US2226694A

US2226694A - Neutralization circuit for short wave transmitters

Info

Publication number: US2226694A
Application number: US188233A
Authority: US
Inventors: Buschbeck Werner
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1937-03-05
Filing date: 1938-02-02
Publication date: 1940-12-31
Anticipated expiration: 1957-12-31
Also published as: NL53699C; FR834462A

Description

Dem 3 1, 1940. w. BUSCHBECK 2,226,694

NEUTRALIZATION CIRCUIT FOR SHORT WAVE TRANSMITTERS Filed Feb. 2, 1938 OUTPUT wpu'r INPUT aurpur INVEN TOR. WEI??? BUS C HBEC' K BY A TTORNEY.

Patented Dec. 31, 1940 PATENT OFFICE NEUTRALIZATION CIRCUIT FOR. SHORT WAVE TRANSMITTERS Werner Buschbeck, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berli of Germany 11, Germany, a corporation Application February 2, 1938, Serial No. 188,233

In Germany 9 Claims.

The invention relates to a neutralizing circuit for short waves in which essential drawbacks of the hitherto known circuits are overcome.

In order to more readily understand the invention, a discussion will first be given with respect to known circuit arrangements and their difiiculties.

, Figs. and 6 represent two well known neutralizing circuit arrangements of the prior art.

In Fig. 5 a balance may be readily achieved between tube capacity Cag and neutralizing capacity Cn, such that a voltage introduced in the input does not result in developing a voltage across the output. However, in this condition of adjustment, voltage across the output circuit sets up a potential difierence between grid and cathode by way of the voltage dividing capacity path Cag, C1. back through the neutralizing condenser Cn because the balance before mentioned assures that no current fiows in the input coil system as a result of voltage across the output circuit, and therefore there is no way for current through the neutralizing condenser to influence the potential difference between grid and cathode. Thus, in spite of the bridge arrangement being theoretically perfect for preventing output voltage from reacting upon the input circuit, it nevertheless does not prevent output voltage-from being fed back in degenerative phase to the input electrodes, that is, between grid and cathode, Fig. 5 is sometimes rearranged so that thecathode of the amplifier is connected to the center of the input coil system rather than to the center of the capacity branch thereacross. In this case the same phenomenon occurs except that the amount of voltage fed back is reduced in proportion to the coefiicient of coupling between the two halves of the input coil, and the phase of the feed back becomes regenerative due to the re versal of the sign of the reactance between grid and cathode.

In Fig. 6 a similar known neutralizing arrangement demonstrates that while a perfect bridge balance will prevent any coupling between input and output circuits, except by, virtue of the desired relay action of the tube, the voltage impressed upon the input circuit will produce a voltage between anode and cathode and vice versa. This again is true whether the cathode be connected to an intermediate point on the capacitive branch of the output circuit or tea corresponding intermediate point on the inductive branch thereof. a

Thus, it is evident that in the arrangements of This is not neutralized by any feed March 5, 1937 (01. run-171) the known art a bridge balancing achieves only one of two desirable results. It is the object of the present invention to attain both the complete decoupling of input and output circuits other than through the electron relaying action of the tube and also to prevent voltage in the output circuit from causing any potential difference between the tube input electrodes. This is done by employing an auxiliary, symmetrically arranged network, arranged to provide a resonant short circuit path at the operating frequency between the cathode and the cold electrode which is connected to the dividedcircuit of the ampliher. This auxiliary circuit may, however, in practice be coalesced with the already existing divided circuit.

The invention will now be described in greater detail in connection with the accompanying drawings, wherein:

Figs. 1 and 2 illustrate two ways of eliminating feed-back in the grid neutralizing circuit in accordance with the invention, and

Figs. 3 and 4 illustrate two ways of eliminating feed-back in the anode neutralizing circuit in accordance with the invention.

Figs. 5 and 6 represent well known circuit arrangements shown for the purpose of the above exposition.

Fig. 1 shows a grid neutralizing circuit comprising the tube R, the grid-anode capacity GAG, the neutralizing capacity Cu and the capacities C1 and C2 of the oscillatory circuit. Item G represents the grid point, K is the cathode point, while A designates the anode point and N the neutral point. The oscillatory input circuit lies between N and G. In accordance with the invention a T element is placed in parallel to this circuit, said T member consisting of the two inductances L and a capacity C. The inductances L may serve at the same time as the coil of the oscillatory circuit. Without the condenser C a reactive coupling potential would exist at the grid point G which is determined by the proportion of the capacities CAG- and 01. This reactive coupling could, of course, be reduced at will by increasing the value of C1, but this is not feasible in case of short waves, and ultra short waves. If the capacity C is inserted and tuned in such a manner that the parallel connection of the two coil halves through which the currents arriving via Cu and Gag pass in opposite directions, in other,

words the value (wherein M is the mutual inductance between the two halves) is in resonance with C, a short circuit will be formed between G and K and between N and K as viewed from the plate cathode circuit. In other words, the feed back will be reduced to zero. The T element may consist either of two inductances and one capacity, as shown in Fig. 1, or it may consist of two capacities and one inductance, according to Fig. 2. In applying the invention, it is wholly immaterial whether the voltage division in the neutralizing bridge proper is capacitive or inductive.

In like manner, the passing of energy from the control transmitter to the main transmitter can be eliminated in the anode neutralizing circuit while the circuit need not be further developed into a push-pull double bridge as Was hitherto the case. The T element lies, as shown in Fig. 3, between the points A, N, and K. In Fig. 3 there is represented for the sake of clearness the bridge arrangement for the entire circuit, whereby R is again the tube, C1 and C2 the voltage divider capacities and A, N, K the anode point, neutral point and cathode point respectively. Between K and G the control transmitter is inserted and between A and N the main transmitter. At the proper tuning of the T element, the anodecathode path is short circuited as viewed from the control transmitter. Fig. 4 shows another mode of embodiment of Fig. 3 which corresponds to Fig. 1. It should, moreover, be emphasized that the efiectiveness of the arrangement described is not limited to rigorously exact series resonance tuning of the T element and that anywhere in the proximity of resonance an essential improvement over the hitherto known circuits is obtained. The resultant impedance X of a series element having the resonance resistance X0 increases at first gradually as the actual frequency w departs from the resonant frequency 200, in accordance with the equation For obtaining substantially all the results of the invention, it is only necessary that this value remain lower than the reactance XAG of the gridanode capacity.

The conditions are not quite as simple if the cathode, or anode, or both electrodes are not directly accessible, which in the case of ultra short waves is mostly the case owing to the electrode lead-ins. In this case, at anode neutralization, the resistance value of the T member, as viewed from the side of the control transmitter, must no longer be zero, but it must be so apportioned that the voltage produced directly at the anode-cathode path by the exciting alternating voltage disappears. The determination of the required resistance of the T element, by way of calculation, depends on the type of the circuit and after all on the type of the tube employed. An especially simple calculation is possible in case of tubes having a concentric grid and cathode and twin cathode structure, since hereby a bridge relationship can be deduced in which the anodecathode path lies in a diagonal of the bridge containing the inductances of the electrode leadins. The actual calculation will not be carried through herein, since it does not modify the general prin-' ciple of the invention. It may be said that there lies a greater advantage in carrying out the correct tuning of the T member through experimentation.

The invention can be applied in almost all bridge neutralizing circuits in which, at exact balance, a counter coupling or feed back occurs between an input or output circuit and a pair of tube electrodes.

What is claimed is:

1. The combination with a high frequency system having an input andan output circuit, and an electron discharge device having a grid and a cathode connected across a portion of the input circuit, and an anode and said cathode connected to said output circuit, said system having means for preventing voltage across said output circuit trom producing a potential diiierence between the terminals of said input circuit, of a reactance in the connection between said cathode and said input circuit, said reactance being of opposite sign to the reactance of that portion of the input circuit to which it is connected and having a magnitude such that voltage across said output circuit produces a voltage drop across said reactance equal and opposite to the voltage across said portion of said input circuit at the operating frequency, whereby voltage across said output circuit produces neither any potential difference across said input circuit nor any appreciable potential difierence between grid and cathode.

2. The combination with a highfrequency system having an input and an output circuit, and an electron discharge device having an anode and a cathode connected across a portion of the out put circuit, anda grid and said cathode connected to said input circuit, said system having means for preventing voltage across said input circuit from producing a potential difierence between the terminals of said output circuit, of a reactance in the connection between said cathode and said output circuit, said reactance being of opposite sign to the reactance of that portion of the output circuit to which it is connected and having a magnitude such that voltage across said input circuit produces a voltage drop across said reactance equal and opposite to the voltage across said portion of said output circuit at the operating frequency, whereby voltage across said input circuit produces neither any potential diiierence across said output circuit nor any appreciable potential difference between anode and cathode.

3. In an amplifier circuit having a vacuum tube having input and output electrodes, an output circuit connected to said output electrodes, and an input circuit for energizing said input electrodes, the method of eliminating feed-back of voltage from said output circuit to said input electrodes due to inherent interelectrode capacity, Which'inoludes as a first step neutralizing voltage across said input circuit due to voltage across saidoutput circuit, and as a second step utilizing resonance eiiects to eliminate residual voltage between input electrodes due to potential difierence existing across the portion of said input circuit to which said input electrodes are connected.

4. In an amplifier circuit having a vacuum tube having input and outputelectrodes, an output circuit connected to said output electrodes, and an input circuit for energizing said input electrodes, the method of eliminating feed-back of voltage from said output circuit to said input electrodes due to inherent interelectrode capacity, which includes as a first step neutralizing voltage across said input circuit due to voltage across said output circuit, and as a second step utilizing series resonance to eliminate residual voltage between input electrodes due to potential difference existing across the portion of said input circuit to which said'input electrodes are connected.

5. The combination with an amplifier circuit having a vacuum tube having a cathode and a pair of cold electrodes and input and output circuits therefor, a bridge neutralizing circuit connected to said electrodes in such manner that a voltage introduced in the input circuit will not result in developing a voltage across the output, except by virtue of the desired relay action of the tube, said bridge neutralizing circuit including a divided circuit to which the cathode and one of said cold electrodes are connected, of means providing a resonant short circuit path at the operating (frequency between said cathode and said one cold electrode.

6. In an amplifier circuit having a vacuum tube having input and output electrodes, an output circuit connected to said output electrodes, and an input circuit for energizing said input electrodes, the method of eliminating transfer of voltage from said input circuit to said output electrodes due to inherent interelectrode capacity, which includes as a. first step neutralizing voltage across said input circuit due to voltage across said output circuit, and as a second step utilizing resonance efiects to eliminate residual voltage between output electrodes due to potential difierence existing across the portion of said output circuit to which said output electrodes are connected.

'7. In an amplifier circuit having a vacuum tube having input and output electrodes, an output circuit connected to said output electrodes, and an input circuit for energizing said input electrodes, the method of eliminating transfer of voltage from said input circuit to said output electrodes due to inherent interelectrode capacity, which includes as a first step neutralizing voltage across said input circuit due to voltage across said output circuit, and as a second step utilizing series resonance to eliminate residual voltage between output electrodes due to potential diiTerence existing across the portion of said output circuit to which said output electrodes are connected.

8. In an amplifier circuit having a vacuum tube having first and second sets of electrodes, an output circuit connected to said second electrodes and an input circuit for energizing said first electrodes, the method of eliminating transfer of voltage from one of said circuits to that set of electrodes to which it is not directly connected due to inherent interelectrode capacity, which includes as a first step neutralizing voltage across said input circuit due tovoltage across said output circuit, and as a second step utilizing resonance efiects to eliminate residual voltage between the electrodes of said one set due to potential difierence existing across the portion of the circuit to which said one set of electrodes is connected.

9. In an amplifier circuit having a vacuum tube having first and second sets of electrodes, an output circuit connected to said second electrodes and an input circuit for energizing said first electrodes, the method of eliminating transfer of voltage from one of said circuits to that set of electrodes to which it is not directly connected due to inherent interelectrode capacity, which includes as a first step neutralizing voltage across said input circuit due to voltage across said output circuit, and as a second step utilizing series resonance to eliminate residual voltage between the electrodes of said one set due to potential difierence existing across the portion of the circuit to which said one set of electrodes is connected.

WERNER BUSCI-IBECK.