US2235198A - Anode neutralizing circuit for short waves - Google Patents

Description

March 18, 1941. w BUSCHBEQK" 2,235,198

AN01E."NEUTRALIZING cmcurr FOR SHORT. WAVES Filed April 15, 1937 lNVENTOR WERNER BUSCH BECK ATTORNEY Patented Mar. 18, 1941 ATENT orrlcs ANODE NEUTRALIZING CIRCUKT FOR SHORT WAVES Werner Buschbeck, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application April 13,

1937, Serial No. 136,537

In Germany April 24, 1936- 6 Claims.

My invention relates to neutralizing circuits and in describing the same reference will be made to the attached drawing wherein Figures 1 and 2 show two embodiments of my plate neutralized amplifier or relay.

Experiences have taught that in short Waves and more especially in ultra-short waves remote controlled triodes operating in the ordinary capacitive anode-neutrodyne circuit according to Figure 1, require additional control power which may amount to a multiple of the actual control power determined by the grid current, and which cannot be explained by influences upon the travel time, and bridge detunings owing to space charge variations or the like. In Figure 1 item R is a remotely controlled tube whose gridplate capacity CAG (shown in dash lines) is new tralized by the neutralizing-condenser UN. The voltage division in the plate circuit is obtained by capacitive means across the capacitances CsP while the useful energy is derived from the inductance of L. Now, the exact calculation shows that the additional control energy i due to the fact that owing to the voltage division of the al- 25 ternating grid potential Ug in addition to the potential produced on account of the amplifying action of the tube a voltage component proportional to Ug appears at the anode-cathode path across the anode-grid capacity and the upper voltage division capacity C'sP, said voltage component having the effect that from the control power source an efiective power passes to the load. With the permissible neglect of certain factors, this consumption of power can be represented by a fictitious additional grid resistance Re zus appearing in parallel to the grid-cathode path and having the value:

in which R1 denotes the inner resistance obtained from l/ (reciprocal of amplification constant of tube) and the mean working steepness Sm of the tube. CAK represents the total capacity appearing between anode and cathode, i. e., the parallel circuit of the tube, and of the capacity Csr. D=1/[.t. In screen grid tubes or generally in tubes having a small l/ (reciprocal of amplification constant of tube) i. e., tubes having a high inner resistance, the Formula 1 assumes the simpler expression 1 m +m sz The conditions will be elucidated by a numerical example.

CAK

OAK ne is approximately 0.5 in other words:

1.5 a zus X" 10 3 ohms and for an alternating grid potential of for instance U =370 v. there will be obtained as additional grid power W R. thus the entire control power is N =228+=273 watts, which is almost exactly 6 times the control power actually required in case of long waves (45 watts). The calculation further shows that the requirement in additional control power enters the consumer in the form of useful energy 5 I Without detrimentally affecting the efficiency of the tube.

It is the task of the present invention to reduce this aditional control power to a minimum. The. manner in which this can be accomplished is shown by the Formulae 1 and 2. The parallel resistance Re zus will be high, and hence the additional power derived from the control transmitter becomes low, when the quotient is large. This quotient is always large where long wavesare involved and this is why the matter of the additional control energy was hitherto never considered in the long wave range. In short waves and more particualrly in ultra-short waves, it is necessary to maintain all capacities, both of tubes and circuits, as low as possible in order to tune to these short waves, so that therefore ranges are soon arrived at in which CAG and OAK are of the same order, or in which CAK is even lower than CAG. Despite this the desired efiect of the increase in Re zus can also be attained in this case. This is accomplished in accordance 228 watts with the invention as shown in Figure 2. The I inductance of the plate circuit is divided into two parallel branches I and II. The branch II serves for deriving the useful power while branch I may be varied for tuning purposes thereby avoiding the need of extra capacity for this purpose. The parallel coil I is connected in accordance with the invention at its center M to the grid point G by way of a direct current voltage blocking condenser CB. In this way, the upper half of the parallel coil is connected as regards high frequency in parallel to the grid-anode capacity, and the lower half in parallel to the neutralizing capacity, thereby increasing the resultant reactance of the said partial paths. Since through multiplication with w in the numerator, and denominator the expression for Rg zus can also be written in the form: I

it can be readily seen that R; z'us has increased by the described measure, without increase at the same time of the entire wattless volt amperes oi the circuit.

If the center of the coil M would be connected to the cathode point K instead of grid G, as a result XA'K would be increased, i. e., Rg'zus would be decreased so that in this case, it would be possible by an increase of N; zu's to increase the resultant consumer powerbeyond' the power supply of the amplifier tube. This could be of advantage even when producing very short waves which could be attained only with a single transmitter tube, since in this case a higher useful power could be attained simply by a greater dimensioning of the control transmitter.

In principle the increase of XAG could be extended in a resultant fashion up to the formatio'nof a blocking circuit or even further up to 'a high inductive resistance (it should be remarked that for purposes of neutralization it is known to construct the plate grid path alone as a blocking circuit, but owing to the neutralization depending on the frequency, and which exists only for the fre uency of the blocking circuit, this blocking circuit could not practically be used) Since the circuits betweengrid-anode, gridneutrodyne point N and anode Aneutrody'ne point N, despite the neutralization being maintained independent of the waves, afford a self excitation of the type of the Huth-Kuehn circuit, the blocking condenser CB is preferably made variable, in view of the fact that below a certain limit determined by the natural waves of the circuits, this possibility of self excitation no longer exists. The coils placed in parallel to the grid-anode capacity or to the neutralizing condenser CN may also be blocked separately or instead of connecting the anode choke to the center point M of the coupling coil, it may also be connected to A or N.

The method according to the present invention may alsobe applied to the more complicated anode=neutralizing-bridge circuits such as or dinarily used in short wave transmitters. In this'case, the tests have even revealed an improvement of the eiiiciency of the amplifier tubes as com-pared with the ordinary arrangement.

I claim:

1-. In aneutralized ultra-high frequency relay circuit, an electron discharge device having a control electrode, a cathode, and an anode, means for impressing wave energy on said control electrode and cathode, an anode circuit including reactance, a connection between a point on said anode circuit and. said cathode, a neutralizing circuit connecting a secon point on said anode circuit to said control electrode, and supplemental neutralizing means comprising a second reactance shunting a portion of said first reactance of said anode circuit, a point on which second reactance is connected to the control electrode of said tube.

2. A wave relaying system comprising in combination, an electron discharge device having a control grid on which wave energy to be relayed is impressed, said device having an anode in an alternating current output circuit from which relayed energy may be derived, variable inductive means for reducing the eifective capacity between said grid and anode, said variable inductive means simultaneously tuning the alternating current output circuit of said device, and means including additional inductance for neutralizing the resulting admittance introduced by said first inductance between said grid and anode.

3. Means for preventing feedback in an amplifying system comprising an electron discharge device having a controlling electrode on which wave energy to be amplified is impressed, and an output electrode from which amplified wave energy is derived which includes, means for substantially eliminating the feedbackdue to susceptance between the controlling electrode and. output electrode comprising connected therebetween an additional susceptance of substantially equal magnitude and opposite sign, and means for neutralizing the feedback due to the inherent resultant conductance introduced by said additional susceptance comprising a combination of circuit elements connected between one of the said electrodes and a point having a potential of a phase opposite to the phase of the potential of the other electrode, said circuit elements being arranged to provide an admittanc similar to the total effective admittance between the controlling electrode and output electrode.

4. In a neutralized amplifier system, an electron discharge device having a control electrode and cathode on which wave energy to be amplified is impressed, said device having an output electrode from which amplified wave energy is derived, inductive means for tuning out the capacitive susceptance between the control electrode and output electrode to substantially reduce voltage transfer from the latter to the former, and means including inductance for balanc'ing out the conductance introduced between said control electrode and output electrode by said inductive'means to additionally neutralize said device and circuit.

5. In a neutralized amplifier system, an electron discharge device having a control electrode and cathode on which wave energy to be amplified is impressed, said device having an output electrode from which wave energy is derived, means for tuning out the capacity between the control electrode and output electrode comprising an inductance connected in shunt to the capacity between said control electrode and output electrode and means for balancing the conductance introduced between the control electrode and output electrode by said inductance comprising a second inductance and a neutralizing condenser connected to provide a coupling between said output electrode and said control electrode substantially equal and opposite to the coupling introduced by said conductance.

$3. in an ultra-high frequency wave relaying system, an electron discharge tube having a control grid, an anode and a cathode, a tank circuit comprising variable inductance shunted by series capacities, means connecting one end of said inductance to the anode of said tube, a neutralizing condenser connecting the other end of said inductance to the control electrode of said tube, a capacity connecting a point on said inductance intermediate the terminals thereof to the control electrode of said tube, a connection between said series capacities and the cathode of said tube, means for impressing wave energy to be relayed on the control grid and cathode of said tube, and means for deriving relayed wave energy from said tank circuit.

WERNER BUSCHBECK.

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