US2492748A

US2492748A - Oscillatory circuit

Info

Publication number: US2492748A
Application number: US628565A
Authority: US
Inventors: Robert G Hibberd
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1944-12-19
Filing date: 1945-11-14
Publication date: 1949-12-27
Anticipated expiration: 1966-12-27

Description

Dec. 27, 1949 R. G. HIBBERD 2,492,748

OSCILLATORY CIRCUIT Filed Nov. 14, 1945 inventor:

b MW 47% His Attorney.

Robert G. Hibberd, I

Patented Dec. 27, 1949 OSCILLATORY CIRCUIT Robert G. Hibberd, Rugby, England, assignor to General Electric Company a corporation of New York Application November 14, 1945, Serial No. 628,565 In Great Britain December 19, 1944 Claims. 1 This invention relates to thermionic valve os-' cillation generators adapted for the generation of oscillations of ultra high frequency.

In such oscillation generators, it is important to avoid the generation of oscillations of spurious frequencies and to eliminate unwanted capacity and inductance in the circuit. This generally involves the use of push-pull circuits which are very carefully balanced.

One satisfactory circuit which has become known in the art is what has been termed a "butterfly oscillator. Such an oscillator is diagrammatically illustrated in Fig. 1 of the accompanying drawing. It comprises a split-stator variable condenser having a rotor l and stator 2 in combination with inductances 3 symmetrically connected between the two sections of the stator 2 of the condenser. The rotor of the condenser is connected to earth at 4. A pair of thermionic valves have their anodes 5 connected to the respective sections of the stator, their cathodes 6 connected through radio frequency choke coils 1 to earth at 8, and their grids also connected to earth through a resistance 9. The cathode heaters are also connected through radio frequency choke coils 1 and Ill to a source of heating current at H. Anode potential is supplied from the source of positive potential B+ through a radio frequency choke coil I2 to the middle of one of the inductances 3 as indicated. It will be observed that this circuit is perfectly balanced electrically, but in order to obtain the optimum results therefrom it is also necessary to arrange symmetrically the components therein to obtain physical as well as electrical balance. Furthermore, for the generation of ultra high frequency oscillations the inductance in the oscillatory circuit must be reduced to a very low value.

In butterfly oscillator circuits as hitherto used, for wave-lengths of the order of a decimeter, a condenser having plates of the form illustrated in Fig. 2 has been employed. In this construction the rotor plates l interleave with stator plates 2 which are interconnected at their periphery by portions 2a which constitute the inductances 3 of the circuit illustrated in Fig. 1. Thus for any given circuit, the ratio of inductance to capacity is fixed. Furthermore, a condenser of the character shown in Fig. 2 is difficult to In an oscillatory circuit for a "butterfiy oscillator comprising a split stator condenser and a pair of inductances according to the invention the inductances are constituted by a pair of metal plates symmetrically arranged with relation to the condenser, each plate being connected at its opposite edges to regions of opposite potential on the fixed'plates of the condenser, the contour of the plates following that of the outer edges of the fixed and movable plates. The inductance plates may be substantially coextensive with the stator of the condenser and by thus extending the superficial area of the plates the inductance thereof is reduced to a value commensurate with the capacity of the condenser,

thereby enabling the generation of ultra high Y frequencies. 7

In order to maintain balance in the circuit of the oscillator, the pair of valves is located symmetrically with respect to, and with their longitudinal axes substantially parallel with, the axis of rotation of the condenser rotor, the anodes being connected as directly as possible to the respective sections of the split-stator.

In order to adjust the range of 1 frequency through which the'oscillator is tunable, the inductance plates are preferably provided with adjustable supporting means so that the spacing between these plates and the plates of the condenser can be varied.

This may conveniently be effected by flanging the edges of the plates and forming slots in the flanges. The slots engage on set screws which attach the plates to the respective sections of the fixed plates of the condenser and the slots permit of the adjustment of the plates towards and away from the stator.

An important further feature consists in shortcircuiting the fixed and moving plates at their edges in order to reduce the electrical length of the path along the plates which might constitute a resonant circuit at a frequency different from the operating frequency. This materially assists in the elimination of spurious frequencies.

To enable the invention to be readily understood I have illustrated in Fig. 3 of the accom panying drawing in perspective view a practical embodiment of the same; Fig. 4 indicates one form of plate for the split-stator condenser; and Fig. 5 is an explanatory diagram of the modification illustrated in Fig. 6; and Fig. '7 shows the application of the invention to a wave meter.

Indescribing Figs. 3 and 4, the same reference numerals are used as are employed in describ ing Fig. 1 to indicate similar parts of the em-- bodiment of the invention. The stator plates l3 of the condenser are spaced somewhat as indicated in Fig. i. Interleaving into the stator plates are the moving plates I mounted on the control shaft 14. The stator plates i3 are, as shown in Fig. 3, clamped together with suitable spacing means by the longitudinal pillars l5 engaging headers l6. The headers 16 are of X- shape in end view. The header at the near end of Fig. 3 is formed by the channel-shaped insulating member l'l. Spacers [8 separate the header I! from the nearest stator plates by a distance suiiicient to permit of the mounting of the valves IS in the space so provided. In the embodiment illustrated, these valves are of the acorn type and one is inverted with respect to the other. Spring contacts 20 form the connections for the lead-through conductors which are brought radially through the envelope in the customary manner. To these contacts are connected the radio frequency choke coils l and it] respectively.

The inductance plates 3 are shaped, as shown, to conform with the contour of the fixed and moving plates of the condenser. It will be noted that the plates 3 are substantially coextensive with the fixed plates of the condenser. This extension of the superficial area of the plates materially reduces their inductance and brings it to a value commensurate with the capacity of condenser, thus enabling the generation of ultra high frequencies. They are flanged at 2|, the flanges being slotted to receive set screws 22 which secure the plates to the stator of the condenser and make the necessary electric connections therewith. The slotting of the flanges permits the adjustment of the plates towards and away from the condenser plates, thereby enabling the range over which the oscillator is tunable to be adjusted.

In the arrangement above described, there exists the possibility of spurious frequencies being generated by the circuit. It has been found that the circuit has two modes of resonance, the first or normal mode round the inductance plates being the fundamental mode normally required, while the second mode is in space quadrature with the fundamental mode and is illustrated in the diagram shown in Fig. 5. In this figure, the adjacent plates of the stator are shown to form condensers 24 in parallel with the inductance constituted by the plates 3, thus providing a resonant circuit. It has been found that the unwanted. frequency resulting from the presence of this secondary mode is of the order of 3 times the fundamental and desired resonance frequency.

A further important feature of the invention accordingly resides in the provision of means for raising the frequency of these unwanted oscillations so that they are less harmful. To this end the edges of the fixed and moving plates of the condenser shown at 23 in Fig. 3 and are indicated more clearly in the view of Fig. 6. The unwanted frequencies may be damped out by loops 25 shown in Fig. 6 which couple these to but are in space quadrature with the fundamental mode.

In a circuit arrangement as above described using a split-stator condenser of known construction with seven stator and six rotor plates and employing acorn" valves designated VRfiS, it was found that with the inductance plates 3 closed right in, the oscillator would tune from 280 to 680 megacycles. With the plates 3 set at the maximum inductance position, it would tune are short-circuited by conductors from 230 t 620 megacycles. The anode voltage employed was 160 volts, resistance 9 had a value of 20,000 ohms, and chokes 1, I0, and I2, consisted each of 11 turns of .020 enamelled wire on a 4 diameter former. Oscillations could be obtained with an anode voltage of as low as volts.

Fig. 7 shows the application of the butterfly oscillatory circuit to a wavemeter. In this figure similar reference numerals have again been used to indicate elements corresponding to those in the previous diagrams. The oscillations to be measured are fed in through a loop 26 which couples to one of the inductance plates 3. A crystal detector 7.1 is connected in series with a condenser 28 (of about 2 mf. capacity for the order of wave length above mentioned) across the oscillatory circuit and a micro-ammeter 29 is connected in series with the radio frequency choke 3|} as indicated. The components may conveniently be mounted in a screening metal box with the ammeter and tuning scales in juxtaposition so that they can be read easily by the operator. The box may be provided with a socket (indicated at 3! in Fig. '7) into which an aerial of rod form may be plugged.

What I claim as new and desire to secure by letters Patent of the United States, is:

1. A balanced oscillatory circuit comprising a capacitor including an arcuate rotor plate and a pair of diametrically opposite stator plates extending beyond said rotor plates, a pair of symmetrically positioned inductor plates perpendicular to and overlying the edges of stator and rotor plates, and means for adjustably connecting said inductor plates at opposite ends to the extending ends of said stator plates.

2. A balanced oscillatory circuit comprising a capacitor having a pair of stacks of stator plates arranged opposite each other, a plurality of rotor plates between said stacks arranged for movement into interleaved relation with the plates thereof, a pair of enclosing inductor plates perpendicular to said stator and rotor plates and having the general contour of the peripheral edges of said stator and rotor plates and embracing the ends of said stacks, and means connecting opposite ends of said inductor plates to the outer ends of said stacks of stator plates.

3. A balanced oscillatory circuit comprising a capacitor including a stack of spaced sectorshaped rotor plates and a pair of diametrically opposite interleaving stacks of spaced stator plates extending beyond said rotor plates, and a pair of inductor plates substantially enclosing opposite peripheral edges of said rotor and stator plates and having the general contour of said peripheral edges, said inductor plates being electrically connected at opposite ends to the ex ends of said stator plates.

4. A. balanced oscillatory circuit comprising a capacitor having a pair of diametrically opposite sector-shaped rotor plates and a pair of diametrically opposite sector-shaped stator plates having extending beyond said rotor plates, a pair of enclosing inductor plates having opposite ends connected to the extending ends of said stator plates and having the general contour of the peripheral edges of stator and rotor plates, and means for adiustably positioning said inductor plates with respect to the peripheral edges of said rotor and stator plates, thereby to tune said circuit to a desired frequency within a predetermined range of frequencies.

5 5. A balanced oscillatory circuit comprising 1;, REFERENCES CITED capacitor including a stack of spaced sectorshaped rotor plates and a pair of diametrically The following references are of record in the opposite interleaving stacks of spaced stator me of pa'tent:

plates extending beyond said rotor plates, short- UNITED STATES PATENTS circulting means electncally connecting the edges of said stator and rotor plates respectively, Number Name Date and a p ir of inductor plates substantially en- 6,8 8 Brown Aug. 16,, 1938 closing opposite peripheral edges of said stator 2,135,672 Morris et 1938 and or plates and having the general contour m 7 aiOO May 30, 1939 of said peripheral edges, said inductor plates 2,235,010 Chime? 1941 being electrically connected at opposite ends to 2,341,345 Van Bllllal'd 1944 the extending ends of said stator plates. 2,367,631 Kal'plus e l- 4 ROBERT G. HIBBERD. 9, 77 Raskhodoff Feb. 13, 1945