US2510338A

US2510338A - Means for and method of scrambling speech signals

Info

Publication number: US2510338A
Application number: US695030A
Authority: US
Inventors: Guanella Gustav
Original assignee: Radio Patents Corp
Current assignee: Radio Patents Corp
Priority date: 1945-09-15
Filing date: 1946-09-05
Publication date: 1950-06-06
Anticipated expiration: 1967-06-06
Also published as: CH246844A

Description

G. GUANELLA 2,510,338

MEANS FOR AND METHOD 0E SCRAMELING SPEECH SIGNALS June 6, 1950 2 Sheets-Sheet 1 Filed Sept. 5, 1946 alumdwy lNvENToR G'z/srnv Gun/VELE LJ i@ ATTORNEY June 6, 1950 G. GUANELLA 2,510,338

MEANS EoR AND METHOD oE SCRAMBLING SPEECH SIGNALS Filed Sept. 5, 1946 2 SheetsSheet 2 /m/L T/ FREQUENCY GENE/En Toe INVENTOR Gusrnv Guan/gun ZM i@ ATTORNEY Patented June 6, 1950 'FET MEANS FOR AND METHOD OF SCRAMIBLING SPEECH SIGNALS Gustav Guanella, Zurich, Switzerland, assignorV to Radio Patents Corporation, New York, N. Y., a corporation of New York Application September 5, 1946, Serial No. 695,030 In Switzerland September 15, 1945 mission, into a plurality of frequency sub-bands,

which are interchanged by the aid of auxiliary displacement carrier oscillations in their relative positions within the original frequency band. Additionally, the frequencies of one or more subbands may be inverted by known means to increase the degree of secrecy obtained.

The present invention also relates to a scrambling method of this general type known as frequency substitution scrambling, and has for its main object to further increase the degree of secrecy obtained and to substantially prevent the deciphering or decoding of a scrambled message by an unauthorized listener or receiver.

With this general object in view, the invention involves basically the subdivision of a given signal frequency band, such as a speech frequency band, into a plurality of sub-bands which are mutually interchanged in accordance with the substitution scrambling method.

According to the present improvement, the thus obtained scrambled frequency band is divided into at least two secondary or partial frequency ranges which are mutually interchanged and at least one of which may be inverted, said secondary frequency ranges being so related to the primary scrambling sub-bands that their common limit or separating frequency or frequencies coincide with a frequency within one of said sub-bands. In other words, the limit or separating frequency of the partial ranges should not coincide with any of the limit frequencies of the primary scrambling sub-bands, as will become further evident from the following.

The invention, both as to its further objects and novel aspects, will become more apparent from the following detailed description taken in reference to the accompanying drawings forming part of this specification, and wherein:

Fig. 1 is a theoretical diagram illustrating the successive steps of converting a given speech frequency band into a final scrambled band in accordance with the invention.

Fig. 2 shows a practical system in block diagram form for carrying into effect the scrambling method illustrated in Fig. 1.

Figs. 3 and 4 are partial diagrams illustrating,

respectively, a. preferred multi-frequency gen-v erator and modulator or frequency transposing device suitable for use in connection with the invention.

Referring more particularly to Fig. 1, wherein the abscissae along the various horizontal lines represent frequency and the ordinates represent amplitude, an original speech frequency band a covering a range from 300 cycles to 2,700 cycles, which has been found in practice to be fully sufcient' for the transmission of intelligible speech, is at first transposed or shifted to the range between 8,300 and 10,700 cycles by modulating it in the modulator M1, Fig. 2, upon an auxiliary displacement carrier oscillation u1 supplied by a multi-frequency or harmonic generator G and having a frequency f,1=8,000 cycles. By segregating, by means of band pass lter F1, the upper side band from the output of modulator M1, the frequency band b is obtained in a manner well understood. The frequency band b is in turn subjected to a further modulation in the modulator L@ to which are applied in succession by means of a distributor U six auxiliary oscillations ua, ul ua also supplied by the harmonic generator G and having frequencies f3= 7,600 cycles, j4=7,200 cycles, f5=6,800 cycles, fs=6,400 cycles, f1=6,000 cycles, fa=5,600 cycles. respectively.

In order to increase the degree of secrecy, it is desirable to change the sequence of application of the auxiliary oscillations ua, u4 ua to the modulator M2 by correspondingly connecting the distributor contacts to the supply leads from the generator G.

As a result of the modulation in modulatorl M2, periodic lower side bands c1, cz ce are obtained successively displaced relative to the original band a by differences of 1/6 of the latter, i. e., equal to 400 cycles. The signal bands c1, c2 es are amplified in a standard amplifier A1. Each of the amplied signal frequency bands c1, c2 c3 is then divided into two partial frequency ranges separated at the fixed or separating frequency t, the latter amounting to 2,900 cycles, in the example shown. This separation is effected by means of an electrical switch consisting in the case illustrated of two filters F2 and F3 connected in parallel and having frequency passing ranges adjoining each other at the common separating frequency t. Filters F2 and F3 may be band-pass or low-pass and highpass lters, respectively, of known design, as is readily understood. 4An essential requirement to obtain a high degree of secrecy is the fact that within each of the frequency bands c1, c2 c6 there exists a different ratio between the partial ranges produced in accordance with the above. In other Words, the individual frequency bands c1, c2 .ce is displaced periodically relative to the fixed frequency t in the manner clearly seen from the drawing.

According to the next step, the partial frequency ranges or primary subgbands containingv the lower frequencies of the bands c1, c2 .cs are in turn intermodulated in the modulator M3 with a further auxiliary oscillation 'uz supplied by the generator G and having a fixed frequency f2=ll,2)o cycles in the example illustrated. The' resulting lower and accordingly Vinyerted side bands obtained from this modulation are seg-f regated by means of a band-pass filter F4.

Furthermore, the partial ranges or 'primary sub-bands .of higher frequency of the speech frequency bands ci', jcz ce are again inter- Vno ulated the :modulator Mtv-lith the respectite aukiliary'os'cillations "us, '1 4 L. u8 and the upper side bands' ofthe'modulation product also segregated by the band-pass filter F4. "n'this er, the'putput vvo `f";tiltrF4 supplies the six Ky inverted'speech' frequency bands d1, y de all falling` within'the" 'same frequency range of '8,300 to'10,"7'00cycles, corresponding to thipas'rsig ranglebf tl''el `nF4. As is understood; the "prirraiy""" b-#band's "of the frequency ff' CfifC'z ,cf y'brflitually nt'el'changed by meansl of any'onfe' 'f 'the''lz'nwn methods and devlces to 'increase th degree of secrecy obtained..v `For the sake'b'f simplic'ty, there nas'been inustrateain rigl ozliytne cm1-ef scrambling of tue'split or d edfreduency tand di', it being understood 'that'tue fart r scrambling or the bands d1; cada.' d5; and di; takes 'place in a substantiall'y analogousl manner'. The frequency banaal-is again period iyishiftedrto'diffrent frequency 'range's'ty intermodiilating' it "in 'the paralisi demented ,modul-attrs Ma; Ma; Ms; en with auxiuarysenlations *ui tia; whereby ther-)wer met .a are bb; ta'i'n d'which are nu ally displaced 'by 'a dise iatis; equal to nessifgtri'lf H lf'F-,G ll'yxbad lQV I'* respondng'ttheb'a disci" dc." S'blba'll'sf gwn gg g, each falling within the. range of 270g-aloe cycles, are uien sieg gated `fromcada offthe frequent:v lo 'd'sfifcz' .iffeby .means of identical bandepass l'te'rslaaf F515" Fei," respectively. sub-bands' ci," c@ arie 'in turn'shifted to produce an 'ad y 'inmfg' frequency band by modulation With 'the `a li'ary 'oscillations ul. .u8 in "the "m cratersV` Ma, Ma .'Mef, respectively. thismannenthe final and completely scrambled frequency 'bandit falling Within the'all'g Vf' 8,3100'to' 10,700 yles is obtained. VThe final vsc'ra'znbl'ed frequency bandy h, in addition' to 'its sub-division into! 'a 'pairof primarylsub-bands, oriifof which isinverteu, is thus additionally divided into a relatively larger numberof secondarysu'bbant''s gi, y2' gs, in suc'ha manner thatthelimit frequencies of -said secondary'sub-'bands each coincidfswitli anni# ter'mefd'iate frequency 'of 'the primary -sub-'bands oryn other words, that the' separating Vfrequency' of the Cprimary sub-"bands "coincides sequentially and "pel'dcally'lwith' a predetermined inter; mediate such vasfthe center Jfrequency of different secondary subeb'ands gi; g2

' 6. 'Since ytlfie`sepa'rating frequency of 2,900 cycles in Ithe eX-ample' illustrated at'whic'h the frequency 4 bands c1, cz ce are split or divided is exactly in the center of the frequency range of 2,700 to 3,100 cycles, which corresponds to the passing range of the filters F511, Feb Fsf, the subband g4 in the nal scrambled signal is comlised of two Isublloan'd portions orlarflgesrgli and 14" each having a bandwidth equal to 200 cycles. .YFurthermore, in the example illustrated, subba-'nd portion g4 is uninverted, While sub-band ponticn fyi jisvigxryerted and contains the lowest q ,i equencies of the original speech frequnecy band g. An essential condition for the attainment of crecyV is the fact that the lowest s which are predominantly e intelligibility of speech are always cohtainedin the sub-band portion g4 of only i200 cycles band Width.

lt. is .understood that the separating frequency tlnay' b'e so chosen as to coincide with any other 2o frsqueey Within the, frequency .range Qf the Fsc, F51; F5f. lattecafs 13h@ subband Vpcqrrtli'ons 'g4' and g4" will 4be ofr unequai and the con ons are advantageously =so chosen hatthe su and prtionjghas a nar rower :width tharitlh'e Is1.jl l3'lca`nd. portion g4.

The teme Sffemliin' as decibs'd "in connection With the speech Vfr'eq-rient'y' bands di 'will occur with. @little-ether bands d l' for'instan'ce, 'in the case ofthe 1of,1'lnds'v ds and d; the @responding Sub-tenet [ya adf 'ya rasee@ tively, vin the rfinal Vs cranitljeclY signal h will be divided into corresponcli g subeband portions, as

4tlf'reir sequence Scrambled 'Speech signal, band h is,

shown 'to be a pied vto Va 'further ampli''er'Az followed by a ben '-PSS mi@ .Ffhyin'g'a pssie frequency range'of 8139@ @790 cycles. Finally', the flieqncy "bend h is Sebi-@cieli t a ``frthr iliary lsv rllatibnh-rto" return it to the original low 'frequency range :of A"ill22;;(00 cycles corre-l '111'Q0n dividedintoa rilv A l changed lsub-"bands to, Hoducje .a final scrambled signal. ,As is understood, trie` sequence of `operatin trav be 'reverted that is the initial band. may 'be'rst subjected {tosubsm onscrainbling 15 -rby dividing it into a plurality'o 'sub-bands. and

ity olf-.mutually inten d2, da, d5, de. Thus,'

Asare'sult, the subiV r `M7 with the 'auxthe' same conversion steps as d scribed'but :in rel the thus scrambled signal then split into the two partial ranges in accordance with the present invention. It is furthermore possible to separate a scrambled signal comprising a pluralityl of interchanged sub-bands obtained by a substitution method, into more than two partial ranges, care being taken in accordance with the invention that the limit frequencies of said partial ranges do not coincide with any of the limit frequencies of the primary sub-bands in order-V to obtain the novel effects and increased degree of secrecy in accordance with the invention.

It is also possible to utilize the arrangementv described in such a manner that the speech frequency band is repeatedly or successively separated into partial .ranges to secure an addedsecrecy. y A

The various elements and parts required for carrying the invention into effect may be of standard design and construction well known in the art. This applies especially to the lters and amplifiers, all of which are common and standard equipment in communication systems. The multi-frequency generator -G may also be of any known construction. A suitable form of such generator is shown in Fig. 3, comprising a tuning fork Oscillator O feeding a harmonic generator A3 in the form of a vacuum tube amplifier designed and operated to produce a highly distorted output wave form, such as by the provision ofa high negative grid bias, as indicated in the drawing. By means of a plurality of filters N1, N2 Ns connected in the plate circuit of theA tube, the auxiliary frequencies u1, u2 us are derived from the harmonic spectrum in the anode current. Y

The various modulators used for shifting or transposing the frequency bands to desired points on the frequency scale` may also be of any type known'in the art. A-specially suitable form of modulator-.is shown in Fig. 4,-comprising a balanced circuit of dry-rectiers, such as those of the copper oxide or selenium type well known in the art, wherein one of the signals to be intermodulated is applied toterminals l, l and the other signal is applied t0 terminals 2, 2', theA resultant product or output being derived from' terminals 3, 3' in a manner well known.

While I have shown and described a desirable embodiment of my invention, it is understood that this disclosure is for the purpose of illustration and that various changes and substitutions of equivalent steps and elements for those herein shown and described may be made without departing from the spirit and scope of the invention as definedv in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a limiting sense.

- I claim:

LA system for secret transmission of speech' comprising means for sequentially and periodically producing from an original speech frequency band a plurality of equal components eachl displaced Awith respect to the next one by equal frequency ranges being a fraction of the total band width of one over the number of components produced, means for splitting of said components into two partial frequency ranges atv a common andY xed separting frequency, furtherpmeans for shifting the respective partial ranges into a common frequency range of band width' :equal *to the;v original speech n frequency bandfandwith'one of said partial frequency ranges" being inverted, to produce a plurality of pre-scrambled frequency bands comprising par-lk tial ranges of varying relative width, means for,

in turn producing from each `of said prescrambled frequency bands a plurality of relatively 'displaced components coinciding respectively with said first-mentioned components, band-pass filter means for segregating from said last-mentioned component equal bands of limited width equal to the above-mentioned fraction of the total original frequency band and having upper and'lower limit frequencies lying at both sides of said separating frequency, and means for unequally shifting the bands selected by said filter meansto positions so as to adjoin each otherand toA form a final scrambled signal of band widthl equalto the original speech frequency band.

' 2. A system for secret transmission of speech comprising means for sequentially and periodi` cally producing from an original speech frequency band-a plurality of equal components each displaced with respect to the next one by equal frequency ranges being a fraction of the total band- Width ofA one over the number of components *L produced, means forsplitting of said components into Vtwo partial frequency ranges at a common and fixed separating frequency, further means for shifting the respectivepartial ranges into a.V

common frequency range of band Width equal to the original speech'frequency band and with one-i of said partial frequency ranges being inverted, to

producea plurality ofv sequential pre-scrambledr frequency bands comprising partial ranges ofvarying relative width, means for in turn pro-- separating frequency, and means forunequallyl shifting the bands selected by said filter means to positions so as to adjoin each other and to form a final scrambled signal of band width equal' to the original speech frequency band.

3.`A system for secret transmission of speech comprising means for sequentially and periodically producing from an original speechA frequency band a plurality of equal components each displaced with respect to the next one by equal frequency ranges being a fraction of the total band width of one over the number of components produced, means for splitting of said components into two partial frequency ranges at a common and fixed separating frequency, further means for shifting the respective partial ranges into a` common frequency range of band width equal to the original speech frequency band and with one of said partial frequency` ranges being inverted, to produce a plurality of` sequential prescrambled frequency bands comprising partialI ranges of varying relative width, means for in turn producing from each Vof said pre-scrambled frequency bands a plurality of relatively displaced components coinciding respectively with said first-mentioned components, band-pass filter means for segregating from said last-mentioned components equal bands of limited width equal to the. above-mentioned...fraction of l the totalv original frequency band and having upper andlower Vlimitfrequencies *equally spaced [from said separating frequency, `and@ inearis'ic'nl unequaliyl tabak bend.Y Width aofi/9.11; QYIL components prpdueedfme madre@ f que-miesen ,5, A

- sei Premier ub, n

v neisglqallse .lamme '0.131 Qfjseisgprimerx selbe-20211.11@sA secret signalling compr-is gg ne @semen signal @mehr ad axldmm requeneye. 14. A Smeer/Eigaeetrmnsmsiengoierregen.

@geen qQnPfiSipr emmener ubmuim scrambling s querxtigllx er. Aeddie.

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dlenentlntermediategfrequencx.ofnsaid@fprimara Sutrebands.

for periodically varying the interchanging code of said secondary sub-bands.

16. A system for secret transmission of speech comprising scrambling means for subdividing a given speech frequency band into a pair of primary sub-bands, means for frequency inverting one of said sub-bands, means for sequentially and periodically varying the relative band Width of said primary sub-bands further means for additionally dividing the pre-scrambled frequency band into a number greater than two of secondary frequency sub-bands the limit frequencies of which coincide with diierent intermediate frequencies of said primary sub-bands, means for frequency inverting part of said secondary frequency bands, further means for sequentially and periodically varying the relative band width of said primary sub-bands, and means operated in synchronism with said last mentioned means for varying the interchanging code of said secondary sub-bands.

17. The method of secret signalling consisting in subdividing, by sequential steps of frequency substitution scrambling, a given signal frequency band into groups of different numbers of partially inverted frequency sub-bands, the limit frequencies of the sub-bands resulting from one scrambling step coinciding with intermediate frequencies of the sub-bands resulting from another scrambling step.

18. A system for secret transmission of speech comprising scrambling means for subdividing a given speech frequency band into a pair of primary sub-bands, means for frequency inverting one of said sub-bands, further means for additionally dividing the pre-scrambled frequency band into a number greater than two of partially inverted secondary frequency sub-bands, means for sequentially and periodically varying the relative band width of said primary frequency subbands whereby the separating frequency of said primary sub-bands successively coincides with the center frequencies of different secondary subbands, and further means operated in synchronism with said last-mentioned means for varying the interchanging code of said secondary sub-bands.

GUSTAV GUANELLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,725,566 Chesnut Aug. 20, 1929 2,301,455 Roberts Nov. 10, 1942 2,402,059 Craib June 11, 1946 2,411,206 Guanella Nov. 19, 1946 2,411,683 Guanella Nov. 26, 1946