US2121737A - Variable reactance modulator circuit - Google Patents

Description

June 21 1938. c, w HANSELL 2,121,737

VARIABLE REACTANCE MODULATOR CIRCUIT Filed July 24, 1933 4 Sheets-Sheet l INVENTOR CLARENCE W. HANSELL ATTORNEY June 21, 1938. c. w. HANSELL VARIABLE REACTANCE MODULATOR CIRCUIT Filed July 24, 1955 4 Sheets-Sheet 2 a I QI 'ARENCE W. HANSELL ATTORNEY June 21, 1938.

C. W. HANSELL VARIABLE REACTANCE MODULATOR CIRCUIT Filed July 24, 195-3 4 Sheets-Sheet 3 L L s m R Y M E E Nmm L Y B June 21, 1938.

c. w. HANSELL VARIABLE REACTANCE MODULATOR CIRCUIT Filed July 24, 1955 4 Sheets-Sheet 4 alalala gillillilllgl Q ik' Q \i f R 5 a: g A A TE Q {h INVENTOR 8 CLARENCE W.HANSELL i BY g i Q Q H M Q ATTORNEY Patented June 21, 1938 UNET SATS Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application July 24, 1933, Serial No. 681,945

7 Claims.

This invention relates to circuits, such as used in phase modulation apparatus, whose reactance may be rapidly varied. More particularly, my present invention relates to variable condensers "'5 of a type whose reactance may be varied from relatively low frequencies up to a rate corresponding to frequencies of millions of cycles per second. Such condensers are particularly useful as already indicated, to produce phase and often times frequency modulation of ultra high frequency transmitters, especially those which require high frequency modulation such as, for example, a television transmitter. They also may be used in some systems for producing amplitude modulation.

It has been proposed heretofore, in order to provide a condenser whose reactance may rapidly be varied, to change the ionization of vapor molecules within thedielectric between a pair of electrodes mount-ed within an hermetically sealed container. Such a variable gas system suffers from the disadvantages that it has a non-linear characteristic and is subject to temperature and other variations. It is also limited in the maximum rate or frequency at which its capacity may be varied due to the relatively slow rate of change of ionization of the gas with changes in control currents or potentials. To provide a condenser which is free of those disadvantages, is the principal object of my present invention and to do so I vary the distribution of electrons or clouds of electrons in the space between electrodes contained within an hermetically sealed container at least one of the electrodes being made in the form of an electron emitter such as the cathode of an electron discharge device. Briefly, I control the distribution or location of electrons about the cathode electrode with respect to another associated electrode electromagnetically, electrostatically, or by the combined action of magnetic and electrostatic fields. The presence of free electrons in a space subjected to alternating current fields changes the effective dielectric constant and magnetic permeability of a space and variations in the electron positions or density varies the capacity and permeability. This phenomena is used in my invention.

My present invention will be described in greater detail in connection with the accompanying drawings which, it is to be clearly understood, are merely illustrative of it and are not to be considered in any way limitative. Turning to them,

Figures 1 to 5 inclusive indicate the electronic flow or distribution or both of electrons about an electron emitting cathode in the absence and in the presence of electric or magnetic fields or both;

Figure 6 diagrammatically indicates a system utilizing a circuit whose capacitive reactance is varied rapidly by means of one form of my improved magnetically controlled electron condenser having two electrodes;

Figure 7 illustrates a modification wherein the distribution of electrons is effected by a magnetic field and rapidly varied in accordance with modulating potentials applied to one or more auxiliary electrodes;

Figure 8 illustrates, in wiring diagram form, a system utilizing an electronic condenser whose capacity or electronic distribution is controlled purely electrostatically; and,

Figure 9 illustrates a system wherein capacity variation is accomplished by the combined action of magnetic and electric fields, or in the alternative by either alone.

Turning specifically to the drawings, Figures 1 to 3 inclusive indicate cross sections of an electron discharge device having an electron emitting cathode 2 and a relatively cold electrode 4 spaced concentrically from the electron emitting cathode. Obviously, the glass containers have been omitted from the figures for the sake of simplicity.

In Figures 4 and 5 there is placed between the electron emitting cathode 2 and cold electron receiving anode 4, a further concentric control or cold electrode 6.

Now, if the electron emitting cathode 2, of Figure 1, is heated to incandescence or otherwise arranged to emit electrons and assuming a relatively positive potential applied to the relatively cold electrode 4, electrons will be attracted to the anode or cold electrode 4 as illustrated by the dotted arrowed lines. Obviously, this action takes place over each infinitesimal area on the cathode so that there is effectively a cloud like flow of electrons from the cathode 2 to the anode 4 in the direction of the arrows.

As an electron represents a change in motion,

' application of a magnetic field thereto will cause it to become deflected. Thus, by applying a sufficiently strong magnetic field, to the space between the cathode 2 and anode 4 of Figure 1, in a direction normal or perpendicular to the paths of the electrons, clouds of electrons, or any particular finite number of electrons, are made to travel in curved paths such as illustrated in Figure 2. That is to say, by applying a magnetic field of sufficient strength to the space traversed by the electrons, such that the lines of magnetic flux are coaxial with or parallel to the linear or cylindrical filament 2, the electron paths become curved. With increasing strength of magnetic field the electrons will be caused to return substantially to the filament, or looked at in a little different light, may be so curved that no electrons strike the anode and the flow of socalled anode current ceases. Figure 3 illustrates the concentrating electron effect of increased strength of magnetic field. The crowding" effect of electrons about the cathode may also be varied with variations in potential applied to anode 4.

By causing the electrons to described curves of various radii either by variation in plate potential or by variation in magnetic field strength, or by variation of both, the density and paths of electrons in the space between the cold electrode and cathode is varied. Because of the fluctuations in electronic positioning and density with respect to the anode, the effective dielectric capacity of the space between the anode and cathode varies. Stated a little differently, over a considerable range of anode cathode voltage variation, with a given value of magnetic field, no

anode current flows but the average density and space distribution of electrons within the tube changes. The change in density and distribution of electron charge around the cathode varies the effective cathode diameter so far as dielectric capacity and reactance for radio frequency currents are concerned. This reactance, of course, can be varied as will be described more fully hereinafter with variations in plate potential or magnetic field strength or both.

As an additional control, further electrodes may be interposed between the cathode 2 and cold electrode 4 as shown in Figure 4 wherein the cross-section of a control grid or control electrode 6 has been illustrated. Variations in po tential applied to this control electrode will also vary electronic distribution and hence affect the capacity between the cathode 2 and cold electrode 4, between cathode and grid and between anode and grid. In the case of Figure 4, if the control grid is varied over a range of positive potential with respect to the cathode, we may dispense with the magnetic field, if desired, by applying suificient negative potential to the cold electrode 4 to stop electrons from striking it.

An arrangement for utilizing this variable capacitive action when produced by. variable cold electrode potential and a constant magnetic field is illustrated in Figure 6. A pair of electron dis charge devices 8, H) are provided with grid and plate circuits I2, I4, respectively, having uniformly distributed inductance and capacity. These circuits are reactively associated through the interelement capacity of the tubes whereby regenerative action takes place causing the tubes 8, 10 to generate oscillations which, in turn, are fed inductively to transmission line 16 connected to a radiating antenna l8. If desired, rather than ground the filaments, the cathodes of tubes 8, I!) may be tuned, as described in the copend-.

ing applications of Nils E. Lindenblad, Serial Number 603,310, filed April 5, 1932, now Patent No. 2,052,576, issued September 1, 1936 and Serial Number 651,809, file-d January 14, 1933, now Patent No. 2,052,888, issued September 1, 1936.

For modulation purposes the anodes or control electrodes 26, 22 of electron discharge devices or diodes 24, 26 are connected to the output circuit 14 through radio frequency by-pass- .to the tubes anodes.-

tubes that its magnetic field is perpendicular to V the flow of the electrons from the tubes cathodes Of course, separate field coils for each tube may also be used and iron may be employed in the magnetic circuit outside the tubes to reduce the number of ampere turns required in the coil. Modulation potentials are applied to the cold electrodes 26, 22 through the input transformer 42, which in turn causes variation in distribution of electrons between the oathodes and plates of the modulator tubes. In this manner a portion of the output circuit 14 is parallel with a variable condenser as described hereinabove, as a result of which the frequency of oscillations generated by the tubes 8, I is varied.

If desired, tubes 8, may be adjusted as regards voltage and circuits so that it acts as an amplifier in which case input energy of high frequency may be applied to the input circuit l2. The modulator tubes would then be operated under the same condition as before, namely, that a field is applied having a strength greater than that required to produce cut off, and in that event, the resultant energy fed to the output circuits l6, l8 will be phase modulated in accordance with the modulation frequency input applied through transformer 42. The high frequency source coupled to the input circuit l2 in this case may be, for example, any of the high frequency sources described by Nils E. Lindenblad in his copending applications referred to above. It should also be noted that instead of feeding directly to an antenna the circuit I 4 may feed one or' more amplifier or frequency multiplier stages before the antenna is reached. If frequency multipliers are used the effective phase modulation is increased in proportion to the ratio of frequency multiplication.

It should be noted that positive potential on the anode, as shown on the figure, prevents an electron cloud accumulating inside the outside electrode.

Further, in connection with Figure 6, a separate solenoid may be provided for each tube and both solenoids connected either in series or in parallel as found desirable. Also, the cold electrodes need not be cylindrical in a conventional manner, but may be made cone or trumpet shaped. to give variation in capacity according to any desired law.

Rather than apply the modulating potentials to the plates or positively maintained cold electrodes, modulating potentials may be applied to control electrodes such as grid electrodes 43, 44 of Figure '7. Bias for these electrodes may be maintained by suitable connections, as shown, to potentiometer 46. Also, the plates or cold electrodes of the modulator tubes, in the arrangement shown in Figure 7, are directly connected to the output circuit I4 rather than blocked off therefrom by means of by-passing condensers.

The remarks concerning portions of Figure 6 with respect to tubes 8, i0 and their associated circuits as well as the modulators, are fully applicable to the arrangement shown in Figure '1 and need not be repeated here. Also, the output energy in circuit I6 may be fed to frequency multipliers, amplifiers or limiters or one or more of said devices, for example, as described in the patents of Nils E. 'Lindenblad mentioned hereinbefore, before radiation by antenna 18. Such further amplifiers and frequency multipliers have been diagrammatically indicated by rectangle 2|.

It is not entirely essential that a magnetic field be used for the purposes of my present invention. That is, as illustrated in Figure 5, by applying a negative potential to the anode or cold electrode 4 and a highly positive potential on the control or intermediate electrode. 6, electrons will rush through the meshes of the grid or control electrode'only to approach the negative or breaking field of the plate electrode 4. With suitable potentials, the electrons can be prevented from actually reaching the plate 4 and can be caused, as illustrated in Figure 5, to return to the space between the cathode and grid 6 as well as to the space immediately surrounding the control electrode 6. Variation in potential on the anode 4 or on the control electrode 6, will then cause the effective diameter and density of the electron cloud about the cathode and the grid to vary and this variation in diameter will give desired variations in capacitive reactance from the anode to the grid and cathode. In this case the grid should preferably be connected to the cathode and to ground for radio frequency currents, by

- means of by-pass condensers.

With such an arrangement, and by using such tubes as RCA U'X-852 it is possible to get a usable reactance effect, due to presence of the electrons in thetube, at carrier frequencies up to at least 3,000 megacycles, and the phase or frequency of the carrier wave may be modulated or varied at frequencies up to at least megacycles.

An arrangement for utilizing the effect described in connection with Figure 5 is shown in Figure 8. Oscillations from a crystal controlled amplifier 5B are fed to a series of amplifiers and frequency multipliers 52 and thence to the input circuit 54 of a pair of pushpull connected electron discharge devices 56, 58 whose output in turn is fed to additional frequency multipliers and amplifiers 60 to be radiated over antennae 62 which is preferably a directive type. The apparatus as so far described may correspond to any of the systems described by Nils E. Lindenblad in the copending applications already referred to. To vary the reactance and hence the phase of energy in input circuit 54 so as to cause the final output radiated from antennae 62 to be phase modulat-ed, I provide a pair of electron discharge devices 64, 66 whose electrode emitting cathodes 68-, are maintained at ground potential by lead l2 and whose control electrodes or grids M, 16 are maintained highly positive through lead 18 connected to source 80. For radio frequency currents the grids are Icy-passed to the cathodes and to ground by the condensers I5, H. The anodes or plates 82, 84 are maintained somewhat negative by means of potential source 86. Audio fre quency potentials from amplifier 88 are applied serially through the grids to transformer 90, both grids 14, i6 wobbling cophasally with the modulation frequency currents. The electrons about the cathodes 68, I0, and grids I4, 16 are not allowed to flow to the anodes 82, 86, or if so, only to a limited extent. Modulating potentials will modulating potentials are not, of course, limited i to audio frequencies but may run into exceedingly high present day radio frequencies in which case, of course, amplifier 88 would indicate a source of high frequency modulating potentials.

Figure 9 illustrates an arrangement wherein magnetic or electrostatic control or both may be had. A plurality of tubes 95], 92 are provided with space charge grids 94, 96 suitably polarized by sources 98, Iill]. The tubes are also provided with control grids H32, IE4, screen grids I06, I08, and plates or anodes III], I I2. The cathodes H4, H6 are preferably maintained at ground potential whereas the control grids I32, I0 3 are preferably negative, screen grids I flfi, I08 are preferably positive and plates H0, H2 are either positive or negative depending upon the strength of magnetic field superimposed on the tubes. All are polarized from potential source I I8. By closing switch 20, and by manipulating key I22, a keyed tone from source I26 will cause, by virtue of variation in screen grid potential, variable capacity effects which may be transferred through transmission line I24 to high frequency coupling circuit E26 supplied with energy from a circuit I28 and feeding some utilization circuit I30. As an additional control of the capacity effect, switch I32 may be closed, in which case the electron distribution will be varied electrostatically because of the variable potentials applied to the screen grids I [56, I03 and magnetically, because of the current circulating, due to closure of switch I32, in the magnetic field coils I34, I36 placed about tubes 953, 32 in such a way that a variable magnetic field is applied to the electrons in a direction normal to their natural paths from filaments to plates. Also, switch I may be left open and modulation effected solely by virtue of the magnetic effect upon the electrons.

Further, keyed tones or other modulation of different frequencies may be applied to the control grids through transformer I40. By suitable switches and circuits, similar to those given in connection with the screen grids, simultaneous magnetic variation may be had with anode potential variation and/or control grid potential variation.

Also, if found desirable, the magnetic field coils wherever used may be electrostatically shielded from the tubes by means of metallic cylinders interposed between the coils and tubes and suitably grounded.

Still another means of modulating the capacity of tubes SE], 92 may be had by varying the potentials upon the anodes H0, H2 as for example through transformer I44. Obviously any com bination and degree of modulation by all the various means may be employed simultaneously using like or different modulations on the various means in order to obtain any desired modulation of modulation characteristic within the limitations of the apparatus.

Having thus described my invention, what I claim is:

1. In combination a source of high frequency oscillations, a high frequency circuit coupled thereto, a load coupled to said circuit, an electron discharge device having an electron emitting cathode electrode and a relatively cold electrode spaced therefrom, said electrodes being coupled to said high frequency circuit, a circuit for applying a magnetic field to said electron discharge device whereby electrons are prevented from flowing from said electron emitting cathode to said cold electrode, and, a modulation circuit operatively associated with the electrons emanating from said cathode within said device for varying the distribution of electrons about said cathode and hence the capacity between said cathode and said cold electrode whereby the reactance of said high frequency circuit is varied in accordance with modulation energy in said modulation circuit and whereby the currents flowing in said load vary in accordance with said electronic distribution.

2. In combination, a source of high frequency oscillations, a high" frequency circuit coupled to said source whereby high frequency currents flow in said circuit, a load coupled to said circuit, an electron discharge device having an electron emitting cathode electrode and a relatively cold electrode spaced from said emitting electrode, a circuit connecting said electrodes to said high frequency circuit, a solenoid for applying a magnetic field to said device of such strength as to substantially prevent the flow of electrons from said cathode to said cold electrode, and, a modulating circuit for applying variable modulating potentials to said cold electrode whereby the capacity between the electrodes of said device and hence the reactance of said circuit is varied, whereby currents fed into said load are varied.

3. In high frequency apparatus, the combination of a plurality of hermetically sealed devices each having an electron emitting cathode and a cold electrode spaced therefrom, magnetic means coupled to said devices for preventing the flow of electrons from said cathodes to said cold electrodes, means coupling said cold electrodes in phase opposition to high frequency apparatus,

and means for cophasally electrostatically varying electronic distribution of electrons about said cathodes.

4. In high frequency apparatus, a pair of hermetically sealed devices each having therein an electron emitting cathode and a cold electrode, magnetic means for preventing the fiow of electrons from said cathodes to said cold electrodes, a source of high frequency currents, means connecting said cold electrodes in phase opposition to said source of high frequency potentials, and means for cophasally varying in accordance with alternating potentials the instantaneous potentials upon said cold electrodes whereby said high frequency currents are varied in accordance with said alternating potentials.

5. In high frequency apparatus, a pair of multi-electrode devices each having Within an hermetically sealed container an anode, a cathode and a grid, a source of high frequency currents, means for connecting said anodes in phase opposition to said high frequency current source, means for applying cophasally to said grids, alternating current potentials, and magnetic means for substantially preventing the fiow of electrons from said cathodes to said anodes whereby said cophasal application of alternating current potentials to said grids serve to modulate said high frequency current source.

6. In combination, a pair of electron discharge devices each having an anode, a cathode and a grid, a source of high frequency currents, means for connecting said anodes in phase opposition to said source of high frequency currents, magnetic means for preventing the fiow of electrons from said cathodes to said anodes, and means responsive to signaling waves for cophasally varying the potentials on said grids whereby said high frequency currents are modulated in accordance with said waves.

'7. In combination, a pair of electron discharge devices each having an anode, a cathode and a grid, a source of high frequency currents, means for connecting said anodes in phase opposition to said source of high frequency currents, means a CLARENCE W. HANSELL.

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