US2480820A - Wave length control of wave energy - Google Patents

Description

3 Sheets-Sheet 1 Aug. 30, 1949. "R" L. HOLLINGSWORTH WAVE LENGTH CONTROL OF WAVE ENERGY- Filed Jan. 11, 1943 WAVE LENGTH MODULATED STHGIE MODULATION CARRIER SOURCE 6 H R T MEM R AWN M ML 5 R /P E M M Y HE mu m W M T E T LW V T U L 0 N A R .MR E E E D Y RB P FOM u Em .D FT E 1 w U h MM A n1 w (mg Aug. 30, 1949. "R" L. HOLLINGSWORTH 2,480,820

WAVE LENGTH CONTROL OF WAVE ENERGY Filed Jan. 11, 1943 3 Sheets-Sheet 2 SHIELD 3'9 7'0 INDICATOR I I 'INVENTOR I 4 7? LEE HOLLINGSWORTH MM ATTORNEY Aug. 30, 1949. "R" HOLLINGSWORTH 2,480,820

WAVE LENGTH CONTROL OF WAVE ENERGY Filed Jan. 11, 1943 3 Sheets-Sheet '3 U Q 4.5 46 X Y FREQUENCY I 4.9" 4? k 3 r FREQUENCY MODULA T/ON INPUT g 5' A- F. OUTPUT '70 60 TO COMPL E X gES/STA/VCE I? OSCILLATOR ,2,

ATIIORNEY Patented Aug. 30, 1949 WAVE LENGTH CONTROL OF WAVE ENERGY "R Lee Hollingsworth, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 11, 1943, Serial No. 471,946

13 Claims. 1

This application discloses a new and improved method and system of frequency modulation as applied to radio transmitting and receiving equipment.

In the present invention, I frequency modulate an oscillator by varying the electron stream capacity of a vacuum tube to change the capacity of an associated oscillator tube, or a component part of an oscillator circuit.

In another well known system of frequency modulation it has been the practice to phase modulate the oscillator of a frequency modulation transmitter in accordance with modified modulation currents, and with several frequency multiplying stages of amplification finally arrive at the assigned carrier frequency.

Yet in another method of frequency modulation, reactance tubes are used in association with the tank circuit of an oscillator to more directly produce frequency modulated waves.

It is, therefore, one of the purposes of this invention to produce frequency modulated electromagnetic waves.

It is another purpose of this invention to render an amplitude modulation electro-magnetic wave receiver susceptible to frequency modulated electro-magnetic waves.

Still another purpose of this invention is to produce linear power conversion from an oscillator using only a small amount of control voltage, utilizing a suitable discriminator circuit in association with a suitable rectifier.

Yet another purpose of this invention is to limit automatically the modulation bandwidth of a frequency modulated transmitter.

Further, it is another purpose of this invention to frequency modulate a quartz crystal oscillator.

Also, it is a purpose of this invention to produce improved systems of uni-directional or single sideband frequency modulation.

It is another purpose of this invention to provide'a capacity composed of the individual capacities between the electrons within an electron stream or cloud, and which is variable as a function of an applied control voltage.

A prime purpose of this invention is simplification of the system whereby those schooled in the art and science that it invokes, can easily assemble and use the same.

In describing my invention hereinbefore and hereinafter the term "frequency modulation has been used. It is, of course, understood that the modulation carried out in my system may be termed wave length modulation and may have the characteristics of frequency modulation primarily or phase modulation primarily or may have modified forms of either thereof or characteristics of both phase and frequency modulation and modified forms thereof. Where the modulation or control is as to phase the modulating potentials are modified in amplitude in accordance with their frequency as disclosed in Crosby U. S. Patent No. 2,279,659, dated April 14, 1942.

In a thermionic vacuum tube having a cathode or electron emitter, hereinafter called a cathode, and a control grid for controlling the flow of electrons to a plate or electron collector hereinafter called a plate, the electrical capacity between these elements is somewhat different when the cathode is active. With all elements inactive such as when the cathode is not emitting electrons, and when there is no control voltage applied to the grid and likewise no voltage applied to the plate, the electrical capacity between these elements is constant. When the cathode is active and a stream of electrons is passing from the cathode to the plate, and the grid is tapped into or across this stream of electrons, the capacity between the various elements is somewhat different, and this capacity is variable with the mutual conductance of the vacuum tube. This can be explained by assuming that the hot capacity of a vacuum tube consists of the sum of the individual capacities between each electron and all other electrons within the electron stream or cloud. As small as these electrons are, their capacity may be relatively large in comparison to their surface area because of their close association. It is an established fact that the mutual 7 later circuit capable of being frequency modulated by an associated vacuum tube.

Figures 2a and 2b are modifications of the arrangement of Figure 2.

Figure 3 shows a similar embodiment for frequency modulating a quartz controlled oscillator.

Figure 4 illustrates how a p w r os llat r may be similarly frequency modulated by a small as to conductance by potentials applied at [I in phase with the control of It.

To synchronously tune an antenna to produce uniform radiation over a wide frequency band, the cathode of a vacuum tube I6; is connected or coupled thereto as shown in Figure 2a. The plate of said tube is connected to ground or to a counterpoise system. The modulating voltage is applied to the grid of the vacuum tube, in the same phase relation as that applied to the oscillator and amplifier, that is, if the frequency of the oscillator is increased, the amplifier and antemia would be likewise tuned to a higher frequency in synchronism with the carrier shift due to modulation.

A vacuum tube may be connected across a tuned circuit of any desired variety, and the electron stream capacity of the vacuum tube varied as a result of applied grid voltage variations to change the natural frequency or resonant point of the tuned circuit in the ether spectrum.

It will be appreciated that a vacuum tube in like manner can be connected across or in parallel to a quartz plate that is used to produce stabilized oscillations in association with a vacuum tube in a conventional oscillator circuit to frequency modulate the quartz plate oscillator. Such a circuit is shown in Figure 3, where the oscillator tube is shown at H. The tuned plate circuit is shown at I3 and the output circuit is shown at M. The quartz plate 2|, shown in a conventional manner, is connected between the grid and cathode. The modulating tube I 6' is connected in parallel to the quartz plate. The modulating voltage is applied to the grid of vacuum tube It to produce capacity variations in parallel to the quartz plate, which varies the natural operating frequency of said quartz plate in proportion to the electron stream capacity change within the modulating tube.

Since the power of quartz oscillators is usually low, the output would usually feed into another amplifier before being connected to an antenna. The frequency of the quartz oscillator may be multiplied if desired.

In Figure 4 a power conversion circuit is shown. Vacuum tube H is shown connected in an oscillator circuit similar to that shown in Figure 2. Here modulating tube l 6' is shown to have a positive voltage applied to the plate from battery 24 to increase the electron stream capacity between the cathode and plate. The increased grid bias is negligible since it may be counteracted by the modulating voltage connected at terminals l1 and I8. Modulating tubes 22 and 23 in shunt respectively to tuned circuits l2 and I3 serve to illustrate that additional modulating tubes may be connected in any part of an oscillator circuit to use their electron stream capacity for varying the frequency of the oscillator to a greater degree if so desired. Such a tube may also be connectedbetween the grid and plate of the oscillator tube ll, thereby adding the cathode-to-plate capacity of the modulating tube to that of the grid-to-plate capacity of the oscillator tube. The modulating voltage is applied to the grid of the modulating tube or tubes as heretofore explained.

The action of the circuit of Figure 4 is as follows: The circuit is assumed to be generating a desired amount of radio frequency power. Modulating voltage at a desired or variable frequency is applied to terminals I1 and i8. Vacuum tubes i6, 22 and 23 add or subtract electron stream capacity to or from the oscillator circuit in proportion to the applied modulating voltage. Circuit 26 is coupled to circuit l3 and is tuned to resonance with circuit l3, causing rectifier tube 25 to pass maximum current through resistance 21 which is filtered by condenser 28. The resulting power output appears across terminals 29. Condenser 36 is a radio frequency bypass condenser to prevent transfer of radio frequency energy from the oscillator past the shield 3i in which the oscillator is housed,

This circuit, Figure 4, may operate to deliver maximum power across terminals 29 with no modulating voltage applied, and act to give reduced power across terminals 29 when the modulation is applied, or the oscillator may be detuned to a point where essentially no power would appear across terminals 29, and with modulation applied it would deliver full or proportionate power (at terminals 29) comparable to the applied modulating voltage. The latter method of operation would save power, since the oscillator circuit would draw the maximum power from the power supply source only during the time that the modulation tunes it to maximum output. In the language of the art, zero modulation level would require a minimum of power to be drawn by the oscillator from the power source, and modulation would cause the oscillator to draw the maximum amount of power from the power source.

A commonly known push-pull type of oscillator may be frequency modulated in the manner heretofore explained. and in fact, any type of oscillator can in this manner be frequency modulated, whose frequency can be changed by adding or subtracting capacity to or from any component part of the oscillator in question, without departing from the scope of this invention.

Further, a coupled circuit in association with an oscillator may be shunted by a vacuum tube as heretofore described, and the electron stream capacity of the vacuum tube varied to produce inductive or capacitive loading that would change the frequency of the oscillator, thus producing frequency modulation of said oscillator, without departing from the scope of this invention.

In Figure 5 the same principle is employed to modulate the conventional oscillator shown. In this embodiment another method of producing single sideband transmission is shown, together with a means for automatically controlling the modulation bandwidth, and a means for visually indicating full modulation. The modulator tube 33 is shown to be a commonly known screen grid type. The cathode of tube 33 is connected across the grid tuning circuit l2 to ground. Modulation is accomplished as heretofore shown by applying the modulating voltage to terminals I! and E8. The plate of the modulator tube is connected through the inductance of tuned circuit 34, which is coupled to circuit I3, and through solenoid switch winding 35 to ground. Tuned circuit 36 is coupled to circuit l3 and connected to the plate of rectifier tube 31. When the rectifier draws current, the path of said current is through the inductance winding of tuned circuit 36, resistance 38 and through the winding of solenoid switch 39.

The action of this circuit shown in Figure 5 can best be described with reference also to Figure 6. Let us assume that the oscillator is in operation and that its position in the frequency spectrum is shown to be that of resonance curve 45, and the oscillator is assumed to be unmodulated. Further, let us now assume that the positive half-cycle of modulation is applied at tere tion produced by modulating tube Hi, we can assume that the receiver would receive amplitude wave modulations in a normal manner. Now, if inaudible frequency wave energy is applied after preferably being rectified to terminals l1 and [8, the frequency of the oscillator will be tuned to one side at the rate of the applied inaudible frequency, producing a discriminating effect to allow the detection of frequency modulated waves as the oscillator frequency is varied in and out of tune with the associated tuned circuits of the receiver. The radio frequency amplifiers ahead of the conversion oscillator circuit of such a superheterodyne receiver, and the intermediate frequency amplifiers after the conversion oscillator circuits, and the associated discriminator circuit may in the same manner as heretofore eX- plained be tuned and detuned in step with the swing of the oscillator to cause the receiver to be susceptible to broad sweep or wide band frequency modulated waves. The discriminator circuit may be adjusted to be delivering zero output until the same or separate high frequency. modulation is applied to frequency modulate its tuning in a manner to cause it to deliver maximum power at a point in the frequency spectrum Where the transmitters modulation reached 100%. Such a discriminator circuit would not be unlike that shown by circuit 26 of Figure 4, though it would be shunted by the modulating tube such as heretofore shown and explained.

Thus, by throwing a switch to energize an associated oscillator, any superheterodyne radio Wave amplitude modulation receiver may become an efiicient receiver of frequency modulated radio waves.

Another application of this principle in a radio receiving system is to produce fiat top characteristics in radio wave amplifiers, especially in intermediate frequency amplifiers such as are used in superheterodyne receivers. This is accomplished by rapidly tuning and detuning the stages of amplification to cause the maximum response to traverse a given frequency band in the frequency spectrum.

Further, an oscillator used in checking the characteristics of amplifiers can be frequency modulated in the manner shown in this invention, in the place of using the commonly known motor driven condenser for varying the frequency While visual characteristics are being observed during final adjustments.

Further reference to Figure 5 will show that there is inherently incorporated in this circuit a means for preventing a radio receiver from drifting away from the desired station being received. Assume that the oscillator is that of a conversion oscillator of a superheterodyne amplitude modulation receiver, and further assume that tuned circuits 34 and 36 are tuned immediately above and below the desired frequency channel to be received. If the oscillator drifted higher in frequency than the desired channel, the energy induced into circuit 34 would increase the plate current through tube 33 to cause a capacity increase that would again lower the frequency of the oscillator to the desired frequency. If the oscillator drifted lower in frequency, circuit 36 would produce rectifier current to increase the negative voltage on the screen grid of the modulator tube to decrease the electron stream capacity of this tube, thus causing the capacity of the oscillator to be lowered, increasing the frequency of the oscillator to the normally desired channel. It may be assumed that the oscillator 10 is unusually powerful and that only a part of its output is being used by the receiver for frequency conversion purposes, or that tuned circuits 34 and 36 are located at the output end of the intermediate frequency amplifier, where a suitable amount of signal energy is available.

Thus is shown a means for holding an oscillator within a given frequency band which may be used in either radio receivers or transmitters, or wherever a controlled oscillator can be used to advantage.

It will be further appreciated that this type of frequency modulation is essentially basic in nature, and that there are many possible uses for such a variable electron stream or electron cloud capacity, such as, for instance, to displace the directivity of a directive antenna to cause the beam to cover a wider area, such displacement to take place at a variable or voice frequency, or at a constant rate of variation such as would be used in radio telegraph communication to cover effectively a wider area, and to reduce fading somewhat at the higher frequencies such as are used for long distance communication.

It will be still further appreciated that all of the elements of tubes l6 and Il may be housed in the same bulb or container if so desired.

The applications of this type of variable capacity seem to be so numerous, that in the claims to follow, one basic claim therefore appears to protect this invention in the broad field that it encompasses. An application of the principle chiefly involved in this invention is employed in my United States Patent No. 2,243,423.

What is claimed is:

1. In a wave generating and wave frequency control, an electron stream capacity in a tube comprising a heated cathode, a plate, and at least one control grid, said electron stream flowing from the cathode to the plate, a generator tube having a grid and a cathode, a conductive connection connecting said cathode of the first tube to the grid of the generator tube, a conductive connection between the plate of said electron stream capacity tube and the cathode of said generator tube, and connections for applying a control potential to the grid of said electron stream capacity tube to vary the electrical capacity of the electron stream to control the frequency of the oscillations generated by said generator tube.

2. In a wave generating and wave frequency modulating system, an oscillation generator including an electron discharge device having as electrodes an anode, a cathode and control grid and including generating circuits including a quartz crystal coupled with the device electrodes, an electron stream capacity in a tube comprising a heated cathode, a plate, and a control grid, said electron stream flowing from the cathode to the plate, a substantially direct connection between the cathode of said tube and the grid of said device, a substantially direct connection between the anode of said tube and the cathode of said device, and connections for applying a controlling potential to the grid of said electron stream capacity tube to vary the electrical capacity thereof and in turn modulate the frequency of the oscillations generated in said device as controlled by said quartz crystal.

3. In a power conversion system, an oscillation generator comprising a discharge ,device having a control grid electrode and cathode electrode and having output electrodes, means coupling said two first-named electrodes in an oscilgrease-c l in i li w jin l i a't oiltputjcircuit a tuning' reactance coupIl g:saidbu putcircuitto'said output electrodes, amcamat rrti se having a' cathode coupled to theficontroljgridof said device and having an anodejcoupled to" the cathode of said device, said rnodulat or tube having a control grid, a secondmodulator tube having a cathode and an anofdrej coupljedfljwith said'tuning reactance, said secondmodulator tube having a control grid, and meansjor applying a control potential to be conve djsimhltaneously to'the control grids of said'modulat rtu e [51} lnfjaisystem of the class described, an oscil- Iationjgenerator comprising a tube having a control'jgri'dand a cathode, an electron stream capacity comprising an electron discharge device having ,a'catl o'degja' plate and a control grid ele ode; said'electron stream flowing irom the cathodej'td the plate of said device, means for .ctnneenng the cathode of said device to the cbntrol grid of said tube, a connection between the plate of s'aid device andthe cathode of said tube; and connections for applying a pulsating negative electromotive force to the grid of said lcCtiolLStrfea-in" capacity device to reduce the eI'ectricaLcaigacity or the electron stream to therebyincre'ase the frequency of the oscillations generated, thufsproducing uni-directional or singlesidebandwave length modulation.

5.1m a'systemofgthejclass described, an oscillati'o'nj gen rator comprising a tube having a controlfglid, and afcatho'de, an electron stream capacity comprising an electron discharge device having a cathode, a'plate and a control grid electrode, said electron stream flowing from the cathode tothe plate of said device, means for connecting the cathodeof said device to the con- .trolgrid of,jsaid tube, a connection between the plate of said device and the cathode of said tube, and, connections ror applying a pulsating positive electromotive forceto the grid of said electron streamv capacity device to increase the electrical capacity of the" electron stream to thereby decrease the ,frequnf yoi the oscillations generated, thusproducing unidirectional or single sideband wave length modulation.

In a] system of the nature described, an electron, discharge tube having input and output electrods incliidiiig a control grid, an anode, and 'a' cathode. with 'a tuned circuit coupled between the jgrid,,,ar ijd cathode, an electron stream capacitytcoinprising an electron discharge device having aheatedcathode, a plate, and a control grid, the electron stream in said device "flowing from the cathode to the plate, a con- :ductive connection between the cathode of said device and control grid of said tube, a connection between the anode of said device and the ,Icatho'de of saidv tube, and means for connecting a, pulsatingoralternating current source to the control grid of sai'd device to vary the electrical ca acity of the electron stream to thereby vary the tuning of said tuned circuit. 7.,In a systemoithe class described, a plurality, of electron discharge devices coupled in ,cascade by a plurality of tuned circuits with means ,for setting .up oscillations in the first of said stages and deriving amplified oscillations from the last of said stages, a plurality of electron stream capacity tubes each having a heated cathode, a plate anda control grid with the elec- ,,tfoI 1' stream flowing from the cathode to the plate, therebeinga tube for each of the tuned circuits it is' "desired to control, connections bevery close to their 12 tw fithe catnbdes ci'eacii er safe tubes-and one side ofadiifeieiit one-bi -said-tun'ed'circuits, connebtiqngj bet een the anod'es of-each' of said tubes and-the "othei 'sidewf a different one of said tuned 'cirjcijit'a thle arrangement being such that the'impedahcbtwecn' the anode and cathode of each of saidtubesis connected across a different assassin-"tunedcircuits, at source of control potential;and 'connecticns for applying control 'potefitial' from said source to the control grids of each of said tubesin phase synchronism.

8, In an arrangenifnt'of theclass-described, a wave generator-device havinga grid and a "oathode, an electron stream capacity produced in a thermionic"vacuum fiubeconsisting of a heated cathode; a plate; and at-"leas't two control grids, saidfelectrori-stiahi flowing from 'the' cathode to the plate 'to comp'risaa' wave length modulator tube, a connectio'n-lietWeen-the cathode of the tube and thegii'dbfsaid device, a connection betwee'n th'e plate of; said'electron stream capacitytub' and the cathode of the device, said connection including a 5 solenoid switch winding and aninductance of a first tunedradio frequency circuitatt n'e'd to th'' upper'side of the generatorsf dulated ireqilency', a, second tunedradiojreduehcyf cii'cl'i'itcoupled to the wave v generator ascertained to the lower side of the geiielators u measured frequency and connected in series with a resistanceand 'a' solenoid inging a a rdrtnercenneeiee' to the plate and-cathode re meansfora i plying an electromotive or firstcontrolgrid of the w ereby'th'e fi T L second of 'tuii circuits become energized when full'mo: la Ii iS aEcompliShed to either increase or de H V tes ament of the electron stream'vvit them'odulat'ing tube in opposition to the capac ty'changeasaresult of the"electro motive force afiplied to" th first control grid of ime. ;.neee=Sca n s h wave lengths of w hich 'are tojbe; controlled, flow, said circuit includih controllable reactance comprising an elec ron st earn capacity produced in a thermionic" vacuui'ri tub e, connected to said tuned circuit towave length modulate the oscillations, s'aid tube having two grids, means for applying an alte ng current electromotive force to one grid tube to'control itscapacity, a second I une adio frequency circuit coupled tothc first't 'ed circuit andattuned er'icyof the oscillations when not mbdulate nd means for applying the energy induced in dLSlion'd tuned circuit to another g' ridof the le res stream capacity tube to eliminate the an on oii'one sideof the unmodulated 'walehgth when modulation is g V sectional or single sid'eband waive-lengthjnodul ation. 7

10. In an arrangemeht of the; class described,

a tun'ed circuit wherein wave energy to be modulated flows, said ciruitinclu'cling an electron stream capacity-produced in'a thermionic vacuum tube having a cathcide and at'lea st two other electrodes including an -sameand cathode, c'onnecti'o'n's coupling'th' anode and the cathode of said electron' stream capacity tube to said tuned circuit, two closely assdi'atedtund circuits attuned ahove and'filoiv the desired operating frequency of said first tuned circuit and coupled thereto, and circuits for applying the currents from the respective tuned circuits to said two other electrodes to produce a capacity change to oppositely oppose frequency drift of the wave energy in said tuned circuit.

11. In a system of high deviation frequency modulation transmission, a master oscillator, means for modulating the master oscillator including an electron stream capacity vacuum tube, means for controlling the bandwidth of the modulation applied to the master oscillator, a frequency multiplier-amplifying system coupled to the oscillator, means for tuning said frequency multiplier-amplifying system in synchronism with the modulation applied to said master osciliator, an antenna system coupled to said frequency multiplier and a means for tuning the same in synchronism with the modulation of the master oscillator and with the synchronous tuning of the associated frequency multiplier-amplifying system.

12. In signalling apparatus, means for producing wave energy comprising an electron discharge device having an anode, a cathode, and a control grid, with wave energy producing circuits connected thereto, an electron stream capacity in the form of a thermionic vacuum tube having a heated cathode, a control grid and an anode, the capacity being formed by the electron stream between the cathode and anode, a connection, of low impedance to voltages of the frequency of the wave energy produced, between the anode of said tube and the cathode of said device, a connection, of low impedance to voltages of the frequency of the wave energy produced, between the cathode of said tube and the control grid of said device, and connections to the control grid and cathode of said tube for varying the potential on the control grid relative to the cathode to modulate the frequency of the wave energy produced in said device, the arrangement being such that the Wave energy may be modulated a portion of a cycle thereof or through several megacycles.

13. In a signalling system, a first alternating current circuit tuned to a selected frequency, means for setting up alternating current wave energy in said circuit of a frequency determined by the tuning thereof, an electron stream capacity in a tube having electrodes including a I4 heated cathode, an anode, and at least one control grid, the capacity being formed between the anode and cathode of said tube, connections connecting the anode and cathode impedance of said tube in shunt to said tuned alternating current circuit, a connection to the control grid of said tube for applying a control potential thereto for varying the electron stream between the anode and cathode of said tube to thereby vary the capacity of the tube and the tuning of said alternating current circuit and the frequency of the wave energy therein, a second alternating current circuit excited by current set up in said first circuit and tuned to a frequency above said selected frequency, means connected with said second tuned circuit for rectifying current set up therein for producing a potential and applying the same to an electrode in said tube to control the capacity thereof when the frequency of the alternating current in said first circuit attains the frequency to which said second circuit is tuned, a third circuit excited by current set up in said first circuit and tuned to a frequency below said selected frequency, means connected with said third circuit for rectifying current set up therein for producing a potential and applying the same to an electrode in said tube to control the capacity thereof when the frequency of the alternating current in said first circuit attains the frequency to which said third circuit is tuned, and an output circuit coupled to said first mentioned alternating current circuit.

R" LEE HOLLINGSWORTH.

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

UNITED STATES PATENTS Number Name Date 1,628,905 Nyman May 17, 1927 1,716,161 Allcutt June 4, 1929 1,777,410 Jones Oct. 7, 1930 2,032,620 Langmuir Mar. 3, 1936 2,121,737 Hansell June 21, 1938 2,217,417 Peterson Oct. 8, 1940 2,243,829 Brett et al. June 3, 1941 2,274,184 Bach Feb. 24, 1942 2,274,648 Bach Mar. 3, 1942 2,282,103 Tunick May 5, 1942 2,337,214 Tunick Dec. 21, 1943

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