US2216940A - Modulation - Google Patents

Description

Oct. 8, 940= y gq, Fm 2,216,949

' MoDULATI-ON Filed Aprz.; L 1951' l Egf" Wig. 5

5f' ""h-"J 52 l J-7 VW INVENTCR WMLFMnmhIZ/S mmm BY Patented Oct. 8, 1940 PATENT oil-FICE MODULATION Karl Fritz, Berlin,

, assigner to- Tele- Germany funken Gesellschaft fiir Drahtlose Telegraphie m; h. H., Berlin, Germany, a corporation of Ger- Appui-,mon April 1, 1,931, sei-iai No. 134,375 In Germany April 16, 1936 s claim. (ci. 11s-111.5)

This invention concerns amethod of and means for attaining oscillations modulated in particu-` lar in frequency in magnetron tubes and retarding iield generators.

The presentr invention relates to a modulation method employing short wave tubes more especially magnetron tubes and retarding field tubes with so-called end-plate electrodes.

In short wave tubes having a discharge system almost closed and arranged concentrically wi-th respect to the cathode. it' is known to arrange at the ends of said system, absorption electrodes having the form of covers,.and to impress thereon a positive bias potential relative -to the cathi ode. As a result thereof an electrical ileld is produced havinga component parallel to the axis of the system (electrical cross ileld). By suitably dimensioning the Aelectrode bias potentials used in the retarding neld 4type tubes, or

i the electrode bias potentials and the magnetic fields in magnetrons the greater part ofthe electrons can be caused to only rub against the electrodes serving for the production of oscillation, instead \of impinging thereon. This part of the electrons likewise contributes lto the production of oscillation, namely through innuence. 'I'he electrons move along a screw line under `the in-l fluence of the electrical cross field, the axis of said screw line extending approximately parallel to the axis of the system, so that the electrons reach the positively biased so-called. end-plate electrodes only after describing several turns. It

an alternating potential modulated with signal is superimposed on the end-plate elec'.trodes,'the

.at produced high frequency `will be iniluenced primarily as-regards its amplitude, wherebyhowever, automatically an additional frequency modulation occurs. x

The idea of the present invention is as follows:

o By means of theend-plate electrodes th`ere` shall be carried out practically an exclusive freh4 quency modulation at approximately constant high frequency amplitude.

'I'he method according to the invention, namely i, in attaining oscillations in magnetron and retardlng neld generators primarily modulated in frequency is characterized by such supply of modulation oscillations that the radii or elongations of the electron courses will in practice not be t@ varied by the modulation osci1lations.

A variation of the elongations of the electrons either` necessitates a variation of `the constant, magnetic iield or a variation of the vmean acceleration'potential. For this reason, accelera- 55 tion` potential and magnetic field shall bemaintalned constant. There shall be obtained vonly a turningof lthe planes of the courses of the electrons relative to a position 'at rightangles to the cathode. This turning is accomplished through electrical cross iields which cannot exert any ac- 6 celerating force upon theelectrons. e i 'I'he methodaccording to Ithe invention is preferably carried out through the use of discharge tubes having main electrodes disposed concentrically to the cathode, and further auxiliary elecl0* trodes at the ends of the discharge system. In according with the invention Ithe modulation is applied to the end-plate electrodes, which are highly negatively biased relative to the cathode, eitherin equal sense, or in push-pull. Conse- 15 quently, the electronswill be concentrated to a f greater or lesser degreel in the center of the discharge system, without change in their elongations or in the diameters of the courses they follow.

Figures land 2 represent known constructie of tubes having end-plate electrodes.

Figure 3 clearly indicates the relationship of frequency and amplitude of high frequency oscillations produced in accordance with the method lli: ofthe invention.

Figures 4 and 5 show examples of circuits utii iizing the idea of the invention.

Figure 1 is a discharge tube with -a single cylindrical anode A. The cathode K is disposed in the axis of the cylinder.v At the ends of the disyassumed that the modulation potentials are applied' only'to the end-plate electrodes. 'rnere is shown as abscissa the bias potential of the endfplate electrodes with respect to the cathode. In

Figure 3 the direct bias of the end-plate electrodes S is plotted as the abscissa. A reference ordinate is plotted .in;the 0 point' of the bias for the end-plate -electrodes1(US=UK). The fre- `quency, variations and the lamplitude variations of the radio frequency oscillations generated are et also plotted as ordinates. 'It will be-recognized from this graphic representation that at 0 nega- "tivebias of the end-plate electrodes S and for all values of-negative bias to the left of 0, the radio frequency amplitude remains constant andsthat l only the frequency of the oscillations generated is varying. When approaching the value US=UK, that is tosay, the ,value of the cathode potential from tle negative range, i. e., from the left of 0, then the radio frequency amplitude begins to decrease. Therefore, only the eld at the left of the reference ordinate is to be used for obtaining a sharp frequency modulation, the end-plate electrodes having a negative bias relative to the cathode in said field. It is seen that if the end-plate electrodes have a high negative bias potential, frequency modulation is possible without amplitude variation. It follows therefromvth-at in the modulation 'methods hitherto known, frequency variations and amplitude variations must be produced simultaneously when using positively biased end-plate electrodes.

Figure 4 shows a complete oscillatory circuit utilizing a split plate magnetron in a self excitation circuit. The anodes A1 and A2 have impressed thereon in the known manner a highly positive bias potential U. applied across the oscillatory circuit O. 'I'he end-plates S receive a vnegative bias potential U. relative to the cathode. At the same time there is impressed upon the endplate electrodes, alternating -potentials which vary in rhythm with potentials supplied from a modulation source M across a transformer T.

In a manner similar to that by which frequency modulation can be obtained, it must' also here be possible to suppress an undesirable frequency modulation component with the method according to the invention. Now, methods are known as such for producing electro-magnetic oscillations which have modulated either the amplitude or only the frequency. It is also known to carry out a modulation in a circuit of an electrode other than that for the main modulation, and whereby the first modulation serves for compensating an undesirable side modulation.

Figure 5 shows a circuit in which there is obtained an amplitude modulation for instance by influencing the plate potential, -and a countermodulation by influencing the potential of the end-plate electrodes. Herein, item R designates the tube envelope and P are the poles of a magnet arrangement.

The tube which is used in a device according to Figure 5 is represented in Figure 1. The numeral M shows that at this point a microphone or a modulation amplifier is intended to be connected. A

The modulation potentials impressed upon plate A and on the end-plate electrodes S1 and S2 through the transformer T (Figure 5) have to be in phase opposition if an undesirable frequency modulation is to be suppressed.

It appears to be in place to emphasize a fact revealing the principal difference between the working with positively biased end-plate electrodes and that with "negatively biased vend-plate electrodes.

Positively biased end-plate electrodes are best suited in magnetrons having a single part anode.

A certain improvement in the efiiciency can also I are produced. In case of oscillations of the first order, an electron requires for a course of the loop change in direction until original direction is resumed-approximately one oscillation cycle.

-' An electron Amoving with the proper phase, and

which performs a pendulum movement between the anode and the cathode, always approaches the anode for instance,v when the alternating potential superposed on the direct plate potential has a negative sign. The electrons therefore, rotate in circular courses between cathode and anode such that they always pass towards the incidentally negative electrode thereby delivering their energy in stages. By means of a positively elds which they produce concentrate the electron paths to a greater or lesser degree only to. the center of the discharge path. The efficiency of the high frequency power will thus practically not be influenced at least not in the ranges used.

'I claim:

1. In a. modulation system4 a generator of the magnetron tube type comprising a tube having an anode and a cathode, mean-s for applying a positive potential to said anode relative to said cathode, means for producing a magnetic field of constant strength at right angles to the path which the electrons would follow between said cathode and anode in the absence of said field, means connecting said anode and cathode in oscillation generating circuits, said tube also having.endplate electrodes, means for maintaining said end-plate electrodes negative a substantial amount relative to said cathode, means for varying the potential of said anode in accordance with modulating potentials to amplitude modula'te the oscillations generated, and means for varying the negative potential of said end electrodes in accordance with modulating potentials to produce corresponding variations in the frequency of the oscillations generated.

2. In a system for producing oscillatory energy and modulating the same at signal frequency, a tube device having a substantially linear cathode, an anode concentrically disposed with respect to the cathode, and an end-plate located at each end of said aforesaid electrodes with means for producing a magnetic field of substantially constant -strength in which said electrodes are disposed, means connecting said anode and cathode in an oscillation producing circuit, means for mainf taining said end-plates at high negative potential relative to said cathode, and means for applying modulating potentials to said end-plates comprising a direct connection between said endplates, and a transformer havinga secondary kwinding connected between said end-plates and said cathode, and a primary winding excited by modulating potentials, the values of said modulating potentials and high negative potential being such that said tube operates substantially within the negative portion of its end-plate-output characteristic, whereby the oscillations produced are varied in frequency in accordance with said applied modulating potentials.

3. In a system for producing oscillatory energy and modulating the same in amplitude at signal frequency and for substantially suppressing or preventing frequency modulation\tlereof, a tube device having a substantially linear cathode, an

anode concentrically disposed with respect to the cathode and an end-plate located at each end of said aforesaid electrodes with means for producing a magnetic field of constant strength in which said electrodes are disposed, means for maintaining said end-'plates at relatively high negative potential relative to said cathode, means for applying modulating potentials to said anode to producecorresponding variations in the amplitude of the oscillations generated, and means for applying modulating potentials to said endplates, to produce corresponding variations in the frequency of the oscillations generated'to compensate frequency variations inherently produced therein by applying said modulating potentials to said anode.

`4. A system as recited in claim 3 wherein said means for applying modulating potentials to said end-plates includes a direct connection between said end-plates and a reactance on which said modulating potentials .are impressed connecting said end-plates to said cathodewhereby said end-` plates are modulated in phase.

5. A system as recited in claim 3 wherein said means for applying 4modulating potentials.to said y anode and to said end-plates comprises a transformer having a primary Winding excited by modulating potentials, a .first secondary winding having one terminal connected to -both of said end-plates and the other terminal connected to said cathode and a second secondary winding connected between said anode and cathode.

KARLFRI'I'Z.

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