US1773185A - Radio amplification - Google Patents

Description

Aug. J9, 1930. `1.4. F. HoRLE y 1,773,135

RADIO AMPLIFICATION Filed Feb. 12, 1927y 3 Sheets-Sheet 2 All@ 19, 1930 .c. F. HoRLE 1,773,185

RADIO AMPLIFICATION s sheets-sheet s Filed Feb. 12, 1927 Patented Aug. 19, 1930 ff 1 UNITED STATES PATENT OFFEC i LAWRENCE C. F. HORLE, F NEWARK, NEW JERSEY RADIO AMPLIFICATION Application led February 12, 1927. Serial No. 167,829.

Y My invention relates generally to electri- F ig. 9 illustrates-a further development of cal systems involving rectification, and, while the circuit arrangement of my invention, in not limited in its application or use, has parwhich a head set is employed for each stage ticular reference to radio systems in which no of vacuum tube amplification.

frequencies exist other than those intercept- In the present day reception of radio siged by the antenna and those resulting from nals and particularly broadcast reception, rectification and amplification. a much higher degree of amplification is de- The invention consists essentially in amulsirable than has been available in the past. tistage amplifier and the object of the inven- T o meetthis need, highly developed ampli- 10 tion, broadly stated, is to effect simultaneous fiers of the audio frequency and radio fretu rectification and amplification of all frequenquency types have been produced. These two cies present in the wave form of current or types of amplifiers are essentially the same, voltage that is applied to the input of the in so far as constituent parts are concerned, amplifier. and are, in the last analysis, combinations of This and other important objects of the invacuum tubes and transformers or other in- 15 vention will more clearly appear from the terconnecting devices, which act as the description that follows. means for the transfer of the energy liber- For purposes of illustration, I have shown ated by each tube in the sequence to the tube diagrammatically, in the accompanying neXt in sequence.

2o drawings, circuits suitable for carrying my The vacuum tube amplifier, consisting of 70 invention into effect. vacuum tubes and interconnecting devices,

Fig. .l illustrates a typical circuit for the which may be termed generically inter-valve actual application of the vacuum tube to connectors, functions as it does by reason of radio reception of voice or telegraph signals; the fact that the vacuum tube has the desir- Fig. 2is acurve diagram showing the relation able characteristics of liberating in its outbetween the plate current and grid voltage put circuit, usually termed the plate circuit,

and between grid current and voltage; Fid. more power than is supplied to its input cir- 3 is a curve diagram showing the application cuit, usually termed the grid circuit. of the proper biasing potential to the tube Assuming a typical set of connection, as

so circuit whereby the wave form of the curshown, for example, in Fig. 1,it will be noted S0 rents in the output circuit conform closely to that both the input and output` circuits are the wave form of the voltage applied to the provided with separate sources of direct curgrid; Fig. l is a curve diagram showing, as rent at C and B respectively. ri`he functions a result of making the grid less positive, of thesetwo sources are distinctly different,

5 relative to the filament, greater variation behowever, in that while the plate circuit cur- S5 tween the wave form reproduced in the plate rent supply is designed to be the source from circuit and the wave form impressed on the which the out-put power is drawn, the grid grid circuit; circuit current merely serves to gir/'e a prelim- Fig. 5 is a curve diagram of the wave form inary adjustment to the grid of the tube, to

of the currents in the various parts of the make its operation most effective. No power 90 circuit shown in Fig. l; is drawn from this source of supply', but, on Figs. (i:L and 6b represent two simple cirthe other hand, if any` direct current flows, cuit arrangements embodying the principles it flows in a direction to oppose the voltage of y of my invention; y the battery and hence serves to charge the L15 Fig. 7 shows a further development of my battery instead of discharging it, as is the 95 invention, employing four tubes; but only the case in the plate battery. first and last of which serve as rectiliers; The action of the tube as an amplifier will Fig. 8 illustrates a modification of my inbe best understood from the characteristic vention in which each tube acts simultaneouscurves shown in Fig. 2. These curves show ly as a rectifier and as an amplifier; and the relation between plate current and -grid l0@ volta and between rid current and voltage; t e two curves belng plotted to the same scale. It will be noted that the axis y-y represents the zero of plate and grid currents, While the axis -w represents the zero of grid potential, where grid potentials are expressed relative to the negative end of the filament. Thus, when the battery C, of Fig. 1 is reduced to zero the current in the grid circuit becomes zero and the plate current has some value as shown in the plot of Fig. 2 at a.

If now the grid is made positive relative to the filament terminal by the insertion of abattery or by other means, both the plate and grid currents will increase, the rate of increase in the plate current with applied voltage, being somewhat greater. If the grid is made more negative relative to the filament, the currents will decease. Any volta e that is caused to act on the grid circuit w1`l then cause a change in the plate current.

If the proper choice is made of the constant voltage applied to the.grid,usually termed the biasing voltage, the wave A`form of currents in the output circuit will conform very cloesly to the wave form of the voltage applied to the grid. This condition is shown best in Fig. 3, where the potential of the grid is very positive relative to the lament. On this plot the two characteristic curves of the tube are again shown and the line a-a represeats'. the direct voltage applied to the grld when the connection from the input circuit is completed to the negative side of the fila- /When an alternating voltage is applied tp the `input terminals .of Fig.1, of the magnitude shown by the sinusoid plotted vertically aboutthe axis HOFig. 3, two currents D s are brought into being. These currents have beendetermined b the construction and plotted in Fig. 3. t will be noted that both the plate and grid currents reproduce the applied vWave form of the voltage with remarkable precision, in that they both approximate the` sinusoidal form very closely. It will be further noted that the magnitude of these curleusis distinctly different, the plate currentbeng many times the grid current. Assuming the value Vof the useful resistances through which these currents flow, to be of thcjsame order of magnitude, it is obvious thatthe tube tnakeay available in its output circuit a greater amount o16V power than is supplied toits input circuit and `that it is theref f an amplifier and that the amplification .n withno great-change in the electricalfwave form of the current or voltage being amplified. Thatis, of course, the ideal typeof amplier `since it reproduces, quite faithfully, any electrical waveform supplied toit.

the grid is made less positive relative y i to the ament than in the above case such as i thcimstance where one connection of the input circuit is made to the negative end of the filament, the wave form reproduced in the plate circuit is not as faithful a reproduction of the wave form impressed on the grid circuit, as in the above case. This characteristic is shown in Fig. 4. Here the same characteristie curves of Figs. 2 and 3 are shown and the same magnitude of alternating current grid voltage is plotted about the axis a-a (negative end of the filament) and by the same construction of Fig. 3, the grid and plate currents are plotted. It will be observed, however, that Wliile the magnitude of the grid current, caused to flow by the applied voltage, is very markedly decreased over that of Fig. 3, the plate current is reduced in only a minor degree. Thus the tube becomes a more effective amplifier under these conditions than under those conditions Where the biasing potential is omitted since the ratio of output power to input power is greater in this latter case. The wave of the plate current is, however, distinctly distorted; the lower half of the wave of plate current being smaller in amplitude than is the upper half. Thus the plate current is more nearly symmetrical about an axis d-d and hence is equivalent okfa sinusoi d about this axis plus a direct current component as indicated by the distance along a-ecz between vc-c and d-d, in addition to the constantly flowing direct current as indicated by the distance along w-a between o-c and g/-y.

This condition, in which a direct current is brought into being by the application of an alternating voltage to the grid, in addition to the plate current always present in the plate circuit of the tube, is known as rectification and is that property which makes the vacuum tube useful as a rectifier or detector of alternating current.

The details of its action, in radio circuits, need not be discussed in detail but it must be understood that the effectiveness of any device as a detector or rectifier, is directly proportional to the degree in which it brings into being a direct current in the output circuit, by the application of an alternating voltage to the input circuit.

Vhere the vacuum tube is to be used as a detector primarily, it is necessary that thc rectification be made more complete than is shown in Fig. 4. This is usually accomplished by the introduction of the C battery shown in Fi 1, which allows of the grid being made su ciently negative to greatly augment the rectifying distortion of Fig. 4.

In the actual application of the vacuum tube to radio reception of voice or telegraph signals, this rectifying distortion is made use of for separating out the voice or signal froquency from the radio carrier frequency, so that the voice or signal frequencyv may be made use of in the telephone or other indicating device. AA typical scheme of connections is shown in Fig. 1. This consists of a tuning system 10 for tuning the antenna 11 to the frequency being received, a vacuum.

tube detector 12 With auxiliary batteries and a pair of telephones 14 and by-pass condenser 15. The by-pass condenser 15 is sometimes omitted in practice, since the ordinary telephone cords have all the characteristics of a by-pa-ss condenser.

The Wave form of the currents in the various parts of the circuit are shown in Fig. 5, in Which a shows the Wave form of the antenna current for a damped Wave signal, such as might be secured in spark or telephone reception. This consists of currentsof radio frequency of varying amplitude; the variation of amplitude being determined by the character of the transmitter. a, is also obviously the Wave form of the voltage applied to the grid. b is the Wave form of the current in the plate circuit of the tube, Which current is forced to pass through the joint paths of the telephones and the by-pass condenser. This latter current is broken up into two components by the telephone-condenser combination, as shown in c and al. The radio frequency component is prevented from passing through the telephones because of the high impedance of the ordinary telephones to radio frequencies and passes through the by-pass condenser, which can quite easily be made to have a very low impedance to this current. The second component current c, Which may be viewed as being the two other component currents e and f, passes through the telephones and makes itself evident as the signal. The low frequency component c, is of course, the activating cause in the telephone response, While the telephones merely serve as a ready path for the flow of the direct current of f.

Special means are some times provided whereby the D. C. component of the telephone current is by-passed by a circuit outside of the telephones 1li. This is not essential nor, under certain conditions, desirable, and for .present purposes, the effective telephone current may be considered as merely the low frequency component c.

It Will be observed, from the Wave form of b, that the vacuum tube Was assumed to be a perfect rectifier, in that one-half of the impressed Wave form was entirely lost through rectification. Vhile this is never realized, the curves show What may be expected in the ideal case, and so sufficiently approach the conditions of practice to make valid the useful conclusion drawn from examination of them.

It Will be observed further that in the simplified circuit arrangement of connections referred to, there is a radio frequency current in the plate circuit of very considerable magnitude and that this current is by-passed and i has no effect on the telephones 14.

Based on the above stated fact, my invention consists essentially in means for making useful this normally by-passed radio frequency current.

In previous systems of amplification, the radio frequency component of Z (Fig. 5) 1s completely lost through the shunt path provided bya by-pass condenser in the output circuit of the electron tube or Where such a condenser is not supplied through the inherent capacity of the transformer Winding and is no longer effective in causing signals 1n the telephones.

I have discovered that this radio frequency current can be utilized to advantage in the reception of radio signals, to greatly augment the -signals that are made available to the telephones, Without increasing the number of tubes over What is normally required for the ordinary voice frequency amplification. y

This is due to the fact that practical conditions cause a great departure from the ideal conditions, shown in the above figures.

I have found that even the most effective detectors of the vacuum tube or other types, give a far greater ratio of radio frequenc)7 current to low frequency signal current in the output, than is shown in the case of the ideal rectifier of Fig. 4, and that by making the energy of this radio frequency current, available to the telephones, in the form of lovv frequency current, a greatly augmented signal may be secured.

I have found further that in the ordinary a radio frequency amplifier, when adjusted for maximum amplication, the departure of the Wave form from the faithfulness of Fig. 3, is so great, as to introduce a very readily noticeable magnitude of rectified current. This comes about through the fact, that While the condition for faithful reproduction of Wave form may be very nearly realized by means of the ordinary vacuum tube, the efficiency of amplification-that is i to say, the ratio of output to input poWer,- is greatly augmented if the grids of the amplifier tubes are made more negative than for the conditions of Fig. 3. Thus each succeeding step of amplification becomes a rectifier, f

as Well as an amplifier and an amplifier operatingat the greatest possible ratio of output to input power, in which each tube acts as a detector, almost as effectively as if especially adjusted for that purpose. gree to Which the tube rectiiies is. of course, determined by its grid potential and may be, therefore, qui-te easily controlled and compensated. f f

I have found that a vacuum tube amplifier,

devised to make use of the successive rectifications Which occur in its vacuum tubes, produces a degree of amplification not possible under the conditions of the present Well known circuits shown in several figures The deff ftfthi'series rcctifies the `voltage applied to it,

esabovefdid. I'have termed this method -off c amplilication #duplex amplification both radio frequency and audion frequency amplification occur in each tube, in-

excluding the rectifier.

fr asidescribed above, and has in its plate circuit 1i', a current of the form shown at b, in Fig. 'nillt may be caused to rectify by the use of 1555i biasing' 1volta Y 'from -a-biasing' battery C Lead shown. in Fig. 6% orth'e` biasmg'veltage if may-be secured `bymeans of the grid leak and jmondenser as 4shawn in 'Fig'. 6b at 18. yff'lhe method'ofamplification does not, of ."Jieetlse, "in anyway: depend `upon the method of securing being present in the plate circuit iidiuthnthe llowV andwndiofre uency componentaofthe signal current, oth of which wweamplied. more nearly the rectificaten of the 'first' -tubev approaches' the ideal l shown lat b in Fig. 5, the more effective will fil thefdevice5 beybutuany1 departure from the -=iidbalrectifier will-be counterbalancedl -by the f 'tcation of the-next tube 19.

de: ce thewtwo tubes 16 and 19` are interfuoonnected by bothvrndio frequency transirfnrmers 20,` and"V audioy frequency transformers 21, both the radio and audio` `fre- 'Jiqnegrcy .componentafwill fbe present in the rar-:ultage appliedto'thesecondtube 19. This ffetiibeilsgamplifies both-frequencies and recti- .ndesuas did the Afirst tube-16, -which results in '@lmther eurrent,n-hwving l both radio and .ieumdio frequencyE components. It Will be :z-observed that the audio frequency trans- 21'1arerprovided'with by-pass conl@dansers 23 so that-the radio frequency cur- .r rentmaypass with little impedance. These umdensers 23 -mayrlbeiomitted when there isY lift'.- 'umlf'at 2]. witlr'byspass condensers 23 contherewith. y same-'principlel of the simultaneous rectification andamplification of the radio `caud'audio frequenciesmay-be applied to any ffeaxm'pher; and iby -tsese agiven"numberI of rectification but depends only vof vacuum tube amplification.

sta es of amplification may be made to give a. egree of amplification far in excess of any that could be secured Without the use of the rectifier-amplification circuit herein disclosed. :u In Fig. 8 is shown another application of the same principle. In this circuit, each of the tubes 16, 24 and 19 acts simultaneously as rectifier and amplifier. It is particularly useful Where the signal being received is of 5 such a magnitude as to cause the voltage applied to the last grid, in such a circuit as is shown in Fig. 8, to exceed the efficient capacity of the tube for rectification. This may come about through the fact that the effective input voltage capacity of a vacuum tube rectifier is usually much less than its effective input voltage capacity as an amplifier. Grid leaks and grid condensers 18, 27 and 26 are provided in each input circuit. The radio frequency coupling transformers are shown at and the audio frequency intervalve transformers are shown at 21. In the circuit, shown in Fig. 9, since each tube 16, 24, and 19 acts as a rectifier and thereby on augmente the audio frequency component of the plate current by the amount of its rectification, it serves to operate each successive tube, so far as rectification is concerned, most effectively. 7.

Fig. 9 shows another application of the method for the operation of as many headsets at 28, 29, 30 and 14 as there are stages The radio frequency component in each tube is passed on to the next tube for rectification through transformers 2() and the audio frequency component is delivered to the headset in each tube plate circuit, Where it makes itself evident Vas a signal. By- pass condensers 31, 32 and |05 33 are shown in shunt with telephones 28, 29 and 30 but telephones 14 are not provided with a by-pass shunt.

Having thus described my invention, what I claim is:

1. In a multi-stage amplifier system, a plurality of electron tubes each having input and output circuits, means for adjusting each of said tubes for operation simultaneously as rectifiers and amplifiers of sig- |15 naling energy impressed upon said tubes, and coupling means between the input and output circuits of said tubes comprising independent transformer systems each responsive to different frequencies, one of the trans- :m former systems between each of said tubes having means for by-passing the frequencies for which the other transformer systems are responsive, and means in the output circuit of the last of said electron tubes responsive il-'v to the integral effects of the rectification and amplification properties of all of said tubes.

2. In a multi-stage amplifier system, a plurality of electron tubes each having input and output circuits, a grid leak and shunt connected condenser disposed in each of said input circuits, a pair of transformers interlinlring the output circuit of one tube with the input circuit of a succeeding tube, each transformer having primary and secondary windings, the windings of one transformer being responsive to one range of frequencies and the windings of the other transformer being responsive to a different range of frequencies, each of said tubes operating to simultaneously rectify and amplify signaling energy impressed thereon, and means connected with the last output circuit for integrating the effects of all of said tubes.

3. An amplifier on which is impressed a ban-d of radio frequency carriers modulated by a band of signal frequencies, two vacuum tubes having input and output circuits; means for adjusting the tubes to act as rectifiers and amplifiers simultaneously; coupling means between the output circuit of the first tube and the input circuit of the second tube comprising two-independent inductance sy-stems, one of said inductance systems being responsive to the band of radio frequency carriers, the other of said inductance systems being responsive to the band of modulating signal frequencies and having means for bypassing the band'of radio frequency carriers, means associated with the output circuit 0f the second tube responsive to the integral ef fects of rectification and amplification of both said tubes.

lf. An amplifier on which is impressed. a

N band of radio frequency carriers modulated by a band of signal frequencies, two vacuum tubes having input and output circuits, means for adjusting the first tube to act as a rectifier and amplifier simultaneously, coupling means between the output circuit of the first tube and the input circuit of the second tube comprising two independent inductance systems, one of said inductance systems being responsive to the band of signal frequencies appearing in the output circuit of the first tube acting as a rectifier, the other of said inductance systems being responsive to the band of radio frequency carriers passed through said first tube and appearing in the output circuit of said tube, means to by-pass the band of radio frequency carriers around the inductance system which is responsive tor the band of signal frequencies, means for adjusting the second tube to act as a rectifier and amplifier simultaneously, means associated with the output circuit responsive to the band of signal frequencies rectified by said second tube from the band of modulated radio frequency carriers passed through th-e first tube into the' secon-d and also responsive to the band of signal frequencies rectified by the first tube from the impressed band of modulated radio frequency carrier and patssed through and amplified by the second tu e.

5. An amplifier on which is impressed a band of radio frequency carriers modulatedl by a band of signal frequencies, two vacuum tubes having input and output circuits, means for adjusting the first tubeto act as a rectifier and an amplifier simultaneously, coupling means between the output circuit of the first tube and the input circuit of the second tube comprising two independent transformer systems, one of said transformer systems being responsive to the band of signal frequencies appearing in the output circuit of the first tube acting as a rectifier, the other of said transformer systems being responsive to the band of carriers passed through the first tube and appearing in the output circuit of said tube, means to by-pass the band of radio frequency carriers around the transformer system which is responsive to the band of signal frequencies, means for adjusting the second tube to act as a rectifier and amplifier simultaneously; means associs ated with the output circuit responsive to the band of signal frequencies rectified by `said second tube from the band of the modulated radio frequency carriers passed through ysaid first tube into the second and also responsive to the band of signal frequencies rectified by the first tube from the impressed band of modulated radio frequency carriers land passed through and amplified by the second tube.

LAWRENCE C. F. HORLE.

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