US2230216A - High frequency oscillation generator - Google Patents

Description

Patented Jan. 28, 1941 HIGH FREQUENCY OSCILLATION GEN- E'RATOR Cornelis Jacobus Boers, Eindhoven, Netherlands,

assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application February 17, 1938, Serial No. 190,937 In Germany March 8, 1937 tion to this an increase in the direct voltage of the positive electrodes that are arranged behind the control grid causes the electrons to be conducted away more rapidly from the region of the control grid. Hence there is a decrease in the 5 value of the control grid-cathode capacitance. In the case of an identical percentage variation in' the heating voltage and in the voltage of the positive electrodes, the influence of the last men- 5 Claims.

This invention relates to a circuit for generating ultra-high frequency oscillations in which the supply voltages, that is to say, the direct or alternating voltage used for heating the cathode and the direct voltages supplied to the other electrodes of the oscillator valve or valves are derived from a common source of voltage, for instance, a commercial supply whose terminal voltage is subject to variations.

When generators of ultra-high frequency ostioned voltage will be dominant, so that an incillations are energized from commercial power crease in the terminal voltage of thepower source sources, they are subject to the disadvantage results in a decrease in the control grid-cathode that the frequency of the oscillations generated capacitance. varies materially under the influence of variations According to the invention, means are provided of the supply voltage. This disadvantage occurs for limiting the percentage fluctuations in the particularly with superheterodyne receiving cirdirect current potential supplied at least to the cuits for very short waves. In such case a variafirst of the positive electrodes beyond the contion of the frequency of the oscillations set up trol grid These fluctuations then exert an locally produces an intermediate frequency which influence on the space charge which is equal differs from the frequency to which the interand opposite to the influence of the heating voltmediate frequency amplifier is tuned. This leads age fluctuations. Under these conditions the to a distorted reproduction and in the case of an control grid-cathode capacitance is made indeintense variation of the supply voltage the interpendent of the terminal voltage of the power mediate frequency produced may even fall ensupply source. Hence the frequency of the ostirely outside the transmitting range of the incillations produced is rendered substantially termediate frequency amplifier so that the reconstant. ceiving circuit requires to be retuned or in the According to one embodiment of the invention case of rapid variations the reception becomes the direct voltage for one or more of the positive wholly impossible. electrodes is derived from a potentiometer con- The invention has for its object to obviate nected in series with a resistor whose value de- 3 pends to a large extent on the current or voltage supplied. This resistor is connected between the terminals of a direct current source whose voltage is dependent upon the terminal voltage of the said power supply.

In order that the invention may be clearly understood and readily carried into effect a few embodiments thereof will now be described more fully with reference to the accompanying drawthis disadvantage. According to the invention, for this purpose the percentage fluctuations of the direct voltage which is supplied at least to the positive electrode closest to the cathode of the oscillator valve or valves are decreased to such an extent that the frequency of the oscillations produced is substantially independent of the terminal voltage of the commercial power source.

The invention is based upon recognition of the ing, in which 40 fact that when a variation occurs in the power Figure 1 illustrates diagrammatically the use supply voltage the resultant variation in the for purposes of the invention of a simple circuit frequency of the ultra-high frequency oscilhaving therein an oscillator tube of the triode lations is due to a variation of the space charge type; adjacent the control grid of the oscillator valve. Fig. 2 shows a modified circuit arrangement in A variation of this space charge brings about a which a pentode tube is employed; and variation in the control grid-cathode capacitance Fig. 3 shows still another circuit arrangement and the latter gives effect to a variation in the including a multi-electrode tube which is useful tuning of this oscillatory circuit. both for generating oscillations and for deriving An increase in the direct or alternating voltage a beat frequency with respect to the fundamental 0 serving for heating the cathode results in an frequency of the generator, and of an incoming increased emission and thus in an increase in signal. density of the space charge between the control Fig. 1 shows a circuit for generating ultra-high grid and the cathode so that the control gridfrequency oscillations. An oscillator valve l cathode capacity increases. In contra-distinchas its control grid connected via a leak resist- 5 ance 2 to the cathode and' viaa grid condenser 3 to an oscillatory circuit formed by a tuning condenser 4 and an inductance coil 5. The anode circuit includes a feed-back coil 6. The oscillations produced are supplied to the terminals 9 and II] by means of a coil 1 coupled to the coils 5 and 6. Any suitable load may be connected to the terminals 9 and Ill. The anode voltage and the cathode supply voltage are derived from a direct current source across the terminals of which lies a potentiometer l3 in series with a resistor |4 having a negative temperature coefficient. The cathode heating circuit is connected to terminals of the resistor I2 for obtaining a suitable filament voltage. An increase in terminal voltage of the source increases both the filament voltage and the voltage set up across the resistive elements l3 and I4. The control grid-cathode capacity of the tube I whose value depends on the space charge set up adjacent the control grid is connected in parallel with the oscillatory circuit 4, 5 so that a variation of the said space charge results in a detuning of the oscillatory circuit.

According to the invention, means are provided for avoiding fluctuations of the space charge between the control grid and the cathode as well as fluctuations of the frequency of the oscillations generated. In order to obtain this result the cathode-to-anode circuit is made to include a portion at least of the potentiometer I3 and the temperature dependent resistor |4. When the output voltage from the source II increases, the current that flows through the resistance |4 also increases so that the value of this resistance decreases and that part of the voltage which is supplied to the anode of the tube decreases. The anode voltage consequently exhibits lower percentage fluctuations than the heating voltage. If the potentiometer I3 is correctly adjusted the influence of the heating voltage fluctuations on the space charge is just balanced by the influence of the anode voltage fluctuations.

The circuit shown in Fig. 2 is distinguished from that shown in Fig. 1 by the use of a pentode discharge tube as the oscillator. In addition in this circuit arrangement the oscillatory circuit 4, 5 is included in the anode circuit and the feed-back coil H5 in the control grid circuit. Thus, the control grid-cathode capacity is connected not directly but via the transformer winding H5 in parallel with the oscillatory circuit 4, 5. The oscillations generated are supplied via a coupling condenser 8 to output terminals 9 and ID. The screen grid of the valve |5 is connected via a, condenser 26 to the cathode and via a resistance 25 to a point on the potentiometer 3.

Although the circuit shown in Fig. 1 comprises a resistance 4 having a negative temperature coefficient, Fig. 2 shows the use of a resistance 24 having a positive temperature coefficient. In this case the resistance 24 is connected to the positive terminal of the source H. In case of an increase of the voltage from this source the current passing through the resistance 24 will increase. This results in an increase in the value of this resistance so that the voltage which is sup-plied to the screen grid of thevalve I5 decreases. The operation is consequently identical with that of the circuit shown in Fig. 1.

Since fluctuations of the anode voltage can exercise only a very slight influence on the space charge adjacent the control grid, it is not necessary to take measures for limiting the anode voltage fluctuations. The anode of the valve I5 is, therefore, connected directly to the positive terminal of the source I. I

Fig. 3 shows part of a superheterodyne receiving circuit to which the invention is applied.

The mixing valve 4| serves both for generating local oscillations and for the frequency transformation of the received oscillations. This tube comprises successively an indirectly heated cathode, an oscillator control grid, an oscillator anode, a screening grid, a second control grid, a second screening grid, a suppressor grid and an anode.

The received high-frequency oscillations are fed via terminals I1 and I8 to an inductance coil l9 coupled to an inductance'coil 20 which by means of a condenser 2| is tuned to the frequency of the received oscillations. The condenser 2| is operated jointly with the condenser 4 by a common tuning control 22. Means are provided (though not shown in detail) for causing the frequency to which the circuit 20, 2| is tuned always to differ by a constant amount from the frequency to which the circuit 4, 5 is tuned. The end of the oscillatory circuit 20, 2| which is remote from the second control grid is connected by a condenser 23 to the cathode. The second control grid has supplied to it via a conductor 44 a variable negative bias for automatic volume control. The anode circuit of the valve 4| includes an oscillatory circuit 45, 45 which is tuned to the intermediate frequency and is coupled to a second oscillatory circuit 21, 28, the intermediate frequency oscillations generated being derived from the terminals 29 and 30.

The terminals 3| and 32 are connected to a commercial alternating current source. The primary 33 of the supply transformer is connected to these terminals. The secondary winding 34 is connected via conductors 35 and 36 to the.

heater of the cathode of the Valve 4|. The secrectifier 38 which also contains the usual means for smoothing the voltage of its rectified output current.

The percentage fluctuations of the direct voltage which is supplied to the oscillator anode and the screen grids are decreased by means of the series combination of a potentiometer 3 and a resistance |4 having a negative temperature coeificient down to the desired value in a manner similar to the circuit shown in Fig. 1. Since the anode voltage exercises substantially no influence on the space charge adjacent the control grid, the anode is connected directly to the negative lead 39.

' I claim:

1. A circuit for generating oscillations comprising a discharge tube having a cathode, an anode, and an oscillation-exciting electrode, a direct current potential source having a potentiometer connected across its terminals and connections from suitable points on said potentiometer to each of the electrodes in said tube for operating the same, means in said potentiometer for causing the incidental fluctuations of direct current voltage which is supplied to said oscillation-exciting electrode to be decreased in rela tion to the fluctuations of the potential diiTerence between the cathode and anode, said means being constituted by a resistor having an ohmic value which is highly sensitive to voltage variations across its terminals and having a tap for fixing the extent of such decrease in such manher that the frequency of the oscillations generated is made substantially independent of said voltage fluctuations.

2. In combination with a high frequency oscillation generator comprising a discharge tube having a hot cathode, and cold electrodes, a power supply system having alternating current input terminals and direct current output terminals, a potentiometer connected across the output terminals, a resistor having an ohmic value which is highly sensitive to voltage variations across its terminals and constituting part of said potentiometer, means for feeding operating potentials from said power supply system to certain electrodes of said tube at least in part through said resistor and a remaining portion of said potentiometer, and a cathode heating circuit connected to said power supply system, said potentiometer having a tap which provides compensation between the respective values of the potentials in the heating circuit and in said means such that the frequency of the oscillations generated is substantially uninfluenced by variations in the alternating current potential applied to the input terminals of said power supply system.

3. A device in accordance with claim 2 and further characterized in that said resistor has a negative temperature coefficient and constitutes an intermediate portion of said potentiometer.

4. A device in accordance with claim 2 and further characterized in that said resistor has a positive temperature coeflicient and is connected between the tap on said potentiometer and the positive output terminal of said power supply system.

5. A device in accordance with claim 2 and further characterized in that said discharge tube is a pentode having a screen grid connected in series with said resistor and the tap on said potentiometer.

CORNELIS JACOBUS BOERS.

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