US2170202A - Receiver for frequency-modulated waves - Google Patents

Receiver for frequency-modulated waves Download PDF

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Publication number
US2170202A
US2170202A US250520A US25052039A US2170202A US 2170202 A US2170202 A US 2170202A US 250520 A US250520 A US 250520A US 25052039 A US25052039 A US 25052039A US 2170202 A US2170202 A US 2170202A
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Prior art keywords
frequency
receiver
resonance
resonance curve
width
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Expired - Lifetime
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US250520A
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English (en)
Inventor
Kupfmuller Karl
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Fides Gesellschaft fuer die Verwaltung und Verwertung von Gewerblichen Schutzrechten mbH
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Fides Gesellschaft fuer die Verwaltung und Verwertung von Gewerblichen Schutzrechten mbH
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F21/00—Variable inductances or transformers of the signal type
    • H01F21/02—Variable inductances or transformers of the signal type continuously variable, e.g. variometers
    • H01F21/08—Variable inductances or transformers of the signal type continuously variable, e.g. variometers by varying the permeability of the core, e.g. by varying magnetic bias
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
    • H03D3/001—Details of arrangements applicable to more than one type of frequency demodulator
    • H03D3/003—Arrangements for reducing frequency deviation, e.g. by negative frequency feedback
    • H03D3/005—Arrangements for reducing frequency deviation, e.g. by negative frequency feedback wherein the demodulated signal is used for controlling a bandpass filter

Definitions

  • one slope of the resonance curve is used for demodulation, with the result that the frequency variations are reconverted into amplitude modulations, the current after rectification or detection resulting in the AF modulation.
  • the Width of the slope of the resonance curve must at least be equal to the aggregate frequency variation; for this reason, also the width of the resonance curve measured between the two half values, must be at least equal to this frequency range.
  • the present invention is predicated upon this fact that the noise level due to (tube) noises of the receiver is a function of the width of the resonance curve. It is known that the noise voltage of a receiver which permits of the constant transmission of a frequency band having width A is proportional to /Af.'
  • This noise may be considered as consisting of beat frequencies between noise voltages lying within the radio-frequency acceptance band.
  • beat frequencies may be passed by the audio-frequency system. It is easily seen that, in general, the total noise at the receiver output will be greater as the radiofrequency and audio-frequency pass bands are larger, the first because more noise components are admitted, and the second because a wider range of beat frequencies can pass the audiofrequency system.
  • the radio-frequency band passed by the receiver filter is narrower than the audio-frequency band
  • the highest beat frequency that can be formed between components that pass the radio-frequency filter is equal to the radio-frequency band width, so that it would make no difierenceif the audio-frequency band were much larger.
  • the radiofrequency acceptance band is narrower than the audio-frequency band we have the situation that the total noise depends only on the radio-frequency band Width.
  • a receiver of lower noise voltage level applicable to frequency.- modulated waves is created in that the width of the receiver filter is small compared with the aggregate frequency variation, while an unequivocal relationship between the output potential or current and frequency is established by a feedback.
  • the noise voltage is lessened.
  • the use thereof becomes possible only by virtue of the feedback since with a narrow resonance curve the existing frequency range would be, in contrast,.say, 300 kc.
  • the resonance frequency of the receiver circuit By regenerating, for instance, part of the rectifier output, the resonance frequency of the receiver circuit could be re-set as a function of the output potential or current in the same sense as the incoming frequency. Re-setting of the frequency, in superheterodyne receivers could also be effected by-controlling'the resonance curve of the IF from the rectifier output in accordance with the frequency variation of the transmitter so that as the frequency increases, there is an increase in the resonance frequency of the oscillatory circuit or circuits in the I. F. section, and vice versa.
  • Figure 1 is a resonance curve of a frequency modulated wave receiver using circuits covering a considerable band of frequencies.
  • Figure 2 is the resonance curve of a frequency modulated receiver in which by the use of my invention the resonance characteristic has been narrowed, while;
  • Figure 3 illustrates a receiver arranged in accordance with my invention and includes means for shifting the point of operation of the receiver up and down the sharp resonance characteristic thereof.
  • Fig. 1 indicates the resonance curve of a receiver designed for frequency-modulated waves.
  • the frequency range F extends from )i to f2.
  • For demodulation is used the slope of the resonance curve between f1 and f2.
  • the operating point P shifts, as will be seen, along the slope of the resonance curve between f1 and f2.
  • Fig. 2 by way of example shows a narrow resonance curve B of the receiver, that is, a curve as used according to the disclosure with a view of securing a low noise voltage.
  • the resonance curve B is plotted for a frequency fx lying between f1 and f2.
  • the operation point. P shifts along the working characteristic B, shown by broken lines, across the family of resonance curves rather than along the slope of the resonance curve properly so-called. This shift of the resonance curve occurs at AF rate; hence, the building-up periods can be kept sufiiciently small.
  • the principle hereinbefore described may be carried into practice by shifting the resonance curve, for instance, by causing the rectified current to alter the biasing magnetization (magnetic bias) and thereby the inductance of the oscillatory circuit in a way as illustrated in Fig. 3.
  • Fig. 3 illustrates a conventional type of heterodyne receiver for frequency-modulated waves in which the object of the present invention has been incorporated by shifting the resonance curve of the I. F.
  • the output of the oscillator O and of the antennae are fed to the mixer tube MR.
  • the rectifier G1 and the AF stage NFV After the mixing stage follows an I. F. stage ZV, the rectifier G1 and the AF stage NFV.
  • the rectifier G1 has in its output circuit a. resistance R1 in which a potential is produced by rectification of the amplitude variations on the intermediate-frequency energy passed by circuits I and 2. These amplitude variations are produced due to the sloping characteristics of the circuits and correspond to frequency variations on the received wave.
  • the oscillatory circuit l comprising inductance L1 and condenser C1 and the oscillatory circuit 2 comprising inductanc L2 and condenser C2 according to this invention have a narrow resonance curve.
  • the resonance curve of the oscillatory circuits is shifted by tapping developed in said impedance.
  • the circuit containing the coils causing a change in-the bias may also include a biasing or polarizing voltage battery B2.
  • a frequency modulated wave receiver means for heterodyning a frequency modulated wave to a lower frequency, an intermediate frequency amplifier of a relatively narrow band width coup-led to said first means, detecting means coupled to said amplifier and means controlled by potentials derived from said detectin means for varying the mean frequency of response of said intermediate frequency amplifier in accordance with potentials derived from said detecting means.
  • the method of demodulating frequency modulated wave energy and reducing noise components in the demodulated output which includes the steps of amplifying said frequency modulated wave energy in an amplifier having a relatively narrow band width, and varying the position of said band width in the frequency spectrum in accordance with frequency modulations on said Wave energy.
  • a frequency modulated wave receiver means for heterodyning a frequency modulated wave to wave energy of lower frequency, an electron discharge tube amplifier having input and output circuits, said circuits having a resonance characteristic of a width less than the Width of said frequency modulated wave of lower frequency, means for impressing said Wave energy of lower frequency on said input circuit, a rectifier having an input coupled to said output circuit said rectifier having an output including an impedance wherein potentials characteristic of the frequency modulations on the wave are developed, and means coupled to said impedance and associated with said input and output circuits for varying the tuning of said circuits in accordance with the amplitude of the potentials KARL

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Noise Elimination (AREA)
  • Circuits Of Receivers In General (AREA)
US250520A 1938-01-04 1939-01-12 Receiver for frequency-modulated waves Expired - Lifetime US2170202A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DES130252D DE723384C (de) 1938-01-04 1938-01-04 Empfaenger fuer frequenzmodulierte Wellen

Publications (1)

Publication Number Publication Date
US2170202A true US2170202A (en) 1939-08-22

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ID=7988379

Family Applications (1)

Application Number Title Priority Date Filing Date
US250520A Expired - Lifetime US2170202A (en) 1938-01-04 1939-01-12 Receiver for frequency-modulated waves

Country Status (4)

Country Link
US (1) US2170202A (enrdf_load_stackoverflow)
DE (1) DE723384C (enrdf_load_stackoverflow)
FR (1) FR848415A (enrdf_load_stackoverflow)
GB (1) GB503907A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2488612A (en) * 1940-03-09 1949-11-22 Rca Corp Frequency modulation reception
US2540643A (en) * 1940-01-12 1951-02-06 Edwin H Armstrong Frequency-modulated carrier signal receiver
US2812510A (en) * 1952-06-25 1957-11-05 Elmer H Schulz Frequency modulation system
US2939951A (en) * 1957-11-04 1960-06-07 Paul L Schaffer Conversion of amplitude to phase modulation by means of crystal to reduce noise

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2540643A (en) * 1940-01-12 1951-02-06 Edwin H Armstrong Frequency-modulated carrier signal receiver
US2488612A (en) * 1940-03-09 1949-11-22 Rca Corp Frequency modulation reception
US2812510A (en) * 1952-06-25 1957-11-05 Elmer H Schulz Frequency modulation system
US2939951A (en) * 1957-11-04 1960-06-07 Paul L Schaffer Conversion of amplitude to phase modulation by means of crystal to reduce noise

Also Published As

Publication number Publication date
FR848415A (fr) 1939-10-30
DE723384C (de) 1942-08-04
GB503907A (enrdf_load_stackoverflow) 1939-04-17

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