US2278159A - Oscillator-modulator system - Google Patents

Oscillator-modulator system Download PDF

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Publication number
US2278159A
US2278159A US679997A US67999733A US2278159A US 2278159 A US2278159 A US 2278159A US 679997 A US679997 A US 679997A US 67999733 A US67999733 A US 67999733A US 2278159 A US2278159 A US 2278159A
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United States
Prior art keywords
grid
tube
cathode
anode
frequency
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Expired - Lifetime
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US679997A
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English (en)
Inventor
Harold A Whecler
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BAE Systems Aerospace Inc
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Hazeltine Corp
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Publication date
Priority to BE404162D priority Critical patent/BE404162A/xx
Application filed by Hazeltine Corp filed Critical Hazeltine Corp
Priority to US679997A priority patent/US2278159A/en
Priority to FR775741D priority patent/FR775741A/fr
Priority to GB20377/34A priority patent/GB426855A/en
Application granted granted Critical
Publication of US2278159A publication Critical patent/US2278159A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/16—Amplitude modulation by means of discharge device having at least three electrodes
    • H03C1/18—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid
    • H03C1/24—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid modulating signal applied to different grid

Definitions

  • This invention relates to electric wave transmission and more particularly to means for controlling the transmission of signal waves in a vacuum tube.
  • the present invention is directed to an improvement in a vacuum tube modulator system.
  • This improvement results from forming a virtual cathode in a vacuum tube, and utilizing the virtual cathode as a source of electrons for the signal translating or modulating section of the tube.
  • the properties of the virtual cathode, particularly its electron density, and hence its available emission, are varied periodically in order to modulate the signal.
  • the arrangement is, therefore, designated an emission valve modulator system.
  • the invention is pref rably effected by utilizing a tube having a cathode, an anode and an output control grid therebctween upon which is impressed a source of alternating voltage.
  • the output control grid operates more directly on the virtual cathode, which is a cloud of electrons transferred from the cathode to a position nearer the output control grid.
  • the virtual cathode is formed just outside of a screen located between the cathodeand the output control grid, and held at a positive voltage relative to the cathode.
  • the output control grid is hereinafter called the outer control grid because of its location beyond the virtual cathode. 'The number of electronsreaching the virtual cathode is controlled, and hence its density is caused to fluctuate, by the valve action of an inner control grid located be tween the actual cathode and the virtual cathode.
  • An important embodiment of this invention lies in its application to a combined oscillator andmodulator.
  • the screen is inserted in the space path between the inner and outer control grids, the screen acting also as the anode of an oscillator.
  • the device has, in effect, two anodes with the outer or modulator control grid situated therebetween.
  • An appropriate oscillatory circuit is associated with the cathode, the inner control grid and the screen to produce the oscillations.
  • the effectthus produced in the space path causes by its valve action a modulaton of the signal voltage impressed upon the outer or modulator control grid; there is thus provided an oscillator-modulator requiring the use of onlyone tube having a single cathe ode in a unitary electrode structure.
  • An advantage of this form of oscillator-modulator lies in the fact that only a single tube is required to perform the two functions of producing oscilla tions and modulation.
  • a feature'of this invention is its use in a radiofrequency transmitting system.
  • radio-frequency oscillations are modulated by the audio-frequency which is to be superimposed uponthe radio-frequency carrier wave.
  • This function can be performed by impressing the audio frequency upon one of the control grids of the tube, the radio-frequency carrier voltage being impressed upon the other control grid.
  • the modulated carrier wave at the anode circuit may then be transmitted or radiated by coupling the anode to a suitable radiating antenna.
  • the modulator control grid be constructed to provide a; distortionless, that is, linear modulation for all percentages of modulation up tosubstantially Distortionless modulation is obtained when there is an approximately linear relationship between grid bias andmutual conductance.
  • a bias voltage should be impressed upon the grid of the value equal'to that at the mid-point of the straight line characteristic.
  • control grid for the radio-frequency oscillations be constructed to provide distortionless amplification. This results when there is a linear relationship between grid voltage and anode current. On this grid,
  • quency grid may be operated with an average bias beyond the cutoff, in the case of class C amplification, with high efficiency, any harmon- Alternatively, the carrier fingercs generated being suppressed in the output circuit.
  • the various embodiments of the invention may conveniently be carried out by the use of an emission valve modulator tube having five or siX, or more, electrodes.
  • the output of the modulator system can be greatly increased by the use of an outer positive screen in the modulator section of the tube, between anode and outer control grid.
  • an oscillator-modulator comprises a vacuum tube having an audio-frequency input circuit and. a carrier-frequency output circuit, the vacuum tube having a space current path in which are included at least two grids.
  • the first of these grids has a source of carrier-frequency voltage connected thereto, and the second of the grids has the aforesaid input circuit connected thereto.
  • the oscillator-modulator comprises means including the aforesaid second grid of nonuniform construction or variable mesh for imparting to the tube an approximately linear relationship between the voltage on the second grid and the mutual conductance from the first grid to the anode over a large range of voltages on the second grid, whereby distortionless modulation is effected over a large range of modulation percentages.
  • the modulator' also includes means for coupling the output circuit to a radiating antenna.
  • Figure 1 is a schematic circuit diagram showing a generalized form of the invention.
  • Figure 2 illustrates a radio-transmitting system utilizing a hexode tube as an oscillatormodulator
  • Figure 3 illustrates a somewhat similar system in which the hexode tube acts only as a modulator.
  • Figure 1 shows a circuit diagram of an oscillator-modulator system which may be used in a signaling system.
  • the system comprises a hexode, or six-electrode tube I0 provided with an electron-emitting cathode I and an anode 6.
  • the schematic diagram shows the cathode and anode located at opposite sides of the tube, but this conventional form of illustration is only for the purpose of schematic representation. Any tube actually used for this purpose would be likely to have an orthodox construction, such as a centrally located cathode with helical grids surrounding the cathode, the successive grids having increasing diameters with respect to each other, and an anode in the form of a cylindrical plate surrounding the grid structures.
  • a source of alternating voltage, designated S1 is connected between the outer grid 4 and the cathode I, and a second source of alternating voltage S2 is connected between the inner grid 2' and the cathode.
  • S1 or the source S2, or both may be constituted by a feedback oscillatory system associated with the tube itself.
  • a convenient form of self-oscillatory, or feedback system, for this purpose is shown in Fig. 2 wherein an oscillatory feedback system is associated with the electrodes 2 and 3.
  • the output circuit of the tube includes a tuned circuit comprising a coil and condenser in parallel. This tuned circuit is designated 0 and is connected between the anode and ground. Output terminals 0' and O" are connected, respectively, at opposite sides of the tuned output circuit 0. These output terminals may be connected to any succeeding apparatus to which it is desired to transmit the signals.
  • sources II and I2 of operating voltage making anode 6 and screens 5 and 3 positive relative to the cathode.
  • a voltage source l3 in series between grid 4 and ground, making grid 4 negative relative to the cathode.
  • Grid 2 is placed at a negative potential by a battery 9.
  • the positive voltage on screen 5 should generally be less than that on anode 6 with respect to the cathode.
  • This screen may be omitted, but in any embodiments of the invention its inclusion serves to improve the general operation.
  • This cloud of retarded electrons hovering between the electrodes 3 and 4 is said to constitute a virtual cathode with respect to the succeeding electrodes 4, 5 and 6 of the modulator, because of the fact that electrons can be easily drawn away from the cloud in the same manner that they were originally drawn away from the actual cathode.
  • the virtual cathode and its approximate position is indicated by the dotdash line 1, it being understood that the line I does not represent a physical element of the tube.
  • the positive potentials of the anode B and screen 5 serve to attract electrons from the virtual cathode to the anode, through the outer grid 4 and the screen 5, in the usual manner.
  • the tube therefore, has in effect two anodes, namely, elements 3 and 6, with the inner grid controlling the entire emission from cathode l and the space current to both anodes.
  • the electrodes 4, 5 and 6 together with the'virtual cathode 1 function as an ordinary signal translating vacuum tube of which the output circuit 0 is connected between anode 6 and the virtual cathode (in so far as alternating currents are concerned). From the above-described operation, it is observed that the output controlling electrodes are grids 2 and 4.
  • Modulation results in the system in the following manner.
  • the grid 2 is only slightly negative, or is somewhat positive, there is an abundant supply of electrons at the virtual cathode 1 available to supply an electron stream in the modulator section of the tube.
  • the virtual cathode, and therefore the anode 6 are momentarily deprived of their electron supply, thereby interrupting the output current. It will be observed, then, that the output current of the mod ulator varies in accordance with the oscillations of source S2.
  • the elementsof the tube maybe consideredtobe-situated in two groups: (12) elements 14,5 and 6 associated with source S1; and (2) elements 2 and3 associated with source ,Sz.
  • Figure 2 shows an oscillator-modulator system,.somewhat similar to that of Figure 1, used in a modulated radio-frequency transmitting system.
  • the tube .ill shown in Figure 2 is similar to the tube glll of Figure 1, and includes a space current path betweenthe cathode l and anode 6 in which are included three grids 2, 3 and 4. Similar numerals are used to designate elements which :are. similar in the two figures.
  • the tube of Figure 2 is arranged to oscillate by means of anoscillatory system arranged between screent and cathode I.
  • the oscillatory system comprises .a coil I5, in parallel with condenser I6, connected at one end to ground (and to the oathode) and .coupled at .the other end through a blocking condenser .llto the inner grid 2.
  • a coil l8coupled to the coil 15 of the oscillatorycircuit there is connected in series between the screen 3 and battery 12 a coil l8coupled to the coil 15 of the oscillatorycircuit.
  • the coil 18 feeds back sufficient energy to the grid 2, through the tuned circuit I5, IE, to sustain the oscillations at a sufiiciently high amplitude.
  • the electrode 3 and the circuit elements l4 to IE, inclusive comprise a source of carrier-frequency voltage connected to the first grid '2'.
  • .the'tuned circuit comprises a carrier-frequency output circuit for the vacuum tube It).
  • the instant arrangement also includes an audio-frequency input circuit comprising a microphone 49 which is coupled to and applies an audio frequency voltage to the outer or third grid 4 through an input transformer 20.
  • This audio frequency on the outer grid serves to modulate the oscillations within the tube.
  • Means is included for coupling the output circuit O to a radiating antenna 2
  • the elements of the tube may be considered to be situated in two groups:
  • the operation of the system can often be improved by constructing the modulator, or audio frequency, control grid to provide a distortionless, that is, linear modulation for all percentages of modulation up to substantially Such .distortionless modulation :is obtained over any range of zmodulationpercentages :for which there is anapproximatelylinearrelationship between .grid-bias and mutual conductance.
  • the biasing voltage applied to this grid should be that valuewhich lies approximately at .themidpointof the linear curve.
  • This desirable type of grid characteristic requires a grid'jhavinga nonuniform grid mesh throughout its extent. The exact variation'of grid spacings can best be determined by trial for any particular design of tube.
  • the'inner control grid 2 which controls the carrier-frequency oscillations, be constructed to provide distortionless amplification.
  • distortionless amplification can be arrived at by'the selection of the grid spacing; and the proper spacing can readily be arrived at'by trial and error.
  • this modification of the invention includes means including a nonuniform construction or variable mesh of the grid 4 for imparting to the tube l0 an approximately linear relationship between the voltage on the grid 4 and the mutual conductance from the first grid 2 to the anode 6 over a large-range of voltages onthe second grid, whereby distortionless modulation is effected over alarge range of modulation percentages.
  • Figure 3 shows a variation of the system in Figure 2, the tube It in Figure Bacting only as a modulator. In thisarrangement, the tube does not serve to produce oscillations, but these are applied from an externalsource -23 andapplied to the outer control-grid 4 which, in this case, becomes the carrier or radio-frequency control grid. The audio frequency from the'microphone i9 is impressed upon the inner grid 2.
  • grid 2 may be of uniform or varying mesh. Uniform mesh is preferred for class C operation. Screens 3 and 5 are preferably of fine mesh.
  • the voltages on grid 4, screen 5 and anode B are preferably chosen to hold the average anode current less than one-half the average screen current, or less than one-third the average cathode current, the cathode current being substantially the sum of the screen and anode currents. This relation provides that changes in anode current have a negligible effect on the performance of the oscillator circuit.
  • l 1 I l a 1.'A m'odulated radio-frequency transmitting system comprising a vacuum tube having an audio-frequency' input circuit and a carrier-frequency output circuit, said vacuum tube having a space-current path in which are included at leastv two grids, a first of said grids having a source of carrier-frequency voltage connected thereto, the second of said grids having said input circuit connected thereto, means including a non-uniform construction of said second grid for imparting to said-tube an approximately linear relationship between the voltage on said second grid and the mutual conductance from said first grid to said anode over a large range of voltages on said second grid, whereby distortionless modulation is efiected over a large range of modulation percentages, and means for coupling said output circuit to a radiating antenna,
  • a modulated radio-frequency transmitting system comprising a vacuum tube having an audio-frequency input circuit and a carrier-frequency output circuit, said vacuum tube having a space current path in which are included at least two grids, a first of said grids having a source of carrier-frequency voltage connected thereto, the second of said grids having said input circuit connected thereto, means including a non-uniform construction of said second grid for imparting to said tube an approximately linear relationship between the voltage on said second grid and the mutual conductance from said first grid to said anode over a large range of voltages on said second grid, whereby distortionless modulation is effected over a large range of modulation percentages, means including said first grid for imparting to said tube a linear relationship between said first grid voltage and space current, whereby distortionless amplification is effected, and means for coupling said output circuit to a radiating antenna.
  • an oscillator-modulator comprising a vacuum tube having a cathode, an anode and a first, second and third grid positioned in the space path successively from said cathode to said anode, an audio-frequency input circuit connected between said third grid and said cathode, an output circuit connected between said cathode and said anode, a tuned circuit connected to said cathode and coupled tosaid first and second grids for producing sustained radio-frequency oscillations, said third grid having a non-uniform mesh to provide an approximately linear relationship between'the voltage on said third grid and the mutual conductance from said first grid to said anode over a wide range of voltages on said third grid, whereby distortionless modulation is effected over a large range of modulation percentages, and means for coupling said output circuit to a radiating antenna.
  • an oscillator-modulator comprising a vacuum tube having a cathode, an anode and a first, second and third grid positioned in the space path successively from said cathode to said anode, an audio-frequency input circuit connected between said third grid and said cathode, an output circuit connected between said cathode and said anode, a.
  • tuned circuit connected to said cathode and coupled to said first and second grids for producing sustained radiofrequency oscillations, means including said'first grid for imparting to said tube :a linear relationship between grid bias and space current, whereby distortionless amplification is effected, means including a non-uniform construction of said third grid for imparting to said tube an approximately linear relationship between the voltage on said third grid and the mutual conductance from'said first grid to said anode overa large range of voltages on said third grid, whereby distortionless modulation is effected overa large range of modulation percentages, and means for coupling said output circuit to a radiating antenna.
  • a modulated radio-frequency transmitting system comprising a vacuum tube having an audio-frequency input circuit and a carrier-frequency output circuit, said vacuum tube having a space current path'in which are included at least two grids, a first of said grids having a source of carrier-frequency voltage connected thereto, the second of said'grids having said input circuit connected thereto and having a variable mesh for imparting to said tube an approximately linear relationship between the voltage on said second grid and the mutual conductance from said first grid to said anode over a large range of voltages on'said second grid, whereby distortionless modulation is effected over a large range of modulation percentages, and means for coupling said output circuit to a radiating antenna.

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US679997A 1933-07-12 1933-07-12 Oscillator-modulator system Expired - Lifetime US2278159A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE404162D BE404162A (enrdf_load_stackoverflow) 1933-07-12
US679997A US2278159A (en) 1933-07-12 1933-07-12 Oscillator-modulator system
FR775741D FR775741A (fr) 1933-07-12 1934-07-11 Dispositif de modulation
GB20377/34A GB426855A (en) 1933-07-12 1934-07-11 Modulation system for high frequency wireless transmission

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Application Number Priority Date Filing Date Title
US679997A US2278159A (en) 1933-07-12 1933-07-12 Oscillator-modulator system

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US2278159A true US2278159A (en) 1942-03-31

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US679997A Expired - Lifetime US2278159A (en) 1933-07-12 1933-07-12 Oscillator-modulator system

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US (1) US2278159A (enrdf_load_stackoverflow)
BE (1) BE404162A (enrdf_load_stackoverflow)
FR (1) FR775741A (enrdf_load_stackoverflow)
GB (1) GB426855A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2458830A (en) * 1945-05-23 1949-01-11 John F Byrne Modulation indicator
US2504469A (en) * 1945-11-14 1950-04-18 Telephone Mfg Co Ltd Valve modulator
US2521443A (en) * 1947-10-14 1950-09-05 Hartford Nat Bank & Trust Co Circuit for amplitude modulation
US2614247A (en) * 1947-12-26 1952-10-14 Fr Sadir Carpentier Soc Pulse modulating system
US2642530A (en) * 1948-04-03 1953-06-16 Honeywell Regulator Co Control apparatus

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2458830A (en) * 1945-05-23 1949-01-11 John F Byrne Modulation indicator
US2504469A (en) * 1945-11-14 1950-04-18 Telephone Mfg Co Ltd Valve modulator
US2521443A (en) * 1947-10-14 1950-09-05 Hartford Nat Bank & Trust Co Circuit for amplitude modulation
US2614247A (en) * 1947-12-26 1952-10-14 Fr Sadir Carpentier Soc Pulse modulating system
US2642530A (en) * 1948-04-03 1953-06-16 Honeywell Regulator Co Control apparatus

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GB426855A (en) 1935-04-10
FR775741A (fr) 1935-01-08
BE404162A (enrdf_load_stackoverflow)

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