US1934213A - Oscillation generator - Google Patents

Description

1933- G. L. USSELMAN OSCILLATION GENERATOR 2 sheets-sheet 1 Filed April 5, 1932 INVENTOR 6.L.USSELMAN BY W4? M/ ATTORNEY Nov. 7, 1933;

G. L. USSELMAN 050 ILLATION GENERATOR Filed April 5, 1952 2 Sheets-Sheet 2 i 54 32 z 5,; A

INVENTOR G. L. USSELMAN BY [16%, @W

ATTORNEY Patented Nov. 7, 1933 UNITED STATES PATENT OFFICE Q 4 1,934,213 i Q t: I t

OSCILLATION GENERATOR George L. Usselman, Port Jefferson, N. Y., as-

signor to Radio Corporation 'of America, a corporation of Delaware ApplicationApril 5, 1932. Serial No. 603,348

This invention relates to oscillation generators and especially to constant frequency'oscillation generators of the inductive feed back type. In electron discharge device oscillation generators 5 of the inductive feed back type wherein a certain portion of the oscillator output is fed back from the output circuit to the input circuitfor excitation purposes, I have discovered that, because of the capacitive feed back between the coils of the feed back arrangement, not only is there caused a reduction in the generated oscillations but also, the system is more subject "to parasitic oscillation generation. Thus, and especially in connection with crystal *controlled oscillation generators towards which my present invention is particularly directed, even With the circuit neutralized to prevent all oscillations except those controlled by the crystal, there is still the possibility of spurious or parasitic oscillations because of the capacitive coupling between the feed back coils. Accordingly, the main object of my present invention is to eliminate this capacitive source of feed back, and'to do so, I electrostatically shield the feed back inductors from each other. In the case of concentric coils, this shield may take the form of a concentric, grounded, conductive slitted cylinder between the coils, or in the event of coaxially arranged coils, the shield preferably takes the form of a grounded, slitted sheet of metal.

Since the interelectrode capacity of the elements of the tube or tubes forming part of the oscillation generation system assists in the undesired capacitive feedback and may also give rise 36" to spurious oscillation generation, a further object of my present invention is to eliminate this possible source of undesired action,

Other objects and advantages of my present invention will become apparent upon a reading of the following more detailed description taken in connection with the accompanying drawings wherein,

Figures 1 to 7 inclusive are piezo-electric crystal controlled oscillation generators embodying the principal feature of my present invention; namely, electrostatic shielding between feed back coils of a regenerative oscillation generator.

Turning to Figure 1, I have illustrated within an evacuated container or electron discharge device 2, a cathode or filament 4, a grid or control electrode 6, adjacent the cathode, an anode or plate 8 and a screen grid or grid 10 intermediate the control grid 6 and anodes. Between the anode and cathode there is connected a tunable circuit 12 consisting of an inductance coil 14 and variable tuning condenser 16. 'The cathode is supplied with heating energy from a source 18 and the anode is supplied with energy from a source 20, the screen grid 10 also being biased from that source through the action of polariz ing resistor 22; The screen grid 10 assisted by by-passing action of blocking condenser 24 prevents interelectrode feed back between the anode 8 and control grid 6 and also, therefore, the evils concomitant thereto such as spurious oscillation generation at undesired frequencies. For feed back purposes coil 14 of the tuned anode circuit 12 is in inductive relationship to the tickler or feed back coil 26 which impresses excitation energy upon the piezo-electric crystal 28 connected between the control electrode 6 and the cathodes. The control electrode '6 is maintained at a proper operating potential by the polarizingflaction of grid leak resistor 30 acting inconjunctionwith the capacity formed by the piezo-electric 'chystal system 28 either of quartz tourmaline, Rochelle salts or similar material and its associated electrodes. v

As'the capacity feed back between the plate coil 14 and the input coil 26 may be opposed to 89 the desired inductive feedback and lessen the amplitude of oscillations generated, and, in any event, as such capacity coupling may give rise to spurious or parasitic oscillations which are highly undesirable in oscillation generators of this 5 type, I have provided an electrostatic grounded shield 32. If the tickler coil 26 and plate coil 14 are arranged concentric, say upon cylindrical supports exactly aligned, then the shield 32 is preferably in a plane perpendicular to the axis 940 of thecoilsand slitted longitudinally'to prevent excessive eddy current loss. Or, the shield 32 may simply be a piece of cardboard upon which some tin-foil has been placed, the tin-foil being grounded and slitted; or, the shield 32 may be a pluralityof open ended linear conductors placed in a single plane andgrounded at adjacent ends, and left open-ended at the ends opposite the grounded ends. w a

In the event that the anode coil 14 and the tickler coil are arranged concentrically one withinthe other, then the shield 32 should be in the form of a concentric cylinder between the cylindrical planes formed by the conductors of each v coil andthis cylindrical shield should also be itted and grounded as depicted electrically in Figure 1 at'32.

Output energy from the system shown in Figure 1 maybe taken inductively from the plate coil 14 as illustrated, and ied toa buiie'r amplino the output or" my oscillator may be utilized in a heterodyne radio receiver, or in a wave measuring system. The output may be utilized in other ways, and, of course, the output of every one of my oscillatory circuits described herein may be used in the fashion outlined hereinabove. To lessen load reaction, the arrangement of Figure 1 may be modified as illustrated in Figure 2 wherein screen grid 10 is utilized as a plate, and, a regenerative oscillatory system is formed of the screen grid 10, the control grid 6 and the cathode 4. The plate 8 is connected to a tunable output circuit34, and, is coupled only to the oscillating system just delineated only by virtue of the electron stream within the tube 2. Hence, there is no perceptible reaction of the load or output upon the oscillating system as a result of which frequency stability is enhanced.

Also, in the arrangement shown in Figure 2, an additional grid 36 may be provided to prevent interelectrode or capacity feed back between screen grid 10 and control electrode 6. This grid 36 may be grounded by the action of bypassing condensers 24 and polarized from the screen gridlead by polarizing resistor 22 so as to maintain the grid 36 at a lower potential than grid 10.

Although the screening grids in Figure l in the form of screen grid 10 and in Figure 2 in the formof screen grid 36, are desirable, they are not essential, and, at the expense of a certain amount of frequency stability may be omitted. Or, they may be replaced by the arrangement shown in Figure 3 wherein the interelectrode capacity between the plate 8 and the control grid 6 is neutralized by the action of a neutralizing condenser 38 connected to the control grid 6 and to a point ,on the plate coil 14 of opposite instantaneous polarity to that polarity of the point to which the plate 8 is connected. As before, the electrostatic screen or shield 32 properly grounded is provided. The crystal 28 is here connected on the grid side of the coupling coil 26 since this form of connection gives greater stability, the crystal in this case acting as a filter passing only that frequency for which it is ground to the input circuit or control grid 6 for excitation purposes.

The output of this circuit may be utilized in the same way given for the arrangements illustrated in Figures 1 and 2, and may be taken through coupling condenser or capacitor 40 from the plate rather than by an inductive arrangement.

In the arrangement shown in Figure 3, however, parasitic oscillations may be set up due to the fact that at certain frequencies the crystal and its associated holder may act simply as a condenser. To eliminate this tendency the capacity of the crystal and its holder may be compensated or neutralized by the arrangement shownin Figure 4. Here,.tickler coil 26 is split, the crystal 28 being connected to one side thereof and the crystal electrode neutralizing condenser 42 being'connected to the other endof the grid coil 26 as shown. By suitable adjustment of condenser 42 the capacity of the crystal structure will be neutralized as a result of which the defect just pointed out is entirely eliminated.

In addition, in connection with the circuit illustrated in Figure 4, rather. than use a grid grid 10 is utilized as a plate and is connected to a point of opposite polarity relative to the connection point of grid 6 on the inductor 14 for neutralization purposes thereby eliminating the ill effects of interelectrode feed back between screen grid 10 acting as a plate and the control grid 6. Undesired capacitive feed back between the inductor 14 and coil 26 is, of course, prevented by the electrostatic screen 32 described in detail hereinabove. However, inductive feed back between those coils causes proper feed back between the coils for excitation of piezo-electric crystal 28 causing oscillation generation at a frequency corresponding to that of the crystal by the oscillatorysystem formed by the screen grid 10 acting as a plate,control grid 6 and the cathode 4 together with their allied circuits Output energy may then be taken from the plate or anode 8 as illustrated through the output condenser 40. The plate 8 is coupled to the oscillating system only by virtue of the electron stream within the tube 2. c i

The potentials'applied to the screen grid and plate may be identical, or, adjusted to give best operation. This may involve maintaining the plateat a higher potential than the screen grid or vice versa.

Figure 6 also utilizing a grounded screen 32 between the inductive feedback arrangement is in some respects similar to Figure 1 in that it makes use of a screen grid 10 to prevent inter,- electrode feed back. However, no condenser is provided for tuning the plate coil 14 while on the other hand the tickler coil or. grid coil 26 is tuned by means of variable condenser48. The crystal 28 is connected between ground and one end of the gridcoil and thecrystalsystem capacityneutralizing condenser 50 is connected between the other end of coil 26 and ground.

Figure 7 illustrates a further modification and differs from the arrangement shown in Figure 6 in that the crystal is connected between the grid 6 and one end of the grid tuned circuit com-. prising coil 26 and condenser 48. The neutralizing condenser 50 for neutralizing theinterelectrode capacity of the crystal and its electrodes is connected between the crystal or grid 6 and the other end of coil 26. In both the arrangements illustrated in Figures 6 and 7 the screen grids 10, though preferable, are not essential and in the event that it is desirable to omit them, bypassing condensers 52 and polarizing screen grid resistors 54 may be omitted together with the screen grids 10. As the operation and utilization of output energy of the circuits illus- 14g trated in Figures 6 and 7 are apparent to those skilled in the art, from what has gone on hereinbefore, statements concerning those matters need not be made.

Having thus described my invention, what I claim is:

l. A system for generating high frequencyoscillations comprising an electron discharge device having within an evacuated container an electron emitting cathode, a control grid and an 150 electrode maintained at a positive potential with. respect to said grid and cathode; an inductance coil connected between said control grid and cathode, another inductance coil inductively related to said first mentioned coil connected between said electrode at positive potential and said cathode, for magnetically feeding excitation energy to said electron discharge device control grid, and, a grounded electrostatic shield interposed between said coils in order to prevent undesired capacitive coupling between said coils.

2. Apparatus as claimed in claim 1 wherein in addition, means are provided for preventing the effects of interelectrode feed back between said electrode maintained at the positive potential and said control grid.

3. Apparatus as claimed in claim 1 wherein in addition, a piezo-electric crystal is connected between two of the electrodes of said electron discharge device for frequency stabilizing the oscillations generated thereby.

4. Apparatus for generating constant frequency oscillations comprising an electron discharge device having an anode a cathode and a control electrode, an inductance coil and a piezoelectric crystal connected between said control grid and cathode, an inductance coil inductively related to said first mentioned coil connected between said anode and cathode, and, a grounded electrostatic shield interposed between said coils for preventing the electrostatic transfer of piezoelectric crystal exciting energy between said coils.

5. Apparatus as claimed in claim 4 wherein in addition, means are provided for neutralizing the interelectrode capacity-of said piezo-electric crystal.

GEORGE L. USSELMAN.

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