US2215284A - Frequency modulation signaling system - Google Patents

Frequency modulation signaling system Download PDF

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Publication number
US2215284A
US2215284A US319569A US31956940A US2215284A US 2215284 A US2215284 A US 2215284A US 319569 A US319569 A US 319569A US 31956940 A US31956940 A US 31956940A US 2215284 A US2215284 A US 2215284A
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frequency
modulation
noise
distortion
frequencies
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US319569A
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English (en)
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Edwin H Armstrong
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Individual
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Individual
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Priority to BE472015D priority Critical patent/BE472015A/xx
Priority to US21660D priority patent/USRE21660E/en
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=23242802&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=US2215284(A) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
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Priority to US319569A priority patent/US2215284A/en
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Publication of US2215284A publication Critical patent/US2215284A/en
Priority to FR942970D priority patent/FR942970A/fr
Priority to ES177793A priority patent/ES177793A1/es
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B14/00—Transmission systems not characterised by the medium used for transmission
    • H04B14/002—Transmission systems not characterised by the medium used for transmission characterised by the use of a carrier modulation
    • H04B14/006—Angle modulation

Definitions

  • This invention relates to improvements in frequency modulation transmission systems in radio signaling. It has for its object the improvement of the signal to noise ratio and the ⁇ improvement of the quality of transmission. It is particularly useful for very high fidelity transmission of music.
  • the invention relates to the introduction of a distorting network at the transmitter and a restoring network at the receiver together with the 10 provision of certain detector characteristics in such manner as to produce a lgreat improvement in the quality of transmission.
  • Fig. 1 illustrates the general 1:, arrangement of the transmitter and Fig. 2 the general arrangement of the receiver.
  • Fig. 3 illustrates the arrangement of a predistorting network used at the transmitter and Fig. 4 a restoring or converse network.
  • Fig. 5 shows the electrical characteristics of these networks.
  • Fig. 10 illustrates the details of a modulating arrangement
  • Fig. 11
  • Figs. 12, 13, 14 and 15 illustrate some of the characteristic operations of the receiving system and Figs. 16 and 17 show a simplified form of the predistortion and restoring networks.
  • Fig. 1 which illustrates the ⁇ general arrangement of the transmitter
  • I represents the microphone
  • 2 the usual preamplifier
  • 3 the predistorter
  • 5 the modulator of a frequency modulation transmission system
  • 6 a series of frequency multipliers exciting a finalpower amplier stage 1 which in turn' feeds the radiating system 8.
  • the frequency modulation transmitter components 5, 8 and 1 maylbe of the type described in my U. S. Patent #1,941,068. l
  • I0 represents the receiving antenna, Il an amplifier for thereceived current, and I2, I3 and I4 the usual converter, oscillator and intermediate frequency amplifier of a superheterodyne receiver.
  • I5 represents a limiter for removing amplitude modulation, I6 a filter, and I1 an amplifier for the filter output.
  • , 23 are for the purpose of converting frequency changes into amplitude changes and the circuit is similar to that described in my U. S. Patent #1,941,069. 24,
  • the higher 'frequencies 23 and 23, 21 represent detectors arranged across each half of the circuit, and 3l represents a bal-- anced output transformer connecting into the restorer 3l the audio ampliiier 32 and the speaker or other translating device 33.
  • Fig. 3 and 4 The circuits of ⁇ the predistorter and restorer are illustrated respectively in Fig. 3 and 4. 'I'he transmission characteristics of these two networks are illustrated by curves A and B, respectively, in Fig. 5.
  • curve A the frequencies around 15,000 cycles are raised by the predistorter to some ten times the amplitude of the lowest frequencies, and in the restorer as shown by curve B these high frequencies are cut down an exactly similar amount so as to give an overall uniform transmission characteristic for transmitter and receiver.
  • Fig. 6 shows the envelope of modulation as it appears in an amplitude modulation system at the transmitter under normal circumstances
  • Fig. 7 shows the same characteristic as modiiied when predistortion is included in the transmission.
  • Fig. 8 illustrates the envelope of the current in the detecting system
  • Fig. 9 shows the current voltage curve of the ordinary detector
  • Fig. 10 shows the detailed circuit arrangement of the modulator 5 of Fig. 1, and Fig. 11 certain oi' its characteristics
  • Fig. 12 shows the characteristics of the networks I8, 20, 22 and I9, 2
  • Fig. 13 shows the characteristics of two networks having a somewhat different design.
  • Fig. 14 illustrates the comparative noise voltage distribution with respect to frequency in the detector systems of an amplitude and frequency modulation receiver, respectively
  • Fig. 15 shows the relative improvements which are obtained when the restorer is applied to the two systems.
  • vto Fig. 6 there is illustrated the envelope of the modulation of an amplitude modulated transmitter.
  • the curve shows the variation of the low frequency modulating voltage, the rather complex wave form indicating a deep low frequency modulation with a shallow modulation of higher frequency tones. It will be understood, of course, that this curve represents likewise the peak value of the radio frequency currents radiated. It is .essential in amthe particular plitude modulation in order to produce the best signal to noise ratio to operate the transmitter as nearly as possible at full modulation.
  • the gain of the modulation ampliiier is set so that the depth of the modulation approaches the zero line as closely as possible'without actually touching it. Points A AI in Fig. 6 illustrate this condition.
  • Fig. 8 shows the envelope of the radio frequency current in the rectier or detector circuit. It will be observed from observation of the points C and C1 that two forms of distortion may occur. One is that due to the lack of linearity of the detector characteristic as shown in Fig. 9, and the .other is actual destruction of the form of the fine ripples by cross modulation with the noise components., The last form may be very bad indeed.
  • the predistortion method to amplitude modulation it becomes necessary, therefore, to reduce the percentage modulation at the transmitter to prevent distortion. This results in a rise in the noise level so that the net theoretical gain of the system is substantially reduced.
  • Figs. 10 and l1 show how the distortion due to lack of linearity in the characteristics of the tubes used for modulating may be avoided.
  • Fig. 10 shows a general form of phase shifter which may be used. represents the source of exciting current which is applied to the grid of the carrier amplifier 36 and to the tuned circuit 38 through a phase adjusting network 31, so arranged that the E. M. F.s applied to the grids of 39 and 40 are 90 out of phase from the E. M. F. applied to the grid of 36.
  • the circuit 33 excites the grids of the balanced modulator 39, '40 differentially so that there is no output when no modulation is applied.
  • the screen voltage is modulated by means f the transformer 4l, the voltage being applied differentially so as to unbalance the modulator.
  • Fig. 1l which shows the relation between the screen voltage and the radio frequency voltage output
  • the normal voltage applied to the screens by the battery D to be O A change in the voltage of the screens will/according to the invention described in thq: #1,941,068 patent, add a voltage NS or NT at 90 phase displacement to the output voltage MN of the tube 36.
  • the maximum required is about of the voltage MN to give the shift. Therefore, by properly designing the relative amplications of the tubes 36 and 39, 40it is possible to produce unbalanced voltages of such maximum usable phase distortion due to lack of tube linearity is, en-
  • a. balanced detector system as shown in Fig.
  • the reactance characteristics of the two detector branches are shown, respectively, in Fig. 12 arranged to produce 100% modulation over the range Fi-Fz. It will be observed that one branch is arranged to be non-reactive at F1 and the other to be non-reactive at F2, the extremes of the frequency swing. In this way the changes in frequency are converted completely into changes in amplitude.
  • Figs. 16 and l? show farms of networks which produce substantially the same characteristics as those shown in Figs. 3 and 4. In the predistorter while'a relatively large range of values may be chosen from, I find the following set to be pracf tical and inexpensive.
  • the capacity 44 has a value of .001 'nui'.”rofared the resistance l5 is '15,000 ohms.
  • the input resistance 46 should be 300 ohms and the output resistance 41 should be 30007ohms.
  • 48 represents the detector output impedance and may be of the order of 100,000 ohms.
  • 49 is a resistance of 50,- 000 ohms and 50 a capacity of .001 microfarad.
  • the volume control potentiometer 5I should have sists in amplifying'the high frequencies of the band to a substantially greater degree than the low frequencies thereof, varying the frequency of plitude are minimized, and amplifying the lowy frequency currents of said band to a substantially greaterdegree than the high frequency currents thereof.
  • a detectingdevicecoupled to said converting means 10 mized means arranged to amplify the high frequency currents of the band to a substantially greater degree than the low frequency currents thereof, means for generating a carrier wave of substantially constant frequency, means Vfor causing the amplified currents to vary over a wide range the frequency of the carrier wave, means for transmitting such wave, means for receiving the wave and amplifying the received currents, means coupled to said last-named means for converting the frequency variations into a. band of currents of variable amplitude and having 'an admittance band width substantially greater than the width of the said wide' range of carrier frequencies, a detectingdevicecoupled to said converting means 10 mized.
  • the means for converting the frequency variations into currens of variable ampliiudr ⁇ comprises two parallelpatilsyone of said paths including a. circuit, having a resonant frequency lower than the lowest frequency oi the transmitted band of frequencies and the other of said paths including a circuit havingv a resonant, fxe- Y quency higher than the highest,

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Transmitters (AREA)
US319569A 1940-02-19 1940-02-19 Frequency modulation signaling system Expired - Lifetime US2215284A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BE472015D BE472015A (en)van) 1940-02-19
US21660D USRE21660E (en) 1940-02-19 Frequency modulation signaling
US319569A US2215284A (en) 1940-02-19 1940-02-19 Frequency modulation signaling system
FR942970D FR942970A (fr) 1940-02-19 1947-03-10 Installation de radio-diffusion de signaux modulés en fréquence
ES177793A ES177793A1 (es) 1940-02-19 1947-04-28 Un procedimiento de reproducir las frecuencias de señales de una onda modulada en frecuencia

Applications Claiming Priority (1)

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US319569A US2215284A (en) 1940-02-19 1940-02-19 Frequency modulation signaling system

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US2215284A true US2215284A (en) 1940-09-17

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US21660D Expired USRE21660E (en) 1940-02-19 Frequency modulation signaling
US319569A Expired - Lifetime US2215284A (en) 1940-02-19 1940-02-19 Frequency modulation signaling system

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Application Number Title Priority Date Filing Date
US21660D Expired USRE21660E (en) 1940-02-19 Frequency modulation signaling

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BE (1) BE472015A (en)van)
ES (1) ES177793A1 (en)van)
FR (1) FR942970A (en)van)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2433093A (en) * 1943-04-27 1947-12-23 Rca Corp Amplitude modulation adapter system
US2489313A (en) * 1947-03-08 1949-11-29 Int Standard Electric Corp Frequency modulation discriminator
US2972046A (en) * 1957-08-30 1961-02-14 Research Corp Bandwidth modulation information transfer system
US3311827A (en) * 1961-07-20 1967-03-28 Philips Corp Transmission equipment for the transmission of signals by modulated oscillations of constant amplitude
DE1292202B (de) * 1965-04-16 1969-04-10 Nippon Electric Co Verfahren und Schaltungsanordnung zur frequenz- oder phasenmodulierten Nachrichtenuebertragung
US5729828A (en) * 1989-10-02 1998-03-17 Canon Kabushiki Kaisha Frequency processing circuit with lower sideband suppression and emphasis

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2585605A (en) * 1946-11-12 1952-02-12 Wallace Navigational system
BE489677A (en)van) * 1948-06-19
US2617923A (en) * 1949-08-31 1952-11-11 Kxok Inc Radio broadcasting system with selective program elimination
US4053834A (en) 1973-04-12 1977-10-11 Textron, Inc. Narrowband phase modulation communication system which eliminates thresholding

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2433093A (en) * 1943-04-27 1947-12-23 Rca Corp Amplitude modulation adapter system
US2489313A (en) * 1947-03-08 1949-11-29 Int Standard Electric Corp Frequency modulation discriminator
US2972046A (en) * 1957-08-30 1961-02-14 Research Corp Bandwidth modulation information transfer system
US3311827A (en) * 1961-07-20 1967-03-28 Philips Corp Transmission equipment for the transmission of signals by modulated oscillations of constant amplitude
DE1292202B (de) * 1965-04-16 1969-04-10 Nippon Electric Co Verfahren und Schaltungsanordnung zur frequenz- oder phasenmodulierten Nachrichtenuebertragung
US5729828A (en) * 1989-10-02 1998-03-17 Canon Kabushiki Kaisha Frequency processing circuit with lower sideband suppression and emphasis

Also Published As

Publication number Publication date
ES177793A1 (es) 1947-07-16
FR942970A (fr) 1949-02-23
BE472015A (en)van)
USRE21660E (en) 1940-12-17

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