US1874866A - Method and means for eliminating fading on short wave lengths - Google Patents

Description

Aug. 30, 1932. H. H. BEVERAGE ET AL METHOD AND MEANS FOR ELIMINATING FADING 0N SHORT WAVE LENGTHS Filed March 15, 1928 z/M/rrk- Mow/Mme INVENTORS H H BEVERAGE BY PE RSO" flc/acu A ORNEY Patented Aug. 30, 1932 UNITED sr 'ri-is HAROLDH. BE ER GE AND HARO D PETERSON, ornrvnnmmn; .ivnw Yonm-Asj smnons'ro RADIOCORPORATION OF'AMERIGA, a CORPORATION or DELAWARE mn'rnon AND MEANS FOR ELIMmA'riNe minute on SHORT WAVE Lmre'r s I.

1 Application filed man 15,- 1928. serial-no- 261,736.

':,The invention relates to what is commonly known as fading in radio and wireless signalling and a method and means for eliminating the detrimental effects thereof. The r, invention particularly adapts itself to the any appropriate and desired type of short wave radio signalling apparatus and lends itself especially to use in locations where the 10 effects of fading and troublesome. p

Various theories have frequently been suggested for explanations of the phenomenon f known as fading, but it is believed thatto date no thoroughly proven theory has been developed. However, certain evidences and phenomena in connection with lfading have been discovered in practical observation f which have brought out the factthat short. wave signals fade difierently at? points separated by short distances and that the phase relation between signal voltagesat; these points has been found to be reversed several times per minute, --In accordance with these observations, it hasbeen found that signals have different fading characteristics when picked, up on antennae located atv different. points or upon antennaelocated at the same.

point, where the antennae each have difi'erent '30 directive characteristics. If two antennw are been found that the phase relation between v10100 ft. away, does not remainconstant, from moment to moment. Therefore-if it is tried to combine a radio frequencyvoltage from are praticularly prevalent relationships atthe several antennae, and;

.connection with the QWl1QIG1I113-i Fig. 1 .jillustra-tesa: preferred means for combining the rectified signals from aplu instant may be of minimumintensity upon up upon the several antennasystems 1n ques-;

tion, to some common receiver and add the,- energies directly together at this point, but a this cannot be done efficiently because it has I the signal voltage received at one antenna and that received at another 1 antenna,- say two or more antenna systems located. at:

points several wavelengths apart, it will be found that these voltages would add at one instant and subtract at another instant due to the fact that the radiofrequency voltages at the two antennaewill not hold a V recelving of short waves as transm tted from definitefphase relationship with respect to each other. However, where the receiver is rapidly swltched from one antenna system to anotheras disclosedin our copending' applicationslSerial Nos. 2 61, 757v filed March 15, 1928, and 274,374, filed May2, 1928, efficient results areobtainable,but this is not a direct combining action 4 i 1 The important principles to be followed'in the multi antennae anti-fading ,Qmethods,-, which forms a principal object of this invention, is to combine the signals fromtheplu rality of antennae insuch a way. that the energies will add irrespective'ofthephase combine in such aimanner that a signalinay r be heard or'recorded in a suitable recordlng deviceto produce a signal which "is substanfading on any of the several antennae. The above and other objects form the purpose of this. invention which will be more thoroughly understood. by making reference ltially free from the detrimental effectsjof to the following specification when readin accompanying drawing,

rality ofg'spaced antennae. U:

Fig. 2indicates a system similar tothat;

shown in F ig. 1 wherein two antennaeiof different directive characteristics, which correspond to the spaced antennaeof Fig. 1,arelocated ata common point and the energy from'the combined output is directed to a limiter and modulator' device for thepurpose of obtaining atone signal; and, w

Fig. 3 illustrates; results which may be accomplished by the eifortsand arrangement functioning in accordance with the apparatus diagrammatically illustrated ingFigsl and 2. The Q subject matter of this application forms a continuation in part of oumop nding application filed January 2, 1926, Serial i as frequency energy reaching antennae 1 and 3 .is transferred to radio frequency transformers, or any other preferred formiof cou-Y plings', 9 and 11 and carried through lead circuits 13 and 15 respectively I to; receiving devices generally shown as 17 and 19 for each of said separated antennae member's; I The re- 1 ceivers 1'7 and 19 may each employ a common oscillator as shown by Fig. .3 of Serial #7 8,7 68, above referred to, or each receiver 3 17 and 19 may be provided with an independ ent oscillator, or the energy received upon antennae 1 and 3 may be detected in the receiver 17 and 19 in the usual manner'without the need of oscillator.

The output 'of The energy from the amplifiers :21 and 23' is directed to the primary'windings 29 and- '31 of the transformers 25 and 27, from which 7 it is transferred to the secondaries 33 and-'35 and directed to the rectifiers 37 and 39, which "each may be biased by a common potential j source 19." If desired, the filaments 43 and i 45 may be connected in parallel and" ener-' gi'zed from'a singlefilament battery desi g f nated' l7. Y V In'series with the common bias potential suipply 19 for the pl'atemembers' of the rec to rectified energy pulses and, therefore; does not difierentiate' between the phase 'reers 37 and 39 is a recording device, geni of the 'drawing,'we have illustrated the'form erally designated 41, which only responds lation of the radiosignal input upon the two ' receivers 17 and 19. It is, therefore; seen that the recorder 41 responds; only tothe I. energy andthe matter of phaseflrelationship of the signals reaching the antennae 1' and 3i is immaterial and has no effect upon there sults produced in the recorder 41. I

.As above describedfor producing a rew cording action in 11 it is assumed that the L I switches indicated as 51 and 53 in the plate circuits of thetubes 37 and 39:respectivelyi are closed. .However,-for the purpose of determining the separate energy reaching eachof the recelving ClICLlltSflIlClUdlIlg the tubes 37 and 39 we have provided a means for in-,

dicating this energy by the separate recorders designated asRl and R2. In a case where this energyis desired the switches designated as 51 and 53 may be" opened "and the switches 55 a nd 57 closed, so that an energy response from each of the signals may be recorded in the recorders Bland R2. 7 This switching only resorted to'for eXperi-.

the receivers 17 and 1'9is amplified in any preferred manner by the use of amplifiers generally designated 21 and mental purposes and for the purpose of determining the separate energy'received.

By Figure 3 of the drawing we have shown the result which may be expected by receiving signals on each ofthe separated antennae' members-and represents a P01131011 of typicalsignal which might be received. by placing the recorder R1 or R2 in series with the platesof tubes 37 and 39... To specifical- .lyrefe r'to the part ofEig'Q 3,1l ettered'asfA,

it-will be noted that'the part (Pof the on receiver 17 and recorder R13" but' at'a "different time interval d1 had completely faded out in the recorder R2 associated with the antenna system 3. However, the portion Cof the tape illustratedby Fig. 3 shows the combined signals received from the two antenna systems land 3' in the recorder 11;

and it will be noted that by combining the energy pulses which are totally independent of the phase of the signals reaching the antenna systems 1 and 3thata signal has been recorded which is'accur'ateand that allpor tions'of the same are clearly legible with'the effects of fading' 'on either of the antenna numbers 1 or 3 substantially eliminated. Thesetapes shown byffFig. '3 illustrate the results, which have actually been 'found in practice and are drawn from actualrecords which .have been madein practice using the 'ahovedescrib'ed arrangement.

To "now make; specific reference to 2 located at the same point,and', as shown, 101

represents a vertical doubletand 103a horizont al doublet'both located at the 'samere ceiving point; and whose respective charac-.

teristics vary due; to-their directive characteristics. "Energy from the vertical doublet 101 is directed to aradio frequency amplifier 105, which has not been shown in connection with 'Fig. 1' although it is to be understood that such amplifier may be added and used if desired. Fromthe amplifier 105-the energy is directed to a receiver 109 wherethe; incoming signals are detected andamplified through an audio frequency amplifier 113' and transferred through the primary winding 1210f a transformer'conne'cted withthe audio frequency amplifier to: the secondary feeding its energyfinto the rectifying tube 129. 'Sirhilarl-y, the energy received on "thehoriziontal doublet103 is fed to the radio frequency 'ainplifierQlO'Z to the receiver 111 and then tlirtjnigh the audio frequency plifier which transfers its output energy to .passed to the rectifying'tube 131.

winding 123 of the transformer 119, Where the energy is then transferredto the secondary 127 of the transformer .119 and The rectifying tubes 129 and 131 are shown as the-single filament, double plate type, but

two single'plate rectifiers may'beused with 1 equivalent results. Byfusing full wave rectification, the pulsations of direct current are more uniform, and theripple' frequency :is double the audio input frequency, both'of 'which effects make it easier to produce a pure direct current in the rectifier output. It is desirable to substantially eliminate the ripple in the rectified current, since strong ripples tend tofvib'rate the recorder pen, and

v also beat reactions between theripples'may produce undesirable variations when theoutputs o f'a plurality of rectifiers arecombined.

The ripples maybe eliminated by using condensers such as are commonly usedacross recorder coils. However, for high speed operation, these condensers'tend to reduce the signaling speed, and it would be preferable to use low pass filters. These filters should readily passthe low'frequenc'y corresponding to the keying pulses, but should not pass the relativelyhigh ripple frequency.

In Figure 2, the low pass filters 139 are j shown as a conventional arrangementof series inductanceand shuntcapacitance ele- 'men'ts. After the rectified current has passed through filter 139, a substantially pure 1distantially identical to that of Fig. 1' with the exception of the fact that instead of using the spaced antennae 1- and 3 of Fig. 1 we have 7 R and R of Fig.1 be connected in series,

chosento illustrate antennae 101 and 103 of I different directional characteristics located;

at the same point. If a recorder such as with the circuit atpoints 189 and 1910f Fig. 2, the results and the records obtainable will be substantially the same as are illustrated by the records A and B of'Figl3 above I described. The combinedrecord C ofFig. 3 would be obtained if a recorder were substitute'd in place of resistance 135.

'In Figure 2, we have chosen to show a modification which maybe used for obtain ing a tone signal afterjthe rectifiedcurrents have been combined, andwhich will also pro duce a certain amount of limiting action which is desirable, sinceitreduces the effects of small variations in the combined rectified currents. The arrangement which is enclosed within the dotted line rectangle is the limiter and "modulator arrangement used for the *purpas'e 6i] teaming a tone's'ignal in the tone circuit 17 5 to. bevhereinafter described.

The ungrounded'end of resistance is connected through a bias battery 141 to'fthe grid member 147 o'fthe triode 14-3. The triode 143 has its energy andhigh potential-supply the filamenfimember 149, which is; grounded at 155.; The -grid-member 147 of the til-be 143 is normallyso biased by battery 141 that plate current willflow under conditions when no signal 'is being received. this case,

plate current flows thru' the plate*',-the:

filament 149, the batteryv151 and the resistrO-r the plate 145furnished through a'battery 151 connected in series with a resistance 153. The plate circuit is completed through ance-153. However, wh'en's'ignals-are being 7 received upon the antennae 101' and 1O3 -ajnd directed from the "points 189 and 191 of*the 'rectifiers 129 and'131,' to the .p0int1133, due:

to the voltage drop occurring across-the resistance 135, the point 133- becomes negative with respect to its previous potential, and therefore the normal bias on the grid 147 of the tube 143 is-overcome. It is'to be under stood thatthe cut-oft potential of thetube 143 depends upon both the voltage andpolarity ofthe bias battery 141, and the characterifstics of the tube 143. It is also to beseen that when where resistance 153 forms a connection with the plate 145 of the tube143 and the bias battery 157 for the grid 163' ofithe tube..1"59

that this grid 163 becomes negative; due to the voltage drop occurring across resistance 7 the tube '143'is passing plate current that the point" 153. In this case, with no signal :on, the grid i 163 of the tube 159, is carried to .cutoffpotential and the tube 159 fails-to pass Eplate" current. However, when the -'plate-current flow through thetube 1143' is cut. ofl'due to signals being received upon the antenna members .101 and 103 and the point 133. ofthe resistance 135 becoming negative, r the bias battery. 15? carries the. grid member 163 of the. tube 159 to, a'less negative valueland the tube 159 at once starts to passaplate current, through'the plate member 161, the filament 165, the ground return 167 v and 179 and the plate potential supply 17 7; Connected to the lead with the plate supply source17'lthrough a transformer 181* is an-audio sfrequencyos- -cillator- 187 which feeds its energy into the primary 183 of the transformer- 181 from which the-energyis transferred to the sec- I ondary 185. Also connected-in theplate lead 161 is a transformer 169having its primary winding 171 forming a part i of the plate circuit and secondary 173 transferring 'energy to a tone circuit 175. It isthus seen'that the frequency of the audio oscillato'r 187 is heard in the tone circuit 17 5 during periods when the tube -159 is passing 'platecurrent, or in other words, at periods when signalsare 55 dlrective cha-racter1st1cs, or combinations of being: f p n either of the antenna members r'103; a c

It may thus 'belnoted that thejfunctioning the limitingand modulating arrangement illustrated inthe dotted line rectangle asa partof 'Fig. 2 is determined by the fact of [how negative thepoint183 becomes and how this' eifects the grid 147 of the. tube 143, since it is this characteristic which determines Ewhether or not the tube 143 passes plate current, .and likewise the size of the resistance 153 and the battery .157 which it will be noted 2 should be of a size approximately the same as the battery 151-determines whether or not .the .itube l 59 passes plate current. It will also'be noted that if the limiter is adjusted so that the minimum'signalwill make the point 183 sufiiciently, negative to a reduce the plate current of tube-1l8 to .zero, a further increase in signal will haveno eifect on the 7 tone output of transformer169. Hence, if 1 the combined rectifier currents vary over moderate limits, when proper adjustments 1 are made these variations will not be repeated throughto tube 159 which controls the tone output.

With further reference to Fig. 2, if the radio frequency amplifiers 105 and 107. are capable of delivering considerable energy, it. -is not necessary to convertthe signal to lower frequency, as the output of the radio fre- .-quency amplifiers mayberectified directly :by rectifiers 129 and 1 stages of radio frequency amplification with 131. By using several several tuned circuits, a highdegree of selec tivity may be obtained. Such an arrangementwould make it easy to filter the rectifierv outputs, and this would make it particularly quency.

" desirable for very high speed circuits, where the keying frequency may be several hundred cycles. It would also be desirable in somecases-to convert the signalto an intermediate radio frequency instead of an audio frei This may be accomplished by substituting intermediate frequency amplifiers in place of the audio frequencyamplifiers 113 "and 115. ;'The fundamental operation would be substantially'the .same as that described 6 in connection with Fig. 2.

While only two receivers 5 by Figs. -1 and 2,itis to beunder'stood that anynumber of receivers be used, using combinations of spaced antennae of the same type, combinations of antenna withdiiferent Y v both spaced and directive antennae. It has been determined"experimentally that a par ticularly desirable combination of spaced antennaefor short waves,'for example 15gt o 30 meters, isto use three antennaeof the same directivej characteristics spaced about 1,000

feetapart.

v Itwill be clear thatvarious modificationsv ofthearrangementdescribed and illustrated V have been shown.

by Figs. 1 and-2 and the description thereof maybe made insofar as they fall fairlywith-' in the scope of'the invention as defined by the following claims. j

Havingthus described our invention, what weclaimis;", V i 1. The method of avoiding theefi'ects' of fading on radio signals which includes, re ceiving the samesignal at a pluralityof separated points, separately rectifying the signal so received to produce current pulses of :less than the received radio frequency, commeans for combining the outputs of said r'ectifiers, said means including .aiesi'stangie in the combining circuit, a limiting device, means for controlling the operation of said limiting device by the resistance drop occurring in saidresistance' when signals are received, a modulator, a tone circuit,and means provided by said limiting device for limiting the iresponse of saidomodulator in said tone circuit to a substantially constant value irre-v 1 'spective of moderate intensity variations.

when signals are being received upon said antenna members and the comblned rect fied signals produce, a resistancedrop across said vresistance equal to orgreater'than the lilmiting value of saidlimitingdevice. V j

. 3. In combination, in asystem for reducing fading, aplurality of separated energy collectors, means for reducing thefrequency'of energy collected on said collectors, means for combining the energies of reduced frequency, an impedance, means for applying the com- 'bined energies to said impedance whereby voltage variationsarise across said impedance in accordance'with the combined energies passed therethrough, an electron discharge device having an anode a cathode anda con- .trol electrode, a source of undulatory-electromotive force coupled to the anode circuit of said electron discharge device, an output circuit' coupled to said anode circuit, andmeans for coupling said. impedance to the control "electrode of said electron discharge device whereby current,.corresponding in frequency to thealternating 'electromotive force generated flows'in said output circuit in accordance withthe potential applied to-said control electrode from said impedance.

4. In a systemof thecha-racter described,- anenergy collector for collecting modulated high frequency electrical waves, means for obtaining currents corresponding to the modulation of said waves, a resistance, means for passing said modulation currents through said resistance whereby potentials arise there across corresponding in value to the currents applied, an electron discharge device having an anode circuit and an output circuit coupled to said anode circuit, a local generator of alternating current coupled to said anode circuit, and means coupling said resistance and said electron discharge device whereby the internal impedance of said electron discharge device is varied in accordance with the voltage variations across said resistance, whereby alternating current from said local source flows in said output circuit in varying degree as the conductivity of said electron discharge device is varied. HAROLD H. BEVERAGE.

HAROLD O. PETERSON.

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