US1841489A - Oscillation generator - Google Patents

Description

Jan. 19, 1932. w. A. MARRisoN 1,841,489

OSCILLATION GENERATOR Filed March 24, 1928 A TTDR/VEY i UNITED-STATES fPArENr fate `Patented Jan. 19, 1932 te@ f WARREN A. .MARRISON or ORANGE, NEW JERSEY, AssIGNoR To vBELL TELEPHONE? LABORATORIES, INCORPORATED,- oE NEW YORK, N. Y., A CORPORATION OE NEW OSOILLATION GENERATOR y Applicatin' iearmamn 24, 192s. serial No. 264,432. y

VThis invention relates to oscillation generators and particularly-to systems for generatingoscillations of constant frequencywhich are independent of temperature variations.

For some purposes itis desirable' to generi a wave whose frequency is constant within very narrow limits. One of the difliculties to be overcome in the .production ofv oscillations of constant frequencyis the variations in frequency which occurl with changes In temperature with any system where no means ior compensating for temperature variations is provided. In the absence of such compenf order to sating means it is necessary to take elaborate precautionsl to maintain the frequency controlling means'at a constant temperature in o f A feature of this invention is the provision ciprocal of the ratio of of two temperature compensatingmechanical 4vibrating elements, the frequency of vibrationy of each of whichV controls the'generation of oscillations. These oscillations arecombined to produce lfurther oscillations, the frequencyof which isequal to the sum .ordiffeb ence of those first generated, andfis constant. Another feature of the invention is the provision of two mechanical vibrating elements having temperature coeiiicients of frequency the ratio of which is equal to the rethe frequencies at which they are vibrating.

According to thepresent invention a constant frequency. is obtained, irrespective of temperature variation, by theuse of :two vibrating systems having Ytwo control members with different temperature coefficients of frequency. Any desired frequency may be obl tained, as a ysum or differencefrequency between the two systems, by choosing values of frequency for the control members such that the ratio of the frequency of their vibrations is equal to the reciprocal of the ratio of their temperature coeiiicientspof frequency.

- The drawing illustrates two spaceV discharge tubes 1 and 2 each having an input circuit and. an output circuit. The input and `tionsof a diiferent prevent variations in frequency of YThat is, the oscillator controlled by the vibrating element 3 will produce oscillations of one frequency and the oscillator controlled by the vibrating element 4 .will produceoscillafrequency. ThQOutput circuits of the respective space discharge tubes include electroma netic devices 5 and 6 and coils fand 8; pace current issupplied to the tubes l and 2 from a common source 9. l l The respective input circuits include, electromagnetic devices and 11, and acommon sourcer12 forsupplying biasing potential to their grids.. v f i The filaments of the tubes are supplied with heating current by a common battery 13. As so far described the operation of the i system is as follows r`Assuming that the mechanical elements are vibrating, current in the output of the'spacedischarge tubes l and 2 will 5 and 6 and maintain the mechanical elements 3 and 4 vibrating'at their natural frequencies. Potentials of these frequencies, picked vup by the eleotromagnets y10 and 11 included in the respective input circuits of the space discharge tubes, will be impressed on the respective grids. f f

Coils 7 and 8 are inductivelyA coupledto a secondary winding ycircuit of a third space discharge device which servesto combine the waves of the two frequencies impressed upon its grid to produce oscillations having frequencies equal to pass through the electromagnets 14, included in the inputY the sum and difference of the frequencies of f and a battery 20 for supplyino space current to the device.

The circuit 18, 19 is tuned to the sum or difference frequency of the two impressed waves. Energy of the wave selected is inductively supplied through the coupling 19--21 to a load circuit.

For the purpose of illustrating the operation of this invention let it be assumed that mechanical vibrating element 3 has a natural frequency of 300 cycles per second and that mechanical vibrating element 4L has anatural frequency of 200 cycles per second at a given temperature. Also let it be assumed that the temperature coefficients of frequency of those elements are, respectively, A and 3/2 A. Then at any temperature the frequency of element 3 will be equal to 300 (1-*At) and the frequency of element a will be equal to 20o (i-s/e ai),

where t is equal to the diHerence between the temperature at which the elements 3 and 4 have a natural frequency of 800 and .200 cycles per second, respectively, and a common operating temperature at any instant. The difference of these frequencies is 100 cycles per second and does not vary with temperature. The 100 cycle componentwill be selected by the tuned circuit 18, 19 in the output circuit of the modulator.

In the operation of the system described above, if one oscillator is controlled by a mechanical element of frequency f1 having a coefficient of a, and a second oscillator is controlled by a second mechanical element of frequency f2 having a coefficient Vthen f1(1 1t)f2(1t)= I i fffr1 2lf:f

That is, the condition for f to be independent of temperature is that f1af2=0, that The condition identified by the above formula holds for all cases.. whether the temperature coefficients of the controlling elements are of the same or of opposite sign.

In the case where the temperature coefficients of the control elements are of opposite signs it is necessary to select the sum of the frequencies produced by intermodulation of the controlled wave. 1n that case it now be assumed that being used to control and For example, let quartz resonators are the frequencies of the two sets of oscillations and that one control element, having a positive coefficient of 9 10r is vibrating at a frequency of 1,000,000 cycles per second and the other control element having a negative coefficient of 3X10'5, is vibrating at a frequency of 3,000,000 cycles per second. For each degree rise in temperature the first control element will increase its rate of vibration 90 cycles per second, while the second element will decrease its rate of vibration 90 cycles per second. Therefore, a wave obtained as a product of intermodulation of these two waves will remain constant at 4,000,000 cycles per second regardless of temperature variations.

In order that the system described above may operate to produce oscillations of constant frequency, it is only necessary that the ratio of the temperature coefficients of frequency of the two mechanical elements equal the reciprocal of the ratio of the two frequencies. However, this does not make it necessary to use a material having a selected temperature coefficient of frequency in order to produce oscillations of a desired frequency. For any two different temperature coefficients, it is always possible to choose two frequencies such that their sum or difference is `any desired pendent of the temperature of the two elements. For example, if the temperature coefficients of frequency of the elements were as in the first example given, A and 3/2 A, and it was desired to produce a constant frequency of 1,000 cycles per second, it would only be necessary to adjust the vibrating elements to have natural frequencies of 3,000 and 2,000 cycles per second, respectively. 1f a frequency of 1,100 cycles were desired, the elements would be adjusted to 3,300 and 2,200 cycles respectively.

When it is desired to produce a relatively high constant fre uency with elements having temperature coe cients of like sign, it is desirable that the coefficient-s differ by a considerable amount, say in order to keep the control frequencies from being too high.

However, the operation of this invention with elements of like sign is not limited to low frequenciesas the temperature coefficients of frequency of different quartz crystal resonators may vary in the ratio of 3 to 1 or more. Thus, it will be seen that the upper limits of frequency which this device is capable of producing with elements of like sign is very high, and with elements of opposite sign is much higher.

Of course, in a system embodying the invention, it is necessary to maintain the control elements at the same temperature, so that one element does not vary more than the other. This presents no difficulty, since it can be taken care of by mounting both elements on the same base and enclosing them to prevent uneven circulation of the air around them.

frequency and is indc- W'ith the devices. of the present invention, power Huctuations will notaifect the sum or difference frequencies to any great extent. If the two elements were driven by separate power sources, it would be expected that variations in frequency inthis system due to `fluctuations in power would be considerably greater than the variations in a directly driven system, because variations due to the f power supplied by the separate sources would at times add. If both elements are operated from the same power source,however, variations in frequency will, tendV in the same direction in both elements and the frequency variations ywill be approximately the same as in a system driven directly.

kW'haty is claimed is: Y y n l. An oscillation source comprising an oscillator controlled bya mechanical vibrate ing element, and a second oscillator controlled by a second mechanical vibrating element,

the ratio of the frequencies of vibration of the mechanical elements being equal to the reciprocal of the ratio of their temperature coeilicients of frequency. y

2. Asystem for producing oscillations of a desired constant frequency comprising wave producing means, including mechanical vibrating' elements the ratio of whose frequencies of vibration is equal to the reciprocal of the ratio of their temperature coefficients lof frequency, for determining the frequencies of two Waves whose frequencies differ by the desired frequency, and means for combining said waves.

3. In combination an oscillating systeml comprising an oscillator controlled by a me-V chanical vibrating element at a frequency whose temperature"coefcientis Am, and a second oscillator controlled by a mechanical vibrating element at a frequency y and whose temperature coefficient of frequency is n, where p Y el.

'y m 4. Any oscillating Asystem comprising an oscillator the frequency of whose oscillations is controlled by a mechanical vibrating element, a ysecond oscillator the-frequency of Whose oscillations is controlled by a second mechanical vibrating element, the frequency of the vibration of the second element with respect to the first being'equal to the recip- :1 rocal of the ratio of its temperature coefiicient of frequency with respect to the first, and armodulat'or for combining Waves of the frequencies of the two mechanical vibrating elements to produce a constant frequency.

In witness whereof, I hereunto subscribe my name this 22 dayy of March,y 1928.

WARREN A. MARRISON.

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