US2381181A - Radio transmitter - Google Patents

Description

Aug. 7, 1945. v T, H. PRICE RADIO TRANSMITTER Filed April 5, 1943 4 Sheets-Sheet l INVENTUR. 771 omas Henry pjica Ix A A TTORNEYS.

T. H. PRICE RADIO TRANSMITTER Filed April 5, 1945 4 Sheets-Sheet 2' 1 INVENTOR.

Thomas Henry Price ATTORNEYS. 1

Aug. 7, 1945., T. H. PRICE 2,381,181

RADIO TRANSMITTER Filed April 5, 1943 4 Sheets-Sheet 5 k. t I 3 INVENTOR- Thomas Henry Price A TTORNEYS.

Aug-7,1945 T. H; PRICE 2,331,131-

RADIO TRANSMITTER 7 Filed April 5, 1943 4 Sheets-Sheet 4 I y zmaiwpixig pm-w ATTORNEYS.

,of a highmerformance transmitter.

Patented Aug. 7, 1945 RADIO TRANSMITTER Thomas Henry Price, Chelmsford, England, as-

signorto Radio Corporation of corporation of Delaware Application April 5, 1943, Serial No. 481,822-

In Great 16 Claims.

The present invention relates to radio transmitters, and aims at improving such transmitters towards the production of a simple transmitter capable of passing to a power-absorbing device, such'as an aerial, a completely modulated; wave the transmitter being desired-to have the maximum possible efliciency of conversion of supplied'power to output power, and being desired also to satisfy other various requirements Such an aim is, of course, that which many workers in the field of radio-engineering have hadbefore them, and many types of radio-transmitter have been produced achieving, to a greater or less degree, this aim, or at any rate, satis- Britain January 16,194;

fying some of the demands to'be made upon a perfect radio-transmitter.

Fig. 1 is a vector diagram used to explain the nature of my invention. Fig. 2 is a basic diagram of two generators supplyi voltages to a common load.

' Fig. 3 is a simplified diagram of two generatorsarranged in accordance with my invention to supply power to a common load.

Fig. 41s a vector diagram illustrating the operation of the generators of Fig. 3.

Fig. 5 shows by curves the relation between current in the load and the phase relation of the currents flowing toward the load; the ratio of total output power to total input power, etc. Fig. 6 illustrates by simplified diagram a circuit arranged in accordance with my invention.

Fig. 7 is a vector diagram illustrating the operation of the system.

Fig. 8 is a modification of the arrangements of Fig. 6.

Fig. 9 is a vector diagram illustrating operating characteristics for 100% modulation on the negative haliicycles of the modulation.

Fig. 10 is a modification arranged for operaltion asillustrated by the vector diagram of Fig. -9.

Fig. 11 illustrates somewhat completely a phase swing transmitter arranged in accordance with my invention. A Fig. 12 is a vector diagram illustrating the operation of the arrangement'oi Fig 11; and a Fig. 13 is a vector diagram used to illustrate the operation of the arrangement 01 Fig. 1.

Fig. 14 is a modification of the arrangement of Fig. 11.

In the present state. of the art of radio-transmission, thermionic valves have to be used and.

the best-efllciency of conversion that can be obtained is that in which the valves are operated in their class C" mode of operation.

In carrying out they present invention, two valves (or two groups of valves) each valve (or all the valves of each group) operating in its (or their) class C mode of operation, are employed and a. power-absorbing device, for example an aerial, is suitablycoupled between the two valves (or groups ofvalves). Oscillatory energy is applied to the two valves (or groups of valves) and the relative phase positions of the oscillations applied to the two valves (or groups of valves) are so qperated upon during modulation as to produce a variation of the output power, such variation according with the modulation signals applied to the radio-transmitter.

Such a transmitter may be, and hereinafter will be, referred to as a; phase-swing transmitter.

Hereinafter; for greater simplicity or language, the phrase two valves, or groups of valves, will be avoided and the phrase two valve-stages will generally be used alone to indicate the same idea. This is to be understood not to imply a limitation.

According to the invention, each of two valvestages of a. phase-swing transmitter is coupled to a power-absorbmg device, for example an aerial, by a quarter-wave impedance-inverting network or device.

- linearity In considering the matter of connecting or coupling two valves to a power-absorbing device so'as to produce a phase-swing transmitter, it is found, that it is not possible merely to connect or couple the two valves to the power-absorbing device, and, at the same time, to retain high efilciency and to provide for the necessary linearity of output with respect to modulation signal at the input, because power input to the power absorbing device cannot be in phase with the voltages generated by both of the two valves.

-The vector diagram constituting Figure 1 of the drawings illustrates how thisv comes about. The two vectors 0A and OB represent the voltages generated by two alternating current generators (A-and B, respectively of Figure 2) having a phase difference represented by a. The resultant voltage is represented by A, B and this is the eflective voltage across a resistive load R connected from one generator to the other. Current in such a load would be in phase with AB and, therefore, out of phase with both 0A and OB. In practice, owing to the dependency of the resistance-current upon 0, small values of 0 would have to be employed in order to obtain of resistance-current for difierent values of 0. This in its turn would cause a still greater phasedifl'erence between the power component of current and the voltage vectors. This effect could no doubt be compensated for by the use of suitable shunt reactances across the generators, but this solution would introduce the difficulty that as is made to disappear a considerable component of reactance-current would be drawn from the generators. valve generators this would be particularly objectionable in that the efllciency would be low. Therefore, a circuit is required with which the power component of current is held closely inphase with the generator voltages throughout the cycle of changes of relatively phase of these voltages.

. An embodiment of the invention is illustrated in Figure 3 of the drawings. In this figure, A and Bare two similar valves to the grids of which in operation high or radio-frequency oscillatory energy is applied in antiphase. The anode circuit of each of these valves includes a tuned circuit, respectively TA and TB, these two circuits being similar, the one to the other. Each tuned circuit is coupled to the power-absorbing device, represented by the resistor R, by means of a quarter-wave impedance invertor,'illustrated, respectively, as networks NA and NB. The two valves A and B operate in their class 0 mode and deliver closely similar voltages which, since they are in antiphase, and since the two impedance inverters are similar, produce zero voltage across points P and E when both tuned circuits are tuned to resistive condition for the valves.

The vector diagram constituting Figure 4 of the drawings illustrates the operation of the below.) Since one of the properties of a quarterwave network is to cause the current flowing out of one end to be out of phase to the extent of 90 with the voltage applied at the other end, the current having a constant amplitude for a constant applied voltage, the voltages across the inputs of the networks, represented respectively by vectors OJ and OH, are 90 behind the currents represented respectively by vectors OA and OB. (Here it may be observed, that whether OJ and OH shall lag behind or lead OA and OB, will In the case of Vectors 0A" and OB" respectively represent the currents flowing towards point P of Figure 3 from networks NA and NE at the instant of peak negative modulation. In this condition the voltage across and current in resistor R is zero. For this instant the voltages across the inputs of the networks are OJ" and OH" and are shifted in phase in opposite senses from their initial positions. away from each other, under the influence of modulation signals applied to the grids of valves A and B. The voltage OJ". across the input of network NA is in phase with the voltage OK" across the series arm of network NA, and the depend upon the kind of quarter-wave network condition being represented by the vector OC" which represents the voltage across and current in resistor R, and which is twice the length of vector 00, For this instant the voltages across the inputs of the networks are OJ and OHNandare shifted in phase in opposite senses from their initial positions towards each other under the influence of modulation signals applied to the grids of valves A and B. The voltage across the series limbs are now OK and CL.

Figure 5 of the drawings shows three curves 0, 631 and e2, 0 and e1 relating to the arrangement of Figure 3. All three of the curves assume negligible loss in the circuits.

Curve 0 connects the angle 0, which is the phase difference between the vectors of the oscillatory voltages at the anodes of the two valves, with output current 0 flowing in the power absorbing device R. The angle 0 is assumed for the preparation of the curves to be varied from Curve 0 shows that there are linear relationships between 0 and O, for high, and for low, values of 0 and a non-linear relationship about the middle of the curve. Also it shows that O is a maximum when 0 is zero and is zero when Since systems of modulation used in the faithful transmission of speech and music require, that in the unmodulated condition there should be a given level of carrier power, that this should be reduced to zero for the trough of the modulating signal, and that it should be increased to four times that corresponding to the unmodulated condition for the peak of the modulating signal, and since such systems also require that the change in the level of output current should correspond substantially linearly with the change in modulating signal, the usable portion of the curve 0 is determined, and an angle 0. for the unmodulated condition, of approximately is chosen.

Curve (21 connects the ratio of total output power to total anode input power with the angle 0 and shows the efliciencies E of the system of Fi ure 3 at different values of 0. This curve has two peaks, one at an angle 0 near to anti-phase, and one at a zero angle 0. The variation in emciency is due to the departure from a unity power factor for changes in the angle 0.

It is clearly desirable that the greatest efficiency' should be found in the region of the usable portion of the curve 0, and that the efljlciency should vary as little'as possible during the cycle of change in phase, that is along the lower linear part of curve 0.

Figure 6 illustrates a circuit arrangement wherein the desired conditions are met. In this figure, the. tuned circuits are representedat TA and TB as before, and the two impedance inscription, series capacitors and shunt inductors are assumed; they might be series inductors and shunt capacitors. The last statement generalised then becomes the shunt-reactorsof the two towards the pointP of Figure 3 from the two networks .NA- and NB,- it is apparent that these two vectors represent resultants which-can be resblvedinto their two'compon ents in quadrature as' represented in Figure "7 where the resultants are named IA and IB and the compo nents of: eitherare-representedby IX and I with the appropriate subscript. VectorF represents thecurrent flowing in resistance (Figure 3); due ,to the appropriate .valve A or B,

and IX represents the reactive-current neces- 1 ara ii be su w provide the resultant. This resolution 7 shows that 'to satisfy the ,conditionithatthesum of the currents, flowing to point P. be zero, each .of the v valve, amplifiers with its associated'network and its portion of the terminatingzresistance R, is to be'regarded having an .additional reactance for its termin-ation.. ,The, .reactance for each cults, and may quite. conveniently be carriedout on either the capacity or inductance limbs. Gauging the two chosen variables to produce the required differential effect is one easy way of achieving the object, provided that the action of .controlling produces equal and opposit changes in the reactors concerned. v I If care has been taken in the choice of components and constants of the circuits, power will now appear in the load resistor Rof the frequencyiof that applied to the grids of the two valves at an emciency ratio of output-power/to: tal-anode power very'little different from that whichwould obtain in thesimplest possible ar-. rangernent of .va1ves and circuits. If the valves bepdriven in Class 0'? condition the efficiency willbe veryclosely. that generally obtained in class ,fC operation, thatis about 70%. The amount by whlch the efllciency departs from that for optimum class C operation will depend on the losses which occur in the circuits. These can easily bekeptrelatively low, particularly in cases of .-high-power;transmitter systems. The .eijficiency curve for thearrangement of Figure dis shown as ez in Figure 5. 7

- It has been mentioned that since one side of thephase swing system oscillates at a different phaseirom, that atwhich the other side oscillatea reacti n loads are reflected into the input ends ofthetwo networks NA and NB andthat 9 m ini au w ower-f o load o h w valves theassociated anode tuned circuits are differentially mistuned. This may be efiected by efiecting a differential change in the values of the apacitative, ,or inductive limbs, preferably,

how 'er, in the values 'of those reactors which arefopposite in type to the typeused as the series half. .of -.the system is represented. by theother half. Whereasthe terminating reactanceiis positive for. one .half, it is negative .for the. other. This effective conditionfor each side of the system is illustrated in Figure 8 where the reactive load of the one valvegenerator'and its network mination of'each networkisrepresented as 2R,.

whichis, of course,: equivalent. when .par'alleled toRa Now reverting to Figure-.6 it; is .cleanthat if the anode tuned circuits are in parallel resonance.-..and..their associated impedance inverting netwcrksare correctlydesigned, and are. terminated: witha combination of resistance andreactanca: .both. valve generators will .have a re-' active load-:condition, and an effectivemistuned state1will exist for both, but whereas. the one valve-has .a positive reactive load, the. .otherhas anegative-reactiveload. If symmetry of electric constants-for the two sides of the circuit has been-provided, an ef'fective resistive or ..un.ity'

power factor condition for the valves can v be-reof one anode tuned circuit andreducingthe re actan'celvalue of: the corresponding.:limb of. the other anode tuned circuit. This operationgmight be called. differential retuning of.v the .tank cir stored by increasing the reactancevalue of. a. limb elements of the networks NA or NB.

1 The exact amount of mistuning is'that which will give substantially class C" anode efficiency for. the Itwovalves of the system when the grid exciting voltages are 'dephased by the angle 0,

chosen as the operating angle and beingabout r 1 This mistuning operation for unity powerfactor for the unmodulated condition produces, for

any different: angle between relative phases of the drivin'g' voltages, such as occurs throughout the modulation cycle, a slightly reactive load condition for each valve, and this causes the phase 'of the actual anode voltage to lag slightly on the phase at the exciting voltage applied to the grid, thus necessitating an'increased degree of relativefchange in" phase'onthe grids than would otherwise be'required.

Ihis'state of reactive loadson'the anodes of the'valves during modulation requires, in order that modulation'for the negative half of modulatingmay -be possible, that the relative phasesofexcitations of the grids of the valves be'increased to somewhat more than into the other" quadrants of the vector diagram, Fig- Infthis Figure 9 0A and 0B represent the grid vectors *for the' two valves of the system in the carrier power setting, 0A and OB representing these vectors at the positive peak of modulation, and 0A and O representing the same vectors atthe negative peak of modulation.

-'-"-I'o=obtain -this mode of'operation of the grid exciting vectors, a valve and circuit assembly, usually called a carrier suppressor system, is used to energise the-grids-ofvalves A and B. Atypical arrangementofsuch a system is'given in Figure 1020f the drawings...

In Figure 10 valves Vl= and- VIreceiVe-on their grids I .antiphase radio-frequency signals" from a source not shown but represented at transformer RF;- f. constant amplitude. These radioefree quehcy or carrier signals are superimposedfon the fixed direct currentsgrid bias: voltage, applied as at DC, which is. son-chosen that-at the'anode voltage ."VAve'ry little anode current'occurs for either 'v'alveand the output power from Vhand V-Z i's zero until a' modulation signal isimpressed atMF. That is, the valves workefiectively in a class B" condit'icn They could beset up to work in theclass" A" condition also, whereiboth valves would be permitted to pass approximately equal anode currents in the "absence of" modula tionfThis-however would be an unnecessa'riHiis s'ipation of powerwhen the stage is u'nmodulatedl The modulation signalMF'is-"applied "to the grids of valves VI-and V2 in antiphase so'fthat that valve to the grid'of which a'posi'tive-halfl cycle of modulation-potential is-being-applied willact as a grid modulated amplifier, whilst the valve, to the gridof which the negative-half cycle of modulation potential is being simultane ously applied will be held in the cut off con'dition'in spite-of the signal-superimposed-on its anode due to the valve which, at the time, is acting as a grid-modulated amplifier. I-he roles .of-the two valves, of course, alternatel- The'circuit' of Figure will be recognised as that of-a carrier suppressor system but for the *pur? pose forwhich it is required' infthe' 'present invention, namely to remove the vectors QA and OB from exact phase-opposition in the-tin modulated condition some carrier 'i's-require'd'. This'requirement may be very simply-'met'by arranging that the DC bias voltagesfor the grids of the valves Viand V-Zjbe obtained from two potentiometers ganged so that operation? of the controlling means reduces the bias applied'to'the grid of one valve as much as the bias applied to the grid of the other is increased. I"

The differential biasing upsets the balance. of the carrier suppressor system, and if the initial working point on the characteristic -curves for these valves is suitably chosen almost perfectly linear change of I high frequency "output voltage against change of low frequency grid voltage is obtained'from the two' valves.

The "outputfr'om' the carrier suppressor system which in the conditions of operation above described consists of modulated radio-frequency energy with thecarrier notentirely suppressed inthe unniodulated conditionJs applied'in pushpush fashion to the grids of valves A and B of the power stage, together ,with. unmodulated radio-frequency energy the. unmodulated energy being applied in pushpull fashionand bein'gin' phase-quadrature with the modulated energy.'.

Figure 11 illustrates acomplete transmitter. In this, figure, 6 represents the'power stage and ill represents the carrier suppressor (as itmay continue-to be called), representsa modulation frequency amplifier of conventional-deslgn,.having its last stage constituted as a phase,

splitter including. potentiometers 20, and 2 4A Inthe amplifier shown feedback as disclosed in Fig. 4 of U. S. application Serial #429,144, filedFeb. 2, 1942, maybe used. Modulating energy is applied at nf and an output, MF, inphase opposition appears, in the leads-ME. :RA;represe nt s a radio-frequency'amplifler. of suitable: design to which radio-frequency energy is applied as at rj.

ass sts;

quencycarrier energy of smoothly controllable relativephase appears in leads RFI and RFZ.

, Amplified modulation frequency applied, over leadsMF, in phase opposition to the grids of val-ves-Vljand V2 inathe carrier suppressor system-10.; Radio-frequency energy is applied over leadREi and by way of transformer T2, in push-pull, to the grids of valves Vland V2. Direct current bias-potentials are applied. to these samegrids;by and are adjustable, differentially,,.- by means of potentiometer PT. Modulated radio frequency carrier appears in lead-MC." y. I

Modulated carrierfrom carrier suppressor system I ll .-is applied, over lead MC, betweenpoints A a do a r BR, hav n arms 11, q. Voltages; due to this-energy. appear as components of the resultant voltages applied to the grids of valves A and B in power stage 6, and are represented by the vector OM; in Figure 12 These voltages appear in phase on the two grids.

Umnodulated radio-frequency carrier is appied over lead RFI, and transformer Tl, between points B and C of bridge BR, and appears as voltages in phase opposition, as further components of the resultant voltages applied to the grids of valves A and B. They are represented, in Figure 12 by the vectors ORA and ORB.

Voltages 0M and ORA, and OM and ORB are in'phase quadrature. Precise quadrature setting is obtained by adjusting the phase adjusting differential condenser CD in the grid circuits of valves V3, and V4.

The resultant voltages, in the unmodulated carrier condition, applied to the grids of valves A and B.v are representedin Figure '12 by the vectors .ORAc and ORBQ.

During one-half-cycle of modulation the energy supplied to the bridge BR over lead MC rises to a. given amplitude. and during the other half-cycle of. modulation thisienergy rises to approximately thesame amplitude but in reversed phase. The vectors representing the components of voltages applied tothe grids of. valves A and B, and- .due .to these two conditions of modulation, are named. OM+ and OM.- in Figure 12 and give rise to resultants CRA+ .and ORB+ or ORA-.- l'and ORB-respectively.

The grid tuned-circuits of valves'A andB, comprising condensers II. and t3: with their shunt dampingresistors l5 and. H, and the other'components leadingback to the anode tuned circuit i=9v of carrier. reducer or suppressor. modulator ID are so.. chosen as to constitute impedance invertors sothat undesired influences, dueto varying grid current in. the valvesof the power stage 6, upon the phases of the applied voltages may beminimised or. eliminated. As explained hereinbefore in showing 'how the arrangement of Fig. 6 is derived from the arrangement of Fig.3, the anodes of both thestages A and. B" are coupled by impedance .invertors to the 1 common load R fedthrough impedance transformer II. This will be obvious when it is kept in mind that each of. the two anode load impedance inverters has its shunt impedance limb lumped. with the anode tuned circuit (TA and TB). inductance .of the appropriate tube. The other. shunt inductance limbs of the impedance inverters are lumped-together and form theiinductance 48 shown across the input end of the'network II.

The ph'aseasplitting .valve Al has potentiometers-.;:20 and :24aas anode and cathode leads-the Unmodulated radio-ire.- outputvoltagesfrom thesebeinz. in phase opas;- a suppressed carrier: transmitter. -justments' consist in balancing *the carrier-suphalf cycle offmodulationl A greater; degree oi phase swing of the controlling..-voltages ,for the negative, half than 'for. the positive half of modulation corrects this unequal voltage condition. The potentiometers-t'll and 124 enable thiscormotion to be obtained, the; eiI-ect being, observed on a cathode ray oscillograph modulation check equipment. 1 H

Included in the modulating: stages, are a pair oi valves 3| and 32 with a system of 30 simple resistance-capacity filters to permit of a con-- siderable level of ieedbackwThe modulation is i applied at mf, amplified in stage 33 to appear intransformer 34 and across the potentiometer resistance 36. andfin a balancingnetwork 30. A portion ofthe outputof stage .33 is--taken by lead 38and also applied to the network 30 which is connected to the .grid of modulation amplifier 31 wherein the modulationfed forward and-fed backward are combined; ;.Feedback energy-:is also derived fromrectifier 40 and fed by potentiometer 42 and lead 44 to the balancing network 30. Noise and hum are blocked .out in tube 3| as described more in detail in my U. S. application Serial #429,144, filed Feb. 2, 1942. The amplifier is otherwise conventional. Y r

Use'of feedback allows of 50- A. C. lighting of all thevalves of the system with a resultant carrier'noise which is well within the usual accepted Reference vMR indicates a monitor which need not be described,-since alsimilar monitor and its mode olE-operation have been described inBrit- ,isl'i Patent No. 540,245, dated October ;'1941, and the corresponding U;.

dated September 1, 1942..." a; .Tetrodes'or pento'des: maybe; used in all stages ing' power required by tetrodes and pentodes.

Aphase-swing=transmitter,.;such as. that de- },Patent #2,294,800

scribed in connection; with Figure 11', provides Y normal modulated carrier; It can, howeverpby' slight 'adjustments, be readily made to operate These adpressor system H] and adjustingthefanode tuned -circuitsof the power stagerfiand their respective networks andload to -be :in, parallel-resonan'ce for an anti-phase excitation of the-grids or valves A and B' (which antiephase condition a trigonometrical function of X1 -A special case isfthat' in which thephaseangle-of'an electrical quantity "is desired "to be" varied, usually :"by linearly varying "aj'modulation or modulated signal X to provide'a'strictly proportional variation'inthev'alue o trigonometrical function little changed an le be" emu-1t can often be arranged thatsuflicintly nearly linear relationship between' the. .two quantities will be obtained without necoursevtoi; special, devices. But if an extended angle of;,change with good linearity be desired, some special device may become essential. ,The ,following describes one ;method of achievingthe purpose. I

If two vector quantities YiandX, which are in quadrature relation be added ,vectorially, the

resultant vector may h Sine Value, which y be expressed by and a cosine value 4 I A l: +Y ,(see Figure lii) wherefl is the anglebetween the resultantqvector and the quantity X.--;1Avariation in the value-oi these expressions canbe obtained by varying the valuelof X-alone, whilst Y is kept constant g v The expressions forthezspecial case mentioned can-be ,written: ym r I sine tan :In many cases X will bear: a valueywhich, for successive instants of time, can be'exp'ressed as some fraction ofY, say KY.' Ifcurvesbe plotted giving the values of the above expressions against changing values of X,:it will be seen that-linearity of relationship is'r'estr'icted to'small changes of X when X is much=smallerthan;;or nearly equal The devi e here proposed effectsan improvement in therelationshipfor a greater-variation of'X; and yields a "result; Ewhich for 'many practical purposes would be regarded as sufliciently near a'linear relationship of thequantities determining the-curves? i; f 'Inoperatingitheidevice the quantityiY is modulated during the'periodbf changing-X, when non-linearity of i the i trigonometrical functions rapidly increases, the rate of changing of the value Y being determined by some influence; such as that of the bottomor top bend of thermionic vacuumtube characteristic'curves. a -The special base-of the application of theidea to-the'cosineiunction; when is smaller than Y, is illustrated in the diagram Figure 14-; The case of the sine function and other trigonometrical functions will not be discussed further, as the specialrequirements for' these will be-clear to those skilled 'in' the art of designing thermionic vacuum tube circuits for special purposes-"l The quantity Y is generated by valve VI, Figure 14, and applied to two corners BC of the bridge formation, p, q, r, s. The quantity X, which we will assume tobe KY, is generatedby valve V2 and :ap'plied'to; corners-AE of the bridge; formation p,-q,-,r, s; 'Theyalves-Vl and VZare shown as pentode' valves and 'receive adequate excitation voltages on their control gridsby-signals applied at :1: aud t respectively. Thesesignal voltages, whichareof thesame radio or signal frequency are iarranged to 'be in quadrature phase relationship. Valves ;V;3;and V4 receive antiphase audio or modulating :voltage's on, their control grids iand have their anodes strapped together,

and V4.

One mode of operation would be that in the absence of modulation at a, valve V2 would be so biased by 9112, on' its control grid that it generated a small signal X=KY (00 of Figure 13) whilst valve VI is generating a considerable amplitude of signal -Y, which appears across the bridge p, q, rr, s, and may be represented by vectors 0A and OB of Figure 13, the resultant vectors being OD, appearing across one arm, say q,

of the bridge 10, q, r, s, and OEappearing across,

another arm, say 1' of the bridge.

When modulation appears at 2 it is passed via the transformer T to the control grids of valves V3 and V4 in antiphase and from one half of the secondary winding of the transformer to the third gridof valve V2. If-valves V3 and V4 are sufficiently biased on their control grids they will have no influence on the performance of the circuit. Under the influence of valve V2, 00 of Figure 13 is modulated to a degree depending on the signal impressed on V2 from transformer T. The resultant vectors might then. describe a change of (hanging from OD to 0D" andfrom OE to CE. of variation of X, i. e. 0C, therewould be some non-linearity of the cosine function.

If now the grid bias gb3,.ofva1vesV3 and. V4

be reduced so as to permit'themto draw anode current alternately through their commonl'anode load, under the influence of their antiphase grid signals, this would have the efl'ect. of a pro- Over this or arfextended rangegressive reduction in the value of the Y vector 7 tion would be unimportant, or could be nullified by various contrivances.

A number of variations of the-circuits are possible.

In the case of the phaseswing transmitter it may be shown. that the expression for the output current is [R52]. cos 2 where'I is the current flowing out from the two networks NA and NB of the scheme, and :0 is the operating anglebetween'these two currents The angle 0 is caused to vary by linearly varying the output from the carrier suppressor 'stage.- In other words the variation ofthe operating angle is produced by the'variation'nf just sucha quantity X as has been discussed in the foregoing.

By adopting the idea describedabove: the choice of operatingangle for the phase swing transr'nitter'is not so restricted. The modifications of Fig ure 14 for application to the phase swing transmitter consists merely in the substitution of a carrier suppressor stagefor the stage of V2 of 'Figure 14 and the additionv of valves corresponding to valves V3 and V4 of Figure 14. The modulation transformer T of Figure 14 would be dispensed with by suitably applying to the valves V3 and V4 the same anti-phase modulation signal as is applied to the carrier suppressor valves of Figure 11'. The output signal from these linearity correcting valves V3 and V4 would beapplied to a controlgrid of'the valve A5 of Figure 11 which corresponds with the valve VI of Figure 14.

This device which has been described and whose purpose is to reduce the restriction in the choice of operating angle of the phase swing transmitter is to be regarded as a. refinement and would be of real value mainly in the case where the phase swing transmitter is to be used as a suppressed carrier transmitter. In such a usage it might be desired to use a bigger angle of phase swing. The device described would permit of this without objectionable effects in the matter of'linearity of response ofthe transmitter.

Having now particularly described and ascertained the nature of my said invention and in what manner the sameis to be performed, I declare that what I claim is: i

1. In a phase-swing radio-frequency transmitter, 'a power-absorbing device, two-tube stages each having input and output electrodes, connections for applying'radio-frequency oscillatory energies to the input electrodes of each stage the relative phase positions of which energies are varied during modulation, and a quarter the unmodulated position, a'tuned circuit couplea to the anode of each tube, the said tuned circuits being substantially similar to each other,

a power-absorbing device coupled to'each tuned "circuit by means of a quarter-wave impedanceinverting device or network, the arrangement being such that as a result of varying the said phase positions the amplitude of the current delivered to the power-absorbing device is substantiallylinearly varied.

3. A transmitter as claimed in claim 1, wherein each separate quarter-wave impedance-invertingnetwork comprises a pair of conductors'coupling'the output electrodesof each tube stage to the power-absorbing device with reactances connected across the conductors of each pair, and

'a reactanc'e connected. in series with oneof the said conductors of each pair at a position be tween two of said shunting reactances.

4. A transmitteras recited in claim 2, where in each network includes a pair of conductors coupling the tuned circuit to the load with two reactances connected across each pair of conductors and a reactance connected in series in one conductor of each pair at a position therein between said first tworeactances.

5. A transmitter as recited inclaim 2, wherein the separate quarter-wave impedance inverting networkseach include a reactance common 6. Atransmitter as claimed to the two networks" connected acrossthe'powerabsorbing'device and each includes areactance in series between the tuned circuits and the power-absorbing device;

v in claim 2, where'- in the two'tuned eircuits are arallel' tuned circuits' l and are slightly mistuned differentially from parallel resonant condition, so as to provide an eifective resistive or unitary power factor for the tubes. 7

7. A transmitter as claimed in claim 2, wherein the two tuned circuits are parallel tuned circuits and are Slightly mistuned differentially from parallel resonant condition and wherein the networks each include a reactance and the reactances are similar, and wherein common control means is connected to said similar reactances to produce equal and opposite changes in the tuning'thereof.

8. A transmitter as claimed in claim 2, wherein the two quarter-wavenetworks each include a series reactance and the said reactances are similar and each thereof are included one in each 'of the tuned circuits and wherein the tuned circuits are differentially mistuned by differentially varying the reactive value of said series reactancesbygang control so as to produce equal and opposite changes in the tuning thereof.

9. A transmitter as recited in claim 1, wherein the phase separation between the energies applied to the input electrodes of the tube stages is in the unmodulated condition substantially 10. A transmitter as claimed in claim 2, wherein said phase relation is about 160 in the unmodulated condition and during modulation varies around said unmodulated 160 relation, and output electrodes of each tube-stage looks into a substantially resistive load presented by the power-absorbing device and the other tube-stage and its associated tuned circuit and quarter-wave impedance-inverting device or network and whereby, to meet the varying reactive load presented by these elements during modulation the angle separating the phase relation of the energies or voltages is during the negative halt-cycle of modulation caused to increase beyond 180.

11. A transmitter as recited in claim 2, wherein said radio voltages of predetermined phase relationship fed to the grids are resultant voltages made up of two components and wherein means is provided for producing modulated radio-frequency energy (or voltage) with the carrier not entirely suppressed inv the unmodulated condition, and feeding the same as one component in push-push fashion to the grids of the tubes, and other means is provided for feeding unmodulated high or radio-frequency energy as the other component in push-pull fashion to the grids of the tubes, the latter unmodulated energy being in phase quadrature with the modulated energy.

12. In a transmitter system, a power-absorbing device, a power stage including two electron discharge devices each having input and output electrodes, a tuned circuit coupled to the output electrodes of one of the devices'of said power stage, a tuned circuit coupled to the output electrodes of the other of the devices of said power stage, a quarter-wave impedance-inverting network coupling each of said tuned circuits to said power-absorbing device, a carrier suppressor modulation system including two tubes each having input and output electrodes, a source of modulation current, a source of radiofrequency voltage, connections from said source of modulation current tosaid input electrodes for applying themodulation-current in push-pull relation to the input electrodes ofsaidtwo tubes, connections :from said source of radio-frequency voltage to-the input electrodes of said two tubes for applying radio-frequency voltage"thereto in push-pull relation, a bridg circuit having one diagonal coupled between the input electrodes of said electron discharge devices and having a second diagonal coupled to the output electrodes of said tubes to feed carrier suppressed modulated radio-frequency energy in phase to the input electrodesof said two devices of the power stage, a radio-frequency amplifier stage having an input coupled to said source of radio-frequency voltage and an output coupled to said one diagonal of said bridge circuit to feed unmodulated radio-frequency energy by way of said bridge to the input electrodes of said two discharge devices of the power stage in phase opposition, the in-phase modulated energy applied to the input electrodes of saiddischarge devices being in phase quadrature with the phase opposed unmodulated energy supplied to the input electrodes of said devices-whereby resultant radio-frequency voltages are produced on the input electrodes of the devices of the power stage which in the unmodulated condition are separated by a phase angle of substantially 160.

13. A system ,as recited in claim 12, wherein the tubes are so biased and operated that the carrier suppression is incomplete, and wherein the modulating current is so applied to the input electrodes of the two tubes that th in-phase radio-frequency energy applied by the carrier suppressorv system to the input electrodes of the two discharge devices increases and decreases in amplitude in accordance with alternate halfcycles of modulation energy above and below the amplitude of the incompletely suppressed carrier applied in the unmodulated condition.

14. A system as recited in claim 12, wherein V the input electrodes of the tubes of the carrier suppressor modulator are so biased that the modulating currents do not operate the tubes to cut-01f 0n the negative cycles of the modulation whereby the carrier is not completely suppressed.

15. A system as recited in claim 12, wherein .a tuned circuit is coupled to the output electrodes of said two tubes and to the said second diagonal of said bridge circuit.

16. In a transmitter system, a power-absorbing device, a power stage comprising two elec tron discharge devices each having input and output electrodes, a coupling between the output electrodes of one of the discharge devices and said absorbing device, a coupling between the output electrodes of th other of the discharge devices and said absorbing device, a pair of tubes each having input and output electrodes, two

trode of the other of said other two tubes, connections from said sourc of radio-frequency voltage to the input electrodes of said two tubes for applying radio-frequency voltage thereto substantially in phase quadrature relation, a

ic s-oi then we s ag dnd a coup in b tw the nutput s'elz-ietroclesof said one of said two tubes and the-rotherg diagonal of the bridge to feed modulated radio-frequ nfl energy by way of said bridge to the input electrodes of said two discharge devices of the power stage co-phasially. v THOMAS HENRY PRICE.

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