US2279930A - Electronic modulator for constant frequency variable dot transmission - Google Patents

Description

April 14, 1942. V HE 2,279,930 ELEGTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION .Original Filed Sept. 14, 1936 4 Sheets-Sheet 1 --1||||||||||l| 'llll ELECTROSTATIC nv uril DEFLECT/NG INVENTOR. ROBERT SHELBY BY 1 ATTORNEY.

April 14, 1942. R. EQSHELBY 2,279,930

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION Original Filed Sept. 14, 19:56

- Ikjgnia A 4 Sheet s-S heet 2 INVENTOR. ROBERT E. SHELBY ATTORNEY.

April R. E. SHELBY 2,279,930

ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DO'I' TRANSMISSION Original Filed Spt. 14, 1936 4 Sheets-Sheet s DEFlECT/NG VOLTAGE 6 DEFLECT/NG VOLTAGE e PHAKF R SHIFT/N6 23 NETWORK 2a a 30 6 o AMPLITUDE 5: f 6/ AND 82 90 7 MODULATED I our 0F PHASE Z CARR/ER a ,0, WA VE 32 7- 52 A T 2/ AMPLITUDE MODULATOR SINUSO/DAL VOLTAGE MODULAT/ON SUPERSWN/C FREQUENCY S/GNAI.

n Hi Wm M U [W] UUEF I I INVENTOR.

ROBERT ESHELBY ATTORNEY.

April 14, 1942.

R. E. SHELBY ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE DOT TRANSMISSION Original Filed Sept. 14, 1936 4 Sheets-Sheet 4 CAT/ 00E STREAM 1 cur/1005 CAT/100E STREAM +5 CAT/{ODE 5 f 6 6 ad r w E m n D 0 m m INVENTOR.

ROBERT E. SHELBY ATTORNEY.

Patented Apr. 14, 1942 TENT OFFICE ELECTRONIC MODULATOR FOR CONSTANT FREQUENCY VARIABLE nor TRANSMIS- SION Robert Evart Shelby, Teaneck, N.

J., assignor to Radio Corporation of America, a corporation of Delaware Original application September 14, 1936, Serial Divided and this application July 28,1939, Serial No. 287,019

' 13 Claims. (01. 250-451) This invention comprises a division of my original application Serial No. 100,627, filed September 14, 1936, which is now U. S. Patent 2,171,150.

In the past, made use of a system of modulation in which the radio frequency carrier is modulated, or keyed, by a flat-topped supersonic wave of constant amplitude which has complementary, but not necessarily equal, variations in its positive and negative areas that are proportional to the modulation signal. Since the complete period of the supersonic wave remains constant while the rectangular dots or areas, comprising its positive and negative portions, vary in accordance facsimile experimenters have with the modulation, this method has been given the name constant frequency variable dot, or

CFVD, modulation. More recetly this same idea has been applied by Kell to the transmission of sound programs. The chief advantage claimed for the system is that it permits the use of voltage limiters in the receiver and thus gives a higher signal-to-noise ratio than is obtained when using the usual system of amplitude modulation under the same conditions. No attempt will be made here to discuss the merits of the system. This application is intended only to disclose a novel method of and means for producing CFVD modulation which it is believed has certain advantages over the methods now used.

In describing my invention, reference will be made to the attached drawings. In the drawings.

Figures 1 and la. illustrate one form which the plate or target anode may take and the relation of the same to the other'electrodes of an electron discharge gun or cathode ray tube used to produce CFVD modulation in accordance with my invention;

Figure 2 shows schematically the essential elements of my novel circuit for producing and applying potentials to the deflecting plates of an electron gun as illustrated in the prior figures and the mode of connecting the output of the novel circuit to the pairs of deflecting plates in an electron tube having a novel plate or target anode arranged in accordance with the present invention;

Figure 2a illustrate a phase shifter used in the circuit of Figure 2;

Figures 3a, 3b, 3c and 4 are curves illustrating the character of the output of an electron gun with an anode as indicated in Figures 1 and 111 when the deflecting plates are excited :as indicated in Figure 2;

Figure 5 shows a modified anode structure; while Figure 6 is a curve representing the output of a system when the anode is as shown in Figure 5.

Figures '7, 7a, 8, 8a, 9 and 9a illustrate modified forms of final or target anodes.

In my United States application No. 72,916, filed April 6, 1936, entitled Electronic modulator and method of modulation, a novel circuit and novel electron discharge device for producing phase and amplitude modulation is described.

In the presentapplication and in the aforesaid application I use :a novel electron gun or tube having a special target anode for converting amplitude modulated wave energy applied to pairs of deflecting plates into energy of the desired character for signalling purposes.

The term "electron gun here, as in the prior application, has the meaning given toitby I. G. Malofl and D. W. Epstein in their paper entitled Theory of electron gun, appearing in the Proceedings of the I. R. E., December 1934, page 1386. The circuit and device to be described here is in many respects similar in arrangement and operation to that disclosed in the said application. Here, however, the configuration of the final anode in the electron discharge device is difierent than that of the aforesaid application in order that CFVD output may be obtained in place of phase or amplitude modulation. Here, as in the said application, the tube illustrated diagrammatically in Figures 1 and 1a consists essentially of an electron tube 4, two sets of electrostatic deflecting plates 6 and 8, and a final anode Ill. The target anode I0 is of special design. Figure 1a shows one form which the final anode 10 may have for production of CFVD modulation. The final anode or target 10 consists of two curved plates l4 and I6, having the complementary boundaries indicated by Figure 1, upon which the electrons from the electron gun impinge. The electrodes l4 and I6 may consist of metallic plates or meshes or metallic deposits on the tube envelope or a surface supported in said tube. Where the electrodes l4 and I6 are of mesh 2. collecting electrode, not shown, may be located back of the targets and properly charged relative to the other electrodes.

In order to obtain a CFVD signal, the plates M and I6 are caused to have the shape or form shown wherein the outer periphery of one side of It follows a curve defined by T=a06 while preferred form of phase shifter is shown in Figure 2a. In this phase shifting circuit, the am- 1 plitude modulated radio frequency or carrier freis the angular-displacement of the same point' from a selected datum line which is the same for each curve; while a and 6 are design constants, the latter depending on the spacing of the anode sections. In the modification illustrated, the

datum line for the curves of "the equations, is

shown by the broken line X. The equations given for the anode contours were departed from sufficiently near the origins to prevent the anode sections from becoming short-circuited. f

In operation, the electron gun is controlled and "quency waves are applied to input terminals and from said input terminals to a resistance in series with condenser 32. By adjusting the condenser 32 and selecting the value of 30, the desired phase relation between 61 and c2 can be produced. The oscillations in 2| may be modulated in amplitude by facsimile signals, by keyed impulses, by voice frequencies, television or any other type. of signals to produce constant frequency' variable dot characters.

focussed by adjusting the direct current potentials applied to the cathode, and to the control grid by 20, and to the screen grid and first anode by 22, just as in the case of oscillograph tubes and kinescopes. The electron stream is sharply focussed on the final anode l0 and when there is no voltage applied to the electrostatic deflecting plates 6 and 8, it strikes the exact geometrical center of the final anode Ill.

voltages, the nature. of which and the manner.

of production of which will be described more in detail hereinafter, are such that they cause the electron stream to trace out a circle on the final anode I0, the diameter of the circle being a variable which is directly proportional to the instantaneous value of the modulation signal on the wave energy applied to the deflecting plates. .When the plates 6 and 8 are excited by proper voltages, there will appear in Za a CFVD voltage characteristic of .the modulating potentials used in producing the-deflecting voltages. The deflecting voltages are preferably sinusoidal and of the supersonicfrequencyselected for the CFVD transmission. The deflecting voltagesare obtained-by phase displacing two portions of amplitude modulated wave energy. The manner in which the deflecting voltages are produced andapplied to the plates 6 and 8 is shown in .Figures land 2 and will now be described, Fig-' ures 2, 3 and 4 being includedin this application for illustrative purposes. i

In Figure'2, voltages of substantiallyconstant frequency and of sinusoidal ,form are supplied from any source to a'modulator of any known type. The oscillations'may be producedby an oscillator of the crystal or line controlled type or of anyother type, the only requirement being that they be of substantially constant frequency and constant alternating current amplitude; The modulator 2| may be of any type havingthe desired characteristics. form supplied to 2| is modulated in amplitude .in accordance with the desired modulation signal impressedfrom any source on 2|. The output of the modulator 2| is connected to an amplitude regulating potentiometer P1 which is connected by a movable point to a phase shifting network 23. This network may take any suitable. form, the essential feature being that the output thereof supplies twoportionsof theamplitude modulated wave in phase displaced relation. The amplitudes of the portions are substantially equal.

Where the plates 6 and 8 are at right angles with respect to each other, the phase displacement of the deflecting voltages should be substantially 90. Other angular'relations between the deflecting plates requires other phase relations between The wave of sinusoidal For a more detailed explanation of how the system works, refer now to Figures 1, 1a, 2, 2a, 3a, 3b and 30.. First, with no modulationinput to 2 I, the phase shifting network in 23 and potentiometer P: of Figure, 2 are adjusted-so that the electron beam of the "gun I describes'a circle on the target or final anode ID. If the potentiometerrP1 is adjusted so that this circle is of the size designated by 01. in Figure 1a, then the voltage appearing across ZA, i. e., the output voltage will be as shown in Figure 311; It will benotedthat the electron stream passes from one segment, say I 4, of the'target anode to the other, say segment l6, and from thelatterto the former at points P1 and P1',"whichare 180 apart. This means that the positive and'negative portions of each cycle of the flat-topped supersonic output voltage wave are equal, and this adjustment therefore corresponds to. zero modulation. If now the two deflecting voltages from 23v are decreased. in amplitude to almost zero by changing potentiometer P1, all other controls being left the same, the locusof the end-point of the electron stream will be 02 of Figure 1a, and the voltage acrossZA will'be as shown inFigure 3b. The electronstreamncw passes from one segment, say M, of the anode to the other, say segment l6, and from the latter tothe former at points P: and P2. Likewise; if the potentiometer P1 is adjusted to'give' voltages, almost double those which produced the locus cithen 03 will be the new locus, the electronstream will pass from one anode segment to the other at points pa and pa and the voltage appearing across ZA will be as shown in Figure 30. Now, if P1 is reset so that the electron circle falls on 01 and amplitude modulation of almost is then applied to the deflecting voltages infthemanner indicated by Figures 1 and 2, the locus of the end-point of the electron stream will expand and contract between the limits c2 and c3 and the output wave will change its delineation, in accordance withthe modulation signalbetween the two extremes shown in Figures 312 and 3c, the delineation of Figure 3a corresponding to zero modulation voltage. In this system, adjustment of circuit constants and monitoring of the system is facilitated by coating the target anodes or plates with willemite or other substance which fluoresces under the bombardment of the electron stream.

This device may be used'to convert potentials of any frequency of sine wave form intovoltages of flattopped wave form of equal'frequency the duration of the dots of which can be adjusted through a wide range. This ismaccoinplished by applying an unmodulated wave of sine wave form to P1 and adjusting the same to make 61 and ez of the desired value. The flat topped wave .so produced is of wide application in .the

radio and allied arts ,and is of particular value for television pictures and synchronization.

Figure 4 shows what a CFVD modulated flat topped supersonic wave looks like. In this example, the modulation is a sine wave the frequency of which is /2 that of the supersonic wave, and the percent of CFVD modulation is 75.. For radio transmission, this CFVD modulated voltage wave may be used to amplitude modulate or key a radio frequency carrier wave which may be used for signalling in any known system. A complete modulating system arranged in accordance with my invention has been shown in Figure and will now be described.

Figure 5 illustrates one form of final or target anode for the electronic modulator or electron gun modulator which will give the modified CFVD modulation outlined above. It is practically the same as the one shown in Figures 1 and 1a except that a third target anode segment H5 has been added between the segments l4 and It. The electrode H5 is electrically independent of the other two segments and is connected to the high voltage direct current supply source through an additional coupling impedance Zn, across which the output appears comprising short sharp impulses.

Thus, as the electron stream passes from It, say to 16, it first impinges on' H5 and produces in Z13 a short sharp impulse of constant duration for all radial positions of the stream. Likewise, when the stream passes from 16 to 14 a short sharp impulse is produced so that each of the usual CFVD impulses is preceded and succeeded by the short impulses of equal duration. The form of the wave is shown in Figure 6.

It is noted in passing that the voltage appearing across ZA in Figure 5 is similar to that produced across ZA of Figure 1 being modified only by the action of H5 and Zn as described above, and it is thus apparent that this one form of anode might be utilized for either type of CFVD modulation. The step by step analysis of the principle of operation will be omitted since it is so similar to the one given above for the anode of Figure 1. C4 is the zero modulation circle and c5 and 0e are the limits between which the electron circle moves when the modulation is 75%. Figure 6 is an example of 75% modulation by the modified CFVD method. The modulating signal in this case is a sine wave, the frequency of the dot wave. For radio transmission the wave of Figure '7 is used to amplitude modulate or, optionally, to key the radio frequency carrier. For example, the modulated wave in Figure '7 may be applied to the grid electrode of a radio frequency amplifier to control its bias and key the tube.

Obviously, many variations are possible in the construction and utilization of this electronic modulator. To mention but two, electromagnetic. instead of electrostatic deflection of the electron beam may be used, and the size of the electron circle may be varied by introducing the modulation signal into the anode supply circuits instead of modulating the deflecting voltages with it.

While I have shown the plate It of Figure 1a and plates l6 and l l5 of Figure 5 as being located within plate I4, I contemplate the use of target anodes wherein H5 is a complete circle plate, while 16 is disposed in front of M as shown in Figures 7 and 7a. This structure simplifies production because only .oneplate, -i.,e., lfi, needs to be .formedin accordance with my equation which may then be modified as shown in Figures 7 and 70. With this form of final target, the wave form is improved because the electron stream falls substantially directly on 14 when .it leaves [6 and vice versa. In,other words, the constant 6 is removed from the equation. The target of Figures 8 and 8a is particularly adapted to production of CFVD as is the anode or target electrode of Figure la. :In this arrangement, electrode It may also ;be utilized as the collecting electrode to supplement or replace the action of electrode 9!! of Figure ;5 of my original application.

The same advantages of production can be obtained by using a target anode as illustrated in Figures 8 and 80, wherein the electrode it has a heart-shaped opening therein and the electrode it! may have any .peripherical contour so long as it completely covers said heart-shaped opening in Hi. This target arrangement is also particularly adapted to the production of CFVD.

It will be noted that in Figures '7, 7a, 8 and 8a., the electrode formed in accordance with my equationcan follow the latter exactly from r=o out since there is no radial spacing necessary between the edges of the plates to prevent short circuiting as in Figures 1a and 5.

For the production of modified CFVD or tuned impulse the target 11-5 may be placed in front of a plate H} as shown in Figures 9 and 9a.

In each modification, the electrodes M and it. and Q and J5 and H5 may be coatings or deposits on the tube envelope properly separated by insulating material or supported thereby.

What I claim is:

1. An electron discharge device having a target anode comprising a, plurality of surface bearing members arranged about a focal point, portions of the boundaries of one of said surface bearing members being defined by T=iczd+5, portions of the boundaries of another of said surface bearing members being defined by r=:a0-5; where r: radial distance from said focal point, a and 6 are constants, and 0 is angular deviation from a straight datum line through said focal point along which r is substantially zero.

2. An electron discharge device having a target comprising a plurality of superimposed surface bearing members arranged about a focal point, one of which surface bearing members is substantially of a shape defined by the intersection of two Archimedes spirals.

3. An electron discharge device having a target comprising two or more surface bearing members arranged about a focal point, one of said surface bearing members being substantially of a shape defined by the intersection of two Archimedes spirals and lying within the area of the other surface bearing member from which it is conductively separated.

4. An electron discharge device having a target comprising two or more surface bearing members arranged about a focal point, one of said surface bearing members being substantially of a shape defined by the intersection of two Archimedes spirals and lying within the projected area of the other surface bearing member.

5. An electron discharge device having a target comprising three surface bearing members arranged about a focal point, two of which surface bearing members are substantially of a shape defined by the intersection of two Archimedes spirals and disposed wholly within the area of the remaining surface bearing member, all of said surface bearing members being conductively separated.

6. An electron discharge device having a target comprising three plates arranged about a focal point, two of which plates are substantially of a shape defined by the intersection oi! two Archimedes spirals and disposed wholly within the projected area'of the remaining plate.

7. An electron discharge device having a target anode comprising a plurality of conducting elements arranged in a saucer-shaped surface about a focal point, at least one of said plates being substantially of a shape defined by the intersection of two Archimedes spirals.

8. Inan electron discharge device, an electron emission element, a-pair of anode electrodes, one of which is substantially of a shape defined by the intersection of two Archimedes spirals, in the path of emission from said emission element, and pairs of similar deflecting electrodes adjacent the path of said emission.

9. In an electron discharge device, an electron emission element, three anode electrodes, two of which are substantially of a shape defined by the intersection of two Archimedes spirals and located wholly within the area oi. the third electrode, and pairs of similar deflecting electrodes adjacent the path of said emission.

10. In an electron discharge device, an electron emission element, a pairof anode electrodes, one of which is substantially of a shape defined by the intersection of two Archimedes spirals, both of which are in the path of emission from said element, pairs of deflecting electrodes adjacent the path of said emission and a collecting anode adjacent said anode electrodes.

11. In a discharge device, an electron emitting electrode, a target electrode comprising two conductive surface bearing members, a portion 01' the boundary of one of which is defined by r=ia06 and a portion of another boundary of which is defined by 1'=-' -a0-|-8 where r the radiusfrom the electron stream focal point, a and 6 are constants, and 0 is the angular deviation from a straight line through said focal point where r: substantially zero and pairs of deflecting electrodes adjacent the path between said emitting electrode and said target electrode.

12. In an electron discharge device, an emission element, a pair of anode electrodes spaced therefrom and a plurality of anode electrodes in the path of emission from said element, one of said electrodes having an opening substantially of a shape definedby the intersection of two Archimedes spirals opening therein and being disposed between another of said anode electrodes and said emission element.

13. In an electron discharge device, an emission element, pairs of deflecting plates, a target anode comprising two conducting elements located around a focal point, a portion of the boundary of one of which conducting elements is defined by T=u0, another portion of the boundary of the said one of said elements being defined by T=a0 where r is the radius from the electron stream focal point, a: is a constant, and 0 is the angular deviation from a straight line through the focal point where r is zero.

ROBERT EVART SHELBY.

Images