US1998792A - Interference elimination system - Google Patents

Description

April 23, 1935. J. SEDLMAYER INTERFERENCE ELIMINATION SYSTEM Filed May 17, 1934 INVENTOR JOSEPH SEDLMAYER E #QQ Aff-wu..

ATTORNEY n Y Patented Apr. 23, 1935 UNITED -sTME-s insana 1,998,792 Y vnrrEnFEaranci.: ELIMINATION SYSTEMl Application May'ir, 1934, serial No. 726,038 Y f y i .Inv Germany April 12, 1933 2 Claims.

The present invention relates to a'method of and means for eliminating interference in the .1 electric signal communication systems whereinmessages are transmitted by means of impulse 5 signals, as for example, in alternating current telegraphy. It is suitable for the transmission over wires as well as over Wireless paths. [The advantage derived from the invention lies in the;

fact that interferences of the most various types are caught and removed simultaneously with the result that an actually reliable transmission lof messages is. guaranteed.

It is known in the field of Wireless communication, particularly in the short-Wave art, that interference phenomena exist in the form of slelective fadings which make their existence known by the variation of the intensity only of a part of the frequencies of a transmitted frequency band. Attempts have heretofore been made to 2O eliminate the influence of fading on this type by emitting simultaneously, or modulating upona joint carrierr wave several frequencies, for in-r stance a fundamental Wave and harmonicwaves of the same frequency. Then again, there are interferences which produce additional currents in the receiving apparatus and which. for in'-VV stance in Wireless transmission, are caused by atmospheric influences. For thepurpose ofreliable reception for this case, the prior art has proposed the use of ,-a so-called double tonal control, i. e. to sendv one frequency for the signal current vand another frequency for the spacing current. In such case there is provided at the receiving end a differential circuit scheme which operates the receiving apparatus with, the alternating reception of the two frequencies. Thus the interferences are povverlessfin that the frequencies used for signal transmission are contained therein which influencesimuLl taneously both parts of the differential circuit 'so that the receiving apparatus is not actuated. In the. transmission by Wire, interferences may appear in similar manner, for instances interfering impulses by adjacent linesorpby for- V eign sources of disturbances maybe produced, or the transmission characteristics'may be teinporarily changed for certain frequencies by-a switch-over, for example in high tensionv lines.`

According to the present invention, the above listed phenomena which cause interference are eliminated for the same transmission channel by combining with each other the two methods described. In other words, use is made of double tonal control and of severalfrequencies which are 'preferably in harmonic relationship, for each the signal current'and the spacing current. Moreover, in addition, there is proposed according to the invention a new arrangement for the elimination ofthe itotal fading, i. e., suchffadings'which do not favor special frequencies but which cause a, uniformfading of the sound intensity. This is accomplished by connecting level regulating arrangements` in those branches in receiving circuits whichare separated for the purpose of the eliminationpof interferences and which act, for'instance with respect to the interferences, in opposition toea'chother orwhich, when interferenceoccurs, carry different-parts of the incoming. energy and act integrating on WVEMF OFFICE the'receiving apparatus.` `It is further suitable i for.- the .purpose of providing a yfurther-'joint coarse regulation in'the`joint part of the input of the receivingv arrangement. The advantages derivedtherefrom consist, inthe `first place, in-

purging the currents fed to the regulating amplifiers of interferences to an appreciable. degree' so thatthes'e latterrcan v*no longer exert a notice-y able inuence on thev adjusting apparatuscontained in the branches` Invithe second place, an advantage must be seen in the fact that with the use of a coarse regulation the adjusting range of the regulators contained in the branches can be kept considerably smaller than Without the use of' a coarse'adjuste'r. ...Thus'the required input can beheld down considerably. By a coupling ofthe'controls Ycontained in the branches the elimination of total fading can be further effected by both regulators jointly, the one of the selectivefading by the', one or the other regulator Whichis in the branchwherein the selective fading falls. In this manner the regulators in the different branches may be kept approximately at the same level during the transmission, the

additional vernier regulation taking place separately in each branch. l

Further. details of the invention are explained by means of the accompanying drawing, which is given vbyiw'ayofiexample: i

Fig. l shows'the frequency scheme of an arrangement according tothe invention.l Fig. 2 represents aschematic diagram of the circuit arrangement according to Fig. l.

Fig. 3 shows closerv details "of the receiving ar y rangement according'to Fig. 2. f V-The circuitembodiment shown by Way of eX- ample isfintended for the transmission of telegraphic signals,'wherein also currents are trans? mitted during the signal spaces which have a frequency different from those of thesignal currents, in other words, use is made of a so-called doubletonal control vAccording to Fig. l the carrier frequency fais modulated during the signal current period with a frequency f1 and its first harmonic'frequency 2jr Vand during the spacing period with a frequency f2 and its rst harmonic 212. Hence, besidethe carrier frequency ft there are sent duringV the signal the side frequenciesA fil-f1 ,and ftiZfi and during .the spacing the side o 'frequencies ftifz and fri-U2. Thechange'between the two frequency pairs f1, 2h and f1, 2fg corresponds to a frequency modulation. The corresponding frequencies of both frequency pairs must be diiferent from each other only so inuch that a sufficient separation by filter can be ef fected. Let it be assumed for instance that the frequencies f1 and 2h according to Fig. l are i090 Hertz and 2000 Hertz and the frequencies f2 and f2 i200 liertz and 2400 Herts.r

f he combination of side band frequencies having harmonic relationship practically removes the influence of the carrier Wave fading. With the absence of the carrier frequency, therev arepro" duced after rectification at the receiving end, frorn the side bands only, the transmitted fundamental frequencies and their upper harmonics, for instance according to Fig. l the frequencies fr, 2f1, 311, and f1 and f2, fz, Biz and'fz, respectively. Compared with the standard transmission, only the amplitude of the individual frequencies then change. Since this amplitude variation can be balanced'by fading regulation, it is possible to practically eliminate the influencefof the carrier wave fading. in order to bring to practical reali-V cation the basic idea of the invention, use could be rnade in place of a fundamental frequency and its first upper harmonic' also of a fundamental frequency and several harmonics, or only ofthe latter alone. It may even be advantageous to employ only frequencies having somehow or other positive relationship with a fundamental frequency andto differentiate signal current and spacing current by variation of the fundamental frequency.

According to Fig. 2 there is arranged at the sending side (left) a generator G which produces with opened contact of thel sending relay Si?,l 1280 l-lertz and with closed contact 1000 Hertz by the addition of a capacityC. Letthe last-.named freu quency. correspond to the signal current. The harmonics ofV the said fundamental frequency are produced by distortion in a strongly biased discharge tube VZ. The net system N serves to filter out the fundamental frequency and the first harmonic and torequalize or make even the amplitudes of both frequencies. The frequencies are then amplified in an amplifier V andmodulated onto the carrier frequency (fr in Fig. l) in the modulator M. The carrier frequency is a'nplified in the emitting amplierS and radif ated from the transmitting antenna SA.

At the receiving end the carrier frequency'is received by the receiving antenna EA and demodulated in receiver E. Connected to receiver E is a coarse regulator RG. The produced inodulation frequencies which correspond to the froquencies produced at the sending end by generator G- or disto-rter VZ respectively are'then filtered through four band filters. The outlets of the band filter for 1000 and 2000 Hertz lead to a branch V1 of the adjusting amplifier RV, the outlets of the filters for i200 and 2460 Hertz to a branch V The adjusting amplifier has three stages or steps of which the last is arranged as rectifier. at Vthe outlet of the rectifier step is disposed the receiving relay ER in differential cir cuit arrangement in such manner that interfer-- ence amplitudes arriving simultaneously in the signal and spacing current channel do not bring the relay to response.

The two adjusting amplifiers low frequency channels V1, V2 are presuniedto 'have such a relationship to each other that the regulator V2 disposed in the spacing channelis entra-ined by regulator and operates in the disposed in the sarne` sense vwhen the latter responds and vice versa. This coupling has the following purpose: If it is desired that all distortions which the signal undergoes during transmission should be compensated to the most possible degree, the duration of adjustment of each regulator must not exceed the duration of an elementary signal even for the maximum occurring level variations.

. If the regulators were independent of each other,

the result would be that the regulator disposed in the non-'used channel at that particular moment would respond, bringing the distortion level, alone present in its inlet, to the theoretical value proscribed for the signal. In this manner, theI distance between used level (in the used channel) and distortion level (in the unused channel) would be-,so much shorter as toA interfere with a reliable Working of the differential relay. In accordance with the invention the regulator clisposed in the usedy cl'rannnell shifts with the response at the saine time as the grid biasing potential of the regulator in the unused channel to such a degree that the latter cannot be made to respond at all from the Adistortion level alone. This locking is only released when the useful amplitude drops in the first regulator and when it jumps over the second channel Whose regulator now again locks the first. The regulation of the total fading is done by both regulators jointly and the one .of the selective fading by the regulators individually, both regulators being approximately at the saine level during the transmission, only the additional fine regulation taking place individually in each channel.

The .arrangement of a coarse regulator RG further accomplishes that the total level which is fed to the band filters Bf, has already experienced a certain regulation. Such a'coarse regulation assures a smaller regulation range of the regulators disposed in the branch channels, considerably smaller than in the case where the Vernier regulators had to take up the entire regulating task. The necessary input can therefore be kept in closer limits. lt is not essential whether the coarse regulator is arranged before or behind the demodulator and care inust only be taken regarding its dirnensioning that jumpy variations of the arriving held intensity are regulated during time period which is. srnall ccrnpared to the time period of an elementary signal.

The band filters Bf must be diinensioned so that the alternating currents fed to the regulation amplifiers V1, V2 are already sharply ltered out. The action of additional interference impulses with respect of regulation amplifiers V1, V2 is greatly lessened by means of such an arrangement. Y

Fig. 3 shows an exemplified embodiment of the regulating amplifier sets VI V2 being coupled with each other. The amplifier V! comprises the two series-connected amplifier tubes RVi, RVZ and the rectifier tube Gl; and the amplifier V 2 similarly comprises the tubes RVi', RVZ and Gi. The outputs of the band-pass filters B'l, designed for l000'and 2000 cps (corresponding to signal current), are united by Way of the input transformers U1 with the grid circuit of tube RVi, and the band-pass filters Effi, designed for the frequencies 1200 and 2400 cps, are irnilarly associated by Way of the transformer U1 with the grid of the tub-e RVi. In the grid circuit of each of the'two tif-.bes is .includn ed a capacity resistance circuit scheine CI, Rl, and CI', Ri', respectively, by which, upon the arising of grid current, there is occasioned a displacement voltage as a function of the amplitude or strength of the incoming current impulses. For instance, as soon as a signal current comes in, that is to say, as soon as currents flow through the band-pass lters Bfl, Bf2, there flows also a grid current in the tube RVI which causes a fall of potential across the resistance RI such that the tube becomes negatively biased. In other words, the Working point is shifted towards the lower knee. The stronger the currents flowing through Bfl, Bf2, the more will the Working point of the tube RV! beshifted downwardsand the lower will become the gain of the tube RVI. However, inasmuch as the amplitude of the grid voltage will grow at the sametime, conditions may be so made that,`if a state of proper balance or adaptationis created, the amplitude by and large will vbe fairly stabilized at the output end of the tube RVH. VThe output of the latter tube is in inductive coupling relationship with the amplifier tube RV2, While the output circuit of thislast-named tube, in turn, is inductively coupled with the rectier tube GI. In the grid circuits of the tubes RVZ and Gi are included the same stabilizing arrangements as in the grid circuit of the tube RVi, i. e., C2, R2, and C3,'R3, respectively. As a result of this cascade arrange; nient of the regulator means, the sensitiveness `of the regulatory action or the degree of constancy of the output amplitude, is enhanced toV an extraordinary extent. The same thing holds good for the tubes RV! RV2, Gl 'Y of the ampliiier end V2. In fact, the grid circuits thereof contain corresponding regulatingk means denoted by CI',

Rl', and C2', R2', and C3', R3.

The grid circuits of the tubes RVI, RVi', and RV2, RVE', respectivelyV are, in addition, coupled leach by a resistance WI and AW2, respectively, with the result. that the regulation of the tubes RVi,

RVi', and RV2, RVZ is rendered independent of each other. This independence consists in that whenever an impulse current iiows through one end Vi or V2, the'respective other branch or end V2 or Vl, as the case may be, is blocked for the passage of an impulse'. For instance, if current iiows through the band-pass filters Bfl, Bf, the grid current above referred to also causes, by way of Rl, a fall of potential across WI, and this occasions, at the grid of tube RVi a negative biasing voltage so that by interference or stray currents liable to reach the grid of the tube RVi by way of the bandpass lters Bf, Bf4, prac-Y tically no current will be caused to iiow inthe plate circuit of the tube BVI. A choke capacity arrangement DI, Kl, and D! KI is arranged'in parallel relation to the resistanceWl.l The capacities Kl, Ki' serve the purpose of short-circuiting the resistance W l for the currents coming from the band-pass filters in order that thecurrents operative at the grid of one of the'tubes RVI or RV! by way of the coupling through resistance W may not, at the same time, be able to reach the grid of the respective other tube RVI or RVi This short-circuiting action is increased and'promoted by the aid of the choke-coils Dl, Di these latter being so dimensioned (voltage division) that, of the voltagearising across the terminals of the capacities Kl and Kl only a small portion will be able to become active across the resistance I Wi. The same thing holds true of the tubes RV2, RVZ (V72, D2, K2, and W2", D2', KZ).

The choke capacity schemesV AI, Cl I, and A2, C22,^and AI', CI', and A2', C22', respectively,

serve, as known from the prior art, for the purpose of precluding the plate alternating current from the plate supply battery and of preventing coupling of the tubes with one another by way of the plate supply. The grid voltage of the rectiized by a circuit arrangement as hereinbefore disclosed is that, as long as one of the amplier branches or ends is traversed by an impulse, the respective other amplier branch is non-transmissive. To be sure, this inter-dependence is obtainable also by thevuse of other suitable Ways and means, say by the coupling Vthrough resistancesWl, W2, etc., or by coupling through suitable tube arrangements. It is also feasible that instead of filter schemes DI, Kl, etc., multi-mesh chains or networks aroused. The time constants of the regulator circuits Ci, Rl ,and Ci Rl may'V moreover bedetermined and iixed independently vof the time constants of the' coupling means WL DI, KI, DI', Kl.

I claim.

f 1. In a radiortelegraph system, the method of eliminating interference in communication which comprises modulating a high frequency carrier frequency by an audio frequencyvcurrent and its rst harmonic during a signalling period, modulating the same carrier by a different audio fre-- quency current and its first harmonic during the spacing period, radiating Vthe resultant energy,

receiving the energy and selectivelyseparating out the two Vaudio frequencies and their respectivefi-l'rst harmonics, passing one audio frequency f current and its first harmonic through one path and vthe other audio frequency current and its .first harmonic through another path, and differ-v entially recording the passage of Asaid energy through said two paths. n

2. A telegraph system comprising, in combination, a signal relay having two positions of operation, an oscillation generator responsive to one position of said relay toA generate one fre-v quency and to the other position of said relay to generate -anotherrfrequency a'distorting device in circuit with the output-of said generator producing a harmonic of bo-th said frequencies, a filter connected to said distorting device for eni abling the passage therethrough of said two frequencies and their harmonics, van amplifier for amplifying said two frequencies and their harmonics, means for modulating a carrier wave by said two frequencies and their harmonics and forv transmitting same, a receiver having filters for separately ltering out and passing said two frequencies and their respective harmonics, a differential relay having two windings, means for applying one of said filtered frequencies andits Y harmonic to one of said windings and the other frequency and its harmonic to the other winding,

whereby interfering currents received by said receiver affect both windings of said relay equally l and in opposite sense. Y JOSEPH SEDLMAYER.

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