US2080571A - Modulation-controlled magnetron oscillator - Google Patents

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y 1937. w H. E. HOLLMANN 2,080,571

MODULATION CONTROLLED MAG NETRON OSCILLATOR Fiied Aug. 15, 1935 INVENTOR. HANS ERICH HOLLMANN BY 7%. v-W

ATTORNEY.

Patented May 18, 1937 UNITED ST T OFFICE signor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application August 15, 1935, Serial No. 36,308 In Germany August 21, 1934 3 Claims.

This invention relates to magnetron oscillators and has particularly to do with the provision of improved means for modulating ultra-high frequency oscillators.

The magnetron, as is known, is extremely well suited for producing ultra-short waves, and especially favorable useful eifects are obtained therewith where the anode cylinder is divided into two or several segments. In a simple magnetron, modulation fluctuations may be superposed on the direct plate potential. In the case of a split anode magnetron with two segments, or in case of a magnetron having a plurality of splits in the anode and two groups of segments, connected in both cases to the two poles of a resonance system, there is obtained a more favorable stabilization of the modulation characteristic and a greater range of control, if the two segments or the two groups of segments instead of being modulated in equal phase, are modulated in push-pull. This was hitherto done in such a manner that two modulation voltages with a phase displacement of 180 such as furnished for instance by a push-pull transformer, were superposed on the equal potentials applied to the two segments, or groups of segments respectively.

This hitherto known method of modulation implies all the disadvantages encountered in the direct anode potential modulation of any transmitter. Moreover, these secondary windings of the push-pull transformer are highly loaded by the inner resistances of the magnetron, thus requiring considerable modulation energies to produce the alternating potentials necessary for full control of the magnetron. A further drawback is to be seen in the fact that the secondary windings must carry a considerable direct current load to the anode. Hence a transformer of large dimensions is necessary, otherwise the ohmic resistance loss would be excessive.

It is an object of my invention to avoid the above mentioned drawbacks by providing means including electron discharge tubes interposed in the anode circuit of a magnetron oscillator through the medium of which modulation may be effected.

In carrying out my invention I have found it preferable to place in parallel with each branch of the anode circuit of a magnetron oscillator an electronic path whereby approximately the same load is carried as in the generator tube. A common load for the anode circuits of the magnetron and for the parallel circuits thus introduced may be applied in series with a source of direct current potential between the cathode and the anodes of the magnetron. In modulating the magnetron, oscillations from any suitable modulating source may be applied to the control electrodes of the parallel tubes. The dissipation of power in the modulating circuits may then be kept within 5 negligibly small amounts due to the fact that only grid control energy is necessary.

The sole figure of the drawing illustrates diagrammatically a preferred embodiment of my invention.

Referring to the diagram I show a magnetron type of electron discharge tube M having a cylindrical arrangement of split anodes S1 and S2. The filament cathode is shown as a small circle centrally disposed with respect to the cylindrical system of anodes. It will be understood that the cathode has two terminals in order that a source of potential may be applied thereto for heating the same. This, however, has not been shown in the drawing because it is well understood by those skilled in the art.

Each of the anode sectors S1 and S2 may be fed with direct current anode potential from any suitable source (not shown) to be inserted between the terminals +Ea and -Ea. In the cir- 5 cui't leads to the anodes, choke coils W1 and W2 are preferably provided. These chokes would naturally have iron cores if audio frequency modulation is to be used. The anode leads themselves are shown as a Lecher-wire system, which may be tuned to the desired frequency of a carrier wave by means of a capacitor C, the terminals of which may be bridged across the Lecher-wire system at suitable points relative to the location of voltage nodes along the transmission wires.

Each of the anode circuit leads of the magnetron is branched to an output circuit of an electron discharge tube such as R1 and R2. These tubes may be operated in a push-pull manher by connecting the grids to opposite terminals of a secondary winding of a transformer T. This transformer secondary has a mid-tap connecting through a gridbias battery 3 to the cathodes of the respective tubes R1 and R2, and of the magnetron tube M.

When modulations are applied to the primary winding of the transformer T it will be clearly seen that the tubes R1 and R2 will be controlled in a push-pull manner. Each tube will carry half of the current to be used in modulating the 5 magnetron since the variation in load which is controlled by one of the modulating tubes afiects only that half of the dissipation of the anode energy in the magnetron which is applied to one of the anode segments.

If desired, the two sides of the magnetron tube may be fed with energy from respectively independent sources. Such an arrangement provides for independent setting of the working points in the two modulation characteristics as applied to the two anode segments S1 and S2. Substantially the same results may be obtained, however, by placing a suitable ohmic resistor in one or in both of the circuit leads to the anode segments of the magnetron. In this manner the effective plate potential will be decreased by the voltage drop through the resistors. Such resistors should preferably be bridged by suitable capacitors in order to prevent alternating voltages across the resistors from disturbing the uniform push-pull modulation.

In the operation of my invention it will be seen that I have provided a means for controlling a magnetron oscillator through a transformer T of relatively small proportions. The push-pull manner of control as applied to the anode sections S1 and S2 has decided advantages over such control as might be applied to the cylindrical anode structure of a magnetron not having split segments. Other advantages of the invention will also be aparent to those skilled in the art.

It is to be understood that various modifications of my invention may be utilized without de-- parting from the spirit and scope thereof as defined by the appended claims.

I claim:

1. In an ultra-high frequency oscillator, a magnetron discharge tube having a cathode and a plurality of anode sectors, a source of direct current in circuit between the cathode and each of the anode sectors, means for modulating said oscillator comprising a push-pull network having a pair of electron discharge tubes the output circuits of which are connected each respectively with one of the anode. sectors of said magnetron tube, a source of modulations, and means including a transformer having a secondary winding with a mid-tap connected to the cathode of said magnetron tube and with the extremities of said winding connected respectively to the grids of said electron discharge tubes, said means being adapted to apply modulating potentials from said source ;of modulations to said grids, thereby to control the impedances of said electron discharge tubes in a push-pull manner and hence to vary the anode potentials applied to the anode sectors of said magnetron tube.

2. In an ultra-high frequency circuit arrangement, a magnetron oscillator tube having a cathode and a plurality of anode sectors, a Lecherwire tuning system having parallel conductors connected to said anode sectors, a source of direct current potential connected between the cathode and said tuning system, a source of modulating energy, a push-pull transformer having a primary winding connected to said modulating source and a secondary winding on which there is a mid-tap connected to the cathode of said oscillator tube, and a push-pull network having two electron discharge tubes the input circuits of which include respectively different portions of said transformer secondary winding, and the output circuits of which are disposed in parallel respectively with different ones of said parallel conductors of said Lecher-wire system.

3. A device in accordance with claim 2 and further characterized in that a capacitive bridge is provided across the. parallel conductors of said Lecher-wire system.

HANS ERICH HOLLMANN.

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