US2093416A - Feedback circuits - Google Patents

Description

SepLZl, 1937. N P. cAsE 2,093,416

FEEDBACK C IRCUITS Filed Feb. 15, 1956 2 Sheets-Sheet 1 FIGJ;

INVENTOR.

NELSON 'P. CASE BY 1 ATTORNEY.

Sept. 21, 1937. N P. CASE FEEDBACK cmcun's 2 Sheets-Sheet 2 Filed Feb. 15, 1956 W r m+ 3+ m+ a o 55 55 J T228255 FPS-52m O 8 on 0Q 0* on On 8 ONO E \EM .w M

; INVENTORf NELSON P. CASE .AAlAL vII'I' I ATTORNEY.

Patented Sept." 21, 1937 PATENT OFFICE 1 rnnnnacx omcnrrs Nelson l. Case, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application lebruary 15, less, Serial m. 64,028

14 Claims.

This invention relates to high-frequency signaling apparatus and more particularly to improvements in regenerative circuits of the type conv entionally employed inelectron discharge oscil 51 lators. j.

The conventional regenerative circuit consists of an electron discharge device to which are connected an output circuit,-a tuned input or freequency-determining circuit and one or more circults, or paths, for feeding energy from the output circuit to the resonant input circuit. Most applications of such circuits require the resonant frequency-determining circuit to be tunable over a range. of frequencies and such tuning is usually 15 accomplished by varying the capacitance of a variable condenser included in the frequency-' determining .circuit. One application, to which this invention is particularly applicable, is that of -a beat frequency or local oscillator conventionally employed in a superheterodyne radio receiver wherein the frequency of the oscillator is varied simultaneously with the resonant frequencies of the signal-selector circuits by means of variable condensers mechanically connected to be adjusted by unicontrol means.

In modernreceivers of the type mentioned it is often necessary to provide an oscillator which maintains its stability ofoperatRn overa fre- 'quency range extending from a lower limit of 550 kilocycles or less to an upper'limitf-o'f 60 megacycles 'or more. Usually thisis accomplished by dividing this wide frequency range into bands and employing different inductance elements in the tunable frequency-determining circuits for cover- I log the several operating bands, switching means being provided for selectivelyiconnecting the inductances of diiferent values-in parallel with the tuning condensers of their respective tunable circuits. 9

system over the high-frequency, portion of the extended frequency range, and for practical reasons ofeconom'y, it i s desirable to use a single inductance in each of the tunable signal-selector circuits and the local oscillator frequency-determining circuit to determine the resonant frequencies of the several circuits over a wide uitra' high-frequency band in the upper portion of the .operating range. This range may include fremegacycle's to 1' ormore.

cillator capable of stable operation over such a wide ultra highefrequ'ency hand. For example,

In order to facilitate the control 6! such'a "quencies-[extending from a lower limit of .18

an upper limit of 60 me'gacycles Certain problems'arise in constructing an os- (o1. est-36) the higheroperating frequencies require the use of an inductance in the frequency-determining circuit of the oscillator having a very low inductance value. Further,the extended frequency range requires the use of a variable condenser having a relatively large capacitance and a wide range of capacitance adjustment. These two factors combine to produce a low LIC ratio beswitch, and the tuning condenser have values of induttance which are appreciable compared to the total inductance in the tuned circuit, thus limiting the mairimum attainable coeflicient of coupling to a value substantially below the usual values attained in lower-frequency circuits.

It has been found that, if. conventional feedback arrangements be employed in'applications of the type mentioned having a feed-back cou-' pling inductance of sufficient size to insure the proper loading and proper (degree of. coupling,

. this feed-baclr'circuit will have a natural frequencywhich approaches and materially reduces the extent of, the operating frequencyrange of the oscillator. i i

It is an object of the present invention, therefore, to obviate the above dimculties by providing a feed-back arrangement, generally applicable to high-frequency regenerative circuits, which is substantially equally eflective in its energy transfer function at all frequencies within a wide range of high frequencies. v

' It is-a further object of this invention to provide a high-frequency electron'discharge oscillator which includes a feed-back arrangement having .the above" operating characteristics,. and

which is capable of stableoperation at'all frequencies within an extended high-frequency range. Y

In accordance with this invention, the above objects are attained "by providing a feed back arrangement which includes a pair of paths eachproviding coupling .between a different elec; 'trode oi the electron discharge control device this circuit over a portion of the operating frequency range, the two feed-back paths acting in aiding phase over the operating frequency range,

that is, acting cumulatively to transfer energy to the frequency-determining circuit. In one embodiment of the invention, one of the feed-back paths is connected to'the output electrode, or anode, of the electron discharge device and is primarily capacitivelycoupled to the tunable frequency-determining circuit. A second path is provided which is connected to one of the auxiliary electrodes as, for example, the suppressor grid of the device-and is inductively coupled to the inductance element included in the frequencydetermining circuit. In another embodiment of the invention, the'two feed-back paths are each 1 inductively coupled to the frequency-determining circuit, one of the paths being connected to the anode of the electron discharge device, and the second path being connected directlyto the suppressor grid and, through a blocking condenser, to the screen grid.

The novel features which are believed to be characteristics of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and the method-of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings, in which Figs. 1 and 2 illustrate different embodiments of the invention; Fig. 3 illus-- 'trates the form of the invention shown in Fig. 2

r as applied to a local oscillator of a superheterodyn'e broadcast receiver; and Fig. 4 illustrates certain operating characteristics of an oscillator embodying the presentdnvention as compared with the characteristics resulting from other feed-back arrangements.

Referring to Fig. I of the drawings, there is illustrated an embodiment of the invention in an electron discharge oscillator circuit. The circuit shown comprises an electron discharge device I having a cathode 2 preferably of the well-known unipotential typeyan anode a control grid 4,-

- and screen and suppressor :grids' land 0, re-

spectively, all enclosed within an evacuated en-' velope I which is surrounded by a grounded metallic shield 8. Connected between the control grid 4 and -ground, through a coupling condenser 8 and a booster winding i0, is a tunable frequencyedetermining circuit II which comprises an inductance l2 shunted by a variable tuning condenser l3; The boosterv winding III is inductively coupled to the inductance l2 and func- Q tions to increase the impedance between the in- .put electrodesthereby'toimprove the loadingof the oscillator tube. The cathode 2 is connected bythe lead I to atap IS on the inductance l2 slightly above alternating ground potential. For

the purpose of-biasing the control grid 4 to the proper negative potential withrespect to the cathode 2, a resistor I6, is connected between this control grid and ground.

1 The anode or output circuit of'the oscillator includes a source of anode potential l1 which is connected to the anode 3 and the auxiliary screen electrode 5 through resistors l8 and I9, re-.

- spectively. 'Iheseries-c onnected source I! and resistor 19 are shunted by a high-frequencypypasscondenser 20.

In accordance with the present invention, sta- "bility of operation is procured over arr-extended the manner shown. One of these paths includes a circuit connected between the anode 3* and the high potential terminal of the circuit II and comprises a blocking condenser 2| connected in series with an inductance 22. The inductance 22 is designed to have a natural resonant'frequency below the low-frequency end of the tuning range, by virtue of which this feed-back path is primarily effective over the lower-frequencyportion of the tuning range. The second feed-back path comprises an inductance 25 having one terminal connected to'the low potential terminal of the frequency-determining circuit II and the other terminal connected to the suppressor grid 6, the

cult. The leakage inductance of this latter feed-back path is resonant with the tube capacihig'h -frequency range by providing two feed-back paths for supplying-energy to the frequencydetermining input circuit II and connected in tance and its distributed capacitance at a natural frequency above the upper limit of the operating band, by virtue of which it functions to transfer energy to the -f-requency-determiningcircuit principally over the upper portion of the'operating frequency range. It will,of course, be undenstood that the portions of the frequency band over which the two paths are respectively effective may be the reverse of that described. It

will be understood that, at the ultrahigh frequencies' contemplated, any stray feed-back couplings, such as those due to' interelectrode ca- ,pacitances and distributed circuit 'capacitances,

must be taken into consideration in proportioning the main feed-back circuits.

With the feed-back paths arranged in the above described manner, and with the condenser l 3 ad-' 'justed to tune the circuit II to a resonant frequency in the low frequency portion of the range approaching the lower limits of the frequency range, the feed-back voltage is impressed on the circuit ll primarily through the path from the. anode 3 to the high alternating potential terminal of the circuit ll. At theselowerfrequencies of the range the second feed-back path, including the inductance 25; is of little eflect. As the condenser I3 is adjusted to tune the circpit to frequencies above this low-frequency portion of the 1 range, the second feed-back path comprising the inductance 25 becomes increasingly effective until a frequency is reached, above which, and until the upper limit of the frequency range is reached, the

transfer of energyto the circuit H is almost entirely through this secondpath; It will be under stood that the energy supplied to thecircuit I] through the two feed-back paths is proportioned to maintain the oscillator voltage substantially constant over the frequency range. It will fur-. I

) the two paths is substantially eliminated, thereby insuring maximum effectiveness of each path inits feed-back function. In this connection it will be seen that the feed-back arrangement represents a distinct improvement over the multi-feedback path arrangements known tothe art, and

particularly the known arrangement whereintwo feed-back paths are coupled in parallel between the oscillator tube anode, or another output electrode, and the frequency-determining circuit. With the latter arrangement the interaction be-' tween the two feed-back paths considerably reduces the extent of the frequency range over which the oscillatpr is capable of stable operation. l The embodiment of the invention illustrated in Fig. 2 is similar to that of Fig. i except that each of the two feed-back paths is inductively coupled to the inductance II of the frequency-determining circuit. Thus, the path which is operative to supply energy to the frequency-determining circuit over the lower portion of the operating frequency range comprises an inductance 28 connected between the lowpotential terminal of the circuit II and .the anode I of the discharge device I through a blocking condenser 21, the coil 28 being tightly coupled to the inductance It. The second feed-back path, which is effective to supply energy to the frequency-determining circuit over the upper portion of the frequency range, is the same as the arrangement of Fig. 1 but is also eflectively connected to theauxiliary electrode I through the blocking condenser ll. With this circuit arrangement, wherein the second feed-back path is capacitively connected to the screen grid 6. the resistance II connected in the screen grid circuit between the source l1 and the-grid I effectively prevents high-frequency currents from flowing through the source ll to ground and insures the passage of such currents through the feed-back path including theinductance 2!.

The operation of the two feed-back paths in the system of Fig. 2 is, in general, the same as that described in connection with the feed-back arrangement of Fig. 1 but possesses certain advantages thereover. Thus, in order to tune the circult of Fig. 1 to extremely high frequencies, it is necessary to raise the natural frequencies of either or both of the feed-back circuits'including in- -ductances2l and ,ihby reducing'the inductances I! or I! or both: or to loosen their'couplingsto the coil II, Either expedient reduces the amount of energy feedback and thereby tends to produce instability in the operation of the oscillator at certain frequencies within 'the specified: range. Withthe circuit of Fig. 2, on the other hand; the 'natural frequency of the circuit including coil 2| .may be raised to a sufilciently high value by 'decreasing the inductance of coil "to enable the circuit ll tobe tuned. over the desired range, while still maintaining suflicient feedback to provide stable operation. The decrease in inductance without a consequent decrease in energy feedback is possible because there ls, inherently less interaction between the feed-back pathsof the circuit of Fig. .2 than between the two paths included in the arra gemcnt of l'lg. 1.

A second practi l advantage in the circuit of 2 over that oi I'ig. 1 has reference toth'e use of the oscillator as a beat frequency or localoscillater in a multi-band superheterodyne radio receiver. In-such-a receiver it is necessary selectively to interchange'the inductances forming the inductive branch of the oscillator frequency-determining circuit as'the receiver is adjusted to different signal. carrier frequencies allocated in the different bands. Withthe arrangement of Fig, 1 it isimpractical to'attempt'to switch the inductance it out of the circuit whenthe inductance I2 is removed. Hence the inductance ID remains in the oscillator circuit at all times; being It permanently connected between one electrode of.

the-tuning condenser l8 and the control electrode l. The capacitance of this element to ground may have a deleterious effect on the frequency coverage of the-other bands. In the circuit of Fig. 2, however, the coil III is omitted and such effects are avoided. N While it will be understood that the circuit specifications may vary according to thedesign of a particular application, the following speclflcation of circuit constants for the oscillator 10 circuit of Fig. 2, is included by way,of example as being satisfactory when'used in conjunction with anoscillator tube commercially known as the OJ! tube;

Condenser I 50 micro-microfarads Condenser 21 'l00 micro-microfarads' Condenser'" -e; 0.01 microfarad Resistance ll. e 100,000 ohms Resistance ll 15,000 ohms Resistance lI -1. e..- 20,000 ohms The inductances s, is aim is were supported on a single support with inductance I! concentricallydisposed within inductances l2 and-ll, and with the inductances .l2 and II forming a 25 continuous winding, the specifications being as follows:"-

I ctw f g, Turns wo Winding pitch Diamsts 3o lacks i I; No. 14s 10 turns per inch 1 No. 14a 10 turns pcr inch, 1 12% No. s 28 turns per inch I Certain refinements in the circuit arrange-r ments shown in Figs. 1 and-2 tend to improve the operation to a considerable extent. One such refinement is that of connecting the cathode 2 to a point ill on the inductance l2 slightly above 40 the ground connection. Using the coil specifications given above this was accomplished by connectingthe cathode to a point on the inductance I! {only a fraction of atom removed from the ground terminal of the inductance. Another refinement particularly effective in improving the operation of the embodim t'oi' the invention illustrated in. l"ig. 2 resides in the connection of the various circuit-ground return leads to a single m a inmr. when the oscillator shown is em'ployed-as-a local oscillator in a -superheterody'nc receiver, this common point ll shouldbe that where the circuit lead from the rotor-of the condenser ills connected to ther ehmisOitnem'eiveL Referring nowyto Pig. 8 of the drawings. there is illustrated the form of the improved oscillator shown in Fig. 2 as applied to a multi-band radio broadcast receiver of the well-known supe'rheterodyne type." Briefly described, the receiver comprises a radio-frequency amplifier, indicated schematically at 8|. connected to an'antennaground circuit Si-Ilahd coupled bya multiband coupling sy'stemgenerally indicated at It to thednput electrodes :4 and "of a modulator tube '80. The radio-frequency selector and ampliiier 30 may be of any conventional type and in cludes for each stage, a variable tuning con-'- denser ll and band-selectingswitching means u. The tube a is of the well-known heptode type connected as a pentodebeing provided with screen grids II and a second control grid ad- Jac'ent the cathode il. to which is applied the output voltage from the local oscillator l. Connected in cascade' with the output circuit of the modulator 38 are an intermediate-frequency amplifier 4 I, a detector and automatic amplification control source 42, an audio-frequency amplifier 43 and a sound reproducer 44. The automatic gain control-bias potential may be applied to one or more of the stages of the radio-frequency selector and amplifier 30', modulator 36 and the intermediate-frequency amplifier 4|, as desired, through the lead 45. The variable tuning condensers included in the several tunable circuits of the system are preferably ganged for unlcontrol, as indicated by the dash lines 46. Similarly,-

the various band-selector switches are ganged for unicontrol adjustment, as indicated by the dot and dash lines 41.

Considering first the operation of the receiveras a whole, without regard to the details of the oscillator, per se, the desired received signal wave is selected and amplified in theradio-frequency selector and amplifier 30, further selected and transferred 'by the coupling system 33 to the modulator 36 where the signal is converted into a modulated intermediate frequency. The signal,

ject to automatic control by the automatic vol-.

ume control bias potentials according to the man-- ner well understood inthe art.

. The signal-selector circuits included in each of the stages of the signal-selector and amplifier system 30 are exemplified by the coupling system indicated generally at 33. This system comprises coupling transformers 48, 49 and Ill each including a primary winding which may be selectively connected in the output circuit of the ra-" dio-frequency amplifier 30 by means of a band- 'selector switch 5 I, and-a secondary winding which may be simultaneously and selectively connected to the input electrodes 34 and 35 of the modulator tube 35 by means of a band selector-switch 52, by-pass condenser 53 and that of the modulator cathode biasing circuit 54. These three transformers 48-50, inclusive, have progressive-' 1y lower inductance values in the order named and are designed to be connected to operate over progressively higher-frequency bands covering different portions of the extended frequency range over which the receiver is designed to operate. A single variable tuning condenser 55 is connected to the input circuit 34, 35 of the tube 38 selectively to vary the resonant frequency of the selector circuit 33 over the several frequency bands. Additional adJu'stably-fixed aligning condensers 56, 51 and '58 are connected in shunt with the respective secondary windings of the transformers 48, 49 and 50.

The local oscillator, which is identical in all.

fundamental respects with that shown in Fig. (2 of the drawings, includes, in addition to the frequency-determining inductance II, a pair of additional frequency-determining inductances 59 and 80 of progressively higherlinductance. The ,inductances I2, 59 and BI! may be selectively connected, by a band-selector switch m parallel with the condenser 13 to control the frequency of the local oscillator. A second selectorswitch 64 is provided for selectively connecting-the inductances 28, 8| and (which are coupled to I the inductances I2, 53 and-60', respectively, to the output circuit of the oscillator, thereby to pro.-

quency-determining circuit.

. anode alone.

vide the necessary energy feedback to the fre- Auxiliary seriesaligning condensers 65 and 66, associated with the circuits of inductances 55 and 60, respectively,

and adjustably fixed trimmer condensers 81, 68 .and. 69, effectively connected in parallel with inductances I2, 59 and 60, respectively, are provided .for maintaining a constant frequency difference between the resonantfrequency of the signal selector and the local oscillator frequency. It will be understood that the unicontrol means 41, to which are mechanically connected the several band- selector switches 38, 5|,'52, 63 and 64, may be actuated simultaneously to connect corresponding inductance coils, designed to operate over anyone selected band of frequencies, in their respective associated circuits. Following such a. band-selecting operation, the several tuning con-,

densers maybe adjusted by unicontrolmeans 4 6 to tune the selector circuits and the local oscillator circuit to make the receiver responsive to any desired signal-carrier wave frequency within the selected frequency band.

Although the receiver illustrated in Fig. 3 and described above isshown as comprising means whereby only three distinct frequency bands, covering difierent portions of the frequency spectrum, may be received, it will be understood that I the number of bands maybe increased by the addition of coupling channels in'theseveral tunable signal-selector circuits and by a corresponding addition of coils having different inductance values in thetunable frequency-determining circuit of the local oscillator. able from 'the standpoint of cost of construction ployed. If this is to be done without reducing However, itis desirto minimize the number of such"elements emthe over-all range of. carrier frequencies to which v the receiver is responsive, it is necessary that one or more of the frequencyxbands be relatively wide. Expansion of the ultra high-frequency band to cover an extended frequency range of, for example, from 18 to 60 megacycles may be effected satisfactorily by employing the feed-back ar-' ,rangement herein disclosed for use in the ultra high-frequency band, as shown in Fig. 3.

The improved operation resulting from. coupling the two feed-back paths, in the previously described -manner, is illustrated by the curves of Fig. 4, wherein the oscillator output in volts is plotted against frequency for Ia number of different oscillator circuit arrangements. In this figure the curve 12 represents the operating characteristic of the oscillator with thetwo feedgrid and the frequency-determining circuit as ,was described in' connection with the oscillator shown in Figs. 2 and 3. It will be seen that the oscillator output voltage remainshigh'and substantially constant over the entire operating frequency range extending between 20 megacycles and '65 megacycles. The remaining curves illustrate the resulting operation when'one or two feed-back paths are coupled between the frequency-determining circuit and .the oscillator l he curve I! shows the corresponding characteristic when the highand lowfrequency energy transfer paths are both loosely inductively coupled to the inductance of the frequency-determining, circuit and are both connected to the anode of the oscillator tube. 'The curve obtained when only the low-frequency path is is shown at 13', and the curve obtained aooaue when only the high-frequency path is used is shown at 12". It will be seen that with any one of the three last-named arrangements the oscillator being loosely coupled to the inductance of the frequency-determining circuit. with this arrangement the limited range of adjustment of the frequency-determining circuit of the oscillatorwould not permit the circuit to be'tuned to v a frequency below approximately 25 megacycles.

The curve II is for a feed-back arrangement similar to that from which curve 14 was obtained with the order of coupling reversed, namely, the

high-frequency path was tightly coupled and the low-frequency path was loosely coupled to the inductance of the frequency-determining circuit. With this arrangement the limited range of ad- Justment of the frequency-determining circuit would not permit the circuit to be tuned to a frequency above 40 megacycles. The characteristic curve II is for a similar arrangement wherein the high-frequency path was moderately tightly coupled, and the low-frequency path was tightly coupled to theinductance forming one branch of the frequency-determining circuit. .With this I it is contemplated'in the appended claims to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

' charge device including an input electrode, a.

What is claimed is: I

1. An oscillator comprising, an electron discathode and a plurality of additional electrodes, a resonant circuit having a series inductance value of less than lrmicrohenry connectedto said input electrode and tunable over a wide range of high frequencies, and a plurality of feed-back paths, each of said paths being coupled between a different one of said additional electrodes and said circuit, said feed-back paths being connected in aidingphase relation and having reactive constants-so ,proportioned that said paths are'individually effective primarily only over diflerent complementary portions ofsald frequency range,

whereby said oscillator is maintained in stable v oscillation over said range.

2. An oscillator comprising, an electron dis-' is ef iective to supply energy to said circuit-pr! marily over a portion'of said frequency range including one limiting i'requenoypand a second 7 feed-hack path coupled'between. at" least one said range.

of said additional electrodes and said circuit and first feed-back circuit and having reactive constants so proportioned that said second path is eflective to supply energy to said circuit primarily over a portion of said frequency range including the otherfrequency limit, saidfeed-back paths being. so proportioned and arranged, that said osciilatoris maintained in stable operation over 3. An oscillator comprising, an electron discharge device including an -.input electrode, a'

connected in aiding phase relation with 'said' cathode, and a plurality of additional electrodes,

a resonant circuit having a series inductance value of less than 1, microhenry connected to said input electrode and tunable over a wide range of high frequencies, and a plurality of feed-back paths for supplying energy to said resonant circuit, each of said paths being coupled between a different one of said additional electrodes and said circuit and the impedance of each of said paths being soproportioned with respect to the impedance of the other of said paths that the energy supplied to said circuit through said paths maintains the oscillator voltage'substantially constant over said frequencyrange; j

4. An oscillator comprisingfianjelectron discharge device including control grid and an auxi iary grid, a resonant circuit connected between said control grid and cathode and including an'inductance element and a condenser effectively connected in parallel, said circuit being tunable over a range of frequencies, a feed-back circuit'connected to said anode and including an inductance element coupled to said first-named inductance elernent, the reactive constants of said feed-back circuit being so proportioned that said feed-back circuit is 5 effective to supply energy to said resonant circuit primarily over the lower portion of said frequency range, and a second feed-back circuit connected to said auxiliary grid and including an inductance element coupled tosaid first-named inductance element, the reactive constants of said second circuit being so proportioned that said last-named circuit is effective to supply energy .inductance elements, included in said feed-back circuits andthe couplings between ,said inductance elements and said first-named inductance element being so proportioned that the oscillator is maintained in' stable oscillation. at all fre quencies within said range,

5. An oscillator comprising, an electron discharge device including a cathode, an anode, a control grid and a pair. of additional grids, a resonant circuit connected between said control grid and cathode including an inductance element and a condenser effectively connected in parallel, said circuit being tunable over a range of frequencies, a feed-back circuit coupled becathode, an anode, a

tween said anode and said resonant circuit, the

reactive constants of said feed-back circuit being so proportioned that said feed back circuit is effective to supply energy to said resonant; circuit pr rily over the iower portion of said frequency range, a second feed-back circuit connected to one of said additional grids and in-v eluding an inductance element coupled said last-named inductance element, and a condenser for coupling said last-named feed-back circuit to the other additional grid, the reactive constants of said second circuit being so proportioned that said last-named feed-back circuit is effective to supply energy to said resonant circuit g ance element, and a condenser for coupling said primarily over the remaining portion of said frequency range.

6. An oscillator comprising, an electron-discharge device including a cathode, an anode, a control grid, a screen grid and an additional grid, a resonant circuit connected between said. control grid and cathode including an inductance element and a condenser effectively connected in parallel, said circuit being tunable over a range of frequencies, ascreen grid circuit including a source-of potential, a feed-back circuit coupled between said anode and said resonant circuit, the reactive constants of said feedback circuit beingso proportioned that said feedback circuit is effective to supply energy to said v resonant circuit primarily over a portion of said frequency range including one limiting frequency,

a second feed-back circuit connected to said additional grid including an inductance element coupled to said last-named inductance element, a condenser for coupling said second feed-back circuit to said screen grid, the reactive constants of said second circuit being so proportioned that said second feed-back circuit is effective to supply energy to said resonant circuit primarily over the remaining portionof said frequency range, and means connected in said screen grid circuit for preventing high-frequency currents from flowing through said source of potential.

nected to said anode and including an inductance element coupled to said flrst-namedinductance element, the reactive constants of said feed-back circuit being so proportioned that said feed-back .circuit is effective to supply energy to said resonant circuit primarily over the-lower portion of said frequency range including the lower limiting frequency, a second feed-back circuit connected to one of said additional grids and including an inductance element coupled to said first-named inductanceelement, and a condenser for coupling said secondfecd-back circuit to said other additional grid, the reactive constants of said second circuit being so proportioned that said second feed-Back circuit is effective to supply energy to said resonant circuit primarily over the remaining portion of said'frequency range.

8. An oscillator comprising, an electron. disf' charge devlcedncluding a cathode, an anode, a

control grid and a pair of additional grids, a

resonant circuit connected between said control.

grid and ground and including an inductance element and a condenser effectively connected in parallel, said circuit being tunable over a range of'frequencies, aconnection between said cathode and a point on isaid inductance element slightly above the ground connection,- a feed back circuit connected to said anode and including aninductance element coupled to said firstnamed inductance element, the reactive constants of said feed-back circuit being so proportioned that said feed-back circuit is effective to supply energy to said resonant circuit primarily over the lower portion of said frequency range, a second feed-back circuit connected to one of said additional-grids and including an inductance element coupled to said first-nam d ind ctsecond feed-back circuit to said other additional grid, the reactive constants of said second circuit being so proportioned that'said second feed-back circuit is effective to supply energy to said resonant circuit primarily over the remaining portion of said frequency range. 9. In combination, an electron discharge device including an input electrode, an output electrode and a pair of additional electrodes, a resonant circuit connected to said input electrode and tunable over a range, of frequencies,'and feed-back means for supplying energy to said resonant circuit, sai d means including apair of paths coupled respectively between said output electrode and said circuit and between saidpair of additional electrodes and said circuit, said feed-back paths being connected in aiding phase I relation and having reactive constants so proportioned that said paths are individually effective primarily over different complementary portions of said frequency range and provide a preselected and substantially uniform feedback of energy throughout said frequency range.

trode and a pair of additional electrodes, a res-.

onant circuit connected to said input electrode and tunable over a range of frequencies, a feedback path coupled between saidoutput electrode and said circuit and having reactive constants so proportioned that said path is effective to supply portioned that said second pathlis effective to supply energy to said circuit primarily over another portion of said frequency range including the other limiting frequency, said feed-back paths being connected in aiding phase relation and being so proportioned that they provide a preselected and substantially uniform feed-back of energy throughout the frequency range. I

11. In combination, an electron discharge device including a cathode, an anode, a control grid, and an auxiliary grid, a resonant circuit comprising an inductance element and a condenser effectively connected in parallel, said circuit being connected between said control grid and ground, a, connection between said cathode and a point on said inductance element slightly above the ground connection, a feed-back circuit connected between said anode and ground and inductance element tightly coupled to said first named inductance element, said ground, connections terminating at a common point.

12. In combination, an electron discharge device includinga cathode, an anode, a control grid, a screen grid, and an auxiliary grid, a resonant circuit comprising an inductance element" and a condenser eilectively connected in parallel, said circuit being connected between-said control grid and ground, a connection between said cathode and apoint on said inductance ele- 'ment slightly above the ground connection, a feedback circuit connected between said anodeand ground including an inductance element tightly coupled to said first-named inductance element, a second feed-back circuit connected between an grid and ground including an inductance element tightly coupled to said nrst-.

namedinductance element, and a condenser COD-y charge device including an lnpu't electrode, a"

nected between said auxiliary grid and said screen one. said ground connections terrninating'ata. v commonpoint, 4

13. An oscillator comprising an -electron cuscathode and a plurality tadditional electrodes; a-

resonant circuit having a series inductance valueof less than 1 microhenry connected to said. input v electrode andtunable over a wide range oi ultrahigh frequencies, and a plurality of teed-back paths, each of said paths being coupled between a difler'ent one 01 said additional electrodes and said circuit. said feed-back paths being connect- .ed in aiding phase relation and having reactiveeonstants so proportioned and arranged that they are individually elective primarily over diil'erent complementary portions of said frequency range,

' '14. An oscillator comprising of is than lfmicrohenry connected to said input electrode andtunable over a wide range of frequencies including th'e range irom approximate-v 1y l8' 'megacy'cles to approximately 60 megaeycles, and a plurality of.ieed-back paths, each of said paths being coupled between 'a diflerent'one ot saidadditional electrodes and" said'circuit, saidteed-baclr paths being connected in aiding phase 1 tot-dammed in stable, t o'scilla'tion overv saidjrange.

cathode and a 'plur'alityio! additional electrodes, a 5 resonant'circuit havinga'jseries inductance value relation'and having'reactive constants so propor- 15 tioned that they are: individually eflec'tive primarily over diflerent complementary' portions of said frequency range, whereby said'oscillator is maintained instable oscillation over said range.

- NELSON P- CASE.

2,Q93,4l6.-Nelabn P. w emmwk, N.'Y.- remit! (imam-15 Patent dated September 21-, 1937 Disclaimer filed June.26,- Hereb enters this disclaimer to claim 9 of [dfflll Ga2etts;Jul; 18,f198 9.]

n 1939, by the inventor. said patent.-' a

an grid and ground including an inductance element tightly coupled to said nrst-.

namedinductance element, and a condenser COD-y charge device including an lnpu't electrode, a"

nected between said auxiliary grid and said screen one. said ground connections terrninating'ata. v commonpoint, 4

13. An oscillator comprising an -electron cuscathode and a plurality tadditional electrodes; a-

resonant circuit having a series inductance valueof less than 1 microhenry connected to said. input v electrode andtunable over a wide range oi ultrahigh frequencies, and a plurality of teed-back paths, each of said paths being coupled between a difler'ent one 01 said additional electrodes and said circuit. said feed-back paths being connect- .ed in aiding phase relation and having reactiveeonstants so proportioned and arranged that they are individually elective primarily over diil'erent complementary portions of said frequency range,

' '14. An oscillator comprising of is than lfmicrohenry connected to said input electrode andtunable over a wide range of frequencies including th'e range irom approximate-v 1y l8' 'megacy'cles to approximately 60 megaeycles, and a plurality of.ieed-back paths, each of said paths being coupled between 'a diflerent'one ot saidadditional electrodes and" said'circuit, saidteed-baclr paths being connected in aiding phase 1 tot-dammed in stable, t o'scilla'tion overv saidjrange.

cathode and a 'plur'alityio! additional electrodes, a 5 resonant'circuit havinga'jseries inductance value relation'and having'reactive constants so propor- 15 tioned that they are: individually eflec'tive primarily over diflerent complementary' portions of said frequency range, whereby said'oscillator is maintained instable oscillation over said range.

- NELSON P- CASE.

2,Q93,4l6.-Nelabn P. w emmwk, N.'Y.- remit! (imam-15 Patent dated September 21-, 1937 Disclaimer filed June.26,- Hereb enters this disclaimer to claim 9 of [dfflll Ga2etts;Jul; 18,f198 9.]

n 1939, by the inventor. said patent.-' a

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