US2101670A - Radio frequency amplifier - Google Patents

Description

Dec. 7, 1937. M. BYK ET AL 2,101,670

RADIO FREQUENCY AMPLIFIER Filed Oct. 26, 1934 fiuperheterod yne Radio Tiece'wer- I 2 fiuper'heteroyne 7 Hadlo'flecejwer E -46 I Inventors:

Their Attorney.

Patented Dec. 7, 1937 UN mm STATES RADI FREQUENCY AMPLIFIER" V Maurice Byk. and Jehan assignm's to General E notation of New .York

de Mare, Paris, France, lectric Company, a cor-.

Application October 26, 1934, Serial No. 'l50,;192

In France Oct ober 27, 1933 '4 Claims. (01. 250-20) Our presentinvention relates to radio frequency amplifier systems ans particularly to amplifiers for superheterodyne radio receivers, and it describes the meanswhich-permit increasing the selectivity of such; receivers and protecting them against. any undesired signai whichhas the same frequency as that" to which one-or more elements of the receiver are tuned intentionally.

In superheterodyne:receivers a kind of interference occurs, which isdue to the fact-that un-' desired signals, which have the same frequency. as that to which-the medium-frequency ampliher is tuned, traverse the selector circuits preceding the frequency-changing system. Several arrangementshavebeen proposed to eliminate this interference. One of these comprises, for example, an antiresonating circuit in: series with the antenna, or a resonating circuit between the antenna and the ground, which circuits are adjusted in accordance with the value of the intermediate frequency. Unfortunately these-solutions are in general of little effectivenessfand the auxiliary circuits which they constitute intro duce, in the tuning'circuits, inductive or capaci' tive components which are variable with the ire .quency;. ll of which complicates considerably the problemrof single control. f i

The present invention has" for one of itsobjects to produce, prior to thefrequency chang- 1mg, a considerable attenuation of the "signals which are transmitted on the same frequency as that for which the intermediate-frequency amplifier is adjusted. A further object of the invention is to provide such means, which do not introduce disturbances in the adjustment of the circuits and in the operation of the receiver within the wave-band to be received. The invention consists in inserting, between the cathode and the point, which the grid and plate circuits have in common, of the tube or tubes preceding the frequency changer, an impedance,.or. a system of impedances, whose value passes through a maximum at the value of the intermediate frequency. This impedance, or system of imped ances, gives rise to'an attenuation, or decrease. in amplification, of the frequencies at which this impedance has its maximum value.

Thus a further object of, our invention is to provide an-amplifier which satisfactorily amplifies the signals to be received and which at the same time produces large attenuation of currents of the undesired frequency.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention'itself, however, both as to its organization and method of operation will best beunderstood by reference to the following description taken in connection with theaccoinpanying drawingin which Fig. 1 represents a circuit embodyingour invention; Fig. 2 shows a'modification thereof, and Fig. 3 illustrates certain characteristics of the operation of the circuits of Figs. 1 and 2.

In Fig. 1 the antenna-ground system comprises a primary l, which is coupled to the secondary 2, which secondaryis tunedby means 'of condenser 3 to the frequency to be received; "I his condenser is, of course, variableover fanydesired range of frequencies. Theoscillating circuit 2- -3 is connected between the; cathode 5-and grid 6- of a pentode 4-, which is a high irequency amplifier of the radio receiver; The circuit of plate 9 is coupled to the input of a'superheterodyne type of radio receiver l6 by means of the transformer l 0-, H. For simplicitys sake the superheterodyne receiver. has been indicated by-a rectangle. It .willfofcourse, be understood that this receiver comprisesthe usual local heterodyne oscillator and first detector whereby the intermediate 'frequency oscillations "are produced, which inter mediate frequency oscillations areamplified and detected in subsequent portions, notshown, of the receiver. The cathode-5 is connected to a point, which is'common to the'grid and plate circuits ,through the 'antiresonatin'g circuit I2, 13 provided in accordance with-our invention, and

which is tuned to the intermediate frequency. f

A resistance M, which is shunted by a capacitance I5 serves to establish the polarization of the grid in the known manner. It goes without saying that several stages, such as the one which has been'described, may be used in cascade, and that the simple oscillating circuit l2, l3 may be constituted by any desirable system of impedance having a high impedance for the intermediate frequency. V g

It will be understood, further, that the invention is not limited to the type of tube represented in Fig. 1. It is applicable to any other amplifying tube and particularly to the multigrid tubes which comprise, besides the grids 6, 1 and 8 shown'on that figure, additional -.grids.which serve, either to confer to that tube the combination role of amplifier and frequency changer, or to regulate the amplification. In such circuits the antiresonant filter circuit is best placed in that branch ,of the circuit which the anode (which may be in the form of a grid acting as an anode), and the grid, which receives the signal impulses, have in common.

In Fig. 1, the suppressor grid 8, which is utilized to avoid the return of the secondary electrons emitted by the plate, is connected directly to the cathode. In Fig. 2, which constitutes likewise a very simplified scheme of the invention, the grid 8, which has the same purpose as in circuit l, is connected between the protecting circuits [2, l3 (or the system of impedances which is intended to replace it), and the resistance I4 which is shunted by the capacitance l5. It may be connected directly to the point which the cathodegrid-plate circuits have in common, in the case where this shunted resistance is not includedin the circuit. 1

Fig. 3 represents curves which give the attenuation produced by the arrangements that have been described. Curve a relates to the circuit of Fig. 2, and curve b relates to the circuit of Fig. 1. The attenuation curves express the relation between the frequency transmitted and the attenuation in decibels. The frequency has been plotted as abscissas and attenuation as ordinates. The vertical dot and dash line corresponds to the intermediate frequency to which, in turn, the maximum attenuation corresponds. It will be observed that considerably greater attenuation is obtained from the circuit of Fig. 2 from that obtained from the circuit of Fig. 1.

While we have shown particular embodiments of our invention, it will of course be understood that we do not wish to be limited thereto since different modifications may be made, and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In a superheterodyne radio receiver, an electron discharge amplifier having an anode, a cathode and two grids, the combination of an input circuit connected between said cathodeand one of said grids, an output circuit connected between said cathode and anode, a connection between the other of said two grids and said cathode, said other grid being maintained at the potential of said cathode, meansto tune said amplifier for operation at a desired frequency, and means to reduce the transfer through said amplifier of energy having a frequency equal to the intermediate frequency of said receiver and received in said circuit between said one grid and said cathode, said means comprising a circuit tuned to said intermediate frequency connected tune said amplifier for operation at a desired frequency and means to reduce the transfer of energy'ofan undesired frequency from said control grid electrode connection to said anode electrode connection through said discharge device, said means comprising a circuit common to all of said connections said circuit being antiresonant at said undesired frequency.

3.31m anelectron discharge amplifier having an anode, a cathode, a control grid, a screen grid, and a suppressor grid between said screen grid and said anode, an 'output circuit between said anode and cathode including a source of operating potential, a bias resistor, and a parallel resonant circuit in the order named, an input circuit between saidcontrol grid and said cathode including said bias resistor and said parallel resonant circuit, a screen grid circuit, and a connection between said suppressor grid and a point on said input and output circuits between said bias resistor and said parallelv resonant circuit whereby said suppressorgrid is maintained at the potential of said cathode except for potentials appearing on said resonantcircuit, said resonant circuit being tuned to a frequency the transmission of which through said amplifier is to be reduced. q I

4. In an electron discharge amplifier having an anode, a cathode, a control grid and. a second grid, an outputcircuitbetween said anode and cathode, an input circuit between said grid and cathode, a bias resistor. common to said input and output circuits, said second grid being connected to the, end of said bias .resistor nearer the cathode whereby said second grid is maintained at-the cathode potential, and-means to prevent transmission through-said amplifier of currents of a certain frequency, said means comprising a tuned circuit connected in said input and output circuits and between said cathode and said second grid,

MAURICE BYK. JEI-IAN (DE MARE.

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