US2020832A - Superheterodyne receiver - Google Patents

Superheterodyne receiver Download PDF

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Publication number
US2020832A
US2020832A US600124A US60012432A US2020832A US 2020832 A US2020832 A US 2020832A US 600124 A US600124 A US 600124A US 60012432 A US60012432 A US 60012432A US 2020832 A US2020832 A US 2020832A
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United States
Prior art keywords
detector
grid
tube
circuit
swing
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Expired - Lifetime
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US600124A
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English (en)
Inventor
Grimes David
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RCA Corp
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RCA Corp
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Priority to US600124A priority Critical patent/US2020832A/en
Priority to FR752130D priority patent/FR752130A/fr
Application granted granted Critical
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D7/00—Transference of modulation from one carrier to another, e.g. frequency-changing
    • H03D7/06—Transference of modulation from one carrier to another, e.g. frequency-changing by means of discharge tubes having more than two electrodes
    • H03D7/08—Transference of modulation from one carrier to another, e.g. frequency-changing by means of discharge tubes having more than two electrodes the signals to be mixed being applied between the same two electrodes

Definitions

  • My present invention relates to superheterodyne receiving systems, and more particularly to an improved type of frequency changer, or first detector, circuit for use in a superheterodyne receiver.
  • a power detector employing l ample grid bias or other types of detectors which are not subject to overload, may be utilized in the first detector stage.
  • the first expedient mentioned above is costly as it necessitates additional tuningv condensers with the associated diiculties of ganging these additional condensers. Furthermore, additional tuning stages required extra precautions in shielding to prevent the undesired stations from reaching the first detector other than through the orthodox path; The secon-d expedient involving reduced local oscillator swing greatly reduces the translation efciency of the rst detector.
  • the third solution referred to above comprises the basis of the present invention, and offers as only real solution to an aggravating problem.
  • it is one of the main objects of the present invention to provide in the rst detector circuitof a superheterodyne receiver an electron discharge tube arrangement so designed that its grid circuit can handle the induced local oscillator voltage swing, the desired channel signal swing, and the maximum amount of undesired signal swing possible to encounter in practice without resulting in an instantaneous grid swing sufliciently great to pass into the positive region of the first detector characteristic.
  • Another important object of the present invention is to provide a superheterodyne receiver employing but a single tuned stage of radio frequency amplification prior to the rst detector, and to operate the rst detector with such plate and grid voltages that the maximum grid voltage swing does not overload the detector tube.
  • Another object of the present invention is to minimize cross modulation between a desired signal and an undesired adjacent channel signal in a superheterodyne receiver by designing the first detector of the superheterodyne receiver in such a manner that. the instantaneous grid swing of the latter is never great enough to run into the positive region of the detector characteristic.
  • Still other objects of the present invention are to improve generally the operating efficiency of superheterodyne receivers, and to especially design the first detector circuit of a superheterodyne receiver as a power detector in such a manner that the first detector circuit is not only reliable in operation, but economically manufactured and installed.
  • the Vusual grounded antenna A, G is employed for collecting intelligence modulated carrier frequency energy, within the so-called broadcast range between 550 to 1500 kilocycles.
  • the collected carrier energy is impressed as. at M1, upon the tuned input circuit of a radio frequency ampliiier l, it being noted that the input circuit of the amplifier is adapted to be tuned through the frequency range of the receiver by a variable condenser 2.
  • the amplified radio frequency energy is then impressed upon the input circuit of the first detector, which includes an electronic discharge tube 3 of the screen grid type.
  • the input circuit of the tube 3 includes the variable condenser 4 which is adapted to tune the input circuit of the first detector in a manner similar to the tuning of the amplifier I.
  • a local oscillator 5 is shown in conventional form, and is adapted to be tuned by a variable condenser 6 through a frequency range which differs from the frequency range through which the condensers 2 and 4 are operative by a desired intermediate frequency.
  • the locally produced energy is impressed, as at M3, upon the grid circuit of the first detector tube 3.
  • Those skilled in the art are well acquainted with the phenomenon occurring in the first detector, or frequency changer circuit, and it may be briefly stated that they energy impressed upon the input circuit of the tube 'through the coupling M2, and the 1ocally produced energy impressed uponthe grid circuit of tube 3 through the coupling M3, heterodyne to produce in the output circuit of the first detectorv the Vdesired intermediate frequency.
  • the intermediate frequency-energy is transmitted through a coupling M4 to the input circuit of the intermediate frequency amplifier 1, the input circuit of the latter being maintained fixedly tuned by a condenser 8 to the desired intermediate frequency.
  • the amplifier l has been conventionally represented, it will be understood that the amplifier may consist of one or more stages of intermediate frequency amplification, and the design thereof is so well known to those skilled in the art that it need not be described in any further detail in the present application.
  • the amplified intermediate frequency energy is then transmitted through the coupling M5 and the desired channel.
  • the amplied audio frequency energy is then utilized in any well known fashion, as by head phones, loud speaker or any other type of reproducer.
  • the second detector l5 may be a power detector since ⁇ both the radio frequency and intermediate frequency amplification have created a signal of considerable strength.
  • the need for a power detector in the first detector stage of the superheterodyne receiver has not been appreciated.
  • the desired signal strength at the first detector point is very weak since it has been subjected to but one stage of radio frequency amplification. It often happens that the strength of signal from an adjacent undesired channel on the grid of the first detector tube 3 is greater than the strength of signal from This arises from the limited amount of tuned radio frequency selectivity ahead of the rst detector.
  • the grid circuit can handle the induced oscillator voltage swing, the desired channel signal swing, and the maximum amount of undesired signal swing possible to encounter in practice without resulting in an instantaneous 76 grid swing sufficiently great to pass into the positive region.
  • the source B conventionally designates the 250 volt source, the latter being shunted by a radio frequency by-pass condenser li, and the source C conventionally designates the grid bias source capable of applying approximately QG to 35 volts to the grid of the tube 3.
  • first detector circuit has been shown to embody a power detector tube 3 employing sufficient grid bias to prevent overload at maximum instantaneous grid swing, it is to be clearly understood that the present invention is not limited to a power detector operating by this manner in virtue of increased grid bias and plate voltage. Any other type of detector which is not subject to overload may be employed in the first detector circuit, since the essential principle underlying the present invention involves utilization of a first detector circuit which is designed in such a manner that maximum instantaneous grid swing never passes into the positive region of the detector tube characteristic.
  • variable mu tube a type of electron discharge tube known as the variable mu tube may be employed for the tube '3 in the first detector circuit.
  • a superheterodyne receiving circuit comprising a single stage of tuned radio frequency amplification, a grid biased tube detector operating as a first detector, an intermediate frequency amplifier, and a second detector all arranged in cascade, the selectivity of the receiving circuit network preceding the said first detector being sufficiently low to permit the impression upon the first detector grid of an undesired adjacent channel signal of substantial intensity, means to impress a high negative biasing voltage on the grid of the first detector tube, a source of high positive plate voltage therefor, the grid and plate voltages being sufficiently high to give a detector characteristic such that the grid circuit of the first detector can handle a desired channel signal swing and the maximum amount of undesired signal swing possible to encounter in practice without resulting in an instantaneous grid swing sufficiently great to pass into the positive region of the said detector characteristic.
  • a superheterodyne receiver comprising a single stage of tuned radio frequency amplification, a local oscillator, a first detector tube circuit,
  • an intermediate frequency amplifier, and a second detector circuit means to impress a negative biasing voltage on the grid of the first detector tube of the order of at least 30 to 35 volts, 45 the selectivity of said single stage preceding the said first detector being insufiicient to reduce the strength of signal from an adjacent undesired channel on the grid of the first detector with respect to the strength of signal from the desired channel, and a source of commensurately high positive plate voltage for the first detector tube, whereby the grid circuit of the first detector can handle the induced oscillator voltage swing, the desired channel swing, and the maximum amount of undesired signal swing possible without result,- ing in an instantaneous grid swing sufficiently great to pass into the positive region of the first detector characteristic.
  • a superheterodyne receiving circuit comprising a radio frequency amplifier, a first detector circuit, a local oscillator circuit, an intermediate frequency amplifier, a second detector circuit, the selectivity of the radio amplifier being sufiiciently low to permit the transmission to the first detector of an undesired adjacent channel signal having an intensity comparable to that of the desired signal intensity, means to impress a negative biasing voltage on the grid of the first detector tube of the order of 30 volts, and a 70 source of positive plate voltage for said first detector which is so high that the maximum instantaneous grid swing of the first detector tube is not capable of running into the positive region of the first detector characteristic.
  • the method which includes reducing the selectivity preceding the first detector to an amount such that the strength of signal from and adjacent undesired channel on the grid of the first detector is comparable with or greater than the strength of signal from the desired channel, obtaining rectification in the first detector tube by negatively biasing the grid thereof, and increasing the negative grid bias and positive anode potentials applied to the first detector tube in tion on adjacent desired channels and multiple responses caused by overloading of the first detector tube, which includes so adjusting the constants of the first detector that the maximum instantaneous grid swing of the latter never runs into the positive region of the first detector characteristic.
  • a superheterodyne receiver including only a single stage of tuned radio frequency amplification prior to the first detector circuit, the selectivity ahead of the rst detector being insufflcient to substantially suppress undesired adjacent channel signals, characterized by the feature that the constants of the rst detector circuit are so adjusted that the maximum instantaneous grid swing of the first detector is prevented from running into the positive region of Kthe first detector characteristic.
  • a superheterodyne receiver comprising a radio frequency amplifier adapted to have its amplification automatically varied to maintain the receiver volume at a predetermined level regardless of carrier fluctuations, a local oscillator, a frequency changer tube circuit coupled to said amplifier and oscillator for producing a desired yaoeosa beat frequency, the said amplifier having insufficient selectivity to reduce the undesired adjacent channel signal intensity whereby the undesired signal is substantially amplified when weak desired signals are received, the constants of the frequency changer tube being so adjusted as to prevent the instantaneous grid swing of .the frequency changer tube from running into the positive region of its characteristic.
  • a superheterodyne receiver comprising a I radio frequency amplifier adapted to have its. amplificationautomatically Yvaried to maintain the receiver volume at aV predetermined level regardless of carrier fiuctuations, a local oscillator, a frequency changer tube circuit coupledl to said amplifier and oscillator for producing a desired beat frequency, the said amplifier having insuflicient selectivity to reduce the undesired adjacent channel signal intensity whereby the undesired signal is substantially amplified
  • the constants of the frequency changer tube being so adjusted as to prevent the instantaneous grid swing of the frequency changerV tube from running into the positive region of its characteristic, means for: amplifying said beat frequency, and a detector circuit coupled to said beat frequency amplifying means, said second detector comprising a power detector capable of delivering sufficient power tooperate a reprcducer with but a single z stage 0f audio frequency amplification.
  • a method of receiving signals with a superheterodyne receiver of the type including a signal collector, a first frequency changer tube, a
  • Vsecond frequency changer tube and a repro-g ducer which consists in collecting broadcast signals, reducing the selectivity between the collector and first frequency changer tube to a point such that undesired signals are applied to the latter with an intensity comparable to the intensity of desired signals whereby reproduction of demodulated desired signals is accompanied by reproduction of demodulated undesired signals, and maintaining the relative grid and plate potentials of the first frequency changer Ytubej such that overloading of the latter by applied collected signals is constantly prevented and the effect of said reduced selectivity substantially compensated for.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Circuits Of Receivers In General (AREA)
  • Superheterodyne Receivers (AREA)
US600124A 1932-03-21 1932-03-21 Superheterodyne receiver Expired - Lifetime US2020832A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US600124A US2020832A (en) 1932-03-21 1932-03-21 Superheterodyne receiver
FR752130D FR752130A (fr) 1932-03-21 1933-03-08 Récepteur superhétérodyne

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US600124A US2020832A (en) 1932-03-21 1932-03-21 Superheterodyne receiver

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US2020832A true US2020832A (en) 1935-11-12

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US600124A Expired - Lifetime US2020832A (en) 1932-03-21 1932-03-21 Superheterodyne receiver

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US (1) US2020832A (fr)
FR (1) FR752130A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2468041A (en) * 1942-03-09 1949-04-26 Int Standard Electric Corp Radio receiver
US2765373A (en) * 1951-02-20 1956-10-02 Alonzo L Smith Hearing aid, construction and support therefor

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2468041A (en) * 1942-03-09 1949-04-26 Int Standard Electric Corp Radio receiver
US2765373A (en) * 1951-02-20 1956-10-02 Alonzo L Smith Hearing aid, construction and support therefor

Also Published As

Publication number Publication date
FR752130A (fr) 1933-09-16

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