US2372231A - Frequency modulation system - Google Patents

Frequency modulation system Download PDF

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Publication number
US2372231A
US2372231A US434098A US43409842A US2372231A US 2372231 A US2372231 A US 2372231A US 434098 A US434098 A US 434098A US 43409842 A US43409842 A US 43409842A US 2372231 A US2372231 A US 2372231A
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United States
Prior art keywords
condenser
frequency
plates
voltage
capacity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US434098A
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English (en)
Inventor
Frederick E Terman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
International Standard Electric Corp
Original Assignee
International Standard Electric Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by International Standard Electric Corp filed Critical International Standard Electric Corp
Priority to US434098A priority Critical patent/US2372231A/en
Application granted granted Critical
Publication of US2372231A publication Critical patent/US2372231A/en
Priority to FR941200D priority patent/FR941200A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/10—Angle modulation by means of variable impedance
    • H03C3/12—Angle modulation by means of variable impedance by means of a variable reactive element
    • H03C3/20—Angle modulation by means of variable impedance by means of a variable reactive element the element being a voltage-dependent capacitor

Definitions

  • the object of the invention is to produce large frequency swings and to operate at relatively high power levels.
  • a capacity is incorporated as part of the resonant circuit of an oscillator.
  • the spacing between plates of the capacity is varied in accordance with the audio signal that isvto be modulated upon the transmitter wave.
  • the entire condenser system is enclosed in a high vacuum, whereby high radiofrequency voltages may be applied between the relatively closely spaced plates.
  • Fig. 1 is a diagrammatic illustration of the invention and Fig. 2 is a cross section of a modification of the condenser system shown in Fig. 1.
  • Fig. -1 shows a conventional Hartley oscillator in which the tuning capacity is provided by the capacity of the special frequency-modulating condenser I. It consists of two membranes or plates 2, 2 (preferably of Duralumin) mounted on stretching rings 3, 3 of conducting material, and held at a conveniently small distance apart by insulating spacers 4, 4'. The rings and spacers 3, 4 and 3', 4' are held within metal sleeves 5, 5, and have a suitable rigid mounting structure (not shown) within an evacuated glass envelope 5.
  • a large D. C. polarizing voltage of several thousand volts such as 5,000 to 20,000 volts is applied between the plates from a suitable source, over secondary winding Iof an iron core transformer 8, conductor 9, sleeve 5, ring 3, plate 2, ring 3', sleeve 5', ring 3, plate 2, ring 3, sleeve 5. conductor l0, inductance II, and ground. Audio modulating voltage is superimposed upon this polarizing voltage from a suitable source over primary winding l2 of transformer 8, so that the total of D. C. plus modulating voltage between plates 2, 2' varies in accordance with the desired modulation envelope. This modulating voltage should be as large as possible, but must never have a peak amplitude exceeding the polarizing voltage.
  • a blocking and a radio frequency bypass condenser I6 is a radio frequency choke and i1 is a B battery.
  • the deflection of the condenser plates must be independent of the modulating frequency. This can be achieved by stretching the membranes 2, 2 so that their resonant frequency approximates the highest frequency that is to be modulated upon the system. At frequencies appreciably below this resonance, the amplitude of vibration will be proportional to the applied force (1. e., to the modulating voltage) and independent of frequency. At the resonant frequency one can prevent excessive response either by an electrical equalizing'network in the audio system, or by providin some form of damping so that the response at resonance will be approximately the same as the response at frequencies below reso nance. This latter result can be obtained by the appropriate use of rubber or other material capable of damping mechanical vibration.
  • the ratio of frequency swing to carrier frequency will be equal to half the ratio of capacity variation in the frequency-modulating condenser to the total capacity of the resonant circuit. For large frequency swings one should therefore keep the total circuit capacity at a minimum and the capacity variations large. This can be accomplished by utilizing the frequency-modulating condenser to supply all of the tuning capacitance of the circuit.
  • a balanced armature 20 is positioned between pole pieces 2
  • a coil .23 to which the voice currents are applied is seated within pole pieces 2
  • the condenser plates are 24 and 24, the former being mechanically linked with armature 20 as indicated at 25 to translate the vibration thereof into capacity variations.
  • the assembly is enclosed in a highly evacuated envelope 26.
  • a frequency modulation system comprising an oscillation generator,
  • variable condenser forming a part of the oscillating circuit thereof, said condenser having two condenser plates only.
  • At least one of said plates being flexible, means for applying a high direct current voltage directly between said condenser plates so as to exert a unilateral force therebetween andmaintain said flexible plate under tension, and means for superposing a variable signal voltage on said direct current voltage.
  • a frequency modulation system comprising a pair of condenser membranes, means for stretching said membranes to tune them to resonance at a frequency corresponding to the highest frequency of the band of signal frequencies to be transmitted, an evacuated envelope for enclosing said membranes, means for apply g a band of signal frequencies across said membranes and filter means for attenuating the highest frequencies of said band to prevent said membranes from resonating at said highest frequencies.
  • a condenser having two I flexible plates, a device for stretching said plates and holding them apart a small distance, an evacuated envelope enclosing said condenser, a source of D. C. polarizing voltage for said condenser, and a modulating voltage superimposed on the polarizing voltage.
  • an oscillator having a resonant circuit including a condenser, two flexible plates for said condenser, stretched so that their resonant, frequency approximates the highest modulating frequency, an evacuated envelope enclosing said condenser, a source of D. C. polarizing voltage applied to one of said plates, and an connection from said source to one of said plates. and an audio-frequency modulating voltage having a peak amplitude below the polarizing voltage applied to the primary of said transformer.
  • a modulation system comprising a condenser including two flexible condenserplates, a mounting circumferentially engaging the plates and maintaining them under tension in slightly spaced juxtaposed position, means for applying .a direct current polarizing voltage between said plates, and means for superposing a modulatin voltage on the polarizing voltage, arranged to flex the plates variably in accordance with variations in the modulating voltage, thereby varying the condenser capacity.
  • a modulation system comprising an oscillator having a resonant circuit including a condenser, said condenser including two flexible metal condenser plates and means for holding said plates under tension and slightly spaced, means for applying a high direct current polarizing voltage of the order of several thousand volts across said plates, an iron core transformer having a secondary winding connected to one of said plates and carrying said polarizing voltage, and,
  • a frequency modulation system comprising an oscillation generator, a source of audio frequency signals, a condenserincluding a pair of juxtaposed flexible condenser plates forming a part of the oscillating circuit of said generator,
  • a frequency modulation system comprising 40 a pair of capacitatively associated condenser plate membranes, means for tensioning said membranes and thereby tuning both membranes to resonance at a frequency corresponding to the highest frequency of the band of signal frequencies to be transmitted, means for applying said band of signal frequencies across said plate membranes, and filter means for attenuating the highest frequencies of said band and thereby preventing said plate membranes from resonating at said highest frequencies.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplitude Modulation (AREA)
US434098A 1942-03-10 1942-03-10 Frequency modulation system Expired - Lifetime US2372231A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US434098A US2372231A (en) 1942-03-10 1942-03-10 Frequency modulation system
FR941200D FR941200A (fr) 1942-03-10 1946-03-27 Système de modulation de fréquence

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US434098A US2372231A (en) 1942-03-10 1942-03-10 Frequency modulation system

Publications (1)

Publication Number Publication Date
US2372231A true US2372231A (en) 1945-03-27

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ID=23722822

Family Applications (1)

Application Number Title Priority Date Filing Date
US434098A Expired - Lifetime US2372231A (en) 1942-03-10 1942-03-10 Frequency modulation system

Country Status (2)

Country Link
US (1) US2372231A (fr)
FR (1) FR941200A (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2543042A (en) * 1945-05-07 1951-02-27 Standard Telephones Cables Ltd Tuning means for coaxial line conductors
US2744222A (en) * 1952-03-24 1956-05-01 Beckman Instruments Inc Dynamic capacitor
US2755419A (en) * 1953-06-12 1956-07-17 Hans E Hollmann Electromechanical nonlinear capacitor
US2830240A (en) * 1954-09-23 1958-04-08 Hoffman Electronics Corp Electromagnetically controlled capacitors or the like
US2921186A (en) * 1954-06-10 1960-01-12 Polarad Electronics Corp Means for generating a voltage linearly proportional to frequency
US3015764A (en) * 1958-07-31 1962-01-02 George V Young Vacuum chopper system
DE1121219B (de) * 1958-01-02 1962-01-04 Siemens Ag Schwingkondensator

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2543042A (en) * 1945-05-07 1951-02-27 Standard Telephones Cables Ltd Tuning means for coaxial line conductors
US2744222A (en) * 1952-03-24 1956-05-01 Beckman Instruments Inc Dynamic capacitor
US2755419A (en) * 1953-06-12 1956-07-17 Hans E Hollmann Electromechanical nonlinear capacitor
US2921186A (en) * 1954-06-10 1960-01-12 Polarad Electronics Corp Means for generating a voltage linearly proportional to frequency
US2830240A (en) * 1954-09-23 1958-04-08 Hoffman Electronics Corp Electromagnetically controlled capacitors or the like
DE1121219B (de) * 1958-01-02 1962-01-04 Siemens Ag Schwingkondensator
US3015764A (en) * 1958-07-31 1962-01-02 George V Young Vacuum chopper system

Also Published As

Publication number Publication date
FR941200A (fr) 1949-01-04

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