US2448055A - Wobbled frequency carrier wave communication system - Google Patents

Description

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Filed Feb. 2l, 1944 M. WOBBLED SILVER El' AL FREQUENCY CARRIER WAVE COMMUNICATION SYSTEM Sheets-Sheet l ATTORNEY ug. 3l, 1948.

Filed Feb. 21, 1944 RECH/WE? 0005001700007@ f-Mfl M) 5d JVA/FM pld SES our/107' 4d M. SILVER ET AL 2,448,055 WOBBLED FREQUENCY CARRIER WAVE COMMUNICATION SYSTEM 5 Sheets-Sheet 2 Hamas@ A minimi Lm :r1-IMA im MV u r ,'rrrf' 1N VEN TORS Mer/N su aff/P cmu fr. 5mi/www1. Je

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BY H P6405 Mug. 3l, i948. VER Er AL 2,448,055

M. SIL WOBBLED FREQUENCY CARRIER WAVE COMMUNICATION SYSTEM Filed Feb. 21, 1944 5 Sheets-Sheet 3 INVENTORS MART/N sa VER cmu 4. .SfGHPSr/POM, Ja,

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Filed Feb. 2l, 1944 M. SILVER ET AL woBBLED FREQUENCY CARRIER WAVE COMMUNICATION SYS TEM 5 Sheets-Sheet 4 Aug. 3l, 1948. SILVER Er AL 2,448,055

M. WOBBLED FREQUENCY CARRIER WAVE COMMUNICATION SYSTEM Filed Feb. 21, 1944 5 Sheets-Sheet 5 ATYPE/V Patented Aug. 31, 1948 2,448,055 WOBBLED FREQUENCY CARRIER WAVE COMMUNICATION Martin Silver, Bronx, N. Jr., Teaneck, N. J., and

dale,

SYSTEM Y., Carl A. Segerstrom, Ralph B. Rcade, River- N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application February 21, 1944, serial No. 523,194

(c1. o-Jn 2,6 Claims.

tempts.

It has been ceived carrier. This synchronism is eiected according to the systems heretofore proposed by periodic transmission of a synchronizing signal or by a separate communicating or synchronizing channel.

It is one of the objects of our invention to provide, for use in private communicating systems wherein the carrier wave used is caused to woblble in frequency over a given frequency band according to a given pattern, a method and means for receiving the transmitted carrier without requiring periodic transmission of synchronizing signals or the provision of a separate communica'ting or synchronizing channel.

Still another object of the invention is to provide a multiplex for transmission of a plurality of carrier waves wobbling over the one or more frequency bands and receivers capable of selective reception from the transmitters.

A further object of the invention is to provide an improved method an-d means for synchronizxnotive force with another cyclic sweeping electromotive force produced at some remote point.

The synchronizing feature, according to the 40 principles of our invention, includes the local generation of oscillations at a selected constant frequency. This constant frequency is selected so that the oscillations produce, when mixed with a lcarrier wave varying periodically over a given R. F. frequency band, a pulse envelope at a selected I. F. frequency at least once during each sweep cycle yof the carrier. The receiver is provided with a narrow band I. F. amplifier which passes only the I. F. frequency of the pulse enor radio communicating system 30 This locally genplaining the opera-tion era/'ted sweeping voltage is used for frequency modul-ation of radio frequency oscillations which generated frequency modulated oscillations. insure accurate phasing of the locally generated trol the local sweeping oscillator.

lt will thus be clear that where a receiver is arranged for broad band reception equal to or greater than the frequency band of a particular v This is all performed at the receiver without th-e aid of specially transmitted periodically synchronizing signals or a separa-te communication or synchronizing channel.

The above and other objects and features of the invention will become more apparent upon consideration of the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a schematic mitter for transmitting a carrier wave, amplitude transmitter of Fig. 1;

Figs. 3 and 4 are graphical illustrations used for explaining the transmitting and receiving operations of the transmitter and receiver sys-tems of Figs. 1 and 2 respectively;

Fig. 5 is a graphical illustration indicating .the operation of the receiver of Fig. 2 for a sinusoidal sweep pattern;

Fig. 6 is a schematic block diagram of a receiver capable of receiving a pulse modulatedc'arrier which is wobbled between ltwo limits of a given frequency band;

Fig. 7 is a graphical illustration used for exof the receiver of Fig. 6

Figs. 8 and 9 are schematic and graphical diagrams used for explaining the TM demodulation features that may be included in the receiver of Fig. 6;

Fig. lll yis graphical illustratien of the select-ive synchronizing of a receiver to one of a plurality of carrier waves wobbling in the same frequency band; and

Fig. 11 is a schematic block diagram of a multiplex signalling system according to Vour invention.

Referring to Fig. l, the transmitter is of the character adapted to transmit a carrier wa've which varies in frequency according to a given pattern such as a saw-tooth, 'sine lwave, etc., whichever is preferred, the variation being be tween limits of a given Tfimiuerlcy band., for example, 115% of a mean frequency. The transmitter circuit includes the usual R. F. oscillator l2 with antenna system I3, a primary oscillater "le, frequency multiplier 'l and buffer arnplier i8. These elements of thecircuit produce "a barrier wave of a given mean frequency. This 'wave is frequency modulated by a 'sweep voltage, rfelectromotive force which varies cyclically acccrdingto a desired sweep pattern. A sweep voltfage ageneratr"21) is provided forthis purpose, and, Tif-desi'red, may-be adjustable to any desired sweep 1frequency 'and '-deviatien. This varying voltage Yis applied t'o a react'ance modulator '22 which "ebntrol's the frequency of the primary oscillator` luca'using` the oscillations produced thereby t'o vary -accrding to the sweep characteristics of -lfle 'varying vltage.

ssflimeffor V-pi'p'oses illustration, that the sweepingr electrointive 'force produced by the 1generator 20 varies according'to a saw-tooth wave bet'ween voltages Vi and V2 as 4indicated by the 'vl'tagewave -25 of vcurve f3a, Fig. 3. The sweep pattern, 'of the'va'rying voltage, however, may'com- 'prise fothe'rshaped patterns such as a sine wave, triangula'r'wa've, etc., as may be desired. When :the oscillations Vare modulated "bythe sweep volt- "age of wave '25,the carrier wave i's'frequen'cy modq 'ulated between `two frequency limits fi and f2 as indicated 'byfthe'wave 50 'and A32 :f Curve i3l). t intelligence mayvbe conveyed by the lcarrier way'eaccording to 'different types of modulation the frequency curve such as amplitude modulation, frequency modui' lation, phase 'modulation and various forms di "pilsermodulatln In'the latter case, `the modulation may incl de amplitude and/,or time modulation of uiepiilses, modulaucn of `pulse repeti- 1n Fig, 1, the intelligence may be regardedlby wayV of example as bein'g'applied to Ythe carrier vwave 4by ak'nown lform of amplitude modulating circuit 34 associated Withthe VR. F. amplifier `|2,`A

thesignal'wave'beirig applied thereto throughan laudio amplifler 4from a microphone '38.

A Curi/ecof Fig. 3`indicates a modulating sigrial wave '4Q such "as microphone 'tothe modulator, Curve- 3d illustrates the carrier wave -`famplitude modulated 'jtviili the signal 'wave 40. it will -be lndice 'that the frequency modulation of the oscillations produced by the sweep voltage from generator 2U Lisy "iridependentfof the envelope definition of the` lcorrespndin'g tofthe sig'nalwave'. The "wave 3b 'thus conveys 4intelligence while, at the same time, it is frequency AVlrlodulated 4over'ia cadence frequency, pulse width rnodil-` l may be applied from thez.65

i 53 is coupled. The

Lio

tilde v-`baiiil df frequencies thereby rendering it i ydilicillt for unauthorized pers ons to receive the combinedin `thesarne elements, 54,56 and 58, 'andithe of oscillator 'landlthe carrier wavedistinguished intelligence by means of the usual receiver or even by a wide band receiver without the provision of special synchronizing means.

The receiver of Fig. 2 for receiving the wobbling carrier of curve 3d, Fig. 3, utilizes the heterodyne principle and includes a broad band R. F. amplifier 52 to which receiving antenna R. F. amplifier has a wide R. F. band pass approximately equal to or slightly larger than the frequency band through which the carrier wave sweeps. The output of the R. F. amplifier is fed to two mixer detectors 54 and 5&0.. The mixer 54 converts the R. F. carrier into a corresponding wave of constant intermediate frequency which is fed through a narrow band, high gain I. F. amplifier 56 to a detector 58 for demodulation of the I. F. wave. The output of the demodulator 58 is fed to the usual integrating network 60 and thence through audio amplifier 62 to a speaker 64.

in order to remove the wobble Variation 'from the carrier 'and provide the constant I. F. wave for the duration 'of the cyclic sweeps of the carrier wave, a varying Ielec'tr'ornotive force is generated by a sweep voltage generator l0 substan- 'tia'lly identical 'to the sweep pattern of the carrier wave.A The generator 'is controlled by 'selected synchronizing pulses from a blocking oscillato'r 69, the 'selective feature of which isdescribed in detail hereinafter.

The generator 'lil is adjustable for a rate of sweep corresponding to the sweep rate or pattern of the generator 20 at the transmitter. This varying 'voltage of the 4generator 'i is adjusted by lphase or time adjuster 'H to agree substantially with the timing of the sweep pattern of the received c'arrie'r. The voltage output of adjuster Tl' is 'appli'ed'to a reactance modulator 4or other suitable modulator 1'2 to modulate the oscillations generated by a sweep oscillator 1li. This produces la frequency varying train of oscillations which when mixed with `the carrier wave at detector 5ft, 'the pattern 'of the sweeping oscillator being timed to the pattern of the carrier wave, 'awave of constant intermediate frequency i'sproduced which bears 'a facsimile of the modulationo'f the carrier-wave. Byvdetecting the I. F. wave at 58, a signal 'wave corresponding to the transmitted intelligence is reproduced for the speaker 54.

Synchronization vof the sweeping oscillations of the oscillator Il is effected by applying to the mixer detector 54a oscillations 'generated by a synchronizing oscillator 16 at a selected frequency such, when "mixed withvthe carrier wave, produces 'a'p'ulse envelope of vthe I. F. frequency of the narrow `band, I. F. amplifier 56a, each timethe received c'arrier"` ave sweeps across the lfrequencyban'd'f thearn'plifier. The I. F. pulse envelope is detected-'at '58a 4to removethe intermediate frequency leaving Vpulse envelopes used for synchronizing purposes. These synchronizing pulses -are sharpened by pulse `Shaper and selector 18, the sharpened pulses being used to control thevolta'ge'sweep cycles produced by the generator TU.

The two series of elements 54, '56,"58 and 54a., a, killal 'separate the 'reception yof intelligence signals yfrom the generation of synchronizing pulses. rhese two functions, however, may 'be such as elements beating of 'the oscillations by suitable filter means from the'intelligence wave produced 'by Ethe beating -of the lcarrier with the 'justing the phase .tor 11 of the nip-HOD by oscillator 14.

sweeposcillations produced by oscillator 14. The filtering of the synchronizing pulses from the than the frequency range of the signal intelligence. A specific example of this feature is given hereinafter.

a frequency wobbling line 80 represents the frequency .band of the amplier 56a. Thus, each time the carrier wave traverses the level 82 a pulse envelope 83, curve 4b, of this particular produced. It will be underand y4d represent the pulse 18, the wave 84 representing the rectangular wave output of the multivibraresenting the sharp pulses produced by differentiation of the Wave 84 by diierentiator 19. The positive pulses may be segregated by the blocking oscillator 59 from the negative pulses of the wave or the wave may be applied, in the absence of lpositive synchronizing pulses produced by other carrier Waves, directly to generator 1U to `control the timing of the sweep pattern of the voltage 86, curve, 4e, generated thereby. The broken line wave 86a represents the timing of the voltage sweep 86 after passing through the locally generated sweep The sweep of the locally produced oscillations occurs between limits fn and fsa at substantially the same rate as the carrier 'f between frequency limits difference between the two for the duration of the .f1 and f2 so that the sweep results in a substantially constant I. F. frequency. It will thus be clear that this I. F. .frequency output of the mixer 54 will be constant for the duration of the sweep thereby enabling the second detector 58 to` demodulate the entire intelligence conveyed by the carrier wave.

In order to insure exact synchronism of the two sweeping patterns, an automatic frequency control 90 is provided between the I, F. amplifier 56 and the reactance modulator 12. This circuit responds 'to any tendency of the I. F. frequency,

voltage, as the case may be, to the reactance modulator 12 to counteract such variation. Thus,

Curve 4a indicates by saw-tooth wave y,

type, and wave 85 rep-,

f eiect produced is pulse modulated,

way of example, -for reception of 'I'M (time modulation), the modulation of the pulses being of the "push-pull character where the successive ous value of the modulating signal.

The R. F. amplifier |52, the mixer detector |54, the narrow band I. F. -amplier |58 and the |58 correspond to the elements similarly number-ed in Fig'. 2. The lthe synchronizing pulses, however, i in .the mixer detector |54, I. F. amplifier |56 and detector |58 simultaneously with the conversion to the lmixer detector |54. The double beating by the two locally produced oscillations on the carrier wave results in a train cated at |83. These groups |83 include .the synlchronizing pulse envelope components. By limiting the pulses |58a by limiter |59, the pulses are all .reduced to Ia constant amplitude as indicated by curve 1b. By threshold clipping the @pulses or :eur-ve lafat a level fl-Md :corresponding ,approximately to athe limiting `level of a limiter -ifthe pu-lse groups |f83a, curve '1 c, .are obtained. -.=By integrating the pulse 'groupsgglSaat '|B3, the .pulse envelope is obtained winch may be applied to a multivibrator |65 -to produce rectangular wave la., curve "|d, which by dii-erentiation at 6.1, ,produces sharp .positivepulses '|6111 "which in turn vmay beused to control 'the sweeps `ci :the

,voltage generator :|?|0.

vlVfhere more than one carrier `wave isfpre'sent -onthe same R. F. frequency band, it will be `glesirable to eliminate imdesira'ble pulses :genertated insa similar manner. vThis is done .bymeans tofiafb'locking oscillator ling =circuit .similarly as lhereinbefore 'described .'crFis.. -2. V'The sweep-ing voltage of .the 'generator |10 is corrected for phase Iby `adjuster |`l| and then iapplied toithe reactance modulator |1| which in iturn controls the Asweeping oscillator |14', As :hereinbeiore fdescribed, the frequency of the `locally generated oscillations is lcontrolled bythe Y.autcmfmltic frequency control f90 which counters v`any .tendency of the carrier wave and `the -loca1 nsweeping oscillations to drift out vof synchron-ism. @The `time modulated pulses |5590l of curve 1b l"are demod-ulated at "|60 after which the energy may be amplified amdintegrated at |62 and fapplied -to speaker liii-1l. The-demodulator |00 may `com-prise yany known form ofi translator capable of translating the time dis-placements into ampli- "'tude'dis'placements One form Aof demod'ulator is shown in Fig. 8. The TM pulses received, at

"in-put 230, drive a synchronizer 202 to produce a wave having a frequency corresponding to the .`pulseperiod, that the time interval between f'alternate' pulses. A wave selector 204 selects a desired "harmonic 205, curve 9a, of -thevrave en- "ergy"produced 'at 202,'p`referably an odd harmanic, for demo'dulati'on. purposes. `The har- ;"monic wave 205 and the"TM Vpulses |590, are `m`ixed in a suitably biased 'mixer 1206, whereby "the output energy alt 208 varies in amplitude in proportion to the amount the grid potential .of the mixer "206 exceeds a given thresholdleve-l '2.10, curve'ga. By integrating the output o'f the ,miiier'V 20B, 4the intelligence wave with which the fpulses |59a `are modulated will -be obtained. Wave V2|2 of curve 9b represents the envelope of "the intelligence, such as where the pulses oi curve Se `are modulated with increasing displacements according to a linearly increasing signal, the push-.pullmodulation being indicated -.by the arrows on'curve 9a.. `'lio .tune the receivers of Figs. 2 and "6 to a particular.transmitting station, it 4is first necgsessary to `set the sweep oscillator '14 or |14., as rthe-case may be, .to the mid I. F. frequency corjfresponding to 'the mid frequency of .the R. F. frevquency band of the carrier, itbeing 4asumed that -thelR. l'` amplifier is Vadjusted to cover the spec- .,trum ofthe R. F. frequency band, 'The next i -adizustment is that of controlling the sweep rate which, aslshown in Fig. 2, Vis effected by adjusting fthefsweepfrateof the voltagefgenerator 10. This fin turn controls through a ganged connection 245v thel adjustment -oi vthe blocking oscillator `69. ThisA is particularly important where there are aplurality of ltransmitter stations operating on fthe same R. F. frequency band but nat diierent lisweeprates or patterns. The 4phase/of the `locally @generated-sweeps lis controlled by adjusting embase :shifter Jil.

'|619 'or other pulse divid- With these three adjustmentsV -lator beats with the carrier waves pulses selected.

`made.,:the receiver fis tuned to receivetthevdesixed carrier.

`Itwill be clear from the 'foregoing that your inventionl'contemplates the provision -of a plurality of transmitters for wobbling operation init/he same :broad R. Fnband. These transmitters nwill diierin rate of sweep or some Vother characteristic of the Vsweep pattern such yas limits vvof; sweep or :shape of the sweep` pattern. Assumingr that 'a -sawetooth sweep pattern is used for four different transmitters, the sweeps thereof `may-be represented by the vwaves Ti, TaTc 4and T4, curveflfa, Fig. 10. Assuming that thesynchronizingoscilo these transmitters at a level 220, four series -of synchronizingpulses Si, S2, Scand S4 will be generated, one series each for each carrier. wave. In Vtarder to select "the synchronizing pulses :corresponding to e, particular transmitter, it Ais necessary vthat the blocking oscillator 69 (Fig. 2) bera'djusted Ain-ganged relation with the sweep `voltage igenerator `lllk as indicated-by connection :215. The 'ibloclcing signals .are represented bythe shaded areag22-5 cffcurve 10b. Assoon as asynchronizing pulse is selected, 'automatically -a correspond- '-ing local sweep pattern is produced. 'Dhu-s, the sweep pattern of the locally produced oscillations will -be caused 'to .sweep at a Aclsrcsen lrate and be timed according to the synchronizing' .pulses S1. Likewise, if the signals of a 4different transmitter are desired, `the corresponding adjustment of the elements 69` and l0 of Fig. 2 will block out the undesired synchronizing pulses andprovi-dela sweep rate corresponding to the synchronizing 'It will be readily seen'rom the foregoing description-that each transmitter v`may have two identifying numbers. First, a number *correspending lto thefini'd `frequency of the RJR band in `which it'operates and seoon`d,a number representing the sweep rate. For examplaitheidentifying numbers l27`.5-20 would :indicate ailtransmitter-operating Avat va mid 'frequency fo'127 l5 megacycles, the R. F; carrier of `which swings between l'lin'oitsof-QB and y30 megacycles and at a sweep rate of v20,000 'times per second. I'f many ltransrriltters are needed :forca particular locality, .another band can lbe used,`for example,20 to 25. megacycles in which the transmitters operate :atfdif- 'ferentsweep rates.

In regard .to the secretive feature of the 'invention, it shouldbe noted-that while ra'o'onventlcnal wideband receiver might detect .the carriers :of a plurality of transmitters, it .fwculd not 'beab'le :to segregate the "carriers one from the other.

Consequently, the reception Kwould be :garbledjby many simultaneousfrnessages.

.Asregards the' counterjamrning e'atureiof the invent/ron, it, encule be inidted'ftrratihe.receiver is sensitive ito ronly -a narrow. band #of frequencies at 4any given instant, while, :on they other. hand, .communication fills-up abroad R. Ffffrequeney 5ba-nd. The ratio of 4the R. F. .torthefll'l 'band `width is representative Iof the counter effect :with .respect 4to jamming attempts. Attemptszto siam the communicationfwith .a constant lcarrier .frequency transmitter vwould Ahai/.erizo fill aconsiderable ,portion .of the band-width with `noise :at a ,level equal .to the narrow v,band signal. This obviously would requirey 1an enormousea-mountfof power mals-ing the amming operation impractical. `Should :a jammingrattempt providemulses l `thatyvould iinterfere With `the synohronizingpulse generation byft-he transmission of :a constant .firequency f carrier, this would result in thefigeneiaand a sub-station 3|4 such as commonly used for selectively switching in telephone lines for two-Way conversation. The transmitter 3|0 may be constructed similarly as described in connection with Fig. 1. The receiver may take any of the forms described in connection with Figs. 2 and 6.

As indicated in Fig. 10, the carrier waves of the several transmitters bands.

While we have described above the principles of our invention in connection with specic apcoinpanying claims.

We claim:

said oscillations with the successive sweep patterns of said carrier waveA to produce a Wave of substantially constant intermediate fr synchronizing pulse producing waves, mixing saidI operation includes the g-eneration of oscillations 'at' a given fresynchronizing pulse producing operation includes controlling the recurrence rate of the synchronizing pulses so that such rate is outside the audible frequency range of said intelligence.

the timing sweep patterns of said electric wave.

6. A method according to claim 5 wherein thev synchronizing pulse producing operation includes cillations at a given frequency, and mixing said oscillations with said electric wave to produce a synchronizingpulse of n quency for each sweep pattern of the electric wave.

8. A communication receiving system for reception of intelligence conveyed by a carrier Wave frequency, in addition to producing subrecurring synchronizing carrier wave, means to produce oscillations varying in frequency according to said given sweep pattern, means controlled by said synchronizing pulses to synchronize the sweep patterns of said the successive sweep patterns of method according to claim l wherein the.

the successive sweep patterns of said saidvcarrier wave, means for mixing said oscillations with said carrier wave to produce a wave of substantially constant intermediate frequency, detector means for said intermediate frequency, and means to integrate the output of said detector means to obtain a signal wave according to said intelligence.

9. A system according to claim 8 wherein the means for producing said synchronizing pulses includes means to generate oscillations at a given frequency, means for applying said oscillations to said mixing means for mixing with said carrier wave to produce at least one pulse envelope of a given intermediate frequency during each sweep ofthe carrier wave, and means associated with said detector means for segregating the synchronizing pulse components from said pulse envelopes.

10. A system according to claim 8 wherein the means for producing synchronizing pulses includes means to generate oscillations at a given frequency, means separate from said mixing means for mixing said oscillations of given frequency with said carrier wave to produce at least one pulse envelope of a given intermediate frequency for each sweep cycle of said carrier, and detector means for the pulse envelopes.

11. A system according to claim 8 wherein the carrier wave is pulse modulated, andthe means for. producing synchronizing pulses includes means to generate oscillations at a given frequency, means causing said oscillations of given frequency to mix and beat with said carrier wave to produce pulse envelopes of a given intermediate frequency including at least one of the pulses withwhich the carrier is modulated, and means to obtain the synchronizing pulse components of said envelopes.

12. A communication receiving system for reception of intelligence conveyed by a carrier wave periodically varied in-frequency,'in addition to intelligence modulation, according toy a given sweep pattern between the limits of a given frequency band, comprising means for receiving said carrier wave throughout the spectrum of said frequency band, means for producing substantially regularly recurring synchronizing pulses from the successive sweep patterns of said carrier wave including means for deriving said synchronizing pulses from frequencies of said frequency band, means controlled by said synchronizlng pulses to produce a varying electromotive force having a cyclic sweeping characteristic substantially the same as the sweep pattern of said carrier wave, means for producing oscillations, means for frequency modulating said oscillations according to said varying electromotive force, means for adjusting the timing of the sweep pattern of said oscillations to the timing of the sweep pattern of said carrier wave, means for mixing said oscillations with said carrier wave to produce ya wave of substantially constant intermediate frequency, detector means for said intermediate frequency, and means to integrate the output of said detector means to obtain a signal wave according to said intelligence.

13. A system according to claim 12 in combination with an automatic frequency control responsive to variations in said intermediate frequency wave to vary the instantaneous value of the electromotive force, thereby offsetting any tendency of the sweep patterns of the carrier wave and the electromotive force to vary one from the other.v

' by a varying electromotive force sweep pattern of said carrier wave follows a saw tooth by a steadily increasing change from one to the other of said limits and then repeating,

and the means for producing a varying electrofmotive force includes a voltage generator wherewhich has a saw-tooth pattern substantially the same as the sweep pattern of saidcarrier. wave.

15. A system according to claim 12 wherein the sweep pattern of said carrier wave varies in a sinusoidal manner between said limits thereby producing two synchronizing pulses per cycle, and the means for producing said varying electromotive force includes a sine wave voltage generator and a blocking oscillator whereby alternate synchronizing pulses only blocking oscillator for synchronizing of said sine wave voltage generator.

16. A communication receiving system for reception of intelligence conveyed by a carrierwaveV periodically varied infrequency, in addition toA intelligence modulation, sweep pattern between the limits of` a given frequency band, comprising a mixer detector, means` for receiving and applying saidv carrier wave throughout the spectrum of said frequency band tosaid detector, means to generate oscillations at a selected frequency, cillations to said detector to mix'with said carrier wave to produce at least one pulse envelope of a given intermediate frequency foreach sweep` of the carrier wave, means to produce oscillations varying in frequency according to said given sweep pattern, means controlled by energy of said pulse envelopes to synchronize the sweep patterns of said varying patterns of said carrier wave, means to retardl the timing of the sweep pattern or saidoscillatlon-s a given amount, means for changing the selected frequencyof said oscillator to adjust the timing ofthe synchronizing pulse envelopes, means for mixing said varying oscillations with said carrier wave to produce a, wave of substantially constant intermediate frequency, detector means for said intermediate frequency, and means to integrate the output of said detector meansl to obtain-ia signal wave according to said intelligence.

1'1. A system for synchronizing a locally produced cyclically varying electromotive force with a remotely generatedelectric wave varied in frequency according to a given sweep pattern between the limits of a given frequency band, comprising means for receiving said electric wave throughout the spectrum of saidv frequency baind, means regularly recurring synchronizing pulses from the cyclic character of the received wave, said synchronizing pulses being timed to at least certain of the successive sweep patterns ofthe received wave, means controlled by said synchronizing pulses for producing a varying electromotive force having a cyclic sweeping characteristic substantially the same as the sweep pattern of said wave, said synchronizing pulses operating to time the sweep patterns of said varying electromotive force to the timing of the successive sweep patterns of said electric wave.

18. A system according to claim 17 wherein the means for producing synchronizing pulses includes means for generating oscillations at a given frequency,'and means for mixing said oscillations with said electric wave to produce at least one synchronizing pulse envelope of a given intermediate frequencyv foreach sweep pattern of 14. A system according to claim 12 wherein the 75 said electric wave,

is producedare passed by saidv according to a given means to apply said os'V oscillations with the sweep periodically Y to produce substantially f is synchronizing pulses includes means for generating oscillations at a given frequency, and means for mixing said oscillations with said electric *n sinusoidal manner, and the means for producing synchronizing pulses includes the generation of oscillations at a given frequency,

of said frequency band, means for producing a separa-te series of substantially regularly recurring synchronizing pulses from the successive sweep patterns of each of said carrier waves, means to produce oscillations varying in frequency according to said given sweep pattern, means adjustable to select the series of synchronizing pulses corresponding to rier wave, detector means for said intermediate frequency, and means to integrate the output f said detector means to obtain the intelligence conveyed by the selected channel.

22. A two-way communication system comprising first and second terminals each having a transmitter :and a` receiver, each transmitter having means for modulating a carrier wave with intelligence, means at the transmitter of a first carrier wave beat the transmitter of said second terminal to vary a second carrier wave between limits of said given frequency band but differing from said first carrier wave by a given characteristic of the sweep pattern, means to transmit the rst and second waves over a common medium between said terminals, the receivers of each terminal having means to produce substantially regularly recurring synchronizing pulses from the successive sweep patterns of the carrier Wave transmitted from the other terminal, means controlled by said synchronizing pulses to produce oscillations varying in frequency in a manner similar to the carrier waves, means to vary the sweep pattern of said oscillations with 23. A system according to claim 22 wherein the sweep pattern of the carrier waves is a sawtooth wave and the given characteristic is the sweep rate of. the.'sawtooth, and the means controlled by said synchronizing pulses for produc- 24. A multiplex communication system comprising first and second terminals each having a plurality of transmitters and receivers, each transmitter having means for modulating a carrier wave with intelligence, the carrier wave of al1 the transmitters varying between limits of a given frequency band according to a given type of sweep pattern,

of synchronizing pulses to sweep pattern thereof corresponds substantially to the sweep pattern of the desired carrier wave, means for mixing said oscillations with said carrier Waves whereby a wave of substantially constant intermediate frequency is produced by interaction of the oscillations with said desired carrier wave, detector means for said intermediate frequency, and means to integrate the output of said detector means to obtain the intelligence of said desired carrier wave.

25. A communication system according to claim 24 wherein the carrier waves of the transmitters of the first terminal are varied between the limits of a given frequency band, the carrier waves of the transmitters of the second terminal are varied between limits of a dilferent wave band, the receivers at the first terminal include means for receiving the carrier waves of said second frequency band and the receivers of said second terminal include means for receiving the carrier Waves of said rst frequency band.

26. A method of synchronizing a locally produced cyclic sweeping electromotive force with a remotely generated electric wave periodically varied in the frequency in a sinusoidal manner between limits of a given frequency band to provide a sweep pattern comprising generating oscillations at a given frequency, mixing oscillations with saidelectrlc wave to produce asynchrenirf ing pulse etV .agiven intermediate frequency for each half: cycle ofthe sweep pattern of said electrimwave, blockingout ofisaid-pulses to insure onesynchronizing pulse only for each sweep pat,- ternr of the electric wave, blocking alternate pulses to insure one synchronizing pulse only for each sweep pattern of theelectric wave, producinga varying electromotive force having a cyclic sweeping characteristic substantially the same as the sweep pattern of said wave, and using said synchronizing pulses to time thesweep patterns of saidwarying,electromotive force to the timing ofthesuccessive sweep pattern of lsaid electric Wavev MARTIN SILVER.

CARL A. SEGERSTROM, Jn; RALPH B. READE.

16 REFERENCES CITED The following references are of. record in the leof this patent: I

Number 1r Number UNITED STATES PATENTS Name Date Mills Jan. 8,-1924 Kendall July 20, 1926 Guanella July 2, 1940 Loughren Sept. 2,1941 Reeves Dec. 16, 1941 FOREIGNWPATENTS Country Date .Y Great Britain June 5, 1931

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