US2034647A - Signal receiving system - Google Patents

Signal receiving system Download PDF

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Publication number
US2034647A
US2034647A US500468A US50046830A US2034647A US 2034647 A US2034647 A US 2034647A US 500468 A US500468 A US 500468A US 50046830 A US50046830 A US 50046830A US 2034647 A US2034647 A US 2034647A
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United States
Prior art keywords
carrier
wave
detector
signal
component
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Expired - Lifetime
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US500468A
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English (en)
Inventor
George L Beers
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RCA Corp
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RCA Corp
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Priority to BE384744D priority Critical patent/BE384744A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US500468A priority patent/US2034647A/en
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Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/16—Circuits
    • H04B1/30—Circuits for homodyne or synchrodyne receivers

Definitions

  • radio signals during their travel between a transmitting station and a receiving station, are subject, at times, to certain inuences that cause attenuation of the carrier-wave without appreciably affecting the amplitude of the side-bands and that, conversely, one or more side-bands may, preferentially, be attenuated.
  • the phenomenon is generally known as selective fading.
  • Selective fading causes distortion of the received signal.
  • the distortion is of the same type as that occasioned by over-modulating the carrier at the transmitting station and it is, also, equivalent to that introduced through the use of detectors of certain types.
  • An object of my invention is to provide a signal-receiving system whereby the effects of selective fading shall be minimized.
  • a related object is to provide a radio-receiving system such that the signal-output therefrom, at audio-frequency, shall be free from distortion of the type introduced by certain conventional demodulating devices.
  • An additional object of my invention is to so design a radio-receiving system that it shall function satisfactorily independently of the percentmodulation of a received signal.
  • Another object of my invention is to provide a radio-receiver that shall have extreme selectivity.
  • An analogous object is to provide a radio receiving system which shall be substantially unaffected by carrier-waves other than that from a desired transmitting station.
  • the improved adjacent channel selectivity of a receiving-system constructed according to my invention results from very careful filtering of the component representing the carrier-wave before combining it with the component representing the side-bands.
  • l' make use of one or more piezo-electric crystals for filtering purposes and I provide means whereby the crystal and the electrode structure associated therewith are rendered substantially opaque to frequencies other than that of the carrier-Wave component.
  • Fig. l is a diagrammatic view of a simplified receiving-system comprising an embodiment of my invention.
  • Fig. 2 is a diagrammatic view of a complete radio receiving-system of the superheterodyne type wherein is incorporated a preferred embodiment of my invention.
  • an incoming radio signal received upon an antenna I, is simultaneously impressed upon the input circuits of a radio-frequency amplifier 3, and a balanced detector stage constituted by a plurality of thermionic devices 5 and T, disposed in pushpull relation.
  • the input circuit of the balanced detector includes an inductor 9 and a tuning condenser Il, the grids of the detector tubes being connected, respectively, to the opposite ends of the inductor.
  • a connection i3 extends between an intermediate point on the input inductor and a conductor l5 common to the cathodes of the detector tubes, a coupling coli l1 and a, biasing battery I9 being included therein. 'I'he potential of the biasing battery is such as to bring the detector tubes substantially to the cut-off point.
  • Both of the detector tubes are supplied with plate potential from a common source 2l, the
  • a common source 21 supplies filament potential for the two tubes.
  • the detectors 5 and 1 are so chosen as to have substantially identical characteristics.
  • the audio output currents therefrom therefore, are practically equal and, since their inductive effect upon the secondary winding of the outputtransformer is balanced, no audio output is obtained by reason of the unmodified action of the detector stage alone.
  • the radio-frequency amplifier 3 is, accordingly, provided with an output circuit, including a coil 29 that is disposed in inductive relation to the coupling coil I1, whereby the carrier-wave may be impressed upon the grids of the detector tubes, simultaneously, in phase.
  • the output circuit of the amplifier includes filtering means, such as piezo-electric crystals 3
  • the detector tubes 5 and 1 are unresponsive to the carrier-wave alone, as impressed thereon from the amplifier 3, or to potentials conveyed directly thereto from the antenna, insofar as audio output is concerned.
  • the carrier plus the side-bands and the carrier, deprived substantially of side-band frequencies are simultaneously impressed upon the detector stage, the balanced inductive effect upon the secondary winding of the output transformer 25 is disturbed and audio potentials are developed across the secondary winding.
  • coupling coils 9 and l1 may be interchanged without affecting the operation of the system. That is to say, the incoming signal may, alternatively, be impressed on the coil I1 while the output from the RF amplier may be impressed on the coils 9.
  • the selectivity of the system is measured by the ability of the ltering system to prevent signals at frequencies other than the carrier-wave from passing.
  • the intermediate-frequency carrier-wave through the use of my improved crystal-'filten may be substantially freed from variations representing the modulation, and, thereafter, may be combined with the unfiltered modulated intermediate frequency carrier wave to produce an audible signal.
  • a receiver of the superheterodyne type, modified in accordance with a preferred embodiment of my invention, is illustrated in Fig. 2 of the drawings.
  • the receiver includes a radio-frequency amplifier 39, a rst detector 4l, and a local source of oscillations 43.
  • the radio frequency amplifier, the oscillator and the first detector may be constructed in any well-known manner, since the details thereof constitute no part of the present invention.
  • I employ a plurality of thermionic tubes 55 and 41, disposed in balanced relation, as hereinbefore described in connection with Fig. l of the drawings, having a common output circuit constituted by the primary winding i9 of a push-pull audio transformer 5
  • the detector tubes have a common tunable input circuit, including an inductor 53 and a condenser 55, and a connection including a coupling coil 51 and a grid biasing battery 59, extends between an intermediate point on the inductor and the cathode'circuit of the tubes.
  • a common tunable input circuit including an inductor 53 and a condenser 55
  • a connection including a coupling coil 51 and a grid biasing battery 59
  • a side-band amplifier Si is provided, the output circuit 53 of which is disposed in inductive relation to the coupling coil 51 and the input terminals of which receive excitation from the output circuit 55 of the first detector.
  • the intermediate carrier-wave shall be effectively freed from the side-bands, before it is impressed on the balanced detector, I interpose a filter, substantially opaque to the sidebands, between the output circuit of the first detector and the said balanced detector.
  • the side-band amplifier may also be provided with filtering means, (not shown) of any desired type, whereby the intermediate carrierwave is prevented from being impressed upon the coupling coil 51.
  • a preferred lter is constituted by a plurality of thermionic devices 51 and 59, each having a cathode 1l, a grid 13 and a plate 15.
  • the first thermionic device is provided with an input circuit constituted by an inductor 11 and a tuning condenser 19, the said inductor being coupled to the output circuit 65 of the rst detector.
  • the plate of the first thermionic device is connected to the grid of the second thermionic device through a piezo-electric crystal 8
  • the dimensions of the crystal are so chosen that its natural frequency is the same as that of the intermediate carrier-wave and it, accordingly, is substantially unresponsive to the side-bands accompanying the said wave, and to undesired carrier-waves.
  • the system shown in the drawings is adapted to be controlled by automatic volume control means and it has been found that the use of an automatic volume control system is particularly advantageous in the event that the signals from any given station are greatly subject to fading since, by use, the relative amplitudes of the intermediate carrier-wave, and the side-bands, may be maintained within fairly definite limits in the receiving apparatus irrespective of changes in the carrier-wave during transmission from the distant broadcasting station.
  • the automatic volume-control (not shown) associated with the carrier-amplifier and filter could well serve to keep the amplitude of the carrier impressed upon the balanced detector thoroughly constant with the result that the signal strength would not be impaired.
  • the piezo-electric crystal has a definite tendency toward free oscillation after the excitation provided by an incoming signal has been removed. This tendency serves to keep the intermediate carrier frequency input to the balanced detector system relatively constant in amplitude through fading periods.
  • a signal receiving system including a pair of signal transmission circuits, means for separating an incoming modulated carrier wave into carrier component and side-band components and for applying same selectively to said signal transmission circuits, means including an automatic volume control device for maintaining substantially constant the amplitude of said side band components, means including a piezo-electric crystal and an amplifier device in that one of said circuits which transmits the carrier component for filtering and greatly amplifying' the carrier component with respect to said side-band components, a pair of line-ar detectors each having a contro-l grid and a cathode, a coupling device connected between said grids, a second coupling device constituting a common connection from said grids to said cathodes, and means including said coupling devices for electrically connecting said signal transmission circuits to said linear detectors.
  • a plurality of detector devices each having a control grid and a cathode, a coupling device connected between said grids, a second coupling device constituting a common connection from said grids to said cathodes, a common output circuit for said devices, means for amplifying a modulated carrier wave, means for separating said carrier Wave into a carrier component and side band components corresponding to a modulation of said modulated carrier wave, means for supplying gain to the carrier component and to the side band components, the gain supplied to the carrier component being sufficiently greater in proportion to that supplied to the side band components that over-modulation and consequent distortion is substantially avoided, means including a piezoelectric device for impressing said carrier component upon said grid electrodes through one of said coupling devices, means for neutralizing the capacitive coupling effects of said piezo electric device in respect to frequencies other than that of the carrier Wave, and means for impressing said side band components upon said grids through the other of said coupling devices.
  • automatic volume control means to which an incoming signal is subjected, means for separating said signal into a plurality of components one of which is a carrier Wave, means for greatly increasing the amplitude of the carrier Wave component with respect to the other components, linear detector means comprising a pair of electron discharge devices, each of which is provided with an input circuit, means including a frequency selective de- Vice for impressing said carrier Wave component simultaneously and in phase opposition upon the two said input circuits, means for impressing another of said components simultaneously and in phase agreement upon the two said input circuits, and means responsive only to the joint action of the several components for producing an audible signal.
  • said frequency selective device includes a piezo electric crystal having a 10W decrement of o'scillation during intervals of fading.
  • a device in accordance with claim 7 in which means are provided in combination with said frequency selective device for neutralizing the inherent capacitive coupling effects thereof.
  • a signaling system having an input and an output, means eifective upon the reception of signals subject to indiscriminate fading and selective fading to automatically control the amplitude of output of said system, said means comprising means for separating said signals into carrier component and side-band components, means for amplifying the carrier component much more than the side-band components, means including a piezo electric device having a low decrement of oscillation under fading conditions for ltering said carrier component, a linear detector device having an input circuit, and means for impressing the several components upon said detector input circuit, said detector device constituting means for demodulating the signals.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Superheterodyne Receivers (AREA)
US500468A 1930-12-06 1930-12-06 Signal receiving system Expired - Lifetime US2034647A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BE384744D BE384744A (en(2012)) 1930-12-06
US500468A US2034647A (en) 1930-12-06 1930-12-06 Signal receiving system

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220158743A1 (en) * 2019-03-14 2022-05-19 University Of York Methods and apparatus for coherent signal amplification and detection

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220158743A1 (en) * 2019-03-14 2022-05-19 University Of York Methods and apparatus for coherent signal amplification and detection
US11824589B2 (en) * 2019-03-14 2023-11-21 University Of York Methods and apparatus for coherent signal amplification and detection

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