US2428930A - Controllable reactance - Google Patents

Description

Oct. 14, 1947.

CLARK ET AL coNTRLLABLE REACTANCE Filed April -30. 1943 llllll S00E05 OF MooumrnvG INVEN 0R3 ROBE/PT W LARK FRANK J SOMERS- A TTOPNEY.

Patented ()ct. 14, 1947 "Robert "were fsomers Newlfork, N.

orporation or America, a corporation of 'DelaiClark, Teaneck, N QL, "and Frank 3.

'e si ne s .Bad

Application-April 30, 1943, senamo. assure scams. (cr me-i715 This application concerns-reactanceof the tube type and control means for controlling the size of the said reactance, :Ina'n application the reactance -is in an oscillation generating circuit or in-atuned-circuit ;Means is ,provided to control the said reactance and thereby control the "tuning of the generator circuit or tuned circuit to control the timing oi the oscillatory energy in the generating --circuit iortuned circui-tr An object of our invention is to improve the operation of reactance tube circuits of the type -:described above in general. A more specific object is to improve such systems 'whenthe oscillations generated or flowing in the tuned circuit Y are=of large amplitude. The voltage 'fed to the reactance tube control grid in phase quadrature :15 derived from the cathodecircuit of a cathode follower type stage. The amplitude o'ith'e'voltage on the cathode circuit of the cathode follower typestage will be less than that on the "grid and the yoltage on the cathode circuit may be ad;- justed to the desired amount. Thus animproved means for regulating the quadrature voltage for .best operation is-provided.

Another 'obiect of the-present invention is to reduce the "efi-ects of-regeneration in the reactance tube, say for example, in case -a reactance tube of the triode type is used. Since the grid *of the reactance tube derives "the quadrature voltage from the cathode impedance cfa stage of the cathode follower type and the cathode to ground impedance of such a stage is generally of a low value, regeneration effiects in the reactan'ce tube are reduced.

In addition the modulation amplifier feeding into the grid of the reactancetube, which is also connected to the cathode impedanceof the oathode followerstage; is feeding into a lovv'im-pedance load and the system is particularly useful in case a; Wide band oi modulation'frequencies"are used, such as, for example, video or similar signals.

In'our system -the-control of the tube reactan'ce may "be in accordance with control potentials 'suchas used in automatic frequency control systerns or in accordance with modulating potentials of any type. It is especially useful where the modulating :potentials extend over a wide range of frequencies. The'c'ontr'ollable reactance may be used to control 'or modulate the phase orfreque'n-cy =o'r the phasean'd irequen'cyof wave energy.

Throughout the specification and claims the terin timing m'odulation'will be used and is intendypes of'phase and freed to cover theyarious quncy"modulationormodified formsthereoi.

In describing our-invention in d'etailrefer'ence will be :made' to the drawings wherein the "single figure illustrates tube and circuit arrangement wherein a controllable capacity "is'developed "bewherei-n-oscil'latory energy flows.

tween the electrodesofthetubein a new and improved manner andused in-a-nove1 manner to control the timing of oscillatory energy, 7 In the =drawings, l0 is an oscillation generator having itsfirst and seco d grids and cathode regeneratively coupled-in 'a tuned circuit comprising capacity ;C -and inductance L, [The mode of operation of this-type generator is believed well :lcnownanda=detai1ed-stateme t thereof is believed unnecessary. W The generator is, however, ofthe-regenerative'type -and 9f the electron coupledtype -In thegene-rator the second gridacts -as-an :anpd-aand the cathodeis inair-rtai ned above ground alternating current potential by the choleing-inductance +2. oscillation generating BlGGtIOdGSffiI'ECdU-Plfid substantially by the electronstreamonly in the tube to the output circuit i e e e th n l l. l, a

y The tube 20 ;has itsanode to cathode internal impedance-in shunt 't'o L and C and in this tube the reactive eijfectis developed. The reactive effect is across -the circuit LG and as aconsequence determines the re actance thereof and the timfing lo f the pscillationsgenerated inay be a tuned circuit wherein an alternating current is induced ratherthan thetanl; of a generator. :The-Qhigh-patntial endoi and L and the anode 12 of tube 20 are 'coupled to' thefirsjt grid 24 of an amplifier tube'fslso that the phase ofthe alternating current-potentialbn the "first grid?! oftube ZB and on the anode '52 of tube 20 and entheniginpdteuua1 end of c ircuitLC is the 's'ame. 'The'tubefz't of the ca thode follower type having in its cathode groundcircuit a resistance potentiometer 30. hlpfoint on this resistance poten-tiorneter is coupled by resistance 3| to the contra-1' grid "to provide :the required grid bias in tl i i stubeg; The amount o f the voltage developed in th'ebathode 'c'ir'cu' -is determined by the re- "s'istlan cetn -typeof tube 26, and-the voltage on grid 24. The "potential drop across the potentiometer; is supplied to aphase shifting networkipcluding resistance R and condenser C l. BI is the-grid-resistorfortube 28- and normally --is large "in-comparison with Ranol may be disregarded in considering the phase shifting network. However, where RI is small it :must be taken into accountwhen"considering the phase shifting network. The common terminals of resistance Band Cl are connectedto the control grid -32 of tube 20 The -resisto-r-34, shuntedby radio and-modulation frequency bypass condenser 35, provides the bias tor the control grid of tube 20.

-In my --system,-dur-ing operation the;alternating current potential at thepathode-end-of resistance =30 varies "in-phase with the alternating current -:potential"suppIied'-to "the grid 24 of tube 26, andin the arrangement this alternating current potential is of the same Tphas'e 'a's the alternating our- '60 rent potentialonte-anode -22 of tube '20. The

3 resistance R and condenser CI provide a phase shifting network by means of which the alternating voltage fed to the grid 32 from the potentiometer resistance 30 is shifted about 90 in phase so that in the tube 20 we have a phase quadrature relation between the high frequency voltages on the anode 22 and grid 32. In other words, in this tube 28 the current to theanode is 90 out of phase with respect to the anode voltage and the tube instead of being an amplifier, simulates a reactive efiect which is reflected into the tank circuit CL. If the current to the anode leads the anode voltage the reactive efiect which is complex is essentially capacitive. If the current to the anode lags the anode voltage the complex reactance is essentially inductive.

In an arrangement shown B, Cl and RI (BI is large and neglecting the capacity of cathode 31 to ground) are dimensioned so that the phase of the voltage on the grid 32 is in quadrature with the voltage on the anode 253. In the arrangement shown the resistance of R is made large as compared to the reactance of Cl so that the current through the circuit is largely resistive and is in phase with the voltage. The reactance drop across the condenser Cl is 90 out of phase with the current, 1. e., lags the current by about 90 so that the voltage on the control grid 32 lags the voltage on the anode 22 by about 90 and the reactive effect is inductive. If BI is small so that the reactive drop across Cl is not 90 out of phase (less than 90) with the current in the condenser Cl an inductance L2 is added to the phase shifting network say in series WlthR or in series with RI. This inductance then retards the current and causes the current to lag the Voltage an amount sufficient to bring the reactance drop across CI to about a phase quadrature relation with respect to the voltage at the oathode of tube 26. V

The capacity to ground of cathode 31 may be of such value as to create an appreciable phase angle between the voltage on grid 24 and the voltage on cathode 31. This phase angle can be corrected by connecting an inductance in series or parallel with resistor 30. The value of this inductance is such that at the mean frequency of the generated oscillations it will resonate with the capacity to ground of cathode 37.

By modulating an electrode in tube 28 in accordance with control or modulating potentials the tube conductance is varied, thereby varying the size of the reactive efiect and changing the tuning of the circuit CL. The controlling or modulating potentialsmay be applied to tube 29. In a particular application a video amplifier tube 46 has its output electrodes coupled by a video peaking choke LX and loading resistance LR to the control grid 32 of tube 20. This connection includes a radio frequency blocking circuit in the form of an inductance Ly which with its distributed capacity is parallel tuned to the center frequency at which the oscillator tube or tuned circuit LC is operating.

Considerable advantage is derived from the use of my novel arrangement where it is desirable or necessary to use a triode tube reactance at 2!] or where a relatively strong oscillation generator is used or oscillations of considerable amplitude are set up in tank LC.

Where a reactance tube of the triode type is used at 20 the anode 22 to grid 32 feed-back inherent in such tubes is minimized by the low impedance of the output circuit of tube 26.

The phase shifting network may have the posi- I, ductance instead of tions of R and Cl, reversed so the reactive effect across the circuit LC will be capacitive, or the network may be composed of a resistance and ina resistance and capacitance.

The quadrature voltage on the grid 32 of tube 20 most favorable for its operation may be obtained by dimensioning the potentiometer 30. Thus if the oscillations in tank circuit LC are strong, tube 26 may be used as an electronic at- ;enuator to produce the required voltage on grid We claim:

1. In a tube reactance of controllable reactive value, two terminals across which alternating voltages appear and across which a reactive effeet is to be produced, a first tube having output electrodes including a cathode coupled to said terminals, said tube having a control electrode, a second tube having input electrodes coupled to said terminals, said second tube having a cathode connected by an impedance to the cathode of said first tube, a phase shifting circuit coupling said impedance to the control electrode of said first tube, whereby a reactive effect is produced in said first tube, and connections for controlling the conductance of said first tube to thereby control the produced reactive effect.

2. In a tube reactance of controllable reactive value, a tuned circuit wherein alternating current flows and across which a controllable reactive effect is to be produced, a first tube having an anode and a cathode coupled in shunt to a part, at least, of said first circuit, said tube having a control electrode, a second tube having input electrodes coupled to said first circuit, said second tube having a cathode connected by an impedance to the cathode of said first tube, a phase shifting circuit coupling said impedance to the input electrodes of said first tube, whereby a reactive effect is produced in said first tube and reflected in said circuit and connections for modulating the conductance of said first tube in accordance with control potentials to vary said reactive effect.

3. ma timing modulation system, a tuned circuit wherein alternating current fiows and across which a variable reactive effect is to be produced, a first tube having output electrodes including a cathode coupled in shunt to a part, at least, of said circuit, said tube having a control electrode, a second tube having input electrodes coupled to said first circuit, said second tube having a cathode connected by an impedance to the cathode of said first tube, a phase shifting circuit coupling said impedance to the control electrode of said first tube, whereby a reactive efiect is produced in said first tube and connections for modulating the conductance of said first tube in accordance with signals to control said reactive effect and thereby correspondingly modulate the timing of said alternating current.

4. In a timing modulation system, a tuned circuit wherein alternating current fiows and across which a variable reactive effect is to be produced, a first tube, a control electrode having an anode and a cathode coupled in shunt to a part, at least, of said circuit, whereby alternating voltage of a first phase is set up on said anode, a second tube having a control electrode coupled to the anode of said first tube, said second tube having a cathode, an impedance connecting said last named cathode to the cathode of said first tube, a phase shifting network circuit coupling said impedance to the control electrode of said first tube, whereby a voltage is set up on said last named electrode which is about 90 displaced in phase relative to the phase of the voltage on the anode of said first tube and a reactive efiect is produced in said first tube and added to said tuned circuit and connections for modulating the conductance of said first tube in accordance with signals to control said reactive effect and thereby correspondingly modulate the timing of said alternating current.

5. In a simulated controllable reactance, an electron discharge tube having an anode, a cathode and a control grid and means for applying alternating current voltages substantially in phase quadrature upon the anode and control grid of the tube and for varying the tubes gain by control potentials to produce a variable reactive efiect between the electrodes of said tube comprising, an additional tube having an anode, a cathode and an electron flow control electrode, a coupling for applying said alternating current to said electron fiow control electrode, an impedance coupling the cathode of said additional tube to ground, a source of potential connected with the anode of said additional tube, a phase shifting circuit coupling said impedance to the control grid of said first tube, said phase shifting circuit including between said impedance and the control grid of said first tube a second impedance and between the said control grid and cathode of said first tube a condenser, and means for controlling the transconductance of said first tube in accordance with control potentials.

6. In a wave frequency control system an electron discharge tube having an anode, a cathode and a control grid, a tuned circuit wherein alternating current the timing of which is to be controlled fiows, means for applying alternating cur- 6 rent voltages from said tuned circuit substantially in phase quadrature on the anode and control grid and for varying the tubes gain by control potentials to produce, a variable reactive effect between the electrodes of said tube to vary the reactance of the said tuned circuit and thereby the timing of said voltages comprising, an additional tube having an anode, a cathode and a control electrode, a coupling between the control electrode of said additional tube and said tuned circuit, an impedance coupling the cathode of said additional tube to ground, a source of potential connected with the anode of said additional tube, a phase shifting circuit coupling said impedance to the control grid of said first tube, said phase shifting circuit including between said impedance and said control grid of the first tube an inductance and a second impedance and between the control grid and cathode of said first tube a condenser, a source of video signals and an amplifier tube having input electrodes coupled to said source of video signals and having output electrodes coupled to a load and to the control grid of said first tube.

ROBERT W. CLARK. FRANK J. SOMERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Mathes Crosby Roberts Brailsford Number

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