US2431569A

US2431569A - Frequency modulation

Info

Publication number: US2431569A
Application number: US462013A
Authority: US
Inventors: Labin Edouard
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1942-10-14
Filing date: 1942-10-14
Publication date: 1947-11-25
Anticipated expiration: 1964-11-25

Description

Nov. 25, `194:1'. E. AEN 2,431,569

FREQUENCY y MODULATION l Filed 0Cb. 14, 1942 .slsf/frm cosa' 't' I HG. 3. c'

ATTRNEY Patented Nov. 25, 1947 UNITED STATES PATENT OFFICE FREQUENCY MODULATION Application October 14, 1942, Serial No. 462,013

2 Claims. 1

The present invention relates to radio trans'- mission of the type in which the transmitted wave is frequency modulated. More particularly, the invention is concerned with the production of the frequency modulated Wave by a method of direct phase modulation. Y

In my prior application Serial No. 450,596 of July 11, 1942, on a Method of producing frequency modulated waves for radio transmission, I have set forth the chief difficulties encountered in frequency modulated transmission, and have shown that the frequency modulated wave may be expressed as u=U sin (Slet-Hb) where il/ is a term representing the integrated intelligence and is given by 2vrlcj`s(t)dt=21rkAfa(t)dt=j`a(t) dt, s(t)=Aa(t) being the intelligence to be introduced into the wave. I have further recalled in the aforesaid prior application that the wave u=U sin (uct-ew) may be obtained by mixing a sinusoidal H. F. oscillation w=Ua sin Slet, of the central frequency 9e with an oscillating L. F. tension 'U=V cos 1,0, where the value of the angle is kfsw) di, on the assumption that it were possible to produce, from the integrated intelligence s(t) such an oscillating tension v=V cos ip. In said prior application, a practical solution was found by a particular utilization of the Kerr cell.

In the prior application Serial No. 453,890, led August 6, 1942, in the names of Edouard Labin and Manuel Julio Kobilsky, a thermionic tube is described whereby inter alia an output may be obtained which is a sinusoidal function of an electrical quantity impressed on control members provided in operative relationship with respect to an electronic beam. It likewise describes general methods for determining the shape and/or cornl position of secondary emission surfaces on the basis of which surfaces capable of yielding a sinusoidal output may be constructed. It, is therefore deemed unnecessary to detail in the present specification the construction of the forming device or the manner of designing the forming elements thereof.

Ii; will be sufficient therefore, for the purposes of the present invention to recall that the tubes of said prior specification of Edouard Labin and Manuel Julio Kobilsky are of the kind comprising the generation of a beam of electrons which is passed through aspatial displacement zone on which is impressed an electrical quantity acting to control the extent of the spatial displacement, the beam after leaving said spatial displacement zone passing to a forming zone the geometry and composition of which is such that the intensity of the electriccurrent emerging therefrom is a (Cl. 179-4715)l 2 sinusoidal function of the spatial displacements of the said beam.

For the purposes of the present invention and in accordance with the hereinabove recalled theory, I use for the electrical quantity controlling the spatial displacement a varying and oscillating electrical quantity so that the output of the forming zone is a sinusoidal function of such varying and oscillating electrical quantity. To obtain an output which shall be a sinusoidal function of the sum of two angles, as in frequency modulated transmission, two such forming zones are used, one in quadrature with the other to obtain the terms in sin gb and cos 1,1/ and the two outputs are combined severally with sinusoidal functions of a central frequency obtained by impressing a central frequency generated in a stabilized pilot, on respective phase shifting zones in quadrature, the two combinations then being applied simultaneously to a common point of an electrical system, such as a transmitter.

For frequency modulated transmission, the varying and oscillating electrical quantity is the integrated intelligence so that the resulting wave is Ilt=U sin (9CH-if).

The fundamental advantage of employing the tube mentioned is the new possibility of obtaining in one step values of ,b as high as a number of times 21|. l

It is, therefore, a principal object of the present invention to provide, particularly in connection with frequency modulated radio transmission, a new and improved method of generating an elecf trical quantity varying as a sinusoidal function of the sum of two angles, each of said angles being respectively proportional to one of two other electrical quantities.

A further object of the present invention is to provide a method for generating, for an electrical system, an electrical quantity varying as a sinusoidal function of the sum of two angles, which comprises the steps of generating a stabilized central frequency, passing the central frequency simultaneously through two separate zones of phase displacement in quadrature with each other whereby to obtain two sinusoidal oscillations of central frequency in quadrature with each other and thereby to provide factors which are sinusoidal functions in quadrature of one of said angles, generating a varying and oscillating other electrical quantity, generating two electron beams, each beam corresponding to one of said phase displacement zones, passing each beam through a respective spatial displacement zone and a forming zone the geometry and composition of which is such as to give at its output an emerging electrical quantity which is a sinusoidal func- A further object of the present invention is to provide a method for generating, for an' electrical system, an electrical quantity varying as a sinusoidal function of the sum of two angles, which comprises the steps of generating a stabilized central frequency, passing the central frequency simultaneously through two separate zones of phase displacement in quadrature with each other whereby to obtain two sinusoidal oscillations of central frequency in quadrature with each other and thereby to provide factors which are sinusoidal functions in quadrature of one of said angles. generating a varying and oscillating other electrical quantity, generating two electron beams in respective generating zones while impressing on one generating Zone one of said sinusoidal oscillations of central frequency and the other sinusoidal oscillation of central frequency on the other generating zone to impress on the respective beams sinusoidal variations in intensity in quadrature with each other and representative of said one angle, passing each intensity modulated beam through a respective spatial displacement Zone followed by a forming zone, the geometry and composition of which is such as to impress on the output a modulation which is a sinusoidal function of the spatial displacement impressed on the respective beam during its passage through the spatial displacement zone, controlling the operation of each spatial displacement zone by impressing thereon, as a control factor, said varying and oscillating other electrical quantity, whereby to combine with the intensity modulation corresponding to the sinusoidal function of said one angle a modulation corresponding to a quadratured sinusoidal function of said other angle, and applying the two outputs of the forming Zones simultaneously to a common point of said electrical system.

These and other objects and advantages of the present invention will become apparent in the course of the following detailed description in which reference is made to the accompanying drawings.

In the drawings:

Fig. 1 is a diagram illustrating the application of the invention to the generating of a frequency modulated wave.

Fig. 2 is a diagram illustrating a modied form of application.

Fig. 3 illustrates one form of apparatus suitable for the purposes of the invention.

Given the principle of obtaining the sinusoidal factors of the angle 1p by impressing on a beam of electrons spatial displacements in response to a varying and oscillating electrical quantity, causing said beam to enter a forming zone and deriving from the forming zone a sinusoidal function of said varying oscillating electrical quantity, the

desired final result, namely an electrical quantity varying as the sinusoidal function of the sum of two angles one of which corresponds to said vary- -ing and oscillating electrical quantity, and the other of which corresponds to a central frequency, may readily be obtained by connecting the operative parts in a mannerwhich is in itself quite classical. Such assembly of the operative parts or inter-relationing of the several zones is illustrated diagrammatically in Fig, 1.

The elements PS1 and PS2, labelled Phase- Shifters, are adapted to give to the oscillation ce originating from the stabilized pilot SP, two forms inquadrature,

l1L1=Uo Sill 9ct, and u2=Uo COS Slet sinip, and 122=V0 cos rb The said phase modulators are constituted in accordance with the teaching of the said prior patent application of E. Labin and M. J. Kobilsky. A suitable phase modulator is shown in Fig. 3 and comprises an electron discharge tube l0 having an evacuated and hermetically sealed envelope including anindirectly heated cathode I2, a 'heating filament lil, an intensity control grid I6 and a beamV concentrating means I8, so arranged that from said beam concentrating means I8 there issues a beam of electrons having a desired cross section. The tubeV also `comprises beamfdeflecting electrodes 253-20 arranged on the side of the beam concentrator 20 remote from the cathode.

On the side of the deflecting electrodes20-20 remote from the cathode and'in the path of the electron beam, there is provided a response forming element 22 having a secondary electron emissive surface with sinusoidal undulations. A passive collector electrode 2li is provided for collecting the secondary electrons provided by the element 22. A suitable load impedance 25 is provided in the output circuit of the collector electrode 24.

In operation the phase modulator of Fig. 3 provides anoutput voltage e containing the desired argument. V cos gl/ or V sin 1p by reason of the movement of the electron beam under the influence of the Vdeilecting electrodes 2li-2D whereby a voltage sd) applied to these electrodes causes the beam to scan the undulated surface of the element 22 and produce a secondary emissive current to the collector 24 proportional to the angle of incidence of the beam with respect to the surface of the element. Whether the argument cos ip or sin 1,1/ is generated is determined by the initial or resting position of the beam with respect to the undulated surface of element 22 and one or the other function is obtained by suitable selection of the resting position of the beam with respect to the position of the element.

The arrangement shown in Fig. 1 comprises two tubes of the foregoing type such tubes constituting the phase-modulators PM1 and PM2 and by applying the intelligence voltage s(t) to the defiecting electrodes ZB-Zll thereof, the arguments cos 1p and sin 5b are produced.

The multiplication of each L. F. oscillation, ci, 112, with the corresponding H. F. oscillation, u1, u2, is carried out in two classical modulators M1, M2, which have been designated intensity modulators to distinguish them from the phase modulators. To add the two products thus Job'- tained, mural-:U sin dat. cos d, and muzvz-:U .cos 9ct. sin yb, it is sufficient to apply the outputs of the intensity modulators simultaneously to a common point of an electrical system, such as a transmitter, as indicated at T in the figure.

An ordinary intensity modulation generates not only the products U sin met. cos ,b, and U cos Slet. sin tb, but, at the plate of the modulating tube, there also appear currents which reproduce the two individual oscillations applied. The L. F. oscillation will not give an output voltage, because the plate circuit will loe closed through .a ifilter capable of .rejecting it completely. iB ut sucha filter cannot rejectthe .current opt, :located right in the middle Yof the .band which it must transmit. However, a differential modulator of the classical type can be used for the intensity modulators to eliminate the central frequency by a process of internal opposition. Should the management of such a modulator prove to be too delicate a matter, due to a working frequency ne which is already high, it will be suflicient to use a method of frequency conversion and create the two modulations, in phase and in intensity, on a lower frequency ile. Furthermore, it should be `mentioned that the presence of a certain portion of pure central frequency beyond the modulating system, and hence up to within the aerial, does not do much damage to the reception of the useful wave, so long as such portion does not eX- ceed a value of some tenths (in power) of the useful wave. In fact, it is known that the reception of frequency modulated waves olers a very good protection against interference signals the amplitude of which is a few times lower than that of the desired signal, wherever the frequency of the former is located with respect to that of the latter. The same may be said of any lack of symmetry between the two paths, which is translated by the persistence of a lateral band at the output, alongside the desired wave. It is thus seen that the arrangement of the system of mixture is not critical.

The multiplication of an L. F. tension v1=V cos if by an H. F. voltage u1=Uo sin Q et, may, as shown in Fig. 2, be effected without the differential modulators of Fig, l, whenever the intensity V of the L. F. voltage can be controlled independently, In the arrangement shown in Fig. 2 the outputs of the phase shifters PS1' and PS2 are each applied to the intensity control .grid I6 of the tubes Ill constituting the phase modulators PM1 and PM2 to thereby intensity modulate the respective electron beams. 'Ihe intelligence voltage s t) is applied to the dellecting electrodes 2li-20 of each of the tubes. In this arrangement the desired multiplication is effected in each tube whereby the output voltage e of the phase modulator PMi comprises the desired argument sin Slet. cos tb and the output voltage of phase modulator PM2' comprises the argument cos Slet. sin 1p as indicated in Fig, 2. Let it be supposed tha-t the phase modulator PM1 which provides V cos tlf from s(t) (or from \//=kfs(t) dt) operates without perturbations whatever may be the amplitude V, and, more particularly, even if the amplitude V varies in time with an H. F. rhythm. Then it is purposely controlled by the phase-shifted piloted frequency from PS1', that is to say, the control voltage is made to be of the type V=V0 sin Slet, so that from the phase modulator PM1 the output is directly the product V0 sin 9ct. cos tb. The complementary phase modulation path PM2', which generates sin 1p,

would be modulated in intensity bythe phaseshifted piloted .oscillation in vquadrature cos Slet from PS2'. The combination, at a common point T of the Aoutputs .of the two paths, effects the addition required .to give the complete wave. -In this embodiment, two differential modulators as well ias two .separate outputs for the two phase modulation paths are suppressed, and the necessary devices are added to control the amplitude `of Ithe L. oscillations in accordance with :the rhythm of ythe F. oscillation. The net result of this is always -a simplification of the system.

It .can vbe Shown vthat in .order to obtain the ydesired resultant which shall be a sinusoidal :function of the sum of the .two angles Slet and d, -it' will suice to lcombine the two output points :ofl the for-ming zones, This means in practice that a twin forming device with a collecting anode common to the two parts, may be used. The undesired parts of the output which reproduce the piloted oscilaltions can be eliminated by opposing two voltages of appropriate amplitude taken directly from the phase shifters, since within the range of frequencies utilized, the accurate opposition of two voltages at a point remote from that of formation offers no special diculties. Such elimination is indicated in the broken lines in Fig. 2 leading from the phase shifters PS1' and PS2', to an opposition zone ZO.

Calculation based on suitable assumed values demonstrates that the parasitic phase displacement introduced by differences in the length of path of the electron beam as it moves over a configured secondary emission surface will not prove troublesome.

The only disadvantage of the intensity modulation carried out directly in the tube, is that the amplitude of the useful electrical currents cannot be more than a fraction of the mean c'onstant part thereof, owing to the necessity for the linear control of the grid by the piloted oscillation. Hence, in order to obtain for the proper intensity for said amplitude a total emission a few times greater must be taken from the cathode of the tube. But this is still not a serious matter, if the concentration system is carefully adjusted.

I claim:

1. A method of generating an electrical quantity varying as a sinusoidal function of the sum of two angles, comprising the steps of deriving two oscillations in phase quadrature from a wave having a stable frequency, generating a varying and oscillating electrical quantity, generating two electron beams, modulating the intensity of one of said beams proportional to the amplitude of one of said oscillations, modulating the intensity of the other beam proportional to the amplitude of the other of said oscillations, deilecting each of said beams proportional to the amplitude of the varying and oscillating electrical quantity, deriving from the intensity modulated and deflected electron beams secondary emissive currents proportional to the amplitude of said oscillations and sinusoidal functions in quadrature of said varying and oscillating electrical quantity, and combining the said secondary emissive currents.

2. A method of generating an electrical quantity varying as a sinusoidal function of the sum of two angles, comprising the steps of deriving from a wave having a stable frequency two oscillations in phase quadrature, the argument of said wave constituting the first of said angles, while the second angle is proportional to a generated Vvarying and oscillating electrical quantity. generating two electron beams, modulating the intensity of one of said beams proportional to the amplitude of oneV of said oscillations, modulating the intensity of the other beam proportional to the amplitude of the other of said oscillations, deflecting each of said beams proportional to the amplitude of the varying and oscillating electrical quantity, deriving from the intensity modulated and deflected electron beams secondary emissive currents proportional to the amplitude of said oscillations and sinusoidal functions in quadrature of the second of said angles proportional to said varying and oscillating electrical quantity, combining the said secondary emissioncurrents to produce a resulting quantity comprising a component Varying as a sinusoidal function of the 5 rived from said oscillations.

EDOUARD LABIN.

REFERENCES CITED The following references are of record in the *10 me pf this patent:

UNITED STATES PATENTS Number Name Date 2,294,209 Roder Aug, 25, 1942 15 2,337,272 Roberts Dec, 21, 1943 2,257,795 Gray Oct. 7, 1941