US2031768A - Electromechanical oscillator circuit - Google Patents

Description

Feb. 25, 1936. A, GEBI -IARD ELECTROMECHANICAL OSCILLATOR CIRCUIT Filed Oct. 15, 1932 INVENTOR. @0 5 49L; Qqflfiawfi,

W a M ATTORNEY.

Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE 2,0313 68 ELECTRQMECHANICAL OSCILLATOR a l V I Louis A. Gebhard, Washington, D'. 0., assignor to 'Wired Radio, Inc., New York, N. Y., a corporation of Delaware Application October 15, 1932 Serial No. 638,012 8 Claims. (Cl. 250-36) oscillatorsystem capable of control at any oneof af'plur'ality of high frequencies wherein capacity effects'between the ground and parts of the oscillator circuit are prevented from detrimental- 1y. affecting the operation of the oscillator.

Another object of my invention is to provide a circuit arrangement for a piezoelectric crystal controlled oscillator in which one electrode for the piezoelectric crystal elements and one point in the temperature control circuit is grounded, thereby rendering the ground capacity effects substantially negligible in the operation of the oscillator. Still another object of my invention is to provide'a circuit arrangement for a piezoelectric crystal controlled oscillator having a temperature' regulating system cooperatively related thereto and wherein the capacity to ground between parts of the oscillator and piezoelectric .7 crystal apparatus and associated temperature control mechanism, is rendered substantially negligible in its eifect upon the operation of the oscillator.

A further object of my invention is to provide an arrangement of temperature regulating system for piezoelectric crystal controlled oscillator circuits in which oscillations are sustained at different frequencies over a relatively wide frequency band and wherein losses normally occurring through capacity effects are substantially eliminated for correspondingly eliminating inaccuracies in the operation of the temperature control system.

A still further object of my invention is to provide a circuit arrangement for an electromechanical oscillator system wherein a multiplicity of. electromechanical vibrators, functioning at different frequencies, may be selectively connected with the circuits of an electron tube oscillator system for sustaining oscillations at const'ant. frequency independent of the capacity efmaintains the temperature control equipment in close proximity to ground potential for avoiding losses'and inaccuracies of operation of the temperature control equipment through capacity effects.

Other and further objects of my invention reside in the circuits and improved oscillator system. as set forth more fully in the specification hereinafter following by reference to the accompanying drawing which diagrammatically illustrates my'invention as applied to an oscillator capable of selective operation at any one of three frequencies under control of independent electromechanical oscillator elements.

One of the difficulties with the crystal oscillator circuit heretofore known in which the crystal is connected between grid and plate, is that'one side of the crystal cannot be grounded. This is generally necessary where a large number of crystals must be accurately temperature controlled, since the crystals are supported on a common metal plate which has large capacity to ground and forms one terminal of the piezoelectrio plates. I employ the circuit shown in the accompanying drawing to obviate this difiiculty and permit grounding one side of the crystals.

' In the practical application of the crystal oscillator circuit in which the crystal is connected between grid and plate of an electron tube, certain difficulties are encountered. If the circuit is used in a radio transmitter it is a practical necessity to supply the power for filament heating and plate supply from. common sources which mustbe at substantially ground potential. In order to assure a high degree of frequency stability the crystal or crystals must be temperature controlled. The temperature control circuits are adjacent the crystal, yet they, of practical necessity, afford a considerable capacitance between the crystal and ground. Under such conditions the circuit may refuse to oscillate or if it does oscillate the accuracy of temperature control may be affected detrimentally. If there is a large number of crystals to be selectively engaged in the circuit, these crystals are temperature controlled by placing them on a single common plate with a thermostat and thermometer used in controlling the temperature mounted adjacent to the plate. In some cases the thermometer and thermostat are mounted in apertures in the plate. There exists considerable electrical capacity between the plate and thermometer and thermostat which will prevent or interfere with oscillations of the system or if the system does oscillate the accuracy of temperature control may be affected.

Sufiicient radio frequency energy may be fed through the electrical capacity to cause local heating of the thermostat and thermometer resulting in these inaccuracies. This is particularly true in the case of mercury-glass thermostats and thermometers. The glass forms the dielectric of a condenser and since there are losses in this glass, local heating will occur. The electrical capacity referred to also interferes with the oscillations of the system since it is a radio frequency short circuiting path to ground, the filament and plate power circuits also being grounded as far as radio frequency is concerned.

If a large number of crystals is used the plate on which they are mounted becomes large and has considerable electrical capacity to ground which also forms a radio frequency short circuiting path for the circuits of the tube detrimentally affecting the oscillations of the system.

The circuit shown in the drawing avoids the difiiculties described above in that it may function with the temperature controlled plate in which the crystals are mounted grounded.

Reference character I designates a four-element electron tube including cathode Ia, control grid lb, shield grid Ic and plate electrode ld. A source of potential 2 is provided for supplying potential to the plate circuit and to the screen grid circuit. The power to the screen grid I0 is delivered through tap 2a to screen grid la. The power to the plate electrode Id is supplied from potential source 2 to resistance 3. A resistance 4 is connected in the circuit between control grid lb and cathode la. The cathode la is heated from any suitable source of potential indicated at 5 controlled through rheostat 6. Blocking condenser 8 is connected between one end of resistance 3 and the cathode Ia. Blocking condenser l I is connected between plate Id and transformer primary 9 which connects between the control grid lb and the anode Id of the electron tube I. Condensers II and I2 provide means for electrostatically coupling the primary winding 9 of transformer ID with the plate electrode l d and control electrode I b of the electron tube I. The secondary winding I4 of transformer It! is connected with piezoelectric crystals l5, I6 and I1 through taps I8, I9 and 20 and sets of switch contacts 2l and 22 under control of switch arms 23 and 24'.

The resistance 4 functions as a grid leak and provides the proper bias potential on control grid lb for establishing oscillating conditions. The circuit oscillates as a whole controlled by the frequency of the particular piezoelectric frequency which is effectively connected in the circuit.

. The movement of switch arms 23 and 24 is controlled by shaft 25 operated from knob 26 adjacent the front panel of the oscillator. The power which is delivered by the oscillator is induced in secondary winding 21 and transmitted to output terminals 28 through switch 29 which is movable over sets of contacts 30 electrically connected with taps 3|, 32 and 33, on secondary winding 21. The arrangement of taps 3I, 32, 33 is coordinated with taps IS, IS and 2|! so that the required number of turns of inductance may be selected for the particular operating frequency to which the oscillator is adjusted. The oscillator circuit is provided with taps 34, 35 and 36 on inductance 9 which lead to sets of contacts 31 over which switch arm 38 operates. Switch arm 38 is adjustable simultaneously with the movement of switch arms 29, 23 and 24 under control of shaft 26 so that the proper number of turns of inductance 9 are selected for the cooperation with the proper number of turns in secondary winding I4 in coaction with the proper number of turns in secondary winding 21. The output from the oscillator may also be taken from leads 40 through blocking condenser M at terminals 42 in lieu of the inductive connection through secondary winding 21.

The piezoelectric crystal elements I5, l6 and I! are mounted upon the conductive plate 43 which is apertured to receive the thermometer 44 and the thermostat 45 extending into apertures in the base 43. The base 43 is mounted within a temperature controlled cabinet in which the piezoelectric crystal elements are maintained at constant temperature, the cabinet being heated by heater coil 46 which is adjacent base 43 and is supplied with energy from a suitable potential source connected with terminals 41, the heating circuit being completed through contacts 48 controlled by relay 49. Relay 49 has its actuating winding connected with contacts 50 on the thermostat 45 and energy is supplied from a potential source connected with terminals 5| for controlling the winding 49 of the relay. The conductive plate 43 is connected to ground as indicated at 52. Inasmuch as conductive plate 43 forms one side of the circuit between the piezoelectric crystal elements IE, IS and l! and the oscillator, a lead 53 is taken from the plate 43 to one side of the oscillator adjacent the cathode la. The oscillator is connected to ground as indicated at 54.

The capacity between the windings 9, l4 and 2'! of transformer lil is quite low so that no appreciable effect of such capacity exists with respect to the oscillating condition of the system.

The magnetic coupling is arranged to be great I with the inherent heating of the thermostat and thermometer by eddy currents with the resulting inaccuracies are to all practical purposes. eliminated. In prior structures where the metallic plate which supports the piezoelectric crystal 1 elements is not at'ground potential the capacity effects have been such that transient currents are introduced which interfere with .the operation of the oscillator system.

While I have described a preferred arrangement of my invention, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the ap pended claims.

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

1. A high frequency oscillator system comprising an electron tube including a cathode, control grid, anode and shield grid electrodes, an oscillation circuit for said tube, an inductance coil having means connectable between said control grid and said anode, a multiplicity of piezoelectric crystal elements each having a grounded and an ungrounded. electrode, a coupling coil coupled with said inductance coil, an effective connection between one side of said coil and said grounded electrodes, tapped connections extending from the inductance coil, separate tapped connections extending from said coupling coil, a plurality of switch contacts and connections extending therefrom to the ungrounded electrodes of said piezoelectric crystal elements and means including said tapped connections for selectively connecting a particular piezoelectric crystal element with a portion of said coupling coil and simultaneously including a portion of said inductance coil in said oscillation circuit for adjusting said oscillation circuit for maintaining oscillations at a particular frequency.

I 2. In an oscillator system, an electron tube, an oscillatory network connected therewith, an inductance in said oscillatory network, a coil inductively coupled with said inductance, a plurality of electromechanical vibrators each having different frequency characteristics, a conductive plate member supporting and forming an electrode for said electromechanical vibrators and connected to said coil and ground, other electrodes individualto said vibrators and selectable connections from each of said other electrodes of said electromechanical vibrators and portions of said coil for controlling the operation of said oscillatory network at the frequency of the selected electromechanical vibrator.

3. In a high frequency oscillator system, an electron tube, an oscillatory network connected with said electron tube, an inductance in said oscillatory network, a coil coupled with said inductance, a plurality of electromechanical vibrators each having a grounded and an ungrounded electrode, and means for selectively connecting the ungrounded electrodes of said electromechanical vibrators with taps on said coil for controlling the operation of said oscillatory network at the frequency of a selected electromechanical vibrator, one end of said coil being conductively connected in circuit with said vibrators through said grounded electrodes.

4. In a high frequency oscillator system, an electron tube, an oscillatory network interconnecting the electrodes of said electron tube, an inductance connected in said oscillatory network, a coil inductively coupled with said inductance, a conductive plate member, a plurality of piezoelectric crystal devices each having different frequency characteristics, saidpiezoelectric crystal devices being supported upon said conductive plate member, a connection to ground and to one side of said oscillatory network from said conductive plate member, and means for selectively connecting an individual piezoelectric crystal device with a selected tap on said coil, one end of said coil being conductively connected in circuit with said vibrators through said plate.

5. In a high frequency oscillator system, an electron tube, an oscillatory network interconnecting the electrodes of said electron tube, an inductance included in said oscillatory network, a coil coupled with said inductance, frequency control means comprising a grounded conductive plate member, a plurality of piezoelectric crystals mounted on said grounded conductive plate member, temperature determining and regulating means disposed in juxtaposition to said grounded conductive plate member, an electrode individual to each of said piezoelectric crystals, taps on said coil, and means for selectively connecting an electrode on a selected piezoelectric crystal with a selected tap on said coil, one end of said coil being conductively connected in circuit with said vibrators through said plate member.

6. In a high frequency oscillator system, an electron tube, an oscillatory network interconnecting the electrodes of said electron tube, an inductance included in said oscillatory network, a coil coupled with said inductance, frequency control means comprising a grounded conductive plate member, a plurality of piezoelectric crystals mounted on said grounded conductive plate member, temperature determining and regulating means associated with said grounded conductive plate member, an electrode individual to each of said piezoelectric crystals, means for defining the potential of said conductive plate, contacts connected with taps on said inductance in said oscillatory network, contacts connected with taps on said coil, contacts individual to the electrodes on said piezoelectric crystals, and switching means simultaneously movable over said contacts for coordinating the inductance in said oscillatory circuits with the turns in said coil for cooperation with a piezoelectric crystal of particular frequency, one end of said coil being conductively connected in circuit with said vibrators through said plate member.

7. In a high frequency oscillator system, an electron tube, oscillatory circuits interconnecting the electrodes of said electron tube, an inductance included in said oscillatory circuits, a coil coupled with said inductance, frequency control means comprising a grounded conductive plate member, a plurality of piezoelectric crystals mounted on said grounded conductive plate member, temperature determining and regulating means associated with said grounded conductive plate member, an electrode individual to each of said piezoelectric crystals, an output coil inductively coupled with the inductance in said oscillatory circuits, sets of contacts connected with taps on said inductance, sets of contacts connected with taps on said first mentioned coil, sets of contacts connected with taps on said output coil, contacts individual to each of the electrodes of said piezoelectric crystals, and switching means for effectively changing the inductance values of the inductance in said oscillatory circuits and said coils for operation with a piezoelectric crystal of a particular frequency characteristic, one end of said first mentioned coil being conductively connected in circuit with said vibrators through said plate member.

8. In a high frequency oscillator system, an electron tube having cathode, control grid and plate electrodes, oscillatory circuits interconnecting said electrodes, an inductance coil connected with said control grid and plate electrodes, a coil inductively coupled with said inductance coil, a

grounded conductive plate member, a plurality of piezoelectric crystals mounted upon said grounded conductive plate member, a connection between said grounded conductive plate member and one side of said oscillatory circuits, an electrode individual to each of said piezoelectric crystal elements, and means for selectively connecting said piezoelectric crystal elements with selected taps on said coil for sustaining oscillations in said oscillatory circuits at the frequency of the selected piezoelectric crystal element, one end of said coil being conductively connected in circuit with said vibrators through said plate member.

LOUIS A. GEBI-IARD.

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