US2092049A - Method of reducing quartz crystal activity - Google Patents

Description

Sept. 7, 1937. B. CLARK I 2,092,049

METHOD OF REDUCING QUARTZ CRYSTAL ACTIVITY Filed March 28, 1936 lll fll l l l WITNESSES: INVENTOR 85a ,I' Bernarc/L, C/a/K ATTO NEY Patented Sept. 7, 1937 PATENT OFFICE METHOD OF REDUCING QUARTZ CRYSTAL ACTIVITY Bernard L. Clark, Medfield, Mass., assignor to Westinghouse Electric & Manufacturing Com- Dany, East Pittsburgh,

Pennsylvania Pal, a. corporation of Application March 28, 1936, Serial No. 71,440

5 Claims. (01. 250-36) My invention relates to improvements in radio circuits, and more particularly in improving the operation of a tube circuit embodying as an element thereof a crystal for stabilizing the frequency of its operation.

In operating circuits wherein crystals are employed for obtaining frequency stability, care must be exercised to avoid overloading the crystal, as this causes brushing of the crystal and quite often results in rupturing of the same. I

It is an object of my invention to provide a circuit involving crystal control in which the crystal may be operated without overloading the same.

Another object of my invention is to provide a circuit involving crystal control wherein the safe loading of the crystal may be simply and conveniently adjusted for.

Additional objects of my invention will be disclosed in the following description of the same taken in conjunction with the accompanying drawing wherein the single figure is a circuit diagram of a radio circuit involving crystal control and embodying my invention.

In electron tube circuits wherein crystals are employed to maintain frequency stability, it is customary in one type circuit, as illustrated in the figure, to connect a crystal l between or in circuit with a grid electrode 3 and a cathode 5 and in shunt thereto, there is usually provided a high impedance element 1, usually a high resistance to function as a grid leak whereby to obtain proper bias for the tube 9. The output circuit of such a discharge device usually comprises a tuned circuit including a condenser H and an inductor 13, which tuned circuit is resonant at approximately the frequency of the crystal. A battery IE or other source of potential is connected in the circuit to supply the proper potential for the anode of the tube. This circuit, as just described, comprises a source of frequency in that it will oscillate at the frequency of the crystal. Duringoperation the energy fed back through the crystal from the output circuit by way of the grid plate capacity within the tube, is apt to reach such proportions as to cause brushing of the crystal and possible rupture.

One way of reducing this loading on the crystal would be to lower the value of the grid leak impedance, but to do so would be to alter the bias developed on the tube and correspondingly produce a change in the output current. Satisfactory operation of the system would thereby be impaired.

In order to bring the plate current back to the proper value, it would be necessary to increase the grid leak impedance and thus return to the same conditions as previously existed.

In applying my invention to a circuit of this type, I provide a path of low impedance at radio frequencies between the cathode side of the crystal and a point on the grid leak resistor. This low impedance path at radio frequencies may economically comprise a condenser I 1 between these two points, the proper point on the grid leak being determined most conveniently by making this connection adjustable and shifting it along the resistor until proper desired loading of the crystal is obtained.

The advantages which I attribute to my im-,

proved circuit, reside in the fact that while I am enabled to very conveniently adjust the loading on the crystal, I can accomplish this without interfering with the biasing of thetube, and consequently without in any way destroying the proper operation of the system as a whole. The normal plate current is maintained irrespective of the adjustment of the loading on the crystal. Furthermore, should one desire to alter the value of the grid leak for any desirable reason, this can be accomplished without readjusting the loading on the crystal by merely adding some resistance in series with the grid leak, or if the resistance of the entire leak be changed, the proper loading on the crystal can still be conveniently adjusted to proper operating value.

While I have disclosed my invention as applied to a specific circuit, the principle thereof is applicable to other circuits involving the use of crystals, and I do notdesire to be limited in my protection to the specific disclosure set forth in my drawing, except as may be necessitated by the prior art.

I claim as my invention:

1. In combination, an electron discharge device having a grid electrode and a cathode, a crystal in circuit between said grid and cathode, a grid leak connected in circuit with saidgrid and cathode, means for producing feedback energy into said crystal circuit sufficient to overload said crystal, and means for providing a low impedance path at radio frequencies, between the cathode side of said crystal and a point on said cient to overload said crystal, and means for providing an adjustable low impedance path at crystal frequency around said crystal, said path including a portion of said impedance.

3. In combination, an electron discharge device having a grid electrode and a cathode, a crystal in circuit between said grid and cathode, an impedance connected in a separate circuit between said grid and cathode, means for feeding energy into said crystal sufiicient to overload the same, and means for reducing the loading on said crystal comprising a low impedance path at radio frequencies, between the cathode side of said crystal and a point on said impedance, the connection to said impedance being adjustable.

4. In combination, an electron discharge device having a grid electrode and a cathode, a crystal connected between said grid and cathode, a grid leak connected in a separate circuit between said grid and cathode, means for normally overloading said crystal during operation, and means for shunting said crystal with a low impedance path at radio frequencies, said path including a selectable portion of said grid leak.

5. In combination, an electron discharge device having a grid electrode, an anode and a cathode, a crystal in circuit between said grid and cathode, a grid leak connected in a separate circuit between said grid and cathode, a circuit resonant at approximately the frequency of said crystal, connected between said anode and cathode and comprising means for feeding energy into said crystal sufficient to overload said crystal, and means for shunting said crystal with a low impedance path at radio frequencies, said path including a portion of said grid leak.

BERNARD L. CLARK.

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