US2067081A - Modulation of oscillations - Google Patents

Description

Jan. 5, 1937. H. E. GOLDSTINE MODULATION OF OSCILLATIONS 5 Sheets-Sheet 1 Filed Jan. 5l, 1935 l QN .Mg

INVENTOR- H.E.6OLD5TINE BY @Y ATTORNEY- H. E. GQLDSTINE,

MODULATION OF OSCILLATIONS Jano 5,

3 Sheets-Sheet 2 Filed Jan. 31, 1933 lNvENToR- H E. GOLD STINE lul ATTORNEY- Jan. 5, 1937. H. E. GoLDsTlNE MODULATION OF OSCILLATIONS Filed Jan. 31, 1933 5 SheebS-Sheeb 5 INVENTOR- nfoLosmNE .BY ATTORNEY- @SENER CJD average modulation is about 30%.

`characteristics at Patented Jan. 5, 1937 MODULATION OF OSCILLATIONS Hallan Eugene Goldstine, Rocky Point, N. Y., as-

signor to Radio Corp oration of America, a corporation of Delaware Application January 31, 1933, Serial No. 654,372

14 Claims.

This invention relates to the art of signalling by means of high frequency oscillations, the character of which varies in accordance with signals, and more in particular with a method of and means for displacing the phase of high frequency oscillations in a correct relationship to an applied signal voltage, thereby producing a signal so modulated that intelligent transmission may be made by usingphase modulation.

In the usual method of modulating the output current of a transmitter the amplitude of the oscillations is made to vary in accordance with the signal to be transmitted. When the input signal is of low amplitude, so that a low percentage of modulation lof the carriers is accomplished, the output of the transmitter is less than when the signal is of high amplitude and a larger percentage of modulation is impressed on the carrier. With amplitude modulation the transmitter must be operated below full power output to be able. to follow the signal modulation to its peak value. When using amplitude modulation the power` output of the transmitter varies in accordancewith the percent modulation. In order that the transmitter may be capable of carrying full output on high percent of modulationit must be run at a value below its full output rating on the average modulation. For example, when a broadcast program is sent out over the usual broadcast transmitter lthe 'I'he transmitter must be so adjusted that while it only delivers a small amount of its power `on the average modulation it can carry the peaks or the louder parts of the signal Without distortion. Thus the transmitter must be operated below its Afull output most of the time and less power radiated than would be possible with this transmitter. In phase modulation, however, the phase relation of the carrier and the sidebands varies in such a manner that the resultant output remains constant. In phase modulation the output of the transmitter remains constant and the modulation sidebands and carrier vary in such a manner that the output energy remains constant. A phase modulated transmitter may beV operated ait 4malximum output constantly. This results in increased eciency and permits greater distances to be covered by a given amount of power.. The oscillations modulated in phase. fas indicated above may `be altered in signal frequency in any of the succeeding stages prior to transmission. The character of the phase modulated Wavel may be altered as to amplitude, or phase or frequency, or in one or more of said characters.

In the usual type of phase modulation transmitters, elaborate equipment is needed to produce quality of modulation.

An object of the present invention is to provide a device which is simple in nature andA structure and which modulates a large amount of power output with good quality modulation by means of a signal of comparatively small power.

A further object of the present invention is to provide a novel scheme and means for impressing on high frequency oscillations phase variations truly representative of the signal so that a good quality modulation is obtained and to accomplish the same by the use of a minimum amount of apparatus operating extremely eiliciently.

The above objects are obtained in accordance with the present invention by modulating oscillations of constant frequency at the source of production, that is, in the oscillator. For example, if a crystal oscillator is used to produce constant frequency oscillations, modulation may be accomplished in the crystal oscillator. l In a crystal oscillator the crystal voltage works into the grid to cathode capacity and a resistive component caused by the grid to cathodeV current of the tube. This is 4the input impedance of the tube and, as the grid `current is caused to vary by changing the applied grid voltage, that is, by changing the potential applied to the grid of the oscillator at signal frequency, the grid to cathode resistive component varies and the Variations produce a phase shift proportional to the variations of the grid to cathode resistance.

Any tube that draws sufcient grid to cathode current, so that the resistive component is sufficient, may be modulated in this manner, whether the tube be an oscillator or an amplifier. In a modification of the present invention I provide a new and efcient means for producing phase variations at signal frequency in oscillations repeated in any thermionic relay.

The novel features of my invention have been pointed out with particularity in the claims appended hereto.

My novel method of producing phase Variations in oscillations which are characteristic of signal currents, anddevices for accomplishing the same will be described in detail hereinafter. In this description reference will be made to` the drawings, throughout which like symbols indica-te like parts, vand in which: Y

Figure 1 shows an arrangement for producing oscillation and for modulating the same as to phase in accordance with my novel scheme;

Figure 2 shows diagrammatically the manner in which phase modulation is accomplished in accordance with the present invention;

Figure 2a is a vector diagram illustrating the manner in which phase shift is obtained in certain voltages in the circuit of Figure 2; while,

Figures 3, 4, 4a and 5 show modifications of the arrangement of Figure 1.

A specific embodiment of the invention will now be described. In describing said embodiment reference will be made to Figure 1 of the drawings in which, for purposes of illustration, an oscillator and phase modulating means, arranged in accordance with the present invention, have been shown.

In Figure 1 a thermionic tube C has its anode 4 connected by way of a blocking condenser 5 to an electrode B resting on the piezo-electric crystal 8, through which it is coupled by way of electrode I0 and adjustable resistance I2 to the control grid I4 to complete an oscillatory circuit, by means of which sustained oscillations of con stant frequency are produced. The frequency of the oscillations is determined by the value of the elements included in said circuit, and in particular by the physical dimensions of the piezo-elec tric crystal 8. The anode to cathode and grid to cathode alternating current circuits are completed by connecting the electrode I6, associated with the crystal 8, to ground, as shown. The cathode electrode I8 is heated by means of a lamentary heating element and heating circuit 20 which may be energized from any source not shown by Way of a transformer 2|. To prevent high frequency oscillations from reacting on this transformer each side of the filament heating circuit 20 is connected to ground by way of capacity C1, as shown. The grid electrode I4 is connected to ground by way of a variable inductance 22, which is to compensate for the grid to plate tube capacity, in series with a capacity 23, which is to prevent the rectified direct current from flowing in this circuit. The grid electrode I4 is also connected to ground and to cathode by way of a resistance 24 and a meter 26. This resistance 24 furnishes the effective grid bias for the oscillator and the meter 26 indicates the amount of current flowing through this resistance to produce this bias. A positive potential may be applied to the anode electrode 4 by way of a charging resistance 21 connected with any source of constant direct current potential. The arrangement just described will, as is known, produce oscillations of constant frequency, which frequency will be determined in part by the piezo-electric crystal 8. The oscillations so produced may be applied by way of a blocking condenser 28 and additional apparatus 3l] to a utilization circuit 32.

The manner in which the oscillations produced in C are modulated in phase in accordance with the controlling frequency will now be described. A source of modulating potentials A, as, for eX- ample, an alternating current source of constantl and audible frequency, or a source of Voice modulations, or music, impresses potentials at the signal frequency by way of a coupling condenser 34 and ground to the terminals of a reactor B. The potentials at signal frequency, appearing across B, are applied to the cathode I8 of tube C. In order that radio frequency oscillations produced in C do not react on the oscillations in the reactor B and/or source A, the cathode is connected to ground by way of a radio frequency by-pass condenser C2. 'Ihe condenser C2 forms a low impedance path by which the radio frequency current may return to the cathode without passing through the modulator. The potentials applied at signal frequency to the cathode I8 vary the potential of the cathode with respect to the grid electrode I4 and thereby vary the impedance between the grid and cathode of said tube and, consequently, vary the grid to cathode current. Since the crystal voltage is working into the grid to cathode capacity, and the resistive component caused by the grid to cathode' direct current, this variation of potential and of current results in a phase shift which is proportional to the variation of the resistive component in the grid to cathode circuit. This in turn phase modulates the current in the anode circuit of the oscillator C so that high frequency oscillations, modulated in phase in accordance with the signal, appear on the anode electrode 4 and are impressed therefrom to the coupling condenser 28. The oscillations so produced and modulated may be passed through an amplitude limiter and a frequency multiplier and an amplier or one or more of said devices, all of which may be included in the unit 3U. The phase modulated amplitude limiter and frequency multiplier and amplified oscillations may be utilized in any manner. For example, they may be impressed on a line for transmission or may be impressed, as shown, on an aerial system 32 for radiation. Furthermore, as indicated above the phase modulated oscillations may be further modulated in any known manner before transmission. This modulation may take place any place in the circuits but preferably takes place after the phase modulation as described above is accomplished. When the oscillations are continuously varied in phase by alternating current as disclosed above to increase their transmission range and modulated in amplitude in accordance with signals, the amplitude modulated process should, of course, follow the limiting action. This precaution need not be taken when phase or frequency modulation at signal frequency is accomplished. Any form of modulation may be used to impress the signal modulations on the phase varied or wobbled wave produced as described above. Moreover any circuits known may be used at this point. Since the details ofv the signal modulation circuits per se form no part of the present invention, it is thought undesirable to illustrate them in this specification.

Although it is thought that the manner in which phase modulation has been accomplished will be understood from the above, a further brief explanation of what takes place in the circuits associated with C to produce phase modulation at signal frequency will be given.

Referring to Figure 2, G represents the quartz crystal input to tube C. The crystal may be considered as a constant voltage generator. We can make such an assumption for the crystal has so much stored energy (circulating current) that there is a persistency of oscillation greater than the audio frequency. If the crystal response curve (resonance curve is about fifty cycles wide then any audio frequency above that will not affect the output voltage and will not react back on the crystais frequency of oscillation. This crystal output voltage e1 is impressed into an impedance network, made up of series elements and shunt elements. For purposes of illustration the series elements may be lumped,

`aoevgoei and Z represents the lumped series elements while R `and C represent the shunt elements. R consists mainly of the tube impedance while C is the interelectrode and inter-circuit capacity. By varying the grid voltage (raising and lowering the cathode voltage) the resistivev element R of the shunt impedance is varied. rlhe amount of grid current through R and C changes and this changes the phase of the voltage across R and C, and consequently the phase of the grid voltage in accordance with the input tone Voltage ET. f

In the vector diagram of Fig. 2a., `e1 is the voltage developed by the crystal represented at *G and applied to the network. e2 is the voltage at the input to the shunt impedances and may represent the voltage applied to the grid `of the oscillator for modulation purposes IT is the total grid current which flows through Z. Ic is the current through the capacity C. IR is the current through R. Iz is the potential drop through Z due to current IT. By mere inspection it may be seen that as we change the input impedance of the tube by varying R, the phase of the grid voltage e2 is changed. If R is changed, the phase of the network RC is changed, consequently Yc2 must change in phase. For example, if R is infinite, a large amount of the currentows through C and the circuit is capacitive and the phase of ez is shifted, say relative to the current Z. If R is very small, a large amount of the current flows through R and the network is resistive in character and e2 is in phase with the current through Z. 'Ihe phase shift and other values given above are not by way of limitation but are merely for purposes of illustration. The rule holds good for intermediate values vof 'R as 'well as the extreme values used. The current vector diagram adjacent the voltage vector diagram in Fig. 2a. brings out very clearly vhow the phase shift is produced, when it is kept in mindA that e1 is constant 'and that the relative values of R. and C change at ythe modulating frequency. Applicant is clearly warranted in lumping` theseries impedance of this circuit, which may be composed in 'large Apart of resistance or impedance in the grid circuit, land in lumping the parallel or shunt resistances and capacities which comprise the several internal resistances and capacities of the tube. We can get practically linear phase displacement for input tone voltage over a large enough range so that the effective phase swing after multiplication in the doubler stages gives a displacement equalv to in 'amplitude modulation.

Obviously many different types of crystal control oscillators may be used to replace the oscillator of the Finch type shown in Figure l. Practically any type of piezo-electric controlled `oscillator circuit may be used to produce the oscillations which may in turn be modulated in phase in accordance with my novel scheme as illustrated in Figure l.

Moreover it is not necessary to use a quartz crystal circuit. Any type of circuitV which produces oscillations of suiiicient constancy may be used. For example, oscillators of the long line frequency control type may be used and in using the 'same excellent results may be obtained. For example, an oscillator of the type shown in Figure `3l may be used. This oscillator comprises a pair of thermionic tubes C, C having the-ir control grids I4, I4 connected, by Way of symmetrical circuits including aV resistance 35,. to their iilament-s 2U by way of ground. The oscillations 'generated in this circuit will appear in tank circuit 3B symmetrically coupled between the anodes 4 and 4 of the tubes C and C'. The frequency of the oscillations generated in the tubes C and C may be determined by means of a long line 38 connected, as shown, with the grid electrodes I4 and I4'. The circuits 36 including the variable capacity 3l and inductance 38 may be tuned to the frequency generated and may be coupled, as shown, by way of an amplitude limiter and frequency multiplier and amplifier to a circuit 32. Charging potential for the anodes 4 and 4 may be supplied from a `source not shown by way of a lead 40. Radio frequency oscillations may be prevented from reaching the anode source. not shown, by a by-passing condenser Ca. The potential of the filament 20 is varied or modulated at signal frequency by connecting the electrical center ofA the secondary winding of the transformer 2| to the terminal of the reactor B, which is connected by Way of blocking condenser 34 in parallel with the source. A. In this arrangement phase modulation will be accomplished in substantially the same manner in which phase modulation is accomplished in the circuit of Figure l and a detailed statement of the manner in which phase modulation is accomplished is not thought necessary here.

In Figure l the modulating potentials are applied to the cathode I8. In some cases it may be dfesirable to maintain the cathode I8 at ground potential and to apply the modulating potentials to the control grid I4. Where these features are desired an oscillation generator of the type shown in Figure l may rbe used, and the modulating potentials may be applied as shown in Figure 4 from a source A by way of a transformer T3 to the control electrode I4.

When the modulating potentials are `thus applied to the grid the secondary winding of the transformer T3 should be connected by way of a radio frequency choking coil 40 and a blocking condenser 4I to the control grid I4. The radio frequency choking coils 40 prevent oscil- Vlations from radio frequency from reaching the transformer T3 and reacting on the 4modulation source. The blocking condenser 4I prevents direct current in the grid circuit from flowing through the radio frequency choking coil 40 and the secondary winding of the transformer T3. Here, as in Figure l, phase modulation is accomplished by varying the relative potential between the cathode I8 and the control grid I4 to vary the flow of current in the grid to i? cathode circuit, thereby varying the resistive component of the tube.

The arrangement shown in Figure 4 may be modified as indicated in Figure 4a, wherein the modulating potentials from A are applied to the primary winding of a transformer T4, the secondary winding of which is connected in the Vgrid Vcathode direct current circuit including the resistance 24 and meter 26'.

As indicated above, the present invention contemplates modulating oscillations which have already been produced. This may be accomplished by modulating the oscillations in a thermionic relay or amplifier. For example, as illustrated in Figure 5, any source of high frequency oscillations may be connected by way of a blocking condenser 46 to the control `grid electrode 41 of a thermionic amplifier 48. The cathode 49" of this amplifier may be heated to a point at which emission takes place by means of a Jaz filament 50 connected by Way of transformer 5I to any source of alternating current not shown. Radio frequency oscillations relayed in the tube 48 may be prevented from reaching the heating source fon the lament 5E) by connecting the leads to the filament 58 to ground by way of by-pass condenser Ci. The anode 52 of repeater tube 4S is connected by way of a signal resonance circuit 54 to a source of potential not shown. The signal resonance circuit 54 includes a variable capacity 55 and an inductance 56. Modulating potentials are supplied to the cathode 49 from a source A in the same manner in which they were supplied from the source A to the cathode i8 in Figure l. The phase modulated oscillations appearing in 54 may be applied by way of a lead including a blockingi condenser GQ to a unit 3U, and from the unit 3D to a work circuit 32, as sho-wn.

While tubes of the three electrode type have been shown in the circuits to illustrate the invention it Will be understood that my invention is not limited to the use of such tubes. On the contrary I contemplate the use of any known tube having the desired characteristics in the phase modulation circuit of the present invention. For example, tetrodes and pentodes as known in the radio art may be incorporated in this invention without departing from the spirit of the present invention.

Moreover, while I have shown the modulating potentials applied to the cathode and control grid electrodes it will be understood that I con template the application of the modulating potentials to the plate electrode, and in case tubes of more than three electrodes are used to the screen grid electrode, or any other appropriate electrode.

Having thus described my invention, and the operation thereof, what I claim is:

l. An oscillation generating means comprising, a thermionic tube having anode, cathode and control grid electrodes, a work circuit con nected with the anode of said tubes, a piezoelectric crystal having one electrode connected to ground, a circuit connecting the anode of said tube to another electrode of said crystal, a circuit connecting the control electrode of said tube to a third electrode of said crystal, a direct current circuit connected between the control grid and cathode of said tube whereby sustained oscillations are produced, and a source of modulating potentials connected to the cathode of said tube produce phase modulation of said oscillations.

2. A signalling system comprising, a thermionic tube having an anode, a cathode and a control grid, a piezo electric crystal having one electrode connected to ground. a circuit connecting the other electrode of said crystal to the control grid of said tube, an output circuit connected with the anode of said tube, a circuit coupling the anode of said tube to the control grid of said tube to normally produce in said tube when energized sustained oscillations of a relatively constant frequency as determined in part by said crystal, a variable reactance connected between the control grid of said tube and ground, and means for modulating the phase of the oscillations produced including a reactor connected between the cathode and ground, and a source of modulating potentials connected in parallel with said reactor.

3. In a system for converting oscillations of diierent frequency into phase modulated energy characteristic of both of said oscillations, a thermionic tube having an anode and a control grid, said tube also having a cathode element, a source of high frequency oscillatory energy connected with said control grid, a direct current impedance connected between said control grid and ground to raise said control grid above ground potential, an output circuit connected with said anode, an impedance connected between said cathode element and ground to raise said cathode above ground potential, and means for producing substantially phase modulated oscillations substantially free of amplitude modulations comprising a second source of oscillations of diiferent frequencyconnected with said last named impedance for varying the potential of said cathode relative to ground at the frequency of said second source.

4. In a system for converting oscillations of different frequency into phase modulated energy characteristic of both of said oscillations, a thermionic tube having an anode and a control grid, said tube also having a cathode, a heater element therefor insulated therefrom and a heater circuit for said heater element, a source of radio frequency energy connected With said control grid, an impedance connected between said control grid and ground to raise said control grid above ground radio frequency potential, an alternating current circuit connected with said anode, an alternating current impedance connected between said cathode and ground to raise the same above ground potential, and means for controlling the phase of the radio frequency energy in said tube comprising a source of varying potentials connected in parallel with said last named impedance for varying the potential of said cathode relative to ground.

5. Oscillation generating and phase modulating means comprising, an electron discharge tube having anode, cathode and control grid electrodes, an oscillatory circuit including frequency determining means connected between said control grid and said anode, a connection between said oscillatory circuit and ground, a variable inductance and a capacity connected between said control grid and ground, the value of said inductance being sufficient to compensate the capacity between said anode and control grid electrode, an impedance between the cathode of said tube and ground, and means for applying modulating potentials to the impedance between the cathode of said tube and ground to modulate the phase of the oscillations generated in accordance With said modulating potentials.

6. In a device for varying the phase of high frequency oscillations, an electron discharge tube having anode, cathode and control grid electrodes, circuits at least one of which is resonant at the frequency of said oscillations connected between said anode and cathode and said control grid and cathode, an impedance in a circuit connecting said control grid to ground, a variable inductance and a capacity connected between said control grid and ground, the value of said inductance being sufcient to compensate the capacity between said anode and control grid electrode, an impedance connecting said cathode to ground, said last named impedance being in a direct current path between the grid and cathode, and a source of modulating potentials connected to said last named impedance for varying the current through said last named impedance in accordance with said modulating potentials to thereby vary the phase of the oscillations in the circuit connected between said anode and cathode.

7. A device for varying the phase of high frequency oscillations in accordance with controlling potentials including, a tube having anode, cathode and control grid electrodes, high frequency circuits in which oscillating currents iiow during operation connected between said control grid and cathode and between said anode and cathode, one of said circuits being resonant at the frequency of the oscillations' flowing in said circuits the phase of which is to be varied, a direct current path including an impedance connected between said cathode and ground, an

impedance connected between said Vcontrol gridV and ground, and means for modulating the phase of the high frequency currents flowing in the; anode cathode circuit comprising a circuit for varying the impedance between the cathoder and ground and consequently the flow of direct current in said path in accordance with the controlling potentials to thereby modulate the phase of the high frequency currents flowing in the circuit between said anode and cathode.

8. In a phase modulated wave signalling system an electron discharge tube having an anode, a cathode and a control grid, a high frequency alternating current circuit in which unmodulated alternating current flows connected between the control grid of said tube and ground, a high frequency alternating current circuit in which phase modulated alternating current is to ow connected with the anode of said tube, a direct current impedance connected between said control grid and ground, an audio frequency impedance connected between the cathode of said tube and ground, and means for causing phase modulations of said high frequency alternating current including a source of modulating potentials connected with said audio frequency impedance to vary the potential of said cathode relative to ground in accordance with said modulating potentials.

9. In a signalling system, an electron discharge device having an anode, a cathode and a control grid, a frequency determining and stabilizing circuit connected between the control grid and cathode of said tube, a high frequency alternating current circuit connected with the anode of said tube, a direct current circuit connected between the control grid and ground, an alternating current impedance connected between the cathode of said tube and ground, means for applying energizing potentials to the electrodes of said tube whereby sustaining oscillations are produced in said tube of substantially constant frequency, and means for modulating the phase of the oscillations produced comprising a source of modulating potentials connected with said alternating current impedance.

10. A signalling system as recited in claim 9 in which an amplitude limiter and a signal modulator are coupled to the high frequency alternating current circuit connected with the anode and cathode of said tube.

11. In a phase modulation system, an electron discharge tube having an anode, a cathode, and a control grid, an alternating current circuit in which unmodulated wave energy flows, connected with the control grid of said tube, a direct current impedance connecting said control grid to ground, an alternating current circuit in which wave energy modulated substantially in phase only may ow connected with the anode of said tube, an alternating current impedance connected between the cathode of said tube and ground to raise said cathode above ground potential for alternating current potentials, and means for impressing substantially phase modulations only on said wave energy comprising a source of modulating potentials connected with said alternating current impedance.

12. A phase modulation system as recited in claim 11, wherein an additional modulating means operative at signal frequency is coupled with the anode of said tube.

13. A signalling system as recited in claim 9 in which a signal modulator is coupled toi the] high frequency alternating current circuit connected with the anode and cathode of said tube.

14. In a signalling system, an electron discharge devicev having an anode, a control grid, an indirectly heated cathode, and a heating element and circuit for said cathode, an alternating current input circuit including a reactance in which unmodulated wave energy ows, coupled to said control grid, an alternating current output circuit including a reactance in which phase modulated wave energy may flow, coupled to said anode, means for applying direct current potentials to said anode, a direct current impedance coupling said control grid to ground, an inductive reactance coupling said cathode to ground, a capacity in shunt to said last named reactance and means for modulating substantially the phase only of the alternating currents flowing in said alternating current output circuit comprising a source of potentials characteristic of signals connected with said inductive reactance.

HALLAN EUGENE GOLDS'I'INE.

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