US1896268A - Modulator system - Google Patents

Description

Patented Feb. 7, 1933 UNITED STATES" JOHN AQWILIQOUGHBY, or CAMBRIDGE, MASSACHUSETTS MODULATOR SYSTEM Application filed December 18 1928. Serial No, 326,880.

My invention relates to modulator systems 1n general and more specifically to modulator systems employed in high frequency signalmg V 5 object of my invention isto provide a combination oscillator and modulator system wherein a single thermionic tube is employed. Another object of my invention is to provide a combination oscillator and modulator system wherein the'frequency of the oscillatory circuit is substantially uniform irrespective of modulation.

Still another object of my'invention is to 7 provide a single thermionic tube having associated circuits for the generation and modulation of high frequency electrical energy. Other and further objects of my invention reside in the circuit arrangements I employ, a better understanding of which can be had by referring to the specification following and to the accompanying drawing which is a schematic circuit diagram showing the modulator system of my invention.

In high frequency signaling systems and especially in high frequency signaling systems wherein programs of speech and music are broadcast it is necessary that the modulating system be of the proper design to faithfullyand adequately modulate the carrier energy. The generally employed methods for modulating the carrier energy :are well known to those experienced in the art. A lower frequency is superimposed upon the higher frequency and produces side bands. As an illustration, the carrier energy may have a frequency of 500 kilocycles. The side bands of modulation will be generally or minus a given frequency band of this500 kilocycle frequency.- This is generally accomplished by controlling the input energy to the thermionic tube generator in accordance with the lower or audio frequency. Subsequent amplifiers or precedent modulators and amplifiers usually destroy or distort some of the desired audio frequency varia tions of'e'lectrical energy and hence the received energy is not a like representation of the original audio frequency variations. This is generally referred" to as cutting off certain desirable frequencies which should connected with a with ammeter 13. Chok plus but do not modulate the carrierenergy. The modulator system ofmy invention avoids many disadvantages of other systems and provides a means for efliciently and effectively modulating the carrier energy in strict accordance-with the audio frequency energy.

he accompanyingdrawing is a schematic circuit diagramshowing the modulator system of my invention. Thermionic tube 1 is of the type having a cathode 2, inner. grid 59 electrode3, anode 4 and outer vgriolelectrode 5. v In the circuit here described, the inner grid 3;may be referred to as the control grid electrode, and outer grid 5 may be referred to as the auxiliary grid electrode. Cathode 2 is energizedby transformerfi and the latter is source of alternating current. A positive potential is applied to anode 4 from source 7; A potential of suitable value and polarity is pply to control grid 3 a potential negative with respect to cathode 2 which will be suitable for operation in many cases, A mechanically 7'5 vibratile element '9 is connected to control electrode 3' and cathode 2. Mechanically vibratile element may comprise a quartzor other crystal having piezoelectric properties or may be any suitable frequency stabilizing means. Anode 4 isassociated. withji-nductance 11 by means of capacity 10. "The latter prevents the shortcircuiting of source 7. Inductance 11 is shunted by capacity 12inseries V e coils I5, 16,, ,18 and 19 are adapted to exclude high frequency energy from sources 8, and-transformer B. A connection 20 from the electrical center of the secondary of transformer 6, provides a common return path to cathode 2. Auxiliary electrode 5' is connectedto the common return circuit of cathode2 through winding 21 of transformer22 and in series with the independent source of energy 26. There is thus applied to auxiliary grid 5, a potential which will usually be positive with respect 'to the cathode, 'in operation. Asou-rc'e of energy 23 is connected in series with microphone art-and winding 25 of transformer 22. Microphone 24 may be replaced by any source-of current applied to inner grid 3 from 770 source 8. 'As sown in the drawing, source 8 may conveniently be connected to a variations or a variable resistor such as a photoelectric cell.

In an operation the electrons emitted by cathode 2 are attracted to anode 1. This force of attraction is not perfect however and a space charge immediately adjacent to anode l exists. 'Auxiliary electrode!) is placed in this position and exerts a predominate infiuence upon the space charge. Control electrode 3 functions in the usual manner and constitutes a part of the capacity for feeding back the energy from the anode circuit. The oscillations of energy are sustained by element 9 when the energy fed back from the anode or output circuit is of a frequency approximately corresponding-to the frequency characteristics of element 9or a multiple frequency thereof. Variations in the resistance of microphone 24 cause variations of the current in Winding 25, which variations cause variations of potential in winding 21. Variations of potential in winding 21 cause variations of' potential supplied auxiliary electrode 5'. The potential of electrode 5 exerts a marked influence on the electronic stream, increasing ordecreasing the number of electrons reaching anode fl in accordance with variations of the potential. Variations of the electronic stream between cathode 2 and anode l effect like variations of current in the output circuit tube'l. The percentage of the carrier subjected to modulation may be easily regulated. A relatively low current is ordinarily present in the circuit including auxiliary electrode 5 and the common connection to cathode 2. This; relatively low current is especially desired and makes possible the complete control of the carrier in accordance with the low frequency variations. v lMany modifications of my invention are possible without departing from the spirit of my invention. Succeeding amplifiers may be associated with the output circuit and caused to amplify theenergy before the same is'radiated or transmitted over a wired radio circuit. The modulator system of my inven- "tionconstitutes an eiiicient master oscillator for exciting additional amplifiers. Because of the small amount of current in the auxiliary electrode circuitthe output energy of a thermionic tube of high power may be easily andcompletely modulated. Mechanically vibratile element 9 may be of any suitable design adapted to sustain oscillations and havinga capacity to withstand the'value of energy to which it is subjected.

While I have shown a piezo electric crystal element in the circuit arrangementof my 11 1:: be understood that vention, I desire that it this element may be replaced by a mechanical oscillator composed ,of metal or alloys such as nickel, and other metals which when influenced by alternating current will exhibit 'lations, an'independent source of outer gri or anode circuit of thermionic P such manner that a negative cathode, a .piezo electric crystalelement connected in the other determined frequency,

magneto strictive properties which in turn will hold the frequency constant.

I realize that many modifications of the modulator system of my invention are possible wherein the oscillator and modulator are combined in a single thermionic tube and it is to be-understood that the embodiments of my invention are not to be limited to the specificarrangement shown in the accompanying drawing and described in the foregoing specification but only as defined by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

-' 1. In an electron tube modulatingzand generating system, an electron tube having cathode, anode, inner grid and outer grid, independent circuits connecting said inner gri to said cathode, one of said circuits forming a path forhigh frequency'oscillationls, another of saidcircuits forming a path for direct current biasing potential, an electromechanical vibratordisposedin said first mentioned circuit, an output circuit comprising a source of positive anode potential connected between said anode and said cathode, an input transformer having its primary connected .to a source of voice-frequency oscilotential, said outer grid being connected to said cathode through the secondary of said transformer and said source oflouter grid potential connected in series in such manner that a positive vpotential'is applied to said outer grid withqrespectto, said cathode. 2

2. In an electron'tub'e modulating and generating system, an electron tube having cathode, anode, inner grid and outer grid, a pair of circuits interconnecting-- said cathode and 1 inner grid, asource of inner grid biasing potential connected in one of said circuits in bias is applied to said inner grid with reference to said of, said circuits for sustaining oscillations in said system at aprean output circuit comprisinga source of positive anode potential connected between said anodeand said cathode, an input transformer having its primary connected to a source ofvoice-frequencyoscillations, an, independent source of outer grid potential, said outer grid being connected to saidcathodethrough the secondary of said transformer and said source of outer grid potential connected 9111 series in such manner that a positive potential is applied to said outer grid wi h respect to'said cathode. i I

3. In an'electrontube modulating and gen- ,eratingsystem, anelectron tube having cathode, anode, inner, grid and outer grid, a pair of branch circuitsconnecting' sald lnner grid to saidcathode, ;a frequencyfcontrol element connected between said inner grid and said cathode, in one of said branch circuits, a source of biasing potential for said inner grid connected in the other of said branch circuits an output circuit comprising a source of positive anode potential connected between said anode and said cathode, an input transformer having its primary connected to a source of voice-frequency oscillations, an

independent source of outer grid potential,

said outer grid being connected to said cathode through the secondary of said transformer and said source of outer grid potential connected in series in such manner that a positive potential is applied to said outer grid with respect to said cathode.

4. In an electron tube modulating and generating system, an electron tube having cat-hode, anode, inner grid and outer grid, a source of inner grid biasing potential connected between said inner grid and said cathode in such manner that a negative bias is applied to said inner grid with reference to said cathode, a piezo electric crystal element connected between said inner grid and said cathode and in parallel with said source of inner grid biasing potential, an output circuit comprising a source of positive anode potential connected between said anode and said cathode,

an input transformer having its primary connected to a source of voice-frequency oscillations, an independent source of outer grid potential, said outer grid being connected to said cathode through the secondary of said transformer and said source of outer grid potential connected in series in such manner that a positive potential is applied to said outer grid with respect to said cathode.

In testimony whereof I aflix my signature.

JOHN A. WILLOUGHBY.

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