US2474278A - Frequency modulated oscillator control - Google Patents

Description

June 28, 1949.

R. H. RANGER FREQUENCY MODULATED OSCILLATOR CONTROL Filed Oct. 2, 1944 /NVEA/rof? Patented June 28, 1949 UNITED ISTATES PATENT OFFICE (Granted under the act .of March `3, 1883, `as amended April 30, 1928; 370 O. G. `757) l The invention :described herein may 'be manufactured .and used Ybyor for the Government for governmental purposes, without'thc payment 0f 'any royalty thereon.

This invention relates to means for keeping the output frequency of an electric oscillator substan- `tially constant.

An object of this invention is to lprovide a frequency control in `which a frequency-modulated oscillator is employed as a reference lor basis.

More specilically, it is .an additional object of 1my invention to afford a frequency controller comprising a crystal-controlled oscillator which provides frequencies `of great stability, a controlled oscillator containing an adjustable part by inovemen't of which its output frequency is varied, a frequency-modulated oscillator having a limited yrange of output frequencies, a source of frequencies providing said frequency-modulation, a 'first mixer-detector lin which the output frequencies of said crystal-controlled oscillator and of said controlled oscillator are combined, a second mixer-detector'in whichthe output y'from said first mixer-detector andthe output fromsaid Vfrequency-modulated oscillator are combined in such 4phase relationship that the output frequency of said second mixer-detector is in phase with the frequency outputof said source when the output of -the first mixer-detector is of higher frequency than that of the frequency-modulated oscillator, f-

'and that the output yfrequency of said second :mixer-detector is 180 -outof phase `with the `frequency output of rsaid source when the output of `the mixer-detectorisof'lower frequency than fthat of the frequency-modulated oscillator, a

fspl-it-pl;1ase motor having coils energized respectively :by the Aoutput of said source and by the output of said second mixer-detector, and a me` fchanical connection betweenfsaid'motor and said adiustable part whereby vsaid vmotor moves vsaid `same automatic 'volumecontrol means are vso ar- :ranged as to decrease tthetfrequency swing'of the .frequency-modulated.oscillator circuit as the frelquency of the controlled oscillator approaches its desired value.

I vhavedescribed.and illustrated a preferred embodment of my invention in the annexed specification and drawing to which `reference is now made.

The single figure of the drawing is a block diag-ram.

We start with-acrystal l as seen in thedrawing. Let it he assumed that this is a 200 kc. crystal. The harmonic .amplifier .2 will then build up .the output of this crystal .to give rich harmoniccontent. Harmonic selector 3 will pick out the particular harmonic desired Afor reference. The conv.trolled oscillator .L4 .at the bottom will pass some .of its energy up ,into the .rst mixer-detector 5 .along with theroutput .frequency of the harmonic selector y3 and give a iirst beat, .constant in fre- .quency The output yof the iirstmixer-detector y5 is combined with .that of anadjustable oscillator 6 cover- .ing a band of frequencies from 200 to 4001kc. If .the frequency of the .controlled oscillator .I4 is 290 kc. .away from the selected harmonic in 3, We Willhave a `200 kc. beat-coming out of the first mixer-detector.

If this is vcombined with .a ,200 kc. setting of `the oscillator 6 .we would get 0 beat in the-second mixeradetector l. However, this, of course, would only be by chance. Let it be assumed that the Yfirst mixer-detector ,5 is putting outa frequency of 2.1.0 kc. We will then have a difference frequency at second mixer-detector 'I of 10 kos. between the 20G kc. setting `of oscillator 6 and the output of the .first mixer-.detector f5.

Now assume that we have a (S0-cycle source 'shown at 18. This 60 cycle Works through a gain control i6 to give a mechanical vibration to the plates of thetrimmer condenser 2li connected to oscillator Ci. As is-well known, the gain control I6 vmay be caused to impart this vmechanical vibration "to the Vplates of condenser 20 by feeding out- Iput of gain control i6 to an electromechanical translating device y2l which may be of a convenf'tional type -as an lelectrodynamic or magnetic loudspeaker havingits armature connected either ydirectly or through some form of mechanical coupling to the condenser plates. Common solenoids may also be-used fas the translating devices. The net result will beto give la frequency moduilationto the output of this oscillator 6 at the rat-e of 60 cycles. vhet it be assumed that 'the phases :are such that Lfor -a rising .60 'cycle pulse, the fre- 55 iquenoy-of the 'oscillator i6 is raised. `We will then have an output going over to the second mixerdetector 'I which will give with the 210 kc. coming from the first mixer-detector 5 a second wobbled beat as the output of 1. As the frequency put out by the local oscillator 6 rises, it will approach that of the beat coming out of mixer-detector 5 so that we will get a reduction in frequency in the output of the second mixer-detector I on positive y swing. In other words, the frequency will decrease on positive swing when the local oscillator frequency is below that of the beat frequency coming from 5. On the contrary, if the output of the first mixer-detector 5 was below 20() kc., say 190 lacs., the frequency of the output of mixerdetector I would rise on positive swings given the local oscillator So we have here a complete reversal in action, depending upon whether the rst mixer-detector output is below or above that of the local oscillator 6. Capacity coupling 8 is introduced in the output of second mixer-detector T such that for higher frequencies, more output will be obtained. Under these conditions, we will have passed on through gain control I1 into frequency modulation-discriminator 9 (which may include an amplifier), an alternating current at 60 cycles which will be in phase with the original (iO-cycle impulse I8 working up through the local oscillator, if the frequency of the first mixerdetector output 5 is below that of the local oscillator. Conversely it will be out of phase with the (iO-cycle input I8, if the frequency of the first mixer-detector 5 is above the frequency of the local oscillator 6. The discriminator S, in conventional fashion, serves to eliminate the radiofrequency currents in its input and to confine its output current to the same frequency as that of source i8, which in this example has been chosen as 60 cycles. The net result is that if We apply the same (iO-cycle output I8 into one of the coil windings of the split phase motor Hl and use the output of the frequency modulation-discriminator 9 (which may include an amplifier), to energize the other coil winding of the split phase motor Il), we will have a resultant motion in one direction or the other, depending on whether the output of the first mixer-detector 5 is above or below the frequency of the swinging local oscillator 5. The motor ID is of the well-known split-phase type, with the minor variation that the connections to the main and auxiliary windings, respectively, are not interconnected but the connections for these respective windings are brought out of the machine separately, thus making it possible so to connect the respective windings to their inputs as to provide the desired direction of rotation of the motor. The connections for one of these windings derive input from source I8, while the connections for the other winding derive input from frequency-modulation-discriminator 9. As described in any textbook on alternating-current machinery, (see, for example, pages 474 and 475 of Electrical Circuits and Machinery, vol. II, Alternating Currents, by Hehre Harness, 1942 addition, published by yJohn Wiley & Sons, Inc.) the motor will then operate. The impedance of the auxiliary winding is such that the current in this winding has sufficient phase lag, with respect to the current in the main winding, to produce a rotating iield in the motor. When the two input voltages are in phase, the motor will rotate in one direction. A reversal in phase of the input derived from discriminator 9 will cause the motor to rotate in Athe reverse direction.l Of course, the motor will iz. not operate unless it obtains input from both source I8 and discriminator 9.

Mechanical connections II are taken from the split-phase motor I0 to the controlled oscillator le, working on the adjustable condenser capacitor I2. Mechanical connections are tied in with the phase control such that if the frequency of the controlled oscillator is less than 200 kcs. below the selected harmonic 3, then a correction will be applied to capacitor I2 such as to decrease its capacity and thereby increase the frequency of the controlled oscillator set by capacitor I3.

Automatic volume control is introduced, as shown on I5, which Works off capacity coupling 8 on the output of the second mixer detector 1, such that on rectication of the output of this capacity coupling 8, going into automatic volume control I5, a source of current will be obtained proportional to the intensity of the 60 cycle beat at this point. Automatic volume control i5 may, if desired, be coupled to the output of Second mixer detector l independently of capacity coupling 8. If this 60 cycle beat is lower in intensity, the operation of the automatic volume control i5 will be such as to increase the gain at I'I to give more power to drive the split-phase motor.

It will also be arranged to decrease the gain control iii so that less frequency swing will be accomplished on the local oscillator B. The net result of these operations is such that as the output of the first mixer detector 5 approaches the setting of the local oscillator E, we will get a lower output in the second mixer detector, which will be stepped up again through the gain control il and the discriminator 9 to keep driving the split-phase motor and at the same time the gain control I6 will decrease the frequency swing of oscillator 6 so that the net adjustment will come closer and closer to the desired frequency as this action continues to bring it near the required point.

The output of the controlled oscillator is taken to a transmitter which is not run at the same frequency, but either twice the frequency or onehalf the frequency of the controlled oscillator i4 so that there will be less chance of interaction between the nal output stages of the transmitter and the controlled oscillator stages.

It is obvious that this whole arrangement may be worked to control any point from 200 to 400 kc. on the local oscillator E as any other point from 200 to 400 may be taken such as 230 kc. as the reference note to compare with the difference between the frequencies of the controlled oscillator I4 and the selected harmonic In this case, the controlled oscillator I4 will be locked to a point 230 kc. away from the selected harmonic.

Continuous control of crystal accuracy will thus be realized, at any selected point 200 to 400 kc. away from the selected harmonic, and the accuracy of the local oscillator 6 will only have to be arithmetically accurate to insure overall splitphase frequency control of the entire outfit.

The specification frequencies which are referred to in connection with the above description are merely illustrative and the system may be used with other frequencies of the crystalcontrolled oscillator circuit, with a different range of possible frequency adjustment for the frequency-modulated oscillator circuit, and with a different frequency of the source of frequencies providing frequency-modulation.

Although two mixer detectors have been referred to above, it would of course, be possible to 5 combine the functions of both of these in` a single tube, if desired.

I claim:

l. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator whose output frequency is to be maintained constant, an adjustable p-art of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor and said part move together, a source of relatively low frequencies, a second oscillator having a relatively constant output frequency which normally has a predetermined difference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements cause frequencymodulation of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined. difference, an electric circuit connection between said source and said motor, an electric circuit connection between all three oscillators and said motor, whereby said motor moves said adjustable part and thereby corrects the frequency of said controlled oscillator in accordance with whether or not the difference between the output frequency of said controlled oscillator and of said second oscillator is above or below that of said third oscillator.

2. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator Whose output frequency is to be maintained constant, an adjustable part of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor and said part move together, a source of relatively low frequencies, a second oscillator having a relatively stable output frequency which normally has a predetermined difference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements cause frequency-modulation of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined difference, a first mixer-detector in which the output frequencies of said controlled oscillator and of said second oscillator are combined to give an output equal to any difference between these frequencies, a second mixer-detector in which the output frequencies of said first mixer-detector and of said third oscillator are combined in such phase relation that the output of said second 'T mixer-detector remains in phase with or is shifted 180 out of phase with the output of said source depending upon whether the frequency of said third oscillator is below or above that of said first mixer-detector, an electric circuit connection between said source and said motor, an electric circuit connection between said second mixer-detector and said motor whereby said motor moves said adjustable part in one direction or the other depending upon the phase relations of the outputs of said source and of said second mixerdetector fed to said motor and thereby corrects the frequency of said controlled oscillator.

3. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator whose output frequency is to be maintained constant, an adjustable part of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor andsaid part move together, a source of relatively low frequencies, a second oscillator having a relatively stable outputr frequency which normally has a predetermined dilference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements cause frequency-modulation of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined difference, an electric circuit connection between said source and said motor, capacity coupling electrically connected in circuit to receive out put from all three oscillators and arranged to modify the volume of its own output in proportion to the frequency of its input, an electric circuit connection between said capacity coupling and said motor, whereby said motor moves said adjustable part and thereby corrects the frequency of said controlled oscillator in accordance with whether or not the difference between the output frequency of said controlled oscillator and of said second oscillator is above or below that of said third oscillator.

4. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator whose output frequency is to be maintained constant, an adjustable part of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor and said part move together, a source of relatively low frequencies, a second oscillator having a relatively stable output frequency which normally has a predetermined difference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements cause frequency-modulation of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined difference, an electric circuit connectionbetween said source and said motor, frequency-modulation-discriminator means electrically connected in circuit to receive output from all three oscillators and arranged to pass and amplify current at the frequency of said source, and an electric circuit connection between said discriminator means and said motor, whereby said motor moves said adjustable part and thereby corrects the frequency of said controlled oscillator in accordance with whether or not the difference between the output frequency of said controlled oscillator and of said second oscillator is above or below that of said third oscillator.

5. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator whose output frequency is to be maintained constant, an adjustable part of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor and said part move together, a source of relatively low frequencies, a second oscillator having a relatively stable output frequency which normally has a predetermined difference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements cause frequency-modulation. of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined difference, an electric circuit connection between said source and said motor, capacity coupling electrically connected in circuit to receive output from all three oscillators and arranged to modify the volume of its own output in proportion to the frequency of its input, automatic volume control means electrically connected to the output of said capacity coupling and modifying in proportion to the extent of any departure of the frequency of the controlled oscillator from its desired constant value, the extent of the frequency swing given by said source to said third oscillator, an electric circuit connection between said capacity coupling and said motor, whereby said motor moves said adjustable part and thereby corrects the frequency of said controlled oscillator in accordance with whether or not the difference between the output frequency of said controlled oscillator and of said second oscillator is above or below that of said third oscillator.

5. Means for maintaining constant the output frequency of an oscillator, said means comprising a controlled oscillator whose output frequency is to be maintained constant, an adjustable part of said oscillator whose adjustment varies the output frequency thereof, a split phase motor joined to said part so that said motor and said part move together, a source of relatively low frequencies, a second oscillator having a relatively stable output frequency which normally has a predetermined difference from the frequency of the controlled oscillator, a third oscillator including a movable part controlled by said source and whose movements ycause frequency-modulation of said third oscillator and including also means for adjusting said third oscillator to have a mean frequency which is equal to the above predetermined difference, an electric circuit connection between said source and said motor, capacity coupling electrically connected in circuit to receive output from all three oscillators and arranged to modify the volume of its own output in proportion to the frequency of its input, automatic volume control means electrically connected to the output of said capacity coupling and modifying in inverse proportion to the intensity of that component of said output which has the modulation frequency, the volume of the power supplied said motor, and an electric circuit connection between said capacity coupling and said motor, whereby said motor moves said adjustable part and thereby corrects the frequency of said controlled oscillator in accordance with whether or not the difference between the output frequency of said controlled oscillator and of said second oscillator is above or below that of said third oscillator.

'7. A frequency controller comprising: an oscillator which provides an output having great stability of frequency; a controlled oscillator whose output has a frequency which normally has a predetermined difference from the frequency of the output of the first-mentioned oscillator, such controlled oscillator containing an adjustable part by movement of which its output frequency is varied; a frequency-modulated oscillator capable of adjustment so that its output has a mean frequency which is equal to the above predetermined difference; means for frequency-modulating the frequency-modulated oscillator; a first mixer-detector in which the outputs of said firstmentioned oscillator and of said controlled oscillator are combined; a second mixer-detector in which the outputs of said first mixer-detector and of said frequency-modulated oscillator are combined in such phase relationship that the output of said second mixer-detector is in phase with the output of said frequency-modulating means when the output of the rst mixer-detector is of higher frequency than that of the frequency-modulated oscillator and is 180 out of phase with the output of said frequency-modulating means when the output of the first mixer-detector is of lower frequency than that of the frequency-modulated oscillator; a split-phase motor having coils, energizecl respectively by the output of said frequency-modulating means and by the output of said second mixer-detector; and a mechanical connection between said motor and said adjustable part, whereby said motor moves said adjustable part to bring the frequency of the output o1 said controlled oscillator to the desired value.

8. A frequency controller according to claim '7, h a v i n g frequency modulation discriminator means connected between said second mixerdetector and one of the coils of said split-phase motor.

9. An electrical frequency control system comprising: a first oscillator circuit; a controlled oscillator circuit which includes tuning means and whose frequency normally has a predetermined difference from the frequency of the first circuit; a third oscillator circuit including means for adjusting this circuit so to have a mean frequency which is equal to the above predetermined difference; means for frequency-modulating the third circuit; mixer-detector means which derive input from all three oscillator circ u i t s frequency modulation discriminator means which derive input from the mixer-detector means and which pass only current at substantially the modulation frequency of the third oscillator circuit; and control means which derive input from the frequency-modulation-discriminator means and from the frequency-modulating means and which are responsive to a variation of the controlled frequency from its normal value, to operate the tuning means in the controlled circuit to bring the controlled frequency to its normal value.

10. An electrical frequency control system comprising a first oscillator circuit, a controlled oscillator circuit which includes tuning means and whose frequency normally has a predetermined diiference from the frequency of the first circuit, a third oscillator circuit including means for adjusting this circuit so as to have a mean frequency which is equal to the above predetermined difference, means for frequency-modulating the third circuit, a first mixer-detector deriving input from the first oscillator circuit and from the controlled oscillator circuit, a second mixer-detector deriving input from the first mixer-detector and from the third oscillator circuit, frequency-modulation-discriminator means deriving input from the second mixer-detector and passing only current at substantially the modulation frequency of the third oscillator eircuit, and control means deriving input from the frequency-modulation-discriminator means and from the frequency-modulating means and responsive to a variation of the controlled frequency from its normal value, to operate the tuning means in the controlled circuit to bring the controlled frequency to its normal Value.

1l. An electrical frequency control system7 as described in claim 10, which includes automatic volume control means deriving input from the second mixer-detector for modifying inverse proportion to the volume of that component of the input which has the modulation frequency, the volume of that part of the input to the control means which is derived from the frequencymodulation-discriminator means.

12. An electrical frequency control system, as described in claim l0, which includes automatic volume control means deriving input from the second mixer-detector for modifying the extent of the frequency swing of the third oscillator circuit in proportion to the difference of the controlled frequency from its normal value.

13. An electrical frequency control system, as described in claim 10, which includes automatic volume control means deriving input from the second mixer-detector for modifying in inverse proportion to the volume of that component of the input which has the modulation frequency, the volume of that part of the input to the control means which is derived from the frequencymodulation-discriminator means, such automatic volume control means also modifying the extent of the frequency swing of the third oscillator circuit in proportion to the difference of the controlled frequency from its normal value.

14. An electrical frequency control system, as described in claim 10, which includes coupling means inserted between the second mixerdetector and the frequency-modulation-dlscriminator means for modifying the volume of the input to the latter means in proportion to the frequency of the output of the second mixerdetector.

15. An electrical frequency control system, as described in claim 10, which includes coupling means inserted between the second mixer-detector and the frequency-modulation-discriminator means for modifying the volume of the input to the latter means in proportion to the frequency of the output of the second mixer-detector, and also includes automatic volume control means deriving input from the coupling means for modifying in inverse proportion to the Volume of that component of the input which has the modulation frequency, the volume of that part of the input to the control means which is derived from the frequency-modulation-discriminator means.

16. An electrical frequency control system, as

means described in claim 10, which includes coupling inserted between the second mixerdetector and the frequency-modulation-discriminator means for modifying the volume of the input to the latter means in proportion to the frequency of the output of the second mixerdetector, and also includes automatic volume control means deriving input from the coupling means for modifying the extent of the frequency swing of the third oscillator circuit in proportion to the difference of the controlled frequency from its normal value.

17. An electrical frequency control system as described in claim 10, which includes coupling means inserted between the second mixer-detector and the frequency-modulation-discriminator means for modifying the volume of the input to the latter means in proportion to the frequency of the output of the second mixer-detector, and also includes automatic volume control means deriving input from the coupling means for modifying in inverse proportion to the volume of that component of the input which has the modulation frequency, the volume of that part of the input to the control means which is derived from the frequency-modulation-discriminator means, such automatic volume control means also modifying the extent of the frequency swing of the third oscillator circuit in proportion to the difference of the controlled frequency from its normal value.

RICHARD H. RANGER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,294,942 Varian Sept. 8, 1921 2,297,800 Read Oct. 6, 1942

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