US2350702A

US2350702A - System of radio communication

Info

Publication number: US2350702A
Application number: US418280A
Authority: US
Inventors: Ullrich Edward Hill
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1940-05-21
Filing date: 1941-11-08
Publication date: 1944-06-06
Anticipated expiration: 1961-06-06

Description

June 6, 1944.

E. H. ULLRICH SYSTEM OF RADIO COMMUNICATION Filed Nov. 8, 1941 Patented June 6, 1944 SYSTEM OF RADIO COMMUNICA'IION Edward Hill Ullrich, London, England, assignor to International Standard Electric Corporation,

New York, N. Y.

Application November 8, 1941, Serial No. 418,280 In France May 21,1940

(Cl. Z50-6) 8 Claims.

, This Yinvention relates to a Vsystem of radio n communication and more particularly to radiocally compensated at the reception.

A preferred embodiment of the invention which will now be explained with reference to the single gure of the attached drawing consists in the simultaneous transmission of two or more different wave lengths and in the adjustment of the receiver so as` to receive waves and combine them in a manner to isolate the group of direct signals from the group of first echoes.

The apparent height of the ionosphere which reflects the electromagnetic waves depends on the wave length. Notwithstanding this, changes in this apparent height with changes in the wave length will be very slow except for the so-called critical frequencies. Within the scale of the short waves with which we are particularly concerned, the echoes of two waves, M and A2, spaced in frequency by a few tens of kilocycles per second may be considered as coming from the same layer of the ionosphere. By simultaneously sending on the two wave lengths M and k2, the direct wave M will follow the same path as k2, and the rst echo of wave length M will follow the same path as the rst echo of wave length lf2, etc. The result of this is that the two direct waves as well as the pair of echoes will arrive together, but the echoes will lag behind more and more. At a given moment, there will be in a receiver tuned to receive at wave length M, a direct wave and a series of echoes. rlhe same thing is true for a receiver tuned to receive the wave length x2. In' order to simplify the explanation, a single echo will be considered.

In the receiver, the direct waves will have the same relative phase as they had at the instant of emission in the transmitting antenna. By modifying the wave length and the phase of the wave A2 by a frequency changer (or a, heterodyne circuit) in a manner to bring its frequency to the same frequency and to the same phase as wave M and by super-posing these two waves, the two will be added arithmetically. l

Like the frequency of the wave and the speed of its phase variation, the heterodyne oscillator will change in phase during the time required for the wavesto travel from the transmitterto the receiver. If the phase of this oscillator is so arranged that the direct waves which are received will be aiding in phase, then the echoes which take longer to traverse this space will be added vectorially at an angle which depends on the diierence of frequency corresponding to wave lengths M and )l2 and the duration of the interval between the reception of the direct wave and the rst echo. The frequencies of two waves are so selected that the two echoes will be substantially cancelling one another when the direct waves are added to one another. On the other hand, the system can be so arranged that the direct waves will be cancelling one another and the echoes will be added to one another. It is possible, therefore, to isolate the pair of direct waves and the pair of echoes and to utilise these two pairs, e. g. by combining them in such a manner as to increase as much as possible the relationship between the signal and the parasites. Let

p(t) be the low frequency wave to be transmitted sin wt the carrier wave corresponding to the wave length M sin (w+6)t the carrier wave corresponding to the wave length A2.

If at the receiver the direct wave M is Amt) sin wt where A is a constant, the echo will have the form Y Beit-T) sin w(t-T) Where B is a constant and T the interval of time between the instants when the direct wave and the rst echo are received.

The wave at the input of the receiver tuned to wave length M will have the form R1=A p t sin wt+B p(t-T) sin Kt-T) (1) and the wave at the input of the receiver tuned to A2 BgoG-T) sin (w-i-H) (t-T) (2) If the heterodyne is arranged to reduce all the frequencies of the wave form R2 from 0/21r, we will get To indicate Athe values, a lag T of microseconds will notmaterially Vdiminish the quality of a commercial telephone conversation. "On the other ha'nd, a lag of 1A millisecond may be very l damaging. In this case, since RliRl isr3 `decibels .higher than 'the ratio of the wave-or the echo to the Jparasites in R1 `or. Rarespectively. If all 'the power were concentrated inthechannel ofwave .length XI, then the 'lastmentioned relationship would also be augmented direct` nected in pairs to two receivers 8 and I0 of any suitable well-known type. Their outputs are connected over individual transformers I 4 and MI5 in opposition to a telephone receiver or simibyf:3..decibels. Therefore, the. use of two waveV lengths will not causefany reduction in the-ratio between the signal and the parasites in the direct wave or in the echo. Quite on the contrary, ac cording to another feature of the present inven-v tion, this ratio can be increased by suitably mix--y ing -the `signals Ri-IeRz1 and R`1..-Rz1gbefore-for after detection, but after having retarded the In practice, the mixing is accomplishedv afterA detection because the height of theY reflecting layer is notrigorously constant-*and becausethe relative phase of the additive and subtract/ive signals varies. It is, however, possible automatically to control thefphase of th htei'odyn'e QSCillater in any Suitable i' lWell-knvvr'i. manner S0 that the Waves of the signals or Equationsand 6 Vremain in phase. 4 ,A a

It should be noted that the condition e'irpressed by the relationship 4 is not a necessary condition for isolating the pair of direct waves from the pair of echoes. As armatter of fact, 1in accordance with therelationships 1 and L3, one getsV isolated. By suitably modifying the phase of the heterodyne, the ipair of direct waves can be isolated in a similar manner. v The conditionfl gives, therefore, onlythe optimum relationship between the signal andthe parasites.

The -only gure of theattached drawing schematically illustrates an embodiment of the 4inventionp n a In this figure a pair of transmitters "I6 and I'I respectively tuned to the wave lengths M and A2 are coupled to 1an antenna and simultaneously keyed by a keying means I8. a tuned antenna circuit I is connected between the two

filters

2 and 3 which are respectively tuned-to to the wave lengths M Vand X2. The output of the filter 2 is connected directlyito the primary winding of a transformer I2 having two secondary windings-andthe output of the filter 3 is connected to afrequency changer f4 which is connectedvto aheterodyne oscillator 6 through aphase adjuster 5. The output of the the change of frequency, in other words, tothe wave length of the .other channel. The output ofY In theV receiver,

. cies of-thetwo transmitter waves.

Ylar translating device. 9 is a retardation circuit for retarding-the'waves in one receiving branch :by TV as ,previously explained.

The operation of such circuitv will be clear from the above, the transformers I2 and I3 permitting the application of the outputs of two channels inY series in one and in opposition in the other. In order to reduce to a minimum the effect ofthe frequencies Vin a system embodyingA Y such receiver, the frequency of A2 may beobtained in the transmitter beginnin'gwith XI and then adding or subtracting'the difference between` these two frequencies. In the same manner, the' heterodyneoscillator in the receiver may have 'a theoretical frequency equal to the difference Vof frequencies corresponding to M and A2. lIn 'this manner, the frequency of the heterodyne will-be low and it willV bev easy to obtain frequency stabili-'Zation'which is of 'great importance to the proper functioning of the system. Y

iInorder to simplify the explanation of theV operation, we have assumed in vthe above that only lthe 'frequency `of onewave will be changed Vin order to convert Litinto the second frequency.

In practice,` the frequencies of two waves will be changed byv reducing them to theV same mean frequency. InV this oase, the frequency of a beat oscillatormay be obtained from the frequency of the other beat oscillator by the addition or sub-'- traction of` the difference between the frequen- -A communication Vsystem embodying the feaitures of the present invention .is obviously not limited to the use of two simultaneously transmitted waves. If Vfor example, three waves are transmitted, then by Vcombining in a suitable manner the signals of the three receivers, two of the. waves may be 'suppressed andonly the desired w'ave preserved. We 'will have:

aififiewsin artigiani-Tann o1 j (tl-T1) +C p(t-T2)sin cliff-T2) R2=A p()SiI1 w2t|B` p(-T1)Sin l Y Y .out-,T0 +Co(t--Tt)sinjw2r(t-T2) By heterodyning in order to` obtain: Ri=Ac siniat+f-1 r1f sin [wig-T1)+1+T1(w-w2)]+Q(;Tz) sin Y Y Y r'ldi-(wTz)+1,+Tz(wxw2)] R=41 0 sin (wif-i-fQ-l-BM-tl-Tr) sin [wi T1) -l- 2IT1(w1rg:2)] -I- Co (t- T2) sin v v [w1(-T2`)VY|f2+7:2(011-012)] and by adding the three waves R1, Rc1., :and Rai, we will obtain three vectorial diagrams for. the three directwaves and1for-each` grounfof Vwaves corresponding-to the first or to fthe second'echo,

, frequency changer is connected withaffilteri l Vtuned to the new Wave length obtained after @.ijafcaeae egli-2a..; j L j no;

f where. thersame :sign-will be obtained rinunciations 1'? and: 8 and the same sign in -Eqiations T9 and -,but not necessarily lthe same signin the twopairs 'of equations. Bycon'sideringfthe case when all the signs are positive:

(T2-TD (w1 w2)=2(M-.-N),1`|v ('11)v (T2-,T0 (1+ug3)=2(mn)1 (12) relationships where M, N, `m, n 'are whole numbers. The conditions 11 and 12 determine Q2 and w3 andthe

conditions

7 and 8 determinen and 'e2V 'for the given values of M,`N,m, nlf The sum ofthe waves R1, R21 and R31 is 4therefore independent of the echoes, and the directy wave willV subsist therein at least unless e1 and e becomegequalto l 3 respectivelmN' and' n' being whole numbers. This last case can be easily avoided by choosing in `a suitable manner the values of M, N, m, V11 except inthe case where`Ti=3p (T2-T1),` p being a whole number, having thus isolated the directl wave, it can be` separated from R1 and R2 and rie-,establish the above case where we "owavesl vInstea` fdep'hasing R21 and R31 from ei' and er, respectively,gthe system may also be provided in such a'manner that these dephasing angles beequal `to zeroand 'thatv`R1, R21, and R31 be amplified to"different`degr`ees a, b, c before adding them'. The following are the conditions for the closing of the vectorial diagram of the first echo:` I, j Y w-l-b-wSTi (w1-waivers T1 (w1-w3) =0 f b sin T1v (w1-w2)'+c sin Ti (w1-w3) =0 and, `for the second echo,

a+b,wsTa--(u 11wz) +cus(w1-w3) =0 Al) Sin `T2 (wn-wz) |c sin T2 (w1-w3) =0 'Iliese'four 'equations determine the four quantities `b/a, c/a e1-n2, and wi--ws as a function of TiandTaV 'Y GenerallyL speaking, if the system 4utilises n waves, there will be v2(1L-1) conditions which must be although these Aconditions can always be satis- It is to be `noted that the Wave lengthsare so close to one another that if desired they can be transmitted'by the same output stage Vof the transmitter, -The installation cost of the transmitter is,-therefore, very small.

The adjustmenty of the transmitter and the receiver may be yeffected in accordance with one of the features of the present invention by transmitting an impulse preferably at a. predeterminedfrequency of repetition, e. g. 100 or 200 times per second. iThis impulse or series of impulses is receved and detected at the receiver and then applied to' an` indicating apparatus, such as a cathode ray` oscillator, the spot of which'is subjected toa well-known sweep system, e. g, horizontally to sweep the frame of the oscillograph at a predetermined speed. In the case where a series of impulses is used, the sweeping in the receiver will be synchronised in a Well-known manner. Thus the direct impulse and its echoes will appear on the oscillograph frame and the leg can be measured to determine the optimum frequency of the second wave with respect to the first wave in accordance with relationship l in the case of two waves, n being suitably chosen. In the case of a plurality of waves, it will usually be always possible to nd frequencies which `permit the addition of all di- `satisfied and 2(n-1) unknowns,L

rect-Waves or all the echoes of the nth scale with a sufficiently small displacement.

'- The lag A.ofthe different waves will generally be constant during long intervals of time. It will, therefore, .be suiiicient for the practical application of the above described system if the regulation were effected at relatively widely spaced times, e. g. -once every4 hour. The different waves are not subject to selective fading, but the weakening of an entire wave-carrier and side bands-.is common enough. In practice, the use of more. than onefwave with suitable lag eliminates .the effect.. of fading on the connection. The cost of the .first installation may be reduced by giving up the simultaneous use of the different Waves.V In: this case, in accordance with another feature ofthe invention, the fading will be reduced by selecting the strongest wave, e. g. by means of a'mechanical or electrical relay.

' A system embodying features of the present invention will, therefore, have two principal advantages: Improvement of the quality and suppression: of` fading. Although two or more wave lengths: must be employed, those wave lengths can: be employed which in .practice would other- Wise be useless on account of the phenomenon of echoes.\ l

.- The invention is applicable to the elimination of Aechoes originating in atmospheric layers. However, theA invention is applicable also to cases wherethe echoes are produced by the presence of obstacles in the path of the waves, e. g. mountains or even movable objects. provided that the lag of the echo does notvary too rapidly.

It will be obvious that the inventionis not limited vtothe embodiments herein disclosed, but that itis capable ,of numerous modifications and adaptations without departing-from the spirit thereof. v

.What is claimed is:

1. A radio signalling system comprising a transmitter having means for generating a plurality of carrier waves of different frequencies, meansv for modulating said carrier waves with theV same signals, and means for radiating said modulated carrier waves, and a receiving arrangement comprising means for abstracting energy from said modulated carrier waves means for, convertingv the received waves t0 the same frequency, a,` phase adjuster for converting the directly received waves at the different frequencies to the same phase, two receiving branches, means for isolating direct waves in one of said branches and echo waves produced by reflections in the other of said receiving branches, an output circuit foreach of said branches coupled to a` circuit including an indicating device and a retardation circuit in one ofsaid output circuits whereby the direct signal `waves and the echo signal waves are additive in the circuit of said indicating device.

A 2. A radio signalling system according to claim 1 wherein said retardation circuit retards the direct signal waves an interval equal to the interval between the arrival of the direct signal and the rst echo.

3. In a radio signalling system a transmitter comprising means for generating a plurality of carrier waves of different frequencies, means for modulating said carrier waves with the same signals, and means for radiating said modulated carrier waves, and a receiving arrangement comprising means for abstracting energy from said radiated carrier waves, means for segregating said different frequency waves in separate circuits, means for converting ,they received 'wavescf the different .frequencies to -thegsame frequency,`

means' for'modifying the .relativeyphasesl of thel received `Waves -of ldiierent frequenciesgns-uch manner thatv` 'the directly'. received waves fareriin theV same phase, 2' al circuit vcomp'rising.; two

assurde c eivmia"breiiths and en"cutputcircuitincludmg branchesfandne'ans for impressing ,saidfc'on-r` v verted ldirect'waves Aand echoesproduced by re-f flections' in vsuclfiinanner upon'l said.'last-'men` tionedicircuitsthat in one branch said;- direct waves are additive in effect vand :said .echoes `subv sta-ntially neutralize eachother and in the;.oth'er branch v said vdirect waves' f .substantially neutralize :each other and' said echoes are additive `inreilect' and an loutputcircuit including an indicating dee vice coupled-v tothe .said two branches? 4'. A--radio receiver for simultaneously recei-vin a plurality of carrier waves of different frequenf" cies' modulated by the'A same signals, comprising` Y means for ab'stracting .energy fromsaidfradiated carrier waves, means `for segregating said diiler, y

ent lfrequencyA wavesI in separate circuits, means for converting `the received waves-of the different frequencies to the same frequency,V meanslfor` modif-ying the relativeV -phases `of .thel received waves lof Y- diierent A frequencies "in such manne;1 that the Ydirectly, received waves are inthelfsame phase, yafcircuit comprisingf'two branches?, means'V Y -for impressing-saidconvertedidirect waves/arid echoes lproduce'd Joy., reflections .in such-manner upon fsaid last-mentionedfcircuit...that:inone Y l branch said! direct vvwaves are :additive` in. eifeot and said echoes lsubstantially neutralize :each other-andin the other branch saiddirect waves substantially neutralize reach other4` and.. said echoes are nadditive in effect-and an :output cire l cuit including van indicating device coupled to said twobranches.k Y f 1 5. In a radio signalling system avtransmitter comprising means for generatirigaYplural-ityof carrier- -wavesf of different lirequencies, means` for mo'dulatin-gsaidf carrier waves-.withthe same-sig-l nals--and means for radiating saidmodulatedcare rier' waves; vandY raf receiving- -circuit comprising means for Aalostracting` energy from said radiated i carrierY waves, means for Lsegregat-.ng saiddifferl-4 ent frequency waves in separate .circuitsf means for converting -thereceived waves of ldifferent fren quencies to the sameI frequency, .means for-anodiy"tying-tire relative phases ofthefreaeivedwavesof `diiierent frequencies in suchllfmanner .that-the' 'directly received waves are' `thesame phase,

` the input ,'fcir e f two receiving branches, transformers orfcoupling said separatev Acircuits to` Vsaidwtwol receiving branches, the secondary windings of lsaid transl- `for-mers beingdividedinto sections-andlav section of each secondary/winding being -connectedv in `series aiding relationfintheA input circuit lof-fone of said receiving-branches andlanothensection of each secondary winding :being connected `in series opposed relation in the otherm'i `Saidwre -ceiving lbranches i-andoutput circuits 'fior` saidA re- ,intotwqnaives @neinaltereaehiseeonaarywind;

winding being. connected tion in the other in` the yinput circuit of one lof an indifcatingdevicercqupledwtcs d. wo branches 6. Inv a fradio signallingrfsystema .ftransm tter comprising means f waves of differ" lating'gs'aid :carrie w .W l f l 'all i 'l enemies, meana forj mqduaves With thfsame signals ,receivrie 'arrange 'ent comprising' bstraciine'enrgygfwih radiated means or a o einewaves:numismaticasaidim .diff

ferent: frequency far/ayesf'inf Vvseparate jc` cuitsnat least one 'heterdyne oscillator for cnyertg-th received'waves ofcthetwofrequencies tothe 'same frequency, a phase adjuster forjmodifying the relative'phases ofthe-received waves of thetwo frequencies in such manner Y i',hat"the directly receiv'edvwa'ves are in the samephase; two .receiving branhejs",.transformers.forpupimg said separate circuits to sans wei receiving. t c ches, the 'sjeep'ndarywinemgs. of; said. dans@ gers beingspnp :winding beinglconnectedin series id ingrelation L, i@ PQQ. g branches, and'theother yha'lfof each, s condary quimy. `lbetween Y n being a 'Whole edual "toV the intersyairof'umje'in secridsibetweri theinstais when thejdirect wave and the first echo Wave lare and( means for :radiating said-1 :no matedy pa er t y v Y Y radiated' carri waves, lters, for segregating said two different Certificate of Correction n,Patent No.v 2,350,702. June 6, 1944.

EDWARD HILL ULLRICH It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 45, for sin p1(t-T2) read sin w1(t- T2); and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oice.r

Signed and sealed this 29th day of August, A. D. 1944.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.

Patent No; 2,350,702.

` Certificate of` Correction June 6, 1944. EDWARD HILL ULLRICH Y f It is hereby certified that error appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 2, second column, line `45,

for sin 1(t-T2) read sin Mt-T2); and that the said Letters Patent shold be i read with this correction therein that the saine may conform to the record (of the case in the Patent Office. f

Signed and sealed this 29th day of August, A. D. 1944.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.