US2168924A

US2168924A - Oscillator system

Info

Publication number: US2168924A
Application number: US548656A
Authority: US
Inventors: Jennings B Dow
Original assignee: Individual
Current assignee: Individual
Priority date: 1931-07-03
Filing date: 1931-07-03
Publication date: 1939-08-08
Anticipated expiration: 1956-08-08
Also published as: GB377067A; FR728642A; DE639357C

Description

-Aug. 8, 1939. J. B. DOW

OSCILLATOR SYSTEM Filed July 5; 1951 2 Sheets-Sheet 1 15k I I'I I I IJ I I qwENToR germ:

7155 .5. Dow

ATTORNEY Aug. 8, 1939. J. B. DOW

OSCILLATOR SYSTEM 2 Sheets-Sheet 2 Filed July 5, 1931 lflVENTOR Jenn mgs .5. Dow

ATTORNEY Patented Aug. 8, 1939 UNITEIS STATES PATENT OFFICE 28 Claims.

(Granted under the act of March a, 1883, as amended April so, 1928; :m o. e. 751) My invention relates broadly to oscillator systerns and more particularly to a constant frequency electron tube oscillator system.

One of the objects of my invention is to pro- .5 vide a precision type oscillator which is capable of delivering a large amount of useful energy.

Another object of my invention is to provide a precision type oscillator whose frequency stability is relatively free from the influence of attached circuits.

A further object of my invention is to provide an oscillator circuit, the output portion of which is electrically independent of the frequency determining portion.

A still further object of my invention is to provide means for electrostatically shielding those tube elements which are directly associated with the generator portion of the circuit from an element of the tube which is utilized only to derive energy from the system.

A still further object of my invention is to provide means for maintaining certain elements of the oscillator tube at relatively large high frequency potentials with respect to ground and at the same time, avoiding the use of choke coils which, when employed at the very high frequencies, introduce design diiilculties.

Other and further objects of my invention will' be understood from the specification hereinafter 30 following by reference to the accompanying drawings, in which: 1

Fig. 1 discloses a circuit embodying the principles of my invention; Fig. 2 shows a modified form of circuit; and Figs. 3 and 4 show still further modified forms of the circuit of my invention.

In electron tube oscillators of the two anode type, where one anode of the tube is associated in circuit with certain other elements of the tube for the generation of oscillations, and a second anode of the tube is associated in circuit to derive energy from the system, I have found it essential to electrostatically shield that anode associated with the output circuit from those elements of the tube involved in the oscillation generating portion of the system in order that the frequency of the generated oscillations will not be materially influenced by changes inthe electrical constants of the output circuit caused by tuning adjustments, reaction from attached circuits, etc. ;One method of accomplishing this shielding consists in introducing a separate electrostatic shield element within the tube in the manner disclosed in my copending application Serial No. 515,129, filed February 11, 1931.

In the present invention I dispose the output circuit of the system between the second anode and the anode structure of the oscillation generator, instead of placing the output circuit between the second anode and cathode. This per- 5 mits the anode structure of the oscillation generator to function as an electrostatic shield to isolate the second anode, which is associated only with the output circuit, from the remaining elements of the tube which are associated with the oscillation generating portion of the circuit.

In electron tube oscillators which utilize three elements of the tube and their external circuits for the generation of oscillations, it is customary to so arrange the circuit that the cathode 15 is at a low potential with respect to the shield box or ground in so far as the generated high frequency potentials are concerned. This practice has resulted fromthe fact that any other arrangement of the circuit,which requires the cathode to assume high frequency potentials with respect to ground, requires also that the cathode heating source be isolated by suitable choke coils or equivalent devices. It is a well known fact, however, that anyone of the three tube elements of such oscillator circuits, may be maintained at substantially zero potential with respect to ground in so far as the generated high frequency potentials are concerned, provided that the other two elements are permittedto assume with respect to ground, such high-frequency potentials as they may.

In the circuit of my present invention, I prefer to tie the anode of the oscillation generator to ground or what in effect is the same thing, to tie it to the metal box enclosing the circuits. At the same time, I so arrange the circuit that the cathode and grid elements may assume any desired high frequency potentials with respect to ground. The anode which I employ has a screen- 0 like structure so that electrons from the cathode, or electrons resulting from secondary emission from that anode may pass on to the second anode which is associated with the output circuit of the system. The screen-like anode, by virtue of its low impedance connection to the metal box or to ground, acts to overcome the coupling effects of distributed capacity in the circuit and at the same time so divides the circuit of the generator and output that the screen-like anode effectively removes the other coupling effects due to interelement capacities. By means of such a structure, those impedances in the output circuit and those in the generator are uncoupled to such an extent that they are substantially independent.

The fact that the grid and cathode elements of the oscillation generating portion of the circuit are electrostatically shielded from the second anode which is associated with the output circuit, serves to so isolate the output circuit that reaction caused by changes in the electrical constants of the output circuit has only a quite negligible effect upon the frequency of oscillation.

Fig. 1 shows one form of circuit incorporating the principles of my invention in which I is an electron tube including a grid element 2, a cathode element 3, a screen-like anode element 4, and a second anode element 5. Grid capacitor 8 and leak I are shown connected between the grid 2 and inductance coil 8. Inductance coil 8 in combination with capacitor 9 form a resonant circuit H), which is employed with the grid 2, cathode 3, and screen-like anode 4, for generating electric oscillations the frequency of which is substantially determined by resonant circuit l8. Either the inductance 8 or capacitor 9 or both, may be made variable for adjusting the frequency of oscillation. One end of inductance coil 8 is connected to ground I I. By virtue of blocking capacitor l2 whose impedance at the frequency'of oscillation may be chosen as small as desired, the screen-like anode element 4 is virtually tied to ground. Cathode element 3 is heated by battery l3. The inductance 8, in the case of Fig. 1, consists of a hollow conductor enclosing conductor l4 which connects one terminal of the cathode 3 with battery l3. The other terminal of cathode 3 connects to battery l3 through the hollow conductor itself which serves jointly as inductance 8. Tap connection I5 to battery i3a supplies the screen-like anode 4 at the necessary potential. By-pass capacitors are shown at l6 and H. The second anode 5 connects through inductance 18 to battery l3a for supplying the desired potential to anode 5. Inductance 18 in combination with capacitor i9, form a second resonant circuit 28 which may be tuned to the frequency at which the generating portion of the circuit is oscillating or to a harmonic of that frequency. This second resonant circuit serves as an output circuit for the system. If the circuit of Fig. 1 is employed as a master oscillator for a radio transmitter, I have found it convenient to connect subsequent stages of the transmitter at 2| and 22 for deriving energy from the oscillator system.

As the second anode 5 is electrostatically shielded from grid 2 and cathode 3 by the screenlike anode 4, any reaction across leads 2| and 22 or reaction due to changing the electrical constants of resonant circuit 20, has a negligible effect upon the frequency of oscillation determined by resonant circuit ill in the oscillation generating portion of the circuit. By tracing the high frequency current path between cathode 3 and screen-like anode 4, and the path between second anode 5 and screen-like anode 4, it will be observed that no common impedance exists across which a high frequency current in one path could introduce a potential into the other path. The only common portions of these circuits are by-pass condensers such as l2, the reactance of which is made negligible at the frequency of oscillation. The absence of an impedance common to the above mentioned paths and the screen-like anode structure 4 makes the generator circuit independent of the output or work circuit 28. Moreover, the above mentioned circuit between cathode 3 and screen-like anode 4 and the circuit between second anode 5 and screen-like anode 4 are not coupled, and for best results the arrangement of these circuits should be such that any reactive elements in one circuit should be separated from corresponding parts of the other so that the coeflicient of coupling between these two circuits is substantially zero. Under these conditions the transfer of energy from the generator portion to the output portion takes place only through the electron stream, and the generator portion of the system is almost wholly independent of reaction from the output circuit.

The oscillation generating portion of the circuit of Fig. 1 serves to generate oscillations at a predetermined frequency and controls the flow of electrons from the cathode 3 through the screen-like anode 4 to the second anode 5. Owing to the division of the electric field between screen-like anode 4 and cathode 3 from the elec tric field between second anode 5 and screenlike anode 4, the latter'anode acts just as though it were a cathode which emitted pulses of electrons into the field between the two anodes at a frequency determined by the generator. Experience with the system indicates that the high velocity electrons from cathode 3 in striking the screen-like anode 4 also cause secondary emission from anode 4 and that a portion of the space current to the second anode 5 may be due to electron emission from screen-like anode 4. It has been observed in support of this that under certain conditions, the current through tap connection l5 to screen-like anode 4 completely reverses itself.

The inductance 8 of Fig. 1 which serves both as a portion of the resonant circuit I0 and as the means for supplying cathode heating energy from battery I3, may take many forms of construction. It may be in the form of a metallic tube as shown, or may take the form of a U shaped conductor whose sectional boundary includes return conductor I4 for supplying cathode heating energy.

A modified arrangement of the circuit of my invention is shown in Fig. 2 in which reference characters I, 2, 3, 4, 5, 6, 1, 9, 10, M, i2, 13, Ba, l5, l8, l1, l8, 2| and 22, correspond to similar portions of the circuit of Fig. 1. The inductance 23 in resonant circuit in of Fig. 2 consists in part of two parallel conductors for supplying the necessary cathode heating energy from battery i3. These two conductors are denoted respectively by reference characters 24 and 25. It will be noted that blocking capacitors 26 and 21 serve also to close the resonant circuit i0 and thus serve as'a portion of resonant circuit iii. In the circuit of Fig. 2, inductance I8 is employed alone in the output circuit in lieu of a resonant circuit as shown by reference character of Fig. 1.

In the circuits of Figs. 1 and 2, the grid and anode portions of the generator circuit are coupled to satisfy the required circuit conditions for oscillation, by the two sections of the inductance of resonant circuit III which is divided by the cathode. Fig. 3 is a further modified form of the system of my invention in which the resonant circuit 28, consisting of the inductance 29 and the capacitor 30, fixes the frequency of oscillation. In this case, the circuit condition required for oscillation is satisfied by coupling the grid circuit inductively by auxiliary inductance 3| to the inductance 29 of resonant circuit 28. The screenlike anode 4 of Fig. 3 is connected to ground H through the low impedance blocking capacitor l2. By-pass capacitor 32 is connected as shown.

In the circuit of Fig. 3, the cathode 3 is heated by battery I! through inductance, 29 and its contained conductor It. The output circuit anode 5 of Fig. 3 is connected through resistor 33 to battery I30 for supplying anode I at the desired frequency.

' ary of choke coils 34 and 35.

potential. i

While I have shown a resonant circuit 20 in the output circuit of Fig. 1, an inductance la in the output circuit of Fig. 2 and fa resistor 33 in the output circuit of Fig. 3, any of these impadances may be employed in all three circuits illustrated.

Fig. 4 shows a still further modified form of the circuit of my invention in which the cathode is heated by battery l3 through the intermedi- It will be noted that the grid capacitor 6 and leak l are shown in a different position than in the'preceding figures. When in the position shown in Fig. 4, it is desirable to make capacitor 6 sufficiently large as to have a very low impedance at the oscillator Split capacitor 36 and. inductance 31 form resonant circuit 38 which is adjusted to the frequency of oscillation desired.

While particular mention has been made of the use of the system of my invention for the generation of high frequency currents, it will be understood that by suitable choice of circuit constants, low frequency currents may also be produced The term high frequency is therefore intended to be a generic one including either high or low frequency insofar as my disclosure .and claims are concerned.

The following observational data made upon the circuit basically illus rated in Fig. 4 are of interest. These data were observed when the oscillation generating portion of the circuit was tuned to a frequency of approximately 2000 kilocycles. A conventional type of four element electron tube rated at 75 watts output was employed.

Resonant circuits

38 and 20 were shielded from each other to prevent undesirable coupling. A visual type of beat frequency indicator having a measurement precision of one cycle in a million was employed in making these observations:

(a) Tuning circuit 20 through resonance at the fundamental frequency causes the frequency of oscillation to shift 0.005 per cent.

(b) Tuning circuit 20 through resonance at the second harmonic of the fundamental frequency causes the frequency to shift 0.0015 per cent. 1

(0) With second anode element 5 supplied at 1200 volts and screen-like anode 4 supplied at 500 volts, the output in radio frequency energy at both the fundamental and second harmonic frequencies, is more than ample to fully excite a similar electron tube employed as a radio frequency amplifier.

(d) Changing the voltage supply to second anode 5 and screen-like anode l by 20 per cent, causes the frequency to change 0.0005 per cent. Changing these voltages 50 per cent, causes the frequency to change 0.0013 per cent.

The preceding data serve to indicate the effectiveness of the system of my invention in meeting the need for a circuit combining high output and precision as to frequency stability.

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

The invention described herein may be manufactured and 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 I claim as new and desire to secure by Letters Patent of the United States is as fol- 2. A system for the production of high frequency energy having a generator comprising an electron tube having a cathode, anode and control electrode, sources of potential for energizing said electrodes, a resonant circuit, said resonant circuit including ahollow tubular inductance apertured intermediate the ends thereof, an insulated conductor extending through the tube of said inductance, connections between one of said sources of potential to said inductance and to said insulated conductor, and connections from said cathode to said inductance and to the conductor therein through the apertured por-' tion of said inductance, in combination with an auxiliary element in ,the electron stream of said generator in said tube and an output circuit for said system disposed between said auxiliary element and said anode, and means including said anode electrode for electrostatically shielding said cathode and control electrode from said auxiliary element.

3. In a system in which a cathode and two other electrodes of an electron tubeare employed for the generation of high frequency energy and a fourth electrode is used inconnection with an output circuit for taking off said energy, the method of minimizing changes in frequency due to changes in the electrical constants of said output circuit, which consists in substantially shielding the electron stream of the generator portion of said system from the influence of high frequency potentials on said fourth electrode and in maintaining one of said two other electrodes at substantially zero high frequency potential with respect to ground.

4. An alternating current source having a generator comprising at least three elements of an electron tube and interconnecting external circuits, in combination with a tube element additional to those forming a part of said generator, means including one of said first mentioned elements for substantially shielding the electron stream between the elements of said generator from the alternating component of the electric field of said additional element, and an output circuit disposed between the element of said means and said additional element.

5. A generator of high frequency oscillations comprising a cathode element, control element and screen-like anode element of an electron tube arranged with external circuits and sources of supply potential for the generation of oscillational to those forming a part of said generator,

means including said screen-like anode element for substantially shielding said control element from the high frequency component of the electric field of said additional element, and an output circuit disposed between said additional tube element and said screen-like anode element.

6. A source of high frequency energy having an electron tube including oscillation producing elements, circuits interconnecting the oscillation producing elements of said tube and a power supply and comprising an oscillation generator, in combination with an additional element positioned in spaced relation to one of said oscillation producing elements so as to be in the electron stream of said generator, a circuit having variable electrical constants interconnecting externally of said tube said additional element and the element in spaced relation to which it is disposed and means including the last mentioned element for electrostatically shielding the electron stream between said oscillation producing elements from high frequency variations of potential of said additional element.

7. A source of high frequency energy having an electron tube the cathode, control electrode and grid-like anode of which in combination with external circuits constitute an oscillation generator, a power supply connected to said circuits for the generation of oscillations, an additional electrode positioned in said tube in the electron stream of said generator, high frequency output means for said source disposed between said additional electrode and said grid-like anode and means including said grid-like anode for substantially electrostatically shielding said control electrode from said additional electrode for high frequency potential variations existent across said output means.

8. A source of high frequency energy in accordance with claim 7 in which said oscillation generator is regenerative.

9. A source of high frequency energy according to claim '7 in which said power supply is so connected to the electrodes of said tube as to render said additional element electro-positive with respect to said cathode.

10. A source of high frequency energy accord ing to claim '7 in which said power supply is so connected to the electrodes of said tube as to render said additional element electro-positive with respect to said grid-like anode.

11. A source of high frequency energy having a generator comprising an electron tube including cathode, control and anode elements and circuits including a power supply interconnecting said elements for the generation of oscillations, a resonant circuit cooperating with said circuits for determining the frequency of oscillation of said generator, said resonant circuit comprising at least in part a multiple conductor inductance, means for heating said cathode, said means comprising a circuit from said power supply through two conductors of said inductance to-said oath-- ode, in combination with an auxiliary element in the electron stream of said generator and an output circuit for said source disposed between said auxiliary element and said anode element. and means including said anode element for electrostatically shielding said cathode and control elements from said auxiliary element.

12. A source of high frequency energy according to claim 11 in which said auxiliary element is electropositive with respect to said cathode.

tions, in combination with a tube element addi- 13. A source of high frequency energy according to claim 11 in which said auxiliary element is electropositive with respect to said anode.

14. A source of high frequency energy according to claim 11 in which said multiple conductor inductance comprises a tubular conductor enclosing a second conductor which is insulated therefrom.

15. An electron discharge apparatus including at least one electron tube and having an oscillation generator circuit including generator-electrodes in the discharge path of said tube, in combination with an additional circuit connecting one of said generator-electrodes with an addtional electrode in said discharge path, and means including that one of said generator-electrodes last mentioned whereby the remaining generator-electrodes in said tube are substantially shielded from said additional electrode for potential variations across said additional circuit of frequency corresponding to that for which said oscillation generator circuit is adjusted.

16. An electron discharge apparatus in accordance with claim 15 wherein said additional circuit comprises at least in part a resonant circuit.

17. A source of high frequency energy comprising an electron tube having a cathode, control electrode, grid-like anode and an additional element arranged in the order named, a resonant circuit and a source of potential interposed between said cathode, control electrode and gridlike anode to provide an oscillation generator, an output circuit for said source interposed between said additional element and at least one of the elements included in said oscillation generator, and means comprising a path of low radio frequency impedance connected between said grid-like anode and ground for maintaining the grid-like anode at substantially zero high frequency potential whereby said grid-like anode electrostatically shields the remaining electrodes comprising said oscillation generator from said additional element.

18. A source of high frequency energy in accordance with claim 17 wherein said output circuit includes a resonant section.

19. Asource of high frequency energy in accordancwith claim 17 wherein said output circuit includes a resonant section tuned to a frequency harmonically related to the frequency generated by the oscillation generator.

20. An electron discharge apparatus including an electron tube having a cathode element, control element, grid-like anode element, and an additional element positioned in the order named, means for maintaining said control element, said grid-like anode element, and said additional element at predetermined potentials with respect to said cathode element, a circuit connecting said cathode and control elements, a second circuit connecting said cathode and gridlike anode elements, means for regeneratively coupling said circuits, an output circuit disposed between said grid-like anode element and said additional element including a portion of said second circuit, said output circuit being substantially reactanceless at the frequency for which said first circuits are regenerative over that portion of said output circuit which is common to said second circuit.

21. An electron discharge apparatus including an electron tube having a cathode element, control element, grid-like anode element, and an additional element positioned in the order named, means for maintaining said control element, said grid-like anode element, and said additional element at predetermined potentials with respect to said cathode element, a circuit including an impedance connected between said cathode element and control element, a second circuit including an impedance connected between said cathode element and said grid-like anode element, means for regeneratively cou-' pling said circuits, an output circuit including a tuned resonant circuit and a portion of said second circuit disposed between said grid-like anode element and said additional element, said output circuit being substantially reactanceless at the frequency for which said first circuits are regenerative over that portion of said output circuit which is common to said second circuit.

22. An electron discharge apparatus including an electron tube having a cathode element, control grid element, and grid-like anode element positioned in the order named, means for rendering said cathode electron emitting and means for maintaining said grid-like anode ele- -ment electro-positive with respect to the cathode element, a circuit including-an impedance connected between said cathode element and said control grid, a second circuit including an impedence connected between said cathode element circuit which is common to said second circuit.

23. An electron discharge apparatus including an electron tube having a cathode element,

control grid element, and a grid-like anode element positioned in the order named, means for rendering said cathode elementelectron emitting and means for maintaining said grid-like anode element electro-positive with respect to the cathode, acircuit including an impedance connected between said cathode element and said control grid element, a second circuit including an impedance connected between said cathode element and said grid-like anode element and means for coupling said first and second circuits whereby an oscillation generating means is provided, an additional element in said tube adjacent said grid-like anode element and;

on the side thereof opposite said control grid element and an output circuit including a tunable resonant section and a .portion of said second circuit disposed between, said additional element and said grid-like anodeelement, said output circuit being substantially impedanceless at the frequency of oscillation of said oscillation generating means over that portion of said output circuit which is common to said second circuit and means for maintaining said additional element el'ectro-positive with respect to said cathode element.

24. 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 tunedoutput circuit connected between said anode and screen grid, a coil inductively coupled to said input circuit and hav- -ing 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.

25. An oscillation generator having an electron tube provided with a cathode, a control element, an inner anode and an outer anode, an oscillation generating circuit comprising said cathode, control element and inner anode, an output circuit connected at one side thereof to said outer anode and at the other side thereof to said inner anode, whereby said inner anode is common to both circuits, and means for maintaining said inner anode at radio frequency ground potential for isolating said circuits from each other.

26. In a radio system, the combination of an electron tube having anode, cathode and grid electrodes, means for heating said cathode, an input circuit connected across said cathode and grid electrodes to vary the potential of said cathode at a high frequency rate, and means comprising radio frequency choke coils for preventing said high frequency variations from affecting said cathode heating means.

27. In a radio system, the combination of an electron tube having anode, cathode and grid electrodes, means for heating said cathode, an input circuit connected between said-cathode and grid to vary the potential of said cathode at a high frequency rate, and radio freqdency choke coils between said cathode and said heating means to maintain a high input impedance to said tube.

' 28. Oscillation generating means comprising, a sealed vitreous container, an emission element therein, a plurality of cold electrodes in said container, said cold electrodes being spaced a different distance from said emission element, a frequency determining oscillation circuit connected between a pair of said cold electrodes and to said emission element, an oscillation circuit connected between another of said cold electrodes and said emission element, means for applying direct current charging potential to said electrodes, 'the value of the potential applied to the electrodes connected with said, last named circuit being greater than the potential applied to the other electrodes whereby oscillations of greater amplitude appear in said circuit, the maximum amplitude of the oscillations appearing in said frequency determining circuit being greater than the minimum amplitude of the oscillations appearing in -said other circuit wherebythe intensity of the current flowing in said other circuit alters at a rate greater than the frequency to which the frequency determining circuit is tuned, and means fon tuning said other circuit to a harmonic of the frequency of the, I