US2341937A - Radio receiver - Google Patents

Radio receiver Download PDF

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Publication number
US2341937A
US2341937A US448881A US44888142A US2341937A US 2341937 A US2341937 A US 2341937A US 448881 A US448881 A US 448881A US 44888142 A US44888142 A US 44888142A US 2341937 A US2341937 A US 2341937A
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US
United States
Prior art keywords
waves
frequency
diode
limiter
circuit
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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
US448881A
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English (en)
Inventor
John E Maynard
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General Electric Co
Original Assignee
General Electric Co
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Filing date
Publication date
Priority to BE477489D priority Critical patent/BE477489A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US448881A priority patent/US2341937A/en
Application granted granted Critical
Publication of US2341937A publication Critical patent/US2341937A/en
Priority to FR938808D priority patent/FR938808A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D5/00—Circuits for demodulating amplitude-modulated or angle-modulated oscillations at will

Definitions

  • My invention relates to carrier wave receivers and more particularly to such receivers adapted for reception'of both frequency modulated and amplitude modulated signals in which a stage utilized as a limiter when receiving a frequency modulated signal is used-as a source of voltage the variations of which may be utilized for automatic volume control lpurposes when an amplitude modulated signal is received.
  • l* has for one of its objects to provide a limiter circuit for such a receiver which is capable of acting on weak signals.
  • a further object of myinvention is to provide a diode type of limiter fora radio receiver which sharply limits the intensities of frequencyv modulated carrier waves without loading the following circuits of the receiver and which may be easily adapted, by means of switching in the direct current circuits of the diode whenv the receiver is employed for th'e reception of amplitude modulated carrier waves, to provide a continuous potential for automatic volume control purposes.
  • Fig. 1 represents a receiver for frequency modulated carrier Waves embodying my invention
  • Fig. 2 represents a receiver for both frequency modulated and amplitude modulated carrier waves embodying my invention
  • Fig. 3 represents a modification of the receiver of Fig. 2.
  • high frequency carrier Waves are supplied to th'e amplifier" l, either directly from a receiving antenna-,or through a channel such as a radio frequency amplier.
  • th'e amplifier l
  • a channel such as a radio frequency amplier.
  • a radio frequency amplier In the usual form of super-heterodyne receiving apparatus they are carrier waves having the inter- He'nce it is v mediate frequency of the receiver and may be supplied from a preceding intermediate frequency amplifier.
  • the high frequency carrier waves are subjected to amplitude limitation in the limiter circuit 2. They are then demodulated in a detector and discriminator 3 and the demodulated signals, which areordinarily audio frequency signals, are supplied to a low frequency signal amplifier il. From the output of the amplifier d the signals may go to further stages of amplification or may be coupled'directly, as sh'own, to a sound reproducer 5.
  • the amplier l comprises an electron dischargevdev-ice having a control electrode ll coupled ⁇ to a source of frequency modulated Waves, a cathode i2, and an anode I3.
  • the anode i3 is coupled by means of capacitor lli to the limiter 2.
  • the limiter consists of a pair of diodes l5v and I6 connected with polarity reversed with respect to each other so that one conducts during positive peaks and the other during negative peaks of intermediate frequency voltage.
  • the inductance I1 provides a direct current return path for the diodes so that they function as rectiers.
  • a bypass capacitor I8 is connected between inductance l'l and the anode of diode i5, while a bypass capacitor I9 is connectedbetween inductance Il and the cathode of diode l.
  • the value of inductance Il is so adjusted that, when combined With the straycapacities of the diode circuits, these circuits resonate at the frequency of the carrier wave.
  • th'e limiter 2 presents a high impedance to the anode circuit of amplifier i.
  • prevent the diodes from operating at small intermediate frequency voltages.
  • the capacitor I4 serves to block the anode potential of amplifier I from the limiter diode. Since there is no direct current load circuit for these diodes other than their own internal impedance, when the intermediate frequency voltage rises above the bias voltages 2li and 2l, these diodes present practically a short circuit to the intermediate frequency amplier l.
  • the anode I3 is likewise coupled by means of impedance 22 to th'e primary 23 of the discriminator transformer.
  • This impedance 22, shown as comprising an inductance 24, and a resistance 25, serves both to allow the limiter to cut off sharply the peaks of voltage Waves and to prevent the limiter, from short-circuiting the discriminator transformer.
  • the discriminator circuitv 3 is of well known form. Its function is to demodulate the frequency modulated waves which are coupled thereto from the anode I3.
  • the circuit comprises a transformer having, in addition to the' primary winding 23, a secondary Winding 26, both of these windings being tuned to a desired fixed intermediate frequency.
  • the primary winding isconnected between ground and the mid-point ⁇ of the secondary Winding 25 through a condenser 2l.
  • Unidirectional operating potential for the anode I3 is supplied through the resister 29 from the positive terminal of a source of potential shown as a battery te.
  • the opposite terminals of the secondary winding 26 are connected to the respective anodes ofthe diodes 3l and 32, the cathodes of these diodesv being connected together for alternating current through condenser 33 and for direct current through resistances 34 and 35i. is grounded andthe mid-point between resistances 35i ⁇ and 35 is connected to the mid-point on secondary winding 2S through a choke coil 36.
  • the intermediate frequency has a desired value to which the primary and secondary Windings 23 and 26 are each tuned.
  • the voltage across the secondary winding of the transformer in accordance with Weil known theory, is displaced in phase with the voltage across the primary by 90. With the connection shown, the voltage of the primary is connected in series with one-half the Voltage on the secondary across the discharge device 3i and the condenser 33 and it is connected in series with the other half of the voltage on the secondary across discharge device 32.
  • the voltage on one-half of the secondary leads the voltage on ktheprimary by 90, whereas that on the other half of the secondary lags behind the-voltage on the primary by 90.
  • and 32, when the intermediate frequency is at its desired value is equal and accordingly equal values of unidirectional current iiow through each ofthe diodes and hence through resistances '34 and 35.
  • the quadrature relation between the primary and secondary voltages of the discriminator transformer exist, however, only when the oscillations supplied thereto have the desired intermediate frequency. If this frequency changes in either direction the phase of the secondary voltage varies from its 90 relation with the primary voltage in one direction or the other, dependent on whether the frequency increases or decreases. For example, if the frequency increases, the phase shift may be in such a direction that the voltage on the upper half of the secondary winding approaches the aiding relation with the primary voltage, whereas that on the lower half of the secondary winding approaches the opposing relation with the primary voltage. Thus, the voltage applied to diode 3l' increases and that appliedto diode. 32'.
  • the cathode of the diode 3E jvolume control resistor 38 The output of signal amplifier i may be increased through succeeding stagesL of amplification, if desired, or may be, as shown, coupled directly into an audio transformer 3e, the secondary of the audio transformer being connected to reproducing means such as a loud speaker lill.
  • the pair ci diodes i5 and I6 being connected in reverse polarity, the one conducts on positive peaks and the other on negative peaks of intermediate frequency voltage.
  • the inductance l'l provides a direct current return path to these diodes so that they function as rectiiiers.
  • this inductance is turned with the circuit and stray capacities of the limiter to a resonance condition so that the limiter circuit presents a high impedance to the anode circuit of amplier I while the diodes areV non-conducting, the bias batteries Z and 2l preventing the diodes from operating at small intermediate frequency voltages.
  • the impedance 22 performs the important function of -both preventing the limiter from short-circuiting the discriminator transformer and allowing the limiter to ychop peaks of intermediate frequency voltages abruptly.
  • the limiter ycircuit being' tuned broadly, it has a small fly-wheel effect, that is. a small circulating current; hence, the limiter responds sharply to small .changes in voltage.
  • the limiter circuit and the discriminator transformer would have detrimental inter-acting effects for the presence of the greater y-wheel effect of the discriminator transformer would be detrimental to limiting.
  • the limiter circuit and the discriminator transformer would have detrimental inter-acting effects for the presence of the greater y-wheel effect of the discriminator transformer would be detrimental to limiting.
  • this limiter limits at very small voltages in the anode circuit of the iinal intermediate frequency amplifier l.
  • the iinal intermediate frequency amplifier is of the pentode type, having a high plate impedance and operating in a'con# stant current manner into a-low impedance load, such as the discriminator transformer, itwill be seen that the introduction-of the impedance 22 causes very little reduction gain-and'makesl but a small change in the voltage produced across the primary of the discriminator'transformer. Also, since the amplifier I operates at normal unidirectional potential, its amplifying properties are not compromised byA the action of'fa limiter circuit. i
  • the limiter 2 functions in the above-described manner.v
  • the biasing voltages for the diodes l5 and I6 respectively are obtained from the potential drops across resistors 42 and 43 in the cathode circuit of the preceding amplifier I.
  • the anodes ofthe two diodes are maintained negative with respect tothe cathodes, preventing current flow into these diodes for-a no signal condition in the receiver.
  • the inter-connected switches44, 45,46, 41', and 48 are shifted from the contacts marked F to those marked A. With this shift the resistors 49 and .56 are inserted respectively in the circuits of diodes I5 and I6.
  • the potential across resistor 52 serves to maintain the cathode of diode I6 positive with respect to the anode so that until the intensities of the signals across diode I6 are greater than a predetermined intensity, no current will flow through diode I6 to set up thepotential across resistor 55 for automatic volumeicontrol purposes. Also, by the shifting of switch 44 to the contact A, the cathode of diode I5 vis connected through resistor 54 to the source of 1potential30, thus establishing a positive bias between thecathode and anode of diode I5 to prevent conduction of current by the diode.A
  • a third winding 55 is provided on the discriminator transformer. for tuning the discriminator-primary circuit to the intermediate frequency while capacitor 58 is tuned with coil 55 to the intermediate frequency.
  • Capacitor 57 couples the primary circuit to the circuit of winding 55.-
  • the amplitudeA modulated carrier waves in the resonantcircuit of the coil 55 and capacitor 58 are impressed across the diode 69 for demodulation.
  • the output current of the diode 60 establishes potential drops across resistors 6I and 62 which vary in accordance with the amplitude of the audio frequency currents flowing in diode 60, capacitor 59 providing a bypass across these resistors for radio Capacitors 56 and 51 are presentfrequency currents.
  • Ey means o'f switch 48 thev audiovoltages across resistor 62 are supplied to the coupling capacitor 31 connected to the control electrode of signal amplifier 4. It will be seen from the above description 'that the switches 44-48 all operate in the direct current circuits of the diodes of the limiter 2 and the detector 69.
  • my invention provides a receiver which, lwhile allowing limiting on weak signals, permits the last intermediate frequency amplifier to operate under optimum conditions. This is provided by the use of the diode limiter and the decoupling impedance which permit sharp limiting without unduly loading the discriminator circuit. Moreover, by means of the switching arrangement shown, the limiter circuit is lconverted to an automatic volume control rectier for amplitude modulated Waves. Modification of the circuits to permit reception of amplitude modulated waves or frequency modulatedk Waves is eiTected by a simple switching arrangement in the direct current circuits of the vaudio ⁇ frequency stages of the receiver, thus avoiding any disturbance of the tuning of the radio frequency stages of the receiver.
  • a limiter comprising a plurality oi' diodes arranged to transmit opposite peaks of said waves, a frequency discriminator, and impedance means connected between said limiter and said discriminator, said impedance means comprising an impedance connected serially betweensaid limiter and said discriminatorl and having a magnitude suiiicient to decouple said limiter from said discriminator to prevent the v,inertia of said discriminator from aiecting the limiting action of said diodes.
  • said impedance having a magjnitude of the order of the impedance of said tunedcircuit to prevent the inertia of said ⁇ tuned circuit from affecting the limiting action of said diodes.
  • the combinatiomin a receiver for both frequencyI modulated and 4amplitude modulated carrierwaves, Pof'means for detecting said Waves, a signal channel through which said Waves are supplied to said detecting means, a diode connected in shunt to said channel, means for biasing said diode during reception of frequency modulated Waves to be non-conductive to waves of ⁇ less than a predetermined intensity and conductive to waves of greater than said predeter-y minedfintensity whereby said diode limits said Waves to said predetermined intensity, a resistance, and means to remove said bias and to con-A nect said resistance in series With said diode during reception of amplitude modulated waves thereby to prevent said diode from limiting the amplitude of said amplitude modulated waves.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
US448881A 1942-06-29 1942-06-29 Radio receiver Expired - Lifetime US2341937A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BE477489D BE477489A (en(2012)) 1942-06-29
US448881A US2341937A (en) 1942-06-29 1942-06-29 Radio receiver
FR938808D FR938808A (fr) 1942-06-29 1946-11-19 Perfectionnements aux récepteurs mixtes à modulation de fréquence ou d'amplitude

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US448881A US2341937A (en) 1942-06-29 1942-06-29 Radio receiver

Publications (1)

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US2341937A true US2341937A (en) 1944-02-15

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US448881A Expired - Lifetime US2341937A (en) 1942-06-29 1942-06-29 Radio receiver

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BE (1) BE477489A (en(2012))
FR (1) FR938808A (en(2012))

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2560378A (en) * 1945-06-29 1951-07-10 Emi Ltd Frequency modulation detector
US2569426A (en) * 1945-07-16 1951-09-25 Signal Tuned Radio Corp Radio receiver
US2625589A (en) * 1945-09-27 1953-01-13 Bell Telephone Labor Inc System for measuring phase and gain
US2674690A (en) * 1949-02-26 1954-04-06 Research Corp Frequency modulation receiver
US2798152A (en) * 1953-02-24 1957-07-02 Philips Corp Detector for either frequency modulation or amplitude modulation with noise reductionmeans
US2904675A (en) * 1953-10-21 1959-09-15 Philips Corp Frequency demodulator
US2929924A (en) * 1955-02-21 1960-03-22 Westinghouse Electric Corp Radiation suppression circuit
US3256489A (en) * 1963-01-11 1966-06-14 Rca Corp Amplitude dependent zero shift reduction for frequency discriminators
US3299286A (en) * 1962-05-31 1967-01-17 Neumann Georg Capacitive transformer in bridge connection for producing electrical current output linearly proportional to capacitance

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1002047B (de) * 1952-12-11 1957-02-07 Siemens Ag Schaltungsanordnung zur Erzeugung eines scharfen Knicks in einer Kennlinie

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2560378A (en) * 1945-06-29 1951-07-10 Emi Ltd Frequency modulation detector
US2569426A (en) * 1945-07-16 1951-09-25 Signal Tuned Radio Corp Radio receiver
US2625589A (en) * 1945-09-27 1953-01-13 Bell Telephone Labor Inc System for measuring phase and gain
US2674690A (en) * 1949-02-26 1954-04-06 Research Corp Frequency modulation receiver
US2798152A (en) * 1953-02-24 1957-07-02 Philips Corp Detector for either frequency modulation or amplitude modulation with noise reductionmeans
US2904675A (en) * 1953-10-21 1959-09-15 Philips Corp Frequency demodulator
US2929924A (en) * 1955-02-21 1960-03-22 Westinghouse Electric Corp Radiation suppression circuit
US3299286A (en) * 1962-05-31 1967-01-17 Neumann Georg Capacitive transformer in bridge connection for producing electrical current output linearly proportional to capacitance
US3256489A (en) * 1963-01-11 1966-06-14 Rca Corp Amplitude dependent zero shift reduction for frequency discriminators

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Publication number Publication date
BE477489A (en(2012))
FR938808A (fr) 1948-10-26

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