangevex tendingfromany .low frequency up to ten thou _sand megacycleus _or-„highen The modulation can be . 0111x0118 .-frequenßv, or. bread; Ivhannel , Com. municetion 0f. ßeemesacyßles _or more _Gambe transmitted. The-following‘is only anLexample; Carrier frequency -fc=‘1000 mc.«' ` `

.ordinaril’yused The ,choice in this example` is _Dëi3~2 rnc-,and mfáß. >To meet this vcondi tion„` the intelligence,> is translated Yto the. radio frequency'band.` The maximum frequency­ "of this bandwill be aboutA _

Consequently, we` produce a‘subc'arrier ’The subcarrier gives ybetter _resultsA if ' its fre quency is's'table, andv any means? can be applied 'to accomplish this, such as crystal control," for example. " 'I_‘his subcarrier'is amplitude-modu

-torby means of a-frequencyv modulation cavity. «Any other» type offcurrent source and> 4tion system could also be"ïuti1ized.‘­ I U1 «

m041112 The simplified block ­:diagram is .shown-inf Fig.

'5-and the vsideband distribution in Figgf'G». `The complete block diagram iis shown in'Fig. '7. '

l5 andïFig. 6 show y that magnetron-'I has a carrier’frequenclyïy » 'I ' > >J 4î .

v¿This_carrier is the “tree carrier." AThe_tree car rier ̂ is frequency-modulated by' theifrequency groups ,fr-H1 and .fr-fi by a> balanced' modula tor (not shown in Fig. >5). _ ‘ Y

Fig. 6a^shows the frequency distribution of the l l A wave ñl

ter,'e.'_g.,­V ,of the bandpass type, separates the desired sideband group, which is 1000mm-Hi fßna'- ¿moofmcefaffdo to 15,000 c.) from me tree’carrier and fromthe iirst and higher order rsidebands _below and above the tree carrier. Mag v'rie'tronflïproduces a carrier of 1000 mc.v ̂ The foutput‘of the two'ma'gnetrons is coupled to the

2,604,533 7

antenna.­ by aV method which preventsl any dis turbing interaction between the two magnetron oscillating­ circuits, or` two antennaelements with extremely low ~ mutual ­' coupling _ could be used. The total or.»resultant.AM transmitted output signal is represent loy'liigrbb.V ` " ' A ‘

~ ¿ `Two frequencyA and phase control> vunits are employed. These'control units correct< the mag' netron output frequencies vand phase angles, comparing them~ with one standard frequency oscillator. There are-in existence different-types of frequency and phase control units which are suitable for this purpose. ­ ~ ‘ . . 1 i

Fig. '7 is a complete block diagram of the trans mitter. The highpower units are shaded. VIt may be seen that the' majority of the units are of low power; therefore this invention represents .good technical progress for economical trans' mitter design; ' The negative» vfeedback system reduces the distortion­ and hum. , ' Y ` v

Fig'. 5fis ral simpliñedï block diagramoflthls in vention. If'is> the source‘of _the tree >,carrier or sideband'curr'enu 2 ‘is affreq'uency modulatorìfo'r Vsaid source, 3 is th‘eï’source óf the carri-erj'd is ka. second ïfrequency modulator for- source Y11K-and _5 represents aLunit coupling' elementsY Iy and 3Y to the ïantennas, ­I'and -85V 5 can be'abridge cir ~cuitto prevent interaction between I and-3 and can be constructedbyv coaxial'lines andA cavities, »orïby condensers and‘coils'i' If k5>is a bridge cir cuit, the elements I and-8__coluld form one -an tenna system. Ifgäi'fdoes not separate' electrically elements I and 3„two antenna elements 'l and 8 should be used withv _extremely ̀ ­'low’rnutual'cou pling. 6 is al band pass filter, while 9 represents 'a' modulator and a frequency and: phase-'control 'unitf for ythe current source It, vIl! is the­ fre', quency'L and phase'jcontrol unit` for current SourceS.'v ' ' _ » _ I. Y 'Y

Fig. 7 is a more detailed block diagram'of one of the invented circuits. The elements I, 2, 3, 4, 5, 6, 1, and 8 haventhersame function as in Fig. 5. Y II is an oscillator ­.which produces the l_,snibearrier f_s.- ’,‘Ifhisâ'canbe a> conventional crys `_tal-controlled oscillator,A organy _other source vof `radiofrequency current, _ The oscillator fre quency is lower than the frequencies of I_and 3. I2 ,issn amplifier to feed the intelligence te the _balanced modulatorIS. I4 is an oscillator. T_o >'obtain goodnsignals, I4 ­should'be a stable oscil- . lator.- Crystalfçontrolledioscillator circuits can be used, __if necessary. with frequency multiplier stages or any othertype of stable oscillator such .ase anoscillator¿systemfwithinvar cavity in a thermostat or »withgas spectrumw stabilization. T-hefrequency of VSiisthe sum or diiïerencevof the frequencies of I~I fand„I4.~: I5 _is thefrequency and phase control unit lto stabilize the frequency of I~ by comparìsonjwith the standard oscillator I4. I6 is a similar unit for theY frequency of 3. The standard frequency for I‘Iì> will be produced by one of the beat'frequencies of I4 and II. I1 isy the mixer unit and ñlter.. IB vand I9 are wave .filters VInspecial cases- ̀ I8V and IS> could behand pass filters. _ >-. v «_.. ` I8 and I9 select one predetermined 'frequency

from the frequencies; which".y are“v ­present ‘in- ¿the outputsfofY I¿and"3f The selecte‘dîirequencies are lcompared with'the correspondingg-:standard frequency as y,in'the „System of _Fig ¿ The-'Acir cuit. of Fig. '7_y represents anim'porA ant` technical advance infthat the .Carrier-_ói l. .is Separated@ _fs from its.sid'ebz’rnœ4 this-is generallye‘a; wide _ separation',„_soV therefore. the> ¿wave -ñlter -Ißusqan _discriminate the; >Cf'ßlrlîiel"___frftfrl f ._

v10

15

20

30

40

The carriers vwillrbe comparedwiththe stand ard frequencies. 20 is a negative feedback sys tem to reduce the distortion and hum. In operation, the intelligence f1 is ampliñed

by amplifier I2 and is amplitude-modulated onto 'the subcarrier fs from 'source Il by means of the balanced modulator I3. The subcarrier _ fsmis eliminated by the action of the balanced modu lator, and the produced sidebands, without'sub carrier, frequency'or‘ phase modulate, by 'means of modulator 2, the “tree carrier” 'source I ,i at low modulation index. 'I'he upper or lower ñrst order frequency orphase modulatedvsidebands are separated from the tree carrier and from higher order sidebands by band pass filter I6. In other words, the FM orfPMcarrier, one of theA _first order sidebands and all higher order side bands are suppressed by' ñlter '6. ` ì , A new Vcarrier from source ̀3 is added,'by means

of coupling unit 5, to the selected ñrst order ̀ FM sidebands,k this new carrier being in_phase quad rature to an ordinary FM type carrier. The com bination of the selected upper or lower first or der FM or PM sidebands and the new carrier represents an amplitude-modulated wave, and this resultant or composite AM wave is _trans mitted from the antennas ‘I and ‘3, 'thesideband spectrum of this resultant wave being'l repre' sented adjacent antenna 8 in Fig. 7. vThe circuit of a single sideband transmitter

would be similar to that of the double sideband transmitter, except> that only one of _the side bands is modulated onto the tree carrier. The lower or upper sideband is suppressed. This op

‘ì eration> needs one additional `wave filter. kWe shall now consider one example ­for single

sideband broad band transmission. v The system could be used as an _A. C. transmission system for television pictures. The Ycarrier control pro, duced in television rtransmitters could valso be simulated. The control reducesI thev carrier'ac cording to Vthe average light ofythe picture. The carrier reduction could be produced in this sys- » tem by driving the carrier energy in sidebands'.'

' _Ifa radio frequencyu carrier is frequency modu ' lated the carrier will be reduced accordingto'the

55

60

70

-tube are only examples.`

B0 Bessel function (_see'Fig. 3). Thisphysical effect could Ybe used in this invention for car rier control ori foi-.producing amplitude modu latedvwaves, especially A‘sidebands ~

' . The frequency'modulated beam of the magne

tron II or 3' of Fig. 9 will be modulated, e. g. by the subcarrier fe, by a compressor-expansor tube, e. g. an RCA 6L?. The selected frequency and

Any other frequency or tube could be used for the modulation of the carrier. The super-control grid of the -com pressor tube will be controlled by the D. C. com ‘ponent of the picture byfa circuit of convenient time constant. *_T/‘his _compressor tube' feeds maximum 'excitation> corresponding to White level, e, ggmf=2.0, and Intf-_i0 for the black level. Consequently," the carrier wi'l‘l‘be' controlled in the vratiouof approximately >4.5 to l. kTlielow level corresponds toI a' reduction of' thenormal carrier to about 22% (white'level).l mf=0 co'r responds to full carrier input 'or 75%'modula tion (black' level) which is consequently higher than the normal carrier. ` We choose the follow ing example, .but ­’thisfinvention is not limited to the use of these numbers. y

,Carrier frequency fe=l00o mc. The modulation index for carrier lcontrol §20 b l

2,604,533 9

Modulation band fi=50 c. to 4 mc. ' lrier frequency fs=6 mc. ` ’ . .

The 'modulation index for the picture §15?, The deviation for the frequency modulation for

thepictur'e consequently will be v '

' Dsi1~57><6=ia42 me.

and for the carrier control l* A

' _l ,v _ D§i2><6=i 12 me.

The tree carrier will be 1000-6=­994 me.

.Y These numbers represent only an> example. It ̀ is possible to use this invention with any car rier frequency and the value of the deviation ̀ D

­ can be less or more than that used in this ex ample. The _Value of the. subcarrier fs can also be higher or lower according to the transmit- n terl frequency. Generally, a higher value will be chosen forpfs if the`> carrier frequency is higher, bßcafllse-L the vwave filter "which ’ separates the wanted and unwanted frequency bands can more easily Ybe constructed for a higher carrier value if Í-fs,fwhich represents the. separation between the carrier and sidebands, is higher, _ The distribution of the vfrequencies of the pic

turel transmission for` this example is shown in Fig.v 8..

withY the lowersideband suppressed. The wave filter 22 in the system of Fig. '9 will not suppress, with sharp cut-off, the lower sideband. We as sume .as an' example that 40 db attenuation will be produced at 60 kc., which is 1% of the sub carrier frequency. It is not necessary, however, to cutoff the lower sideband to as close as 60 kc. The higher sideband and the unsuppressed part vofftlie'lower sideband, modulated onto 6 mc. by the balanced modulatorv I3, represent the fre quency groups of 6 mc.-|­<50 c. to 4 mc.) and 6 mc.-(50 c. to 60 kc). This group will be fre quency modulated onto the tree carrier of 994 mc. ' The 2 f1 group remains insignificant if the modulation index of the balanced modulator is low. The 2 fs group is out of the passband. With a bandpass filter 6 the tree carrier and all off the lower frequency modulated sidebands and .the second and higher order upper sidebands are suppressed, as represented in Fig. ‘8b. The tree carrier is separated iri'thisv example by about 6 mc.'from the first order sidebands. lThis high separation­ makes it relatively easy to suppress the undesired lower frequency band. However, low­ power beat frequencies produced by contem poraneous modulation of the carrier by more than' one frequency, ‘couldy be present at about -2 me. distance. The second-order ­sidebands arev about 2v me. separated from the first order sidebands. Thisshorter distance makes a filter with-„sharper cut-01T necessary. vThe strongest frequency in the second order sideband produced byv 100% lmodulation Vis'at least '7 db below the ñrst order sideband, and therefore it is 13 db below the carrier of the amplitude-modulated signali The subcarriers produced by the modu lation fof they ­tree carrier are separated from the main carrier by 6 mc. and multiples thereof; therefore the same filter suppresses all of them, if it is designed according to requirements. ' ¿To ‘the first >order frequency modulated side

band group is added the new carrier produced by magnetron II, and therefore the amplitude modu lated signal represented in Fig. 8c is completed. The'level of Vthe `new carrier can be chosen to

Fig. 8a.` represents the television picture n band after modulation on the 6 mc. subcarrier, '

The subcar- y

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10 _

produce a 100% modulated transmission, but can also'be increased to any desired level; , n

Fig'. 9 represents a block diagram of a circuit usedy in this invention for producing the ̀ pic ture of Figs. 8a-8c. This circuit is for 4use especially with broadband transmission. The elements 5|, 2, 3, 4, 5, 6,1, 8, Il; |2 ,|3, |4,.|5, |6, |'í,1|8,v 'I9 yand 20 have the same function as described above iin connection with Fig. 7, and with Fig. 5. 2| i's a carrierlevelcontrol unit. One expander circuit, e. g. such .as used general ly with the 6L7 tubes, is controlled> by the D. C. component of the television picture. The D. C. component gives îthe average light vinformation of the picture.v . For a black picture, high carrier level is needed. Therefore, the excitation which the expander circuit 2| delivers'to the frequency modulator 4 is low. , For white pictures, the carrier level is low; therefore 4 receiveshigh ex citation from the expander and the energy ofthe carrier, produced by 3',`is driven to thesidebands. These sidebands aresup'pressed by wave filter 6. The auxiliaryv frequency for 2| is in this specific example the subcarrier'frequen'cy of ||, but any other frequency can be used, provided that -the auxiliaryfrequency’is lower than the carrier'fre quency 'and that the: produced sideband is at tenuated by iì. 22is a Wave filter. :It'could be a high-pass or low-pass filter. It attenuates, con sequently, the lower or higher amplitude-modu lated sidebands which are produced by the. bal ari-ced modulator 3; 22 will be designed in some cases as a band-pass filter to suppress parasitic giotlìâilation'l which ­could'accidentally be produced ‘y . > . . ' l ~

The sidebands produced byl frequencyv Inodu lation are not in linear relationship tothe ampli tude ofthe incoming intelligence. ' I can Ause the figuresvof the example discussed before as an'il lustration.’ In the case of broadband transmis sion, as in the selected example, the upper end of the signal'will be modulated less because the maximum deviation isconstant and the modula tion factor, mf, decreases from

Fig. 3 shows that the first order >sideband (B1) has an approximately linear­ amplitude loss'of 2.8 db between mf=1.57 and .94. This loss can be compensated by the preamplifier according to the frequency response represented’by Fig. 10a. AThis compensation does not introduce >over '?iîìdulation'because,_ in theA‘uppe'r end of the passband, less energy is generally transmitted. The preamplifier needs another compensation, due to the fact that in the low frequency region double sideband transmission‘will be produced

mf =1.57 to mf: .94

because the low level sideband filter does not cutl oif'sharply enough (according tolmy example, 60 kc. for 40 db and about 30 kc. for 20 db at tenuation) .ì In double sideband modulation, higher peak‘power can be produced than in single sideband modulation. Fig. 10b shows the cor rection in the video amplifier to compensate for the transition process from the two sidebands to the one sideband transmission to assure constant peak power. This is only an example. For some applications, the radiation of more energy in the double sideband part of the transmission vmay be desirable. In Fig. 10b- it will be assumed that the filter cuts the sideband between 0 and 60 kc. in linear relation from 0 db to 40 db. Fig. 10c showsv a combination of Fig. 10a and Fig. 10b.- - Fig. 10c is the wanted frequencyresponse

2,604,533 11

of the­ video amplifier in'this. example` to produce constant peak power output with consta'ntyideoV input. Obviously,.this4invention is not limited to Y useiof .frequency correction as shown in Figures 10u, 19h or 10c, and,11obvious-ly,» the frequency response correction can be eifectedat anystage following theY video amplifier,` as for example‘on the.;y modulated subcarrier. These figures rep resent only examples.. vIn the .case of a. phase modulated R. source, this kind of correction is not necessary. .. . ~ ` ' Y. ‘ . j

. »The possíbility’exists to utilize both the upper and lower sidebands of. the subcarrier fs/'byfin serting two'newV carriers. ' Intln's form two am plitude-modulated carriers will be produced, sep aratedby 2 fs. If, e'. g., anfs of 4me.. isv chosen, the two. transmitters. are separated by 8 mc. The two V.transmitters together havel improved. eñî ciency because only onezsideband source is. need; ed for both.v` The wave length difference between the twin transmitters, although it is relatively small, could aid in special cases to improve the reception of important communications. ’ The sources of distortion in the present'fsys

tem are different‘from the sources of distortion 'f in theÍclass B or plate-modulated'class C sys

` tems.ï No harmonicv distortion of' the intelligence will~ be produced in the frequency modulation process', because this..kind ofY distortion will. ‘be produced over the Ysubcarrier frequencies, and thefsecond and higher harmonics ofthe sub carrier are in most cases suppressed. Therefore, thea-harmonic distortion is> eliminated.

. Thesourcesof the distortion lin- this system are the change of the modulation index with « they frequency, the' non-linear relation ofV the modulation index „to isideb-and amplitude,V and cross-modulation :due to complex waveform of the audio input. In theforms of the invention using an inserted carrier,l phase modulation of the same can introduce distortion. The different kinds of distortion which are inherently present in the ̀ system can -be substantially eliminated by an over-all negative feedback. Table A shows the approximate values of dis

tortion which can be expected in the new sys tem, assuming the highest possible emciency for the system. For lower system efficiencies, the distortion would be less. ` '

. . . l Y ,

Double or. siuglerside- less Television picture .less band transmission than transmission picture. than

>'with negativo Iecd- 2% details. 10% back. Y

Double sideband trans- Television synchroniz- 20% ..missionwitl1out feed- L ing pulse transmis

l sion.. s

10% Y ' r .'«S'Iïhere have been described'above, various ar

rangements~ forprodu'cing. an amplitude-modu lated wave with frequency-modulated sidebands.

ll)

30

40

DI Cn

Two. additional generation circuits and one new _ carrier control circuit (for TV picture bright nessv information) are shown in Figs. 11 and 13'. NowY referring to Fig; 11,.this figure represents

a simplified ,block dia-gram­ of a balanced side- ` band generator according to this invention. In this. figure, elements the same as those described previously are given the same reference numerals. Thefintelligence is amplitude-modulated onto a 'subcarrier >by means of a balanced modulator, as .in ¿Fig 9. The subcarrier frequency could be chosen to be 6l mc., for example. For TV picture transmission, the Vsideband currents are ñowing through a vestigial sideband (filter. ' The particular first-order sidebands selected,

without subcarrier v(the ysubcarrier beingelim inated by the action of the­ balanced modulator) frequency ior phase modulate, by respective »FM beamsïllñ and ‘46 through push-pull modulation connections lll, two»` radioY frequency current sources 48 and 49, in a balanced modulator cir cuit. As an example, the U. F. tree carrier frequency of sources ¿i8 and 49 could be V994 megacycles. 1 ` `

Fig. 12 is a vector diagram for the modu lator of Fig. 11. The'two “tree carriers" of the magnetrons 45 and 48 are.180° out of phase, and the modulation is push-pull. ' The two modulated tree carriers, from ¿iB_,and

>49, andthe U. H.V F. carrier from a source such as 3' (not shown), are coupled by means of va cou pling unit 5 vto one antenna system. The fre quencies of the tree carriers and the even order sidebands of the modulation process arecan celed out by the push-pull or'balanced modula tion. ~ ­ . ` ~ ‘

The. .requirements for j the band-pass filter 5 are lower than inthe single-ended circuits, such as that oiFig. 9. The advantages of the balanced­ frequency

vmodulator of Fig. 11 are simplified filter design and reduced distortion. . . Y .

The carrier shift in the Figß'circuit'is pro ' ducedfby driving the carriervenergy into theside bands of a subcarrierfrequency, the sidebands produced being suppressed by filter 6. Accord ing to Fig. 13, the same system is used, but the carrier is produced by twov magnetrons 50 and 5| the voutputs of whichv are coupled to the an tenna through a coupling unit 5. The brightness information is „amplitude-modulated onto a sub carrier by means of an expander-_compressor de vice or unit 52. yThe sidebandsselected in the output Vof unit 52r frequency or phase modulate. by respective FM beams Stand 54 through push pull modulation connections 55, the two mag netron sources 5B and 5l, in a balanced modu lator circuit. The two carriers are added' together, and the

sidebands are produced, in push-pull. Therefore, the odd order sidebands are cancelled out in the antenna. . ‘ ' Y

The resultant UQH. F. carrier, from 50 and 5|, and a source of sideband current, from a source such as I (not shown), are coupled by means of a coupling unit 5, which is not identical with unit Y5 in Fig. 11 ­but which may .be constructed in a similar manner, to one antenna system. Fig. 14 is a vector diagram for the arrange

ment ofFig. 13. ' '

As a consequence of the balance of the` Fig. 13 system, the antennaiilterß, which is not identical with ñlter 6 in Fig. 11, can have less attenuation for the first order sidebands. The circuit dis closed yhere provides the possibility of using a lower deviation than i12 mc. for the FM mag netron to produce maximum carrier shift. If the subcarrier for this service has a frequency of 3 mc., a modulation factor, mf, of 2 is obtained with :1:6 mc. deviation. The advantage of the push-pull carrier shift

circuit of Fig. 13 is that the maximum deviation of the magnetron can be half as high ̀as in the case of a single tube. », .

sidebands could be producedby balanced phase modulated magnetrons or klystrons without uti lizing a subcarrier.- The circuit for accomplish ing this would be the same as that shown in Fig. 11, but the sideband ñlter t is-'not needed and,

' vof course, no iîrst 4balanced modulatoris used.

2,604,533 13

The vector Ádiagram'for single tone input is the same as shown in'Fig. 12. 4The even harmonics are balanced out. rIn this circuit, .all'of the har monics which arenot balanced outrepresent dis tortion, because Athey are produced directly in the input intelligence, and not over a subcarrier as before. ' ‘ ’ f s

. 'I'he amplitude-modulated carrier'is` added to thesidebands as'in the' circuits described previ ously. In such> a system, single sideband trans mission can be‘produced only by an antenna filter. In the'systems‘ previously‘described, the side

band energy is produced .by a' process of fre quency modulation.4 However, it is Withinthe scope of this invention to'produce such energy by ay processïof absorption modulation, if vde sired. ‘ l ' . ' f ~ Y

It may be seen, from the foregoing, that a sim ple and inexpensive amplitude-modulated trans mitte'rarrang'ement has been devised. ,» ' ,

ff What I‘claim‘a's'my invention is .as follows: f1. .In azfsystem .for transmitting amplitude

modulated signals on «a 1 radio .frequency ­carrier, a source of carrier current,"a source of subcar rier current, :means for amplitude. modulating said second-named source by signals to be trans mitted, .means >for frequency modulating said first-named source -ibyî'­ the amplitude modulated output of said second-named source at modula tion indices less than 1.57, and means for select ing-,one of thesideband groupsiresulting from said frequency modulation» l _- » _ _ _ - _

~ 112. 4The method-of transmitting. signals,gwhich consists'in producing carriergenergy, producing subcarrier energy; amplitude modulating ̀ the sub carrier energy by signals, frequency modulating .the ,carrier­ energyv‘by .the ,amplitude vmodulated subcarrier energy at _modulationfindicesless _than ~1'.,5'7, , and „selecting ' one of'- ,the .sideband groups resulting from thelast-named 'modulation proc ess;A f _­ 1. .. ,

3; In a; system `for _transmitting amplitude modulatedv ­signals ' on' a radio _frequency carrier, a source of carrier current, a source of subcarrier 'current,lmeans=.for' amplitude modulating said >second-Í-named source by signals to _be- transmit .ted,‘mean's.forî substantially suppressing one side band'iresulting i ­from said amplitude 'modulation means 'for frequency modulating saidçiirst-named sourceyby ‘the amplitude­ modulated sideband ì passedpby saidsuppressing means, at modulation indices less ,than 1.57, and meanslforïselecting one of the sideband groupsl resulting_from,_said frequency. modulation. ’ _ _ . 1 _ -l .

„'4. The method of transmitti gsignals, which rconsists in producingfcarrier energy, _producing subcarrier energy,- amplitude modulating thesub carrier energy Lby signals, - selecting -one _ sideband .resulting'from said amplitudemodulation proc ess', frequency modulatingA the- carrier _energyby the` selected sideband at modulationindices less Ythan ¿1.57; and selecting one of _the `sideband groups. resulting” from ' the last-named modula tionzprocess. ». »5.1m- a .system ,foftrarisgìitung‘ amplitude _ _ modulated'teleyision-signals:on a radio frequency carrier, especially forvdirectional television relay service, a source of carrier current, -a ’source of .subcarriercurrenu means _for amplitude modu lating said second-named source by television sig na-ls to be transmitted, awave'fiilter _forsubstan tially suppressing-one'sideband ­resulting Afrom _said modulation, means for frequencymodulating said first-named source, bythe amplitude modu lated »sideband :passed @maid ffl-lieu .at modela.: .i

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40

­'14 tion indices less than 1.57, and a Wavefilter for selecting one of the sideband groups resulting from said frequency modulation.y ~ > i

6. In a system for transmitting television video signals by amplitude modulation and audio'sig nals by frequency modulation, two sources of car rier current, means for -producingua subcarrier current, means for producing another .subcarrier current, means for amplitude modulating one sub carrier by video signals to be transmitted, means for frequency modulating the other subcarrier by audio signals to be'transmitted, means for fre- quency modulating one of­ said sources by ‘the amplitude modulated subcarrier, means for fre quency >modulating' theother of ­said sources by the frequency modulated subcarrier, separate filters for selecting one of the sideband groups from each of the-frequency modulated carriers, and means for coupling the two selected sidebandy groups which appear _in the outputs-of the corre sponding filters to a common output circuit.

7; In a system >fortransmitting television video signals by amplitude modulation and audio sig- nals by frequency modulation, two »sources of carrier current, means for producing a--subcar rier current of av predetermined­ frequency, means for producing a subcarrier »currentïofan other frequency, means for amplitude modulating one subcarrier by videa signals to be transmitted, means for substantially suppressing onesideband resulting from said amplitude modulation, means for frequency modulating the «other subcarrier by audio signals to be transmitted, means yfor frequency modulating one of» said sources by the amplitude modulated sideband passed by said suppressing means,.me_ans for frequency modu lating the other of said sources by the frequency modulated subcarrier,*separate filters forselect ing vone of the sideband groups from each vof the frequency modulated> carriers, and` means for coupling the two selected sideband groups which appear in the outputs of the corresponding filters to a common output circuit. . ' .

8. The method of transmitting television ̀ sig-_f nals, which consists in producing two carriers,

' producing two subcarriers, amplitude modulat

.5,0

79

ing one 'subcarriery by Video signals, frequency modulating the other subcarrier by audio signals, frequency modulating onel carrier by the ampli tude modulated subcarrier, frequency modulat ing the other carrier by the frequency modulated subcarrier, selecting one of the sideband groups from each of the frequency modulated carriers, and radiating the two selected sideband groups..

9. In a system for transmitting amplitude mod ulated signals on a radio frequency carrier, >a first source of carrier current, a source of sub carrier current, a balanced ­modulator for. am plitude modulating said second-named. source by> signals to be transmitted, means forfrequency modulating said first. source­ bythe amplitude modulated output of said second-named__.source, means for selecting one of the first orderside bands resulting from said frequency ,modula tion, a second source of carrier current having a frequency which is the .resultantV .of` al com bination of the frequencies of said first> source and of said subcarrier» current’fsource,._and common output circuit coupled to theoutputof said­ selecting means and. to said fsecondfsource of carrier current. . ’ -. ._ .l

10. In a system for transmitting amplitude modulated signals on a> radio frequency. carrier., a first source of carrier current, a source of sub carrier-_ current, a balanced f modulator. y .for _am-_.

2,604,533 '15

pli‘tude'^ modulating> said second-named source by'signals to be transmitted, means for ̀ frequency modulating said' ñrst source by the. amplitude modulated' output of said second-named source, means> for selecting oner of the first order side bandsfresulting ̀ from’ said ­ frequency modulation, a second Vsource of‘carrier current having a fre quency'ïwhich is the sum ofthe frequencies'of said' first source and ofV said subcarrier current source, and a 'common output circuit coupled to the output of said selecting- means and to said second vrsource of lcarrier current. ~

Y ‘- `IljA system for transmitting'arnplitude mod ulated signals, comprising a source of carrier current, al separate source vof sideband' current, means coupling both of said ’sources to'a common output circuit, and means -for­ modulating the frequencyof said sidebandcurrent source in ac cordance With-’signals -to be transmitted.

12.» Ak systemfaccording toÍ claimV ll wherein both of said sources are magnetrons; ' ‘

13. A system according to clainfiv ll wherein meansfare ’provided-for controlling> theV leveLof the carrier in accordance with direct current componentv information contained in the' coin posïitefsignal input to said modulating irieans.l

` 14. lA- system according to ‘claim’ llV wherein said‘fcarrier current»Y source has cou'pied thereto means ío'rV modulating the frequency thereof. v15. A system according to claim l1r wherein

each of said sources has coupled thereto a sep arate frequency modulator device.

_16. Aî system for transmitting amplitude mod ulated signals, comprising a source of carrier current, a separate source of sideband current, a frequency modulator device for modulatingtne frequency of said sideband current source in ac Vcordance‘witli signals to> be transmitted, a fre quency modulator device coupled to said carrier current source, va source of auxiliaryalternating current of lower frequency than the carrier, an expander-compressor control unit, means cou

il)

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40

pling the input of said unit to said source of v auxiliary 'alternating current and to a control signal source, means coupling the'output of said unit to one of said frequency modulator devices, and means coupling said source of carrier cur rent and'said lsource of sideband current to> a common output circuit. - l

Y17. A system for transmitting amplitude mod ulated signals, comprising a source of carrier current; a separate source of sideband current, a frequency modulator device for modulating the frequency of said sideband current source in ac cordance with signals to be transmitted, a fre~ quency modulator deviceïcoupled to 4said carrier current source, a source of sub-carrier current, a balanced amplitudemodulator, means coupling _the input of said amplitude modulator to said subcarrier source and to the source of signals to be transmitted, means coupling the output'of said amplitude modulator to one of said fre quency kmodulator devices, an expander-com presser> control unit, means coupling the input of 'said unit to said subcarrier source and to the signal input of said amplitude modulator, means coupling the output of said unit to the otherlof said Ífrequency l modulator > devices, " and means coupling said source of carrier current and said

, source of sideband current 'to a common output circuit. _ Y ,

18. A system for transmitting amplitude mod ulated signals, comprising a ­source of 'carrier current, a separate source o_f sideband current, a frequency modulator device for modulating the

45

so'

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70

16 frequency of said sideband- current source: in ac-A cordance with' signals to. be transmitted, a frc que?cy modulator` devicecoupled toi'said carrier. current. source, a sourceV of subcarrieri current, ai balanced yamplitude modulator, meanscoupli-ng theY input of said amplitudev modulator to y'said subcarrier sourceY and to the source of signals to be transmitted: means coupling the youtputof said amplitude modulator to said first-named Vfrc qu'ency'modulator device, an expander-'compres- o sor' control unit, means lcoupling the inputofv said unit to said subcarri'er »source and tof the signal input of ysaid amplitude modulator, means cou pling the. v'output ofsaidî unitV to said; second named frequencymodulator device,` and means coupling saidl sourcer of> carrier current and'said source of sideband current .to a common output circuit. . . ` ' . > ’ ,

19. »A system for transmitting amplitude modu lated signals comprising ‘a source. of` carrier cur. rent, as'eparate. source of sideband current, a frequency modulator' device for modulating the >frequency ofl said sidebandV current source in accordance with signals Vto be transmitted, a frequency modulator devicercoupled to said car rier current source, a source of subcarrier cur- ' rent, a balanced amplitude modulator, means coupling the input of said amplitude modulator to said subcarrier source and to the source of signals to be transmitted, means coupling kthe output of said amplitude modulator to one of said frequency modulator devices to frequency modulate the corresponding source, an expander compressor control unit, means coupling the input of said unit rto said subcarrier source> and to the signal input of said amplitude modulator, means ­coupling-the’output of said unit to the other of said frequency modulator devices, means for‘selecting one ofthe sideband groups result ingy from said last-named frequency» modulation, and means coupling said source of carrier cur rent and said source of sideband current to a common output circuit through» said selecting means. » , ` f '

j "20. Asystemï for transmittingamplitude-modu lated signals, comprising a source of carrier cur rent, a separate source of sideband current,V means coupling both of said sources to a commonk output circuit, and means for. modulating ,the frequency of said sideband current source,.­in accordance with signals to be transmitted, at modulation indices less than 1.57,Where the modulation index is the frequency deviation divided by the modulatingfrequency.

21. A system for transmitting amplitude modu lated signals, comprising a` signal input channel», an amplitude‘modulator, a source of subcarrier current,»means coupling the input of said modu lator to said source and to said input channel, a first source of radio frequency energy, a fre quencyV modulator coupled to said first source for modulatingl the frequency thereof, ¿'means coupling the output of said amplitude modulator to said frequency modulator as a «modulating signal for the same, 'a second Vsource ofvradio frequency energy, and means coupling the out puts of said first and second sources to a common radiating means. . ~

22. A system for transmitting amplitude modu lated signals, comprising a signal‘input channel, an amplitude modulator, ya 'sourcefoiî subcarrier current, means couplingvthe input ofsaid modu- . lator to said source and to'said inp'ut'channel, ' 'affirst source of radio frequency energy, a fre quency modulator coupled to said>> first source

2,604,533 17

_.f'or , modulating the _frequency thereof,` means 'Í coupling ¿the’output’of 'said _amplitude modulator _to‘îsa‘id‘ frequency modulator las" a modulating signal for _the same. ­a ­standard .oscillator of ­substantially> constantv frequency; a frequency control unit having its` output _coupled to said >frequency 4modulator for controlling ,therest fre :q'uen'cy iofj'said first source, means 'coupling' the Ainput of'saidjunitfto _thejoutput of j said jiirst fsource' andito thesoutput lofjsaid standard_'oscil 'jlator for'comparing the frequencies of such-out ~`puts-in-_said _unit to :produce in _the output thereof a Voltage proportionalî to _the difference between thej_compared'_"frequencies, ai second source of iradio v'­frequency _energy the 4_frequency of *f which ï(_iiifersfrom the rest frequency of saidfirst'source ‘by the- frequency of "said'subcarrier source, a ­"seconcl- frequency lmodulator _ coupled ­ to said f second -source ­ for ’modulating >the frequency thereof,l a ‘second frequency control »unit having its-output coupled to said’second frequency modu latorl for controlling the frequency of said second source; a l mixer unit for-mixing ­the outputs of 'said standard'oscillator-and of Vsaid subcarrier source, means coupling the v input of »said ­second unit ­­to the output of saidvfsecond source and to the Youtput of said mixer unit for comparingy the “frequencies of such ­outputs in saidï second unit >vto lproduce in the output thereof a voltage pro portional» to the difference between such com pared frequencies, and Vmeans -coupling the out puts'of said ?lrst and second sources to a common output circuit’.A - » " Y ” - » y

¿- 23.'> A system for-transmitting'amplitude-modu lated signals, ctpml‘arisinga­ signal input channel, 'a'. :balanced _amplitude modulator, ajsource of subcarrier` current,~­> means -_ coupling the ' input of said» modulator to saidfis'ource-'andto said input channel; a first» source of -sideband current, la frequency modulator-ï coupled» to ' said Afirst source yfor modulating 'the frequency thereof, ¿means coupling the output ofsaid amplitude modulator to ­:said frequency modulator as~ a modulating vsignal for ,the same, a standard .l oscillator ï of 'substantially constantfrequency,A a lfrequency control unit having' .its outputv vcoupled-_to said 'frequency modulator forcontrolling the ̀­rest fre 4,quency îof said: ñrst source;- means . coupling lthe input vof‘ïsaid> unit' to _theï'outpu't' of said first “source and to the output of said standard oscil lator for comparing the frequencies of suchr out -puts in said unit to producelin the output thereof 'a yoltage proportionalfto'the difference lbetween »the compared ‘frequenciesïav second vsource of carrier'current the frequency of which­ differs »from­ the ïrest frequencylof f' said iirst'source by >the frequency of said subcarr-ier source, a second frequency I modulatorl ­coupled to said second -s'ource formodulating the; frequency ­"thereof, a second frequency :control ‘uniti having its "output coupled to said'second _frequency'modula'tor for controlling the frequency íof said _second ­source, a‘I-f'mi'xer '-funit for >mixing 1 the outputs of said standar‘dïoscillator‘ and y.of-“said subcarrier source, means 'Èco'upling the inputïîof's‘aid' second unit to lthe output of' said >"seco'nd'source and to the outpu'tfofA said'mixer» unitffor-comparing the fr_e quencies 'o_f' such 'outputsïin" s_aidfsecond unit­ to >iìïroduce" >inïthe output“ thereofV aA voltage-propor tionalî tol the difference "between such compared frequencies, l'andlmeans*_coupling 'the outputs' of 'said first and second s'ourcesto a common output

f 24.__L_A 'system for transmitting amplitude mod-A u_latedI signals, _ comprising a signal input ~ chan

C1

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40

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18 nel, a balanced _amplitude modulator, a source of _subcarrier current, means coupling the input of said modulator to said source and to said _in put channel,­ a first source of sideband current, a frequency modulator ­coupled yto said first source’ for. modulating _the frequency thereof, means coupling the output Vofsaiol amplitude modulator to said-frequency modulator as a modulating lsignal for the same to­ thereby fre quency modulate said first source, a standard oscillator of substantially constant frequency, a frequency control unit having its output coupled to said frequency modulator for controlling the rest frequency of said first source, _means cou pling the input of said unit to the output _of said first source and to the output of Vsaid standard 4oscillator for comparing the frequencies of such outputs in said unit-to produce in the output thereof a voltage proportional to the difference between the compared frequencies, a second source of carrier current the frequency of which differs from the rest frequencyof said first source by the frequency of said subcarrier source, a sec ond frequency modulator­ coupled to said second source for modulating the frequency thereof, a second frequency control unit having its output coupled to said second frequency modulator for controlling the frequency of vsaid second source, a mixer unit for mixing the outputs of saidstand ard oscillator and of said subcarrier source, _means coupling the­ input of said second unit to the output of said second source andto the out put of said mixer unit for comparing the fre quencies of such outputs in said second unit to produce in the output thereof a ­voltage propor tional to the difference between such compared frequencies, means for selecting one of the side band groups resulting from the frequency modu lation of said first source, and means coupling the outputs' of said first and second sources to a common output circuit _through said selecting means. v _ '_ , . _

25. A system for transmitting amplitude mod ulated signals,­ comprising a signal input chan nel, a balanced-_amplitude modulator, a source vof subcarrier current, means_»coupling the input of said modulatory to said source and to said in put- channel, a first sourceof sideband current, la. frequency modulator coupled to said ’first source for modulating the frequencyy thereof, means coupling the output of said amplitude modulator to said frequency modulator _as a modulating signal for the same to thereby fre quency modulate said first source, a standard os cillator of substantially constant frequency, a frequency controlunit having ̀ its output coupled to said frequency modulator for controlling'the restv frequency of said first source, means, cou pling theinput of said unit to the outputof said first source, said >last-named means having in series therein a Wave filter which passes substan tially only the carrier` frequency of said first source, means_coupling the input of said unit Aalso to the output of said> standardr oscillator, whereby the frequencies of such outputs are compared in said unit tol produce in the output thereof a voltagepro-portional to the difference between the `compared frequencies, Y a second source of carrier current, the frequency of which differs'from the rest frequency of said first source bythe fequency of Vsaid subcarrier source, a sec ond frequency modulator coupled'to said second source formodulating the'frequencythereof, a second frequency control -unit ̀ 'having its output coupled to said second frequency modulator for

'2,664,533 Y y19v , . o 'y

controlling >the "freque'r'ieír of said ysec'oîiìl source,

standard 'oscillator and 'oÍf said subcarrier source, means coupling ̂ the input >of lsaid secondunit to the output of 'said ­second`soíï?ce and to the out pût of Said lnîíièí‘ foi' 'comparing thefre quencies of 'such outputs in said Second ­to produce 'in the output thereof a voltage propor tional'to >theV difference between such. compared frequencies, means for selecting one ofthe ~side bandgrolíps >re'sull‘li'ng from the frequency Inod A"ulation o‘f said f_l'r's't source, and means coupling the ‘outputs of said ñrst second sources to ‘a

>Vu_lated signals, comprising a signal 'input‘cl'ifan ` nel'a balanced amplitude modulator, a source of sùbcai‘rier current, imeansl coupling the input of said _modulator lto soürcef'a’nd Hto said input channel, a'ñ-?s't source o`­f sideband current, a fre qúenoy modulator ooü'pled'to said ñr'st source ’for modulating ­the frequency thereof, means cou "piing um output òf 'sara ampiauuejnoduiaroi 'to 'saidjffèquefia moduiaof ‘a insulating sig nal for .the same to thereby frequency‘modulate said first source, a standard oscillator of sub stantially @distant ’fre/quepasa _frequency cim ti'ol 'üni‘tihavl'ng' its Óütpüt coupled to fre fluency modulator for 'centran-mg ure gest 'fre quén‘c'y Vof Said ‘first Source, means coupling vthe input of said unit )to vthe,outputof said first source, said last-named meansV having ­in series therein a 'wave suer which passes substantially only 'the carrier frequency o’f‘ñr'stsource, Íneanscou- ‘ pling the input of 'said also to the output of said standard oscillator, whereby the frequencies of such lc'?ltputs are compared vin said unit to pro duce, theì output thereof a voltage proportional ~tov the diiference between the compared fre quencies, a second source of carrier currentqthe _frequency of _which diiîersl, from the rest fre quency of said ñrlst source by the frequency of said subc'arrier source, a-second frequency mod ulator coupled to said second sourcer for'modu- y latingfthe lfrequency thereof, a second frequency control unit having 'its output coupled -to said >second frequency modulator rfor controlling the frequency of >saidY second source, a mixer unit »for mixing the outputs: of said standard oscillator and of Ysaid subcarriersource, means coupling the input of said second unit to the output of said second source, said last-named means having in series therein 'a _wave ­filter which passes sub stantially only the carrier ̀ frequency of said sec ond sourcefn'ieansrcoupling­ the input of said second unit also tothe output of said mixer unit, whereby the frequencies of such outputs Yare co-m pared in` said second unit to produce in the out put thereof a voltage proportional to the differ ence between such compared frequencies, means for selecting one of the sideband groups result ing >from the frequency modulation of said first source, and means coupling the outputs of said first and second sources to a common output cir cuit through said selecting means. o _ „

27, A system for transmitting amplitude modu lated signals, comprising a signal input channel, a balanced amplitude modulator, a source’of sub carrier current, means coupling theinput of said modulator to said source and tosaid input chan nel, a first source of _sideband current, a fre quency modulator coupled 'to said first source for modulating _the frequency thereof, means cou pling the output of said amplitude modulator to

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ena "frenesia meenam .as ­ for iure same a thërety ffreq “ y ,e

sanfte, sara ‘isst-'named 'ii-leans; 'having ¿in series ‘therein a ‘wave naa which 'sutaaîçnny sum-mates one 5f ure ‘masses .regelung _nem

:control 'unit having ritsf output „cofüpled to 's'âi'd

source, V‘said last-named. means having lin series therein a wave ñlter winch-„passes 'substantially only the carrier,frequency-¿of said ñ?st source, means coupling 4the input ouf-said i'ir-íitfalsoCv to `the output of said standardwoscillatoï, _whereby Ythe Afrequencies -of- ­such loutputs Y'are.oo_mîoa~red in_saìd unit to lproduce _in >the_.¿output_thereof a 'voltage proportional to fthe difference between the com pared frequencies-ï a .secondA source of carrier vcurrent the 'frequencyvofx which'diiîers fifo-niœthe rest frequency> ofv saidñrstsource bythe _fre fluency of said -subcarrier source, a second fre jquency _modulator coupled to said second source .for modulating the «frequency thereof, _a second frequency control unit havíngit's output coupled to ̀ said «second frequencymodulator for control ling the vfrequency of said-secondsource,` _a irl-beer unit forrmixing the outputs of said standardy os cillator/ and of said .supcarríer source, -means cou p_ling the input of said second unit ̀ to the output of said second source, said laste-named means having in series Vtnereina Wavefilter which passes substantially 'only the carrier ­frequency »of said second source, means coupling the> inputfof said second unit also to the Output ̀iof said mixer unit, `whereby the -frequenciesçof such voutputs are com pared ¿in saidsecond unit; to produce in the out put thereofra voltage'proportional vto the diiïer ence between , such „compared frequencies, means ¿for selecting one of the sideban'dA groups result ing from the frequencyymodulation of said ?lrs't source, and means coupling the outputs o'f said first-and 4secondsources toa common "output cir 'cut through said selecting means.

f »28; AÍ system for »transmitting amplitude modu lated signals. comprising a» signal input channel.

. Van ’amplitude'mo'dulaton a: source iof subcarrie'r

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current», meanscoupling the input of said modu lator to said source and to'ç‘said' input'channel, a first source`V of radio" frequency energyl a vfrei quency modulator coupled to said -ñrst source for modulating the-frequencythereof, means cou' pling the output of said‘ßampli'tude modulator to said frequency _modulatorfasja modulating sig-' nal forrthe same, 'aY standard Aoscillator of sub’ Vstantially constantA frequencyïa >frequency rcon" tro'l unit having its output >'coupled to said 'fre quency modulator lfor ficontrolling Áthe rest fre quency of said /ñrst- source', "means: lcouîpl'ingjthe input tof said unit _to the, loutxput’oi': Fsaid ñrst sourcefand to the outputioffsaidfstandard oscilla- '

' tor ¿for comparing thefrequencies'ìoffsuch out- ' puts insaid unit to :produce-»infthe-output there of a voltage Aproportional vtothe differencei'bel tween the comparent- _frequenciea a 'second ̀'sour-'ce of rad-io freque'ncrenergythefrequency ofïwhich diiîers ¿from the frequency o_f Ysaidfilrst nsource by; vthe ¿frequency-_of ¿said- ­~­subcarrier Source', za second ¿frequency modulator‘coupled Vto'­saic_i­ sec- ' 0nd vsobre@ for. Modula-tins- thec frequènßyzthèrcer of, a second frequency control unit having-its output coupledv to said second rfrequencygmodu lator for controlling the ¿frequenGYQÃSaïd S69 ond source. a miìier unit for" mixing the outputs

2,604,533 . 21

of said standard oscillator and of said subcarrier source, means coupling the input of said second unit to the output of said second source and to the output of said mixer unit for comparing the frequencies of such outputs in said second unit to ¿produce in the output thereof a voltage propor tional to the difference between such compared frequencies, means coupling the outputs of said first and second sources to a comon output cir cuit, and a negative feedback unit havingits in put coupled to said common output circuit and its output coupled to said amplitude modulator.

29. In a system for transmitting amplitude modulated signals on a radio frequency carrier, one source of radio frequency carrier current, two sources of radio frequency sideband current which are 180° out of phase with each other, means for frequency modulating said sideband sources in push-pull by signals to be transmitted, and means coupling all of said sources to a com mon output circuit.

:30. In a system for transmitting television pic tures with direct current information, a source of sideband current consisting mainly of first order sldebands, two sources of carrier current which are in phase with each other, a source of subcar ier current, means for compressing or> expand ing said subcarrier according to the direct cur rent information of the television picture, means for frequency modulating said carrier sources in push-pull by said subcarrier, and means coupling said sideband source and said carrier sources to a common output circuit. f

31. In a system for transmitting amplitude modulated signals on a radio frequency carrier, one source of radio frequency carrier current, two sources of radio frequency sideband cur

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22 rent which are 180° out of phase with each other. means for amplitude modulating the signals to be transmitted onto a subcarrier by means of a balanced modulator, means for frequency modu lating said sideband sources in push-pull by the amplitude modulated subcarrier, and means coupling all of said sources to a common radiat ing means. l

32. In a system for transmitting amplitude modulated signals on a radio frequency carrier, a source of carrier current, a source of subcar rier current, means for amplitude modulating said second-named source by signals to be trans mitted, means for substantially suppressing one sideband resulting from said amplitude modula tion, means for frequency modulating said ñrst named source by the amplitude modulated side band passed by said suppressing means, and means for selecting one of the sideband groups resulting from said frequency modulation.

LESLIE L. KOROS.

REFERENCES CITED

The following references are of record in the ñle of this patent:

UNITED STATES PATENTS

Number Name Date 1,744,044 Green ___________ __ Jan. 21, 1930 2,161,320 Schulze-Herringen __ June 6, 1939 2,247,511 Lewis ___________ __ July l, 1941 2,301,395 Goldsmith ______ __' NOV. 10, 1942 2,305,864 Gottier _________ __ Dec. 22, 1942 2,342,943 Kell ____________ __ Feb. 29, 1944 2,421,727 Thompson _________ __ June 3, 1947 2,476,162 Thompson _______ __ July 12, 1949 2,500,945 Hansen _________ __ Mar. 1, 1950