US2406871A - Triode oscillator circuit - Google Patents

Description

Sept, 3, 1946; \v/ARELA 2,406,871 I TRIODE OSCILLATOR. CIRCUIT Filed Sept. 22, 1941 2 Sheets-Sheet 2 'nwiwron Arlkuzul Varela lur romvsr 7 Patented Sept. 3, 1946 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 192.8; 37 0. G. 757.)

4 Claims.

This invention relates to radio frequency pulse generators and more particularly to self-quenchin oscillator circuits for generating radio frequency pulses.

Self-quenching oscillator circuits that have been proposed heretofore for generating radio frequency pulses comprise a conventional oscillator circuit, includingan electron discharge device having an anode, cathode and at least one control electrode interconnected in such a mannor as to cause said device to oscillate. In order to provide the self-quenching feature and thus produce radio frequency pulses at the. output of the circuit, the prior systems utilize resistance means, of a high value, connected in the control electrode path, with suitable capacitance means shunted across the resistance means. In operation of systems of the foregoing character, when the electron device commences to oscillate, rectified control electrode current is generated which flows to and gradually charges the capacitance means thus producing a gradually rising self-bias on the control electrode which in turncauses the.

angle during which the anode draws current to gradually decreaseuntil the point of extinction is reached. The term anode current angle mentioned above and referred to hereinafter in the specification and the claims has reference to the period that the plate of the oscillator tube draws current with respect to each cycle of excitation voltage applied to the control grid of the tube.

The foregoing operation produces radio frequency pulses having asymmetrically shaped envelopes, due to the inherent operating characteristics of the capacitance means. The magnitude of the pulse envelope is notsubstantially constant throughout any portion thereof, and. the radio frequency voltage magnitude, with respect toan increase in the period of the pulse, gradually becomes less and less as the pointof extinction. is reached. From all practical viewpoints, radio frequency pulses having pulse envelopes of substantially rectangular symmetrical shap wherein the magnitude of each pulse envelope remains substantially constant throughout a greater portion thereof, and wherein the magnitude of the envelopes sharply decreases, from "maximum to the extinction point, through a small period of the pulse, has been found desirable for numerous reasons. As stated above, in operation of the prior systems, the control electrode voltage continually varies throughout the period of the pulse, such voltage variations not only produces asymmetrical pulse envelopes but also produces a shift in the carrier frequency. Such frequency modulation is very objectionable since it requires a corresponding decrease in receiver selectivity with resulting loss in signal to noise ratio. The desired substantially rectangular symmetrical pulse envelopes tend to maintain the carrier frequency substantially constant throughout the period of the pulses, and also tends to compensate for other frequency variations in the'carrie'r wave which occur as the operating time of the circuit increases.

It is therefore an object'of the present invention to provide a novel self-quenching oscillator circuit for generating radio frequency pulses wherein the pulse envelopes are of the aforementioned desired shape."

Another object is to provide a self-quenching oscillator circuitfor generatin radio frequency pulses wherein the direct current voltage applied to the oscillator tube or tubes is substantially constant throughout the principal portion of the pulse.

Another object is to provide a self-quenching radio frequency pulse generator wherein the carrier frequency is maintained substantially constant throughout generation of the pulse.

Another object is to provide a self-quenching oscillator circuit for generatingradio frequency pulses having pulse envelopes with substantially constant magnitude throughout a greater portion thereof, and wherein the magnitude of the envelopes sharply decreases from maximum to an extinction point, through a small period of the pulse.

Another object is to provide a self-quenching oscillator circuit including novel means for generating radio frequency pulses having substantially rectangular pulse envelopes.

Still another object of the present invention is to provide a self-quenching oscillator circuit including an electron discharge device having an anode, cathode and-at least one control electrode and novel means connected between the cathode and the control electrode for producing and controlling a self-bias on the control electrode whereby the angle during which the anode draws current remains substantially constant throughout a predetermined period of time and thereafter decreases to a point of extinction throu out a short period the pulse.

Still another object is to provide aself-quenching oscillator circuit for generating radio frequency pulses having a filter network included in the circuit for producing substantially rectangular Symmetrical .pulse'envelopes.

Still another object of the invention is to provide an oscillator circuit including at least one electron discharge device having an anode, cathode and at least one control electrode, with a filter network connected between the cathode and the control electrode for producing and controlling abias on the control electrode in such a manner that radio frequency pulses having substantially rectangular symmetrical pulse envelopes are formed.

Other objects and features of the inventionwill appear more fully from the following detailed description when considered together with the accompanying drawings which disclose two embodiments of the invention. It is to be expressly understood, however, that the drawings are designed for purposes of illustration only and not as a definition of the limits of the invention, reference being had to the appended claim for the latter purpose.

In the drawings, wherein similar reference characters denote similar parts throughout the several views:

Fig. 1 is a diagrammatic showing of a pulse envelope formed upon operation of the prior systems mentioned heretofore;

Fig. 2 is a schematic showing of a self-quenching oscillator circuit, embodying the principles of the present invention, for generating radio frequency pulses having substantially rectangular symmetrical pulse envelopes;

Fig. 3 is a diagrammatic view of a pulse envelope formed upon operation of the system disclosed in Fig. 2, and

Fig. 4 is a schematic showing of another embodiment of the present invention.

As shown in Fig. 1 of the drawings, and as mentioned heretofore, the prior self-quenching oscillator circuits for generatin radio frequency pulses produce pulses having asymmetrical pulse envelopes in which the magnitude of the pulse is not substantially constant throughout any portion of the pulse. Due to the inherent characteristics of the capacitance means employed in the prior systems, the magnitude of the pulse envelopes gradually decreases, and the rate of such decrease becomes greater as the time of the pulse increases.

As stated heretofore, it is an object of the present invention to provide an oscillator circuit for I lator circuit including the aforementioned means i is shown therein having a pair of electron discharge devices I B and H, such as thermionic tubes ofthe triode type, each of which respectively includes a cathode l2 and I3, an anode l4 and I5 and a control electrode l6 and IT. The cathodes are joined together at point I8 and are connected to ground potential at l9, while the anodes are connected together at point and are maintained at a positive potential with respect to the cathodes. A source of high potential is supplied to points 2| and 22, the former point being connected to the anodes, while the latter is connected to ground potential. The control electrodes l6 and I! are connected together at point 23, and the control electrodecathode circuit includes suitable resistance means 24, a filter network 25, the purpose of which will appear more fully hereinafter, and transformer 26, serially connected between points 23 and IS.

A source of alternating voltage 21 is applied to transformer 26 for purpose of synchronization as will also become more apparent hereinafter. The oscillator circuit disclosed herein is a conventional high frequency, push-pull, linear oscillator wherein the lump inductance and capacity in the plate leads and in the cathode or control electrode leads are replaced by resonant electrical lines. This type of oscillator circuit is capable of producing ultra-high frequency oscillations with high stability and efiiciency. However, it is to be expressly understood that any type of oscillator circuit may be employed herein.

As mentioned heretofore, the present invention provides an oscillator circuit having novel means for producing and controlling a self-bias on the control electrodes in such a manner as to generate radio frequency pulses having substantially rectangular symmetrical envelopes. As shown in Fig. 2, such means include the filter network 25 which takes the form of a low-pass filter network having a plurality of capacitance means 28 and a plurality of inductance means 29 connected together in series-parallel to form a filter network having a plurality of sections. For the purpose of the present invention the filter network need not be symmetrical and any number of sections may be included therein, depending upon the shape of the pulse envelope desired, as will appear more fully hereinafter.

It has been found that when an electromotive force is applied to one end of a filter network of the above character that a voltage wave is propagated down the filter toward the other end thereof from where the wave is reflected and returned to the end of the filter where the force was applied. While this action is taking place, a uniform current flows into the filter network, the value of which depends upon the surge impedance of the filter network and upon the internal impedance of the electromotive force. Since the surge impedance of the network is constant the voltage across the input of the filter is constant during the time the voltage wave is propagated from one end of the filter to the other, or during the charging period of the filter, and the voltage acros the input of the filter abruptly doubles in value at the instant the network is charged or when the reflected voltage wave arrives at the input end of the filter. The time delay, or the time required to completely charge the filter, for a constant K fi lter disclosed, is approximately equal to 1r/3\/LC per section, and that the total time between the application of an electromotive force and return of the reflected voltage wave is approximately equal to /3 N1r /LC, where N is the number of sections, and L and C are the inductance and capacitance values, respectively, per section.

In view of th foregoing, it is to be expressly,

understood that the bias on the control electrodes and hence the electrical angle through which the anodes draw current will be dependent on the internal impedance of the cathode electrode circuit, considered as a self-biasing generator, and the surge impedance of the filter network. The surge impedance of the filter network is approximately equal to and it is preferred 'to properly select values of capacitance means 28 and inductance means 29 so that the ratio formed will produce the desired anode current angle and. to use the filter network alone for self-bias impedance. However, in some instances-it may vbe-desirable to use .a resistor 24., of a small value,in1 series between the control electrodev and the filter "to further provide selfbias. I

When a filter network of the foregoing. type .is inserted in. an oscillator circuit between. the control electrode. and the cathode, as shownin Fig. 2, the filter begins. to charge when oscillations commence and holds the control electrode bias at a constant value during :a time interval equal to /3 N-n/IC, as discussed heretofore, and at the end of such interval the sudden increase in voltage across the filter producesa bias on the control electrodes of such value to block the tubes and to thus prevent the anodes from drawing current. Since the voltages are all constant during the operating period the carrier freequency and'the output power are also constant.

The foregoing operationproduces pulse envelopes of substantially rectangular symmetrical shape, as shown in Fig. 3 of the drawings.

The pulse repetition rate is determined y the time required for the filter to discharge through suitable bleeder resistors 30, and 3|, respectively connected in parallel to capacitance means 28 atopposite ends of the filter. Since the discharge of the filter network is ordinarily relatively slow the discharge will be exponential in character with a period of discharge approximately equal to 1 Fair?) where R is the parallel value of resistance 30' and 3|. The repetition rate may be synchronized with an external source by introduction of an electrornotive force in series with the filter network, such as transformer 26 excited with an appropriate external, alternating current source 21, as shown in Fig. 2.

As shown in Fig. 4, the pulse repetition rate may be controlled by a synchronizing voltage introduced in parallel with the filter network by utilizing proper blocking impedances. In this embodiment, a. two tube triode oscillator circuit is ance 24 included in such connection if desired, 1

and the lower terminal of the filter being connected to ground potential at 32. A source of synchronizing voltage 21 is connected in series with the filter with suitable blocking impedances which includes capacitance 33, inductance 34 and resistance 35. Capacitance 33 serves to prevent discharge of the filter through the synchronizing system, while resistance 35 tends to dampen any oscillations of the circuit. The inductance 39 serves as a high impedance to the current surge and isolates the synchronizing system from the filter network during the period of the pulse. Inductance 39 is to be of such value to have a natural period ten times or more than the period of the pulse. If preferred, the synchronizing system may be connected on the other side of the filter.

In operation of the novel systems described heretofore, when electron discharge devices I0 and II commence oscillating, rectified control electrode current is generated and flows to filter network 25. While filter network is charging, the control electrodes are maintained at a constarry bias determined by the surge impedance /L/C of the filter network and by the value of resistor .26. if employed, for apredeterminedperi- 0d of time approximately equal to 3 Nu/LC. The anode current angle is established by the bias maintained on the control electrode, and since the bias is maintained constant the anode angle remains constant for the period N1r\/LC, and the oscillations generated during such period are symmetrical in form and of equal amplitude. When the period. /3 N1r\/LC lapses, the voltage across the filter abruptly increases to a value substantially twice the constant value to increase the bias. on the control electrodes a corresponding degree, thus blocking the tubes and preventing the anodes from drawin current. Since the tubes are abruptly blocked, theanode current angle necessarily abruptly diminishes to an extinction point. The anodes will not again draw current until the filter discharges through resistances 30. and 3|, the time for such discharge depending upon the value of the resistances, or may also be controlled by an external synchronizin source.

The foregoing operation produces radio frequency pulse envelopes of a substantially rectangular symmetrical shape, as shown in Fig. 3. Sin e a voltage appearsfacross the filter and remains substantially constant throughout a predetermined time. interval following the initial'application of rectified control electrode current thereto, the pulse envelopes have substantially uniform magnitude throughout a greater portion thereof. Moreover, since the voltage rises rapidly across the filter after a lapse of. the predetermined interval of time, thus rapidly causing an increase of the bias on the control electrodes, the angle through which the anode draws current likewise rapidly decreasesto an extinction point, thus causing the magnitude of the pulse envelopes to sharply decrease from maximum to zero through a short period of the pulse.

The present invention thus provides an oscillator circuit having novel means for providing and controlling a bias on the control electrodes included therein in such a manner to vary the angle through which the anodes draw current whereby radio frequency pulses having substantially rectangular symmetrical pulse envelopes are generated. The means disclosed is of such character that during the time \the radio frequency pulses are generated the carrier frequency remains substantially constant, and that the means may be utilized in any self-quenching oscillator circuit, and may be readily tuned to operate on any desired frequency.

Although only two embodiments of the invention have been disclosed and described in detail heretofore, it is to be expressly understood that various changes and substitutions may be made therein without departing from the spirit of the invention as Well understood by those skilled in the art. Reference therefore will be had to the appended claims as a definition of the limits of the invention.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In an oscillator circuit for generating radio frequency pulses, an electron discharge device having a cathode, anode and at least one control electrode, means interconnecting said cathode, anode and control electrode in such a manner as to cause said device to oscillate whereby rectified control electrode current is generated, and a filter network composed of inductance and capacitance connected between said control electrode and said cathode for determining and maintaining, by the action of said rectified control electrode current thereon, the angle of the plate current flow substantially constant throughout a period of time following the initial flow of rectified control electrode current thereto and thereafter for causing the angle of the plate current to rapidly decrease to an extinction point.

2. In a radio frequency pulse generator, an electron discharge device having a cathode, an anode and a control electrode interconnected in such a manner so that said device generates radio frequency oscillations, and means controlling generation of said oscillations in such a manner that radio frequency pulses having ubstantially rectangular pulse envelopes are periodically produced, the last-named means including impedance means for establishing a predetermined bias on said control electrode at the instant said device commences to generate said oscillations, said impedance means comprising inductance and capacitance mean presenting constant impedance to the flow of rectified electrode current therethrough and thus maintaining said bias at said predetermined value for a period of time equal to the charging time of said capacitance means and thereupon abruptly varying said impedance and said bias to abruptly render said device nonoscillating, and resistance means associated with said impedance means for controlling the discharge of said capacitance means whereby said device is maintained in a non-oscillatin state for a second predetermined period of time.

3. In a radio frequency pulse generator, an electron discharge device having a cathode, an anode and a control electrode interconnected in such a manner so that said device produces radio frequency oscillations, and a filter network electrically connected to said device for controlling eneration of said oscillations in such a manner that radio frequency pulses having substantially rectangular symmetrical pulse' envelopes are periodically produced, said filter network having a predetermined impedance value for establishing a, predetermined bias on said control electrode at the instant said device initiates generation of said oscillations, and comprising inductance and capacitance means interconnected in such a manner as to maintain said impedance value and said bias constant for a period of time equal to the charging time of said capacitance means and thereafter for abruptly varying said impedance value and said bias to abruptly terminate generation of said oscillations, and a source of synchronizing voltage connected in parallel with said filter for controlling the discharge of said capacitance means.

4.In a radio frequency pulse generator, an electron discharge device having an anode, a cathode and a control electrode interconnected in such a manner that said device generates radio frequency oscillations, and means controlling the operation of said device in a manner to cause it to produce a series of pulses havingsubstantially rectangular symmetrical envelopes, said means comprising a transmission line connected in bias controlling relation to said control electrode, said transmission line being terminated to produce reflection of a voltage impressed upon it, in such phase as to increase the bias on said control electrode to render said device non-conducting, the delay time of said line being longer than the period of said oscillations.

ARTHUR A. VARELA.

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