US2004171A - Oscillation generator - Google Patents

Description

June 11, 1935. H, MUTH E 2,004,171

OSCILLATION GENERATOR Filed May 2, 1933 INVENTORS HEKBEETMl/Tf/ We 65 7 {z BY W ATTORNEY Patented June 11, 1935 J ":2 L

r OYSCILLATION GENERATOR Herbert Muth and Wilhelm Runge, Berlin, Ger

many, assignors to Telefunken Gesellschaft 1 fur Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application May 2, 1933, Serial No. 668,957

' In Germany April 23, 1932 3 Claims. (01. 250-36) i As is well known in circuits for producing oscillations which are return coupled, the frequency of the oscillations produced is essentially determined by the natural frequency of theoscilla- 5 tory grid circuit. However, this frequency to a small extent is also dependent on the size of all other impedances arranged in the circuit. Where a tube is to be operated so as to utilize its total energy and in which the load resistance in the 0 anode circuit is adapted to the tube, the produced frequency is to a quite essential degree particularly dependent upon the impedance'of the consumer. It is dependent, for instance, upon the tuning and coupling of the coupled antenna. In order to reduce this undesirable relation it is often the custom to refrain from directly connecting the consumer to the self excited stage and instead across amplifier stages, in

which case the transmitter is termed a separately controlled transmitter.

The present invention enables a self excited tube stage to supply larger energies without the produced frequency being essentially dependent on the impedance of the consumer.

In accordance with the present invention a return coupling circuit, comprisingreturncoupling means connected in series to the output circuit and utilizing an amplifier tube with high inner resistance in which the capacitative coupling of the anode with the control electrode is eliminated,

is arranged in such a manner that thezphase, of the potentials transmitted tothe control circuit by the return coupling is essentially determined only by the phase of the emitting current which leaves the cathode. For attaining the result aimed at by the present invention screen grid tubes are suited in particular and also the customary three electrode tubes in which, by the use of neutralizing means, in particular neutralizing capacitative bridges (neutrodyne), the capacitative coupling of the anode with the control grid across the inner capacity is eliminated.

Figures 1 and 2 are merely given by way of example to illustrate schematically known oscillator arrangements, and Figures 3 to '7 show various modifications of the present invention.

If, as was the case hitherto, the tuned grid circuit l of a tube 2 (see Figure l) is return coupled with the anode circuit, oscillations are produced whose frequency is determined by the condition that requires that the phase of the alternating current voltage applied to the grid I of thetube 2 through the anode current across the circuit I must be equal to the phase necessary 5 for maintaining the existing anode current. In

inserting into the anode circuit of the tube any impedance 3, the relation between the phases of grid potential and anode current is thereby changed and the frequency of, the produced oscillations has another value for which the above relation in phase is again fulfilled; In order to render the influence of the useful impedance arranged in the anode circuit independent of the phase of the current flowing in the anode circuit, and thus also. rendering the frequency of the produced oscillations independent of the changes of the impedance of the consuming circuit, it is advisable to connect in series with the consuming circuit 3 a resistance which is high in regard to this circuit. This can be accomplished in such manner thattubes are used whose inner resistance is high as'compared with the outer impedance. Thus the total impedance of the anode circuit is substantially represented by the inner resistance of the tube, and fluctuations of the impedance of the load circuit causeonly slight variations in the phase of the anode current and of the produced frequency. The use of such circuits, namely, in whichfor producing 0scillations a back coupled screen grid tube is employed, forinstance, and whose inner resistance corresponds with the above requirements, does however not yet lead to the desired end. The cause for the produced frequency being much dependent on the fiuctuationsof the impedance'of the load circuit also in such circuits lies in the fact that, in particular for short waves, theleak capacities between the anode and the cathode point present'an essential capacitative parallel connection with regard to the high inner resistance ofthe tube, so that the impedance of the load circuit in regard to the circuit including the return coupling member can no longer be considered. as being connectedin series to .a high resistance. The effective leak capacityis then the capacity between anode and screen grid which in most cases is maintained at cathode high frequency potential, and, furthermore, the capacity directly between anode and the leads thereof and cathode and the leads thereof. Which of these two leak capacities predominates by their detrimental action will depend respectively on the construction of the transmitter. speaking, both act however in the same deleterious sense.

In accordance with the present invention the circuit is arranged in such a manner that the currents passing over the leak capacities, the course of which is shown in Figure 2 by the dotted capacities 4, do no longer produce a direct PATENT OFFICE 1 5 Fundamentally of the currents passing through the return ecupling member is thus determinedby the high inner resistance of the tube used, and the produced frequency of the oscillations-is.therefore independent of the variations in the impedance of the consumer.

Figure 3 shows a circuit in accordancewith the present invention in which: the detrimental; in-

fluence of the screen grid anode capacity is eliminated. The consuming circuit in the form of a tuned circuit 3 coupled with an antenna 8 is placed between anode and screen grid and the return coupling coil 1 connected in seriesto the consuming circuit, connects the cathode to the. screen grid. Thus the currents passing over the anode to screen grid capacity also flow through the return coupling 1. Obviously it is not. necessary to provide the same return coupling member for the currents passing over the screen grid to anode capacity and those flowing through the load circuit As indicated in Figure. 4,..it is. also possible. to provide a special return coupling coil 1' for. the

capacitative currents. passing,- over. the. tube capacity.

Figure 5 shows a circuit in. which. the leakcapacity formed between the. anode. lead and cathe ode lead is made ineflective. To thisendashield. B is placed. around the anode. lead, to which however no cathode potential. is. applied as. is usually the case, but which is connectedtopoints of the. return coupling coil. 1 carrying. high. ire-J quency potential. In. the same manner, as. was previously the case. for the side currents, passing. over the tube capacity, the blind currents. flowing through the electrode lead capacity are utilized for the return coupling. Also in this case. it would be possible to provide, asin the case. of Figure 4, a special return coupling member for the parallel circuit.

Particularly suitableis a combination. of. the two circuits in accordance with Figure 6', in which. the outer shield is connected to the screen grid and wherein the blind currents of both circuits are passed to the return couplingcoil "I.

In the embodiments shown by way. of example the protective shield. and the. screen grid electrode arev directly connected to the cathode across the return coupling means. It is. obviously within the spirit of the invention that in providing a connection in the manner described stress must only be laid in regard to high frequency. Instead of, for instance, providing a conducting connection of the screen grid electrode to the cathode across the return coupling means, and to bridge in this circuit the screen grid direct voltage source by means of a parallel condenser, as illustrated in the figures, it isalso possible to supply the voltage tothe cathode and screen grid through a direct connection therebetween blocked against high frequency and to carry the high. frequency from the screen grid across a blocking condenser to the return coupling member. Such a circuit is shown in Figure '7.

The essential feature of the present invention resides in the fact that the phase of the currents of the circuit including the return'coupling memher is essentially determined by the high tube resistance. It is advisable therefore in the interest of a greater frequency constancy, although to the detriment of optimum utilization of the energy, not to adapt the consumer to the tube, but to choose a smaller resistance thereof, i. e., to dimension thesarne'in the sense of a subordinate adaptation.

It is-then essential that the choke 9, which, if it were directly connected; between anodeand cathode, would again represent, at this time an inductive, bridging for the anode cathode path, is chosen solarge that the parallel connection does not produce. a detrimental efiect or that the current passing therethrough is likewise utilized for the return coupling effect. A

Having thus described our invention and the operation thereof, what we claim is:

1.. A regenerative oscillation generator circuit comprising an electron discharge device characterized by high internal resistance having a cathode, anode, control grid and screen grid, a tuned input. circuit coupled between said control grid and cathode, a tuned output circuit connected be.- tween said anode and screen grid, a coil. indu..- tively coupled to said input circuit and having one'terminal connected to the cathode and the: other terminal connected to the screen grid end of said. output circuit whereby the currents in said screen grid and. anode circuits additively" combine in said coil to affect regeneration.

2;. A regenerative oscillation circuit in accordance withclaim 1, characterized in this that the connection extending from said anode to said tuned output circuit is shielded. V

3. A regenerative oscillation circuit in aecordance with claim 1, characterized in this that the connection extending from said anode to said.

tuned output circuit is shielded, and a connection is provided between said shieldand said screen grid. 1

HERBERT MUTH. WILHELM RUNGE.

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