US2029346A - Oscillator - Google Patents

Description

Feb. 4, 1935. TAYLOR- ET AL 2,029,346

OSCILLATOR Filed May 28, 1954 OUTPUT 7' NEXT AMPLIFIER OR ANTENNA INVENTORS Alber'z H. Taylor y Leo C. Young AT ORNEY Patented Feb. 4, 1936 rm" crries OSCILLATOR Application May 28, 1934, Serial No. 727,838

4 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates broadly to electron tube oscillation generators, and more particularly to a method of and means for compensating for the tendency of an oscillation generator to pro- 5 duce oscillations of varying frequency and varying amplitude as the potential of the source of anode potential of the generator is varied.

Several variations of constant frequency circuits, both for crystal and self-oscillating circuits, have recently been reported, the recent ones beingan endeavor to develop means for protecting the circuit against frequency drift due to variations in plate voltage. By the use of heater type master oscillator tubes, frequency drifts due to variations in filament voltage are not nearly as serious as the drift caused by plate voltage variations.

The circuit disclosed in the application of AlbertH. Taylor, Serial No. 722,217 filed April 24, 1934, shows a tetrode such as is ordinarily used as a'shield grid tube three elements of which are employed as an oscillator with an additional tube which acts as a sort of automatic volume control to stabilize the volume and frequency of the oscillator by controlling the potential on the screen element of the oscillator tube as an inverse function of the potential of the anode of the oscillator tube. The circuit disclosed in the above mentioned application provides a very constant frequency notwithstanding changes of potential of the source of anode potential of the oscillator so long as the control tube is supplied from a fairly constant source of anode potential. However, the circuit disclosed in the above mentioned application has a disadvantage in that the method of exciting the grid of the control tube by radio frequency weakens the delivery of radio frequency energy to the grid of the amplifier tube, since the grid of that tube and the grid of the control tube share the excitation energy from the master.

In common with the above mentioned application it is an object of thepresent invention to provide a method or" and an apparatus for autowhich. comprise an oscillation generatonas an inverse function of the potential applied to -the anode.

matically maintaining the frequency of oscillation of an oscillation generator substantially con Another object of ,this invention is toprovide a method of and an apparatus for rendering the amplitude of the oscillations of an oscillation generator substantially independent-of the po tential of the source of energy for energizing said 5 generator.

Another object of this invention is to provide a method of and an apparatus for deriving a potential which varies as an inverse function of a potential susceptible to variations. 10

Other and further objects of our invention will be apparent from the specification and claims following when taken in connection with the accompanying drawing in which the figure shows diagrammatically one form of circuit incorporatl5 ing the invention. i

In the drawing, I is a tetrode or a thermionic tube having cathode 2, control grid 3, anode ll and an outer grid or shield grid 20. Thecathode 2, control grid 3, and anode 5 are connected with 20 exmrnal circuit connections so as to comprise a conventional type of piezo electric crystal oscillator in which a piezo electric crystal 5. is connected across an inductance 6 which is inturn connected between the cathode 2 and control grid 3, and a battery or other source of anode potential I2 is connected in series with a: parallel resonant inductance l and condenser 8 between the plate or anode i of the tube and the cathode 2. The sliding contact 9 connected to :anode 4 may be varied in position along the inductance 1 so that all or any desired portion of 'ftheinductance may be included in the anode current path.

A condenser H is connected from the: cathode 2 to the inductance I so as to by-passthe battery or other source of potential I2. A sliding contact it adapted to be adjusted to any desired position along inductance I constitutes, together with ground 38, the output terminals ofthe oscillation generator. 40

The oscillation generator .describedabove without element 20 and its associated circuit isa conventional piezo electrically controlled oscillator in which a change .of potential of a source of anode potential 52 may cause the output frequency delivered at It to vary both in frequency and in amplitude. In order to compensate for, the tendency of the above described oscillation generator to change its frequency of oscillation :with a change of the potential of source I2, a positive potential which varies in value substantially inversely as the value of the potential applied to anode 4 isimpressedupon the outergrid 2-8. This potential is controlled asan inverse function of current flowing in thelanode circuit of the 65.-

triode I3 having cathode I4, control electrode I5 and anode Hi. The grid or control electrode I5 is connected by way of choke coil I8 and milliammeter G5 to the negative terminal of battery I9, the positive terminal of which is connected to slider 44 associated with the potentiometer resistor 43 connected in'shunt with battery I2. Anode I B is connected by way of the resistance 22 and battery or other source of anode potential I2 to the cathode. The anode I6 is also con-1 nected by way of the radio frequency choke 2I to the outer grid 20 of tetrode I The biasing potential applied to grid I5 consists of two components, namely the potential of battery I9 and the potential drop in that part of the potentiometer resistor 43 between slider M and the cathode I4. It is to be noted that these grid of the tetrode is varied, it follows that when the potential applied to one of these elements is varied, the potential applied to the other should be varied, so as to make the frequency change tendenciesneutralize. In the particular oscillator circuit shown it has been found that to accomplish this desired result it is necessary to vary the potential of the outer grid of the oscillator tube as an inverse function of the variation of the potential of the anode. V,

Inasmuch as the action of the oscillation generator tube is well understood, the operation thereof is not here described except so far as its action is dependent upon the action of the regulator tube. When tube I of the oscillation generator circuit and. its associated apparatus is generating oscillations, the potential of the battery or other source of potential I2 is likely to change and cause the frequency generated to have a tendencytoi change. A change of potential of the source I2 causes a change of the potential of grid I5. A decrease in the potential of source I2 causes the grid I5 of regulator tube I3 to be driven more negative while an increase in the potential of source I2 causes grid I5 to become less negative. These changes of potential on the grid I5 cause the anode current of tube I3 to markedly increase with an increase in the value of the potential at source I2 and tomarkedly decrease with a decrease in the value of the potential at source I2. As the anode current of tube I3 changes, the voltage drop across resistance 22 changes, and thus the potential of the anode I6 and the outer grid 20 of tube I actually decreases as the potential of source l2 increases. The changing of the potential of the outer grid 20 of the tetrode I inversely as the potential of the anode is changed results in maintaining the output oscillations of the oscillation generator substantially constant. in frequency and amplitude.

The output oscillations generated in the tetrode l and associated circuits are fed by way of condenser 24 to energize the input circuit of the amplifying tetrode 25 which is connected in a more or less conventional manner as a shield grid amplifier with itsshield grid 28 by-passed to the cathode 26 by means of the condenser 32. The 7 anode 29 of the tube 25. is connected by way of inductance 34 to the positive potential terminal of the battery or other source of potential I 2. The shield grid 23 is connected by way of resistance 3| to the high potential terminal of battery I2. The inductance 34 in the anode circult of tube 25'is shunted by a variablecondenser 35 so that the output circuit of the amplifier may be tuned to the fundamental or any desired harmonic of the frequency delivered by the oscillation generator. The control grid 2110f the amplifying tetrode 25 is connected by way of choke coil 30 and slider 25 to a point ofappropriate negative potential on battery 25 to cause the tetrode 25 to amplify the input oscillations 1 efiiciently. The output oscillations from tube 25 may befurther amplified, if desired.

The cathodes of the oscillation generating tetrode I, theregulating triode I 3, and the amplifying tetrode 25 are all shown as filamentary 1 cathodes and as being energized from a single source of cathode potential connected toileads 4i and 42 but it is to be understood that heater types of tubes employing uni-potential cathodes mayalso be used.

The grid 20 is shown connected by way of radio frequency choke coil 2I directly to the anode it of the regulating tube or triode I3 but it is to be understood that this connection need not be made directly to the anode but that the connection to the grid 25 could be made at any desired point on the resistance 22, in which case it might be desirableto connect said grid to a slider that could be selectively varied along the resistance 22; 1 g r In thesystem shown in the drawing, no by-pass condenser is included between the grid 20 and cathode 2 because this particular circuit with which the invention has been illustrated is a 7 crystal controlled circuit which would not oscillate if the shield were by-passeol to filament lator in a self-oscillating type of circuit without the by-pass condenser, whereas with the 7 watt and 75 watt tubes the regulation has been equally good either with or without the by-pass condenser.

. The current through the biasing battery I9 is so small that it is evident that dry cells can be used for this purpose and will have a very long life since it either has no current at all or at other times a slight charging current. In the event of deterioration of the battery, since this voltage is not critical, a slight readjustment of the slider 44 on the potentiometer 43 to which the positive end of. the battery is connected suffices to establish that equilibrium necessary for constant energy and constant frequency. Any sudden deterioration of the battery would immediately be noted by the abnormal current indicated by the d. c. ammeter i5 connected in series with the grid of the control tube; so-that this may be used as a criterion of the healthy and 1 normal condition of the negative C battery. 'It will.be noted that there areno radio frequency voltages in any way associated with the 00 113791 tube, therefore the action of the circuit is substantially independent of frequency.

The shape of the control curve may be modified by the amount of negative C battery used in series with the grid of the control tube. With a very high battery the control is extremely accurate but only over a narrow range of plate voltage variation. With a lower voltage on this C batterythe control is not so good but it acts over an enormously wider range of plate voltage change. Practical values can readily he arrived at for a given situation where the normal fluctuations in supply voltage are known to have certain limits. This flexibility of the circuit is one of its most interesting features. Fairly good controlof both output and frequency can be had even with a variation in supply voltage to the plates, but if the normal fluctuations are not anticipated to be more than say 20%, it will be better to choose a little higher value of C battery to get a finer control within that narrower range. It should be made clear that the points for best frequency control and best output energy control are not absolutely identical but so close together that all preliminary adjustments can readily be made by merely observing the output of the amplifier. When a given variation of plate voltage causes little or no change in this output, we maybe reasonably sure that the frequency is extremely stable.

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

We claim:

1. A source of high frequency oscillations comprising an electron tube having a cathode, an anode, a control grid and an auxiliary grid element, frequency determining means connected between said control grid element and said cathode, a tuned output circuit and a source of anode potential connected in series between said anode and said cathode, and means for applying to said auxiliary grid a potential which varies inversely as the potential of said source of anode potential comprising a triode regulating tube the control grid of which is connected by way of a source of biasing potential of constant value to a point on a resistance shunting said source of anode potential, a resistance included in circuit between the anode of said triode and the high potential side of said source of anode potential the low potential side of which is connected to the cathode of said triode, and an inductive connection between said auxiliary grid and the anode of said triode.

2. A source of high frequency oscillations, comprising an electron tube having a cathode, an anode, and a control grid, a piezo electric crystal operatively associated with said tube between said cathode and said grid, a source of anode potential and a tuned resonant circuit connected between said cathode and anode, and means for maintaining the output frequency of said tube substantially constant notwithstanding variations of potential of said source of anode potential comprising a potential gradient controlling electrode within said tube between said anode and the other electrodes and means for applying to said electrode a positive potential which varies inversely as the potential of said anode including said source of anode potential, and a triode, a resistance connected in series with said source of anode potential between the anode of said triode and the cathode thereof, a resistance connected in shunt with said source of anode potential, a source of biasing potential of constant value connected in circuit between the grid of said triode and an adjustable point along said resistance connected in shunt with said source of anode potential, and a direct current path between the anode of said triode and the said potential gradient controlling electrode.

3. In combination, an oscillation generating system comprising an electron tube having a cathode, a control grid, an auxiliary element and an anode, a source of anode potential, circuits interconnecting the cathode control grid anode and said source of potential together with external devices to constitute an oscillation generator, means for compensating for the tendency of the oscillations generated thereby to change in frequency and amplitude with a change of the potential applied between the anode and cathode of said tube, comprising a regulator triode the anode of which is supplied with potential through a resistance from the same source as the source supplying the anode of said oscillation generating tube, means for applying to the control grid of said triode a static component of potential plus a component of potential which is a function of the potential of the source for supplying said anodes, and a conductive path between the auxiliary electrode of said oscillation generating tube and the anode of said triode.

4. An electric system comprising, in combination, an amplifying relay having a cathode, an inner grid electrode, an outer grid electrode, and an anode, a source of anode potential, circuits interconnecting said cathode, control grid, an-

ode and source of anode potential together with external devices to constitute an oscillation generator, a second amplifying relay having a cathode, an anode and a control electrode, a resistance connected in shunt with said source of anode potential, a second resistance, means connecting said second resistance and said source of anode potential in series between the anode and cathode of said second amplifying relay, means connecting the outer grid electrode of said first amplifying relay with the anode of said second amplifying relay, a source of biasing potential connected in circuit between the control electrode of said second amplifying relay and a point of intermediate potential on said resistance connected in shunt with said source of anode potential, said source of biasing potential being so poled as to oppose the potential between the cathode and said intermediate point, whereby a change in the value of the potential of said source of anode potential tends to change the potential of the control electrode of said second amplifying relay in such a manner as to cause a current change in the resistance connected in the anode circuit of said second amplifying relay of such a value as to control the potential of the outer grid electrode of said first amplifying relay as an inverse function of the potential applied to the anode of said first amplifying relay.

ALBERT H. TAYLOR. LEO C. YOUNG.

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