US2712597A - Superheterodyne radio receiver - Google Patents

Description

SUPERHETERODYNE RADIO RECEIVER Filed Feb. l5, 1950 alancmg m/sedance CanlroL VoLLce 313 d INVENTOR. BERNHARDUS GERHARDUS DAMMERS BYM AGENT United States Patent SUPERHETEROD UNIL RADIO RECEIVER Bernhardus Gerhardus Dammers, Eindhoven, Netherlands, assigner to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application February 15, 1950, Serial N o. 148,728

Claims priority, application Netherlands February 16, 1949 ln such circuit-arrangements it has hithertoA been custornary to supply the signal oscillations from the antenna or from a high-frequency amplifier to the third grid. ln this event, however, the conversion conductance is comparatively low.

The principal object of the present invention is to provide in a simple manner, in a circuit-arrangement as described in the preamble, manual or automatic control means to vary the strength of the intermediate-frequency oscillations in the anode circuit, without appreciably affecting the oscillator, and ensuring a satisfactory conversion conductance and signal-to-noise ratio.

Further object of the invention will appear from the following description.

With frequency converting tubes it is known to prof vide means for controlling the strength of the intermediate-frequency oscillations. Use is generally made of the so-called pentagrid converter, in which the cathode, a control-grid and a grid having positive potential serve as an oscillator, the input signal oscillation being supplied to a second control-grid located outside the two grids and separated from them by a screen-grid. In this event, the second control-grid may at the same time be used as a control-grid. .The oscillator eiect in the tube is substantially not affected by the control.

According to the present invention, in a circuit arrangement as described in the preamble, both the signal oscillation and the local oscillation are supplied to the grid nearest the cathode. Between the anode and the cathode there is interposed the series-combination of an impedance, from which the intermediate-frequency oscillations are derived, and the feedback impedance. The junction of these impedances is connected to the second central grid, which grid has a positive potential withrespect to the cathode. A control voltage is applied to the third grid. By coupling the junction of the impedances to the second grid, it is ensured that the current owing through the oscillator section of the tube is independent of the control-voltage so that a variation of the voltage applied to the third grid does not materially affect the production of local oscillations. However, a control of the intensity of the intermediate frequency oscillations occurs in the anode circuit, since the anode current depends, in large measure, upon the control-voltage.

In the aforesaid mixing circuits, in which so-called additive mixing is used, excessive coupling generally occurs between the circuits across which the local oscillations appear and the antenna circuit, due to which excessive 2,712,597 Patented July 5, 1.955

radiation of the local oscillations by the antenna usually occurs. This disadvantage is obviated in a simple manner in the arrangement according to the invention. For this purpose, there is interposed between the anode and the cathode a series-combination of the impedance from which the intermediate-frequency oscillations are derived and a circuit tuned to the local oscillator frequency. The latter circuit is coupled to an inductance which is connected between grid and cathode. The terminal of this inductance remote from the grid is connected through an impedance, preferably the parallel-connection of a resistance and a condenser, to a point of constant potential. The input signal is supplied to a point of the said inductance, preferably the central point.

As compared with the aforesaid pentagrid arrangement, the arrangement according to the present invention has the advantage that a tube comprising only three grids is sucient.

1n order that the invention may be more clearly under-V stood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which:

Figure l is a schematic diagram of a circuit-arrangement in accordance with the invention,

Figure 2 is a schematic diagram of another circuit# arrangement in accordance with the invention. Referring now to the drawing and more particularly to Fig. 1, there is shown a mixing circuit-arrangement according to the invention. in this figure, an inductance 1 in the antenna circuit is coupled with the inductance of a parallel resonant circuit 2 which is tuned to the input signal frequency. From circuit 2 the signal oscillations arel supplied, through a condenser 3, lters 4, 5 and a tapped inductance 6, to a first control-grid 9 of a pentode tube 7. Tube 7 also comprises a cathode 8, a screen grid 10, a suppressor grid 11 and an anode 12. 'Ihe anode circuit comprises a parallel resonant circuit 15 which is tuned to the intermediate-frequency and coupled with a circuit 16 which is also tuned to this frequency. From thelatter circuit the intermediate-frequency oscillations are taken and supplied to an intermediate-frequency ampliiier (not shown). A parallel resonant circuit 17 tuned vto the local oscillation frequency is connected between the circuit 15 and a positive terminal of a source of supply voltage. The inductance of the circuit 17 is coupled with the inductance 6, the center tap of which is connected to the filter 5. Filters 4 and 5 serve to isolate the antenna circuit 2 from the intermediate-frequency and the oscillator frequency circuits. The lower end of the coil gijs grounded through a parallel-combination of a condenser 18 anda resistance 22.

The cathode 8 is grounded through a biasing-resistor 23 which is suitably by-passed by a capacitor 13. The screen grid 10 is connected, through a condenser 19, to the junction of resonant circuits 1S and 1.7. Screen grid 10 is also connected through a resistance 20 to a positive terminal of the source of supply voltage. Resistance 20 may conveniently be replaced by an inductor. A resistance 14, which serves as a leakage resistance for the first control-grid, is connected between the terminal of iilter 4 remote from ilter 5 and ground. VResistance 20 maybe dispensed with if resistance 22 is provided. The suppressor grid 11 serves as a control-grid and is connected for this purpose to a voltage source (not shown) adapted to be controlled manually or automatically in accordance with the signal strength. This voltage source may be, for instance, a conventional A-V-C source.

The circuit-arrangement operates as follows: Owing to the coupling between resonant circuit 17 and coil 6, local oscillations are produced in the latter. These local oscillations are applied between the cathode 8 and the rst control-grid 9 of the tube. The input oscillations from the antenna are supplied to a tap on coil 6 at which no local oscillation voltage is developed, so that substantially no local oscillation voltage appears across the antenna circuit. Isolation of the antenna circuit is further improved by lters 4 and 5. n

Application of a control voltage to grid 11 causes a variation of the current distribution between anode 1 and screen grid l0. However, this does not vaffect the production of local oscillations, since the screen grid is coupled through the condenser 19 to the oscillator circuit so that current flowing through the oscillator circuit is independent of current distribution between the anode and screen grid. However, this does not apply tothe intermediate-frequency oscillations across-the circuit 15, and for thesean leective control may be obtained 'by varying the 'voltageV applied to suppressor grid 11.

The tapping point of coil 6 is so chosen that no local oscillations areV supplied to the antenna circuit. This tapping point will, as a rule, have to be at the center of the coil andthe capacity of the condenser have to be approximately equal to the capacity between the cathode and the iirst control-grid of the tube. The resistance 22 will haverto be approximately equal to the input resistance of the tube.

Fig. 2 shows a modiiied embodiment` of the invention, which diiers from the arrangement shown in Fig. l in that the oscillator circuit 17 is connected between the cathode and ground. In this case, the screen `grid 10 is directly connected to the positive terminal of the supply and an impedance 21 is connected between the lower `end of inductance 6 and ground to balance lthe inductance 6 relatively to the antenna circuit in such manner that the latter does not radiate local oscillations.

.-While I have described my invention in a specific Vuse thereof and in specic embodiments, I do not'wish to Lbe limited thereto, for obvious modiiications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

1. A mixing circuit arrangement for mixing a rst wave and a second wave to produce an intermediate frequency wave, comprising an electron discharge tube hav- Iingrin successive dispositions a cathode, a first control grid, avscreen grid, a secondV control grid and an anode, a iirst impedance network tuned to the frequency of said intermediate frequency wave and coupled between said anode and said cathode,a second impedance network interposed between said first impedance network and said cathode, means to couple the end of said first impedance network remote from said anode to said screen grid, means to couple said second impedance network to said irst control grid in regenerative relationship at the frequency of said second wave, means to apply said first wave to said rst control grid, and means to apply a control voltage to said second control grid to vary the current-dist tribution between said screen grid and said anode.

2. A mixing circuit arrangement for mixing a rst wave-and a second wave to produce an intermediate frequency wave, comprising an electron discharge tube having in successive dispositions a cathode, a first control grid, a screen grid, a second control grid and an anode, a first impedance network tuned to the frequency of said intermediate frequency wave and coupled between said anode and said cathode, a second impedance network tuned to the frequency of said second wave interposed 18 will i between said first impedance network and said cathode, means to couple the end of said first impedance network remote from said anode to said screen grid, an inductive element inductively coupled to said second impedance network, means to couple said inductive element to said first control grid in regenerative relationship at the frek quency of said second wave, means to apply Ysaid first wave to said first control grid, and means to apply a control voltage to said second control grid to vary theicurrent distribution between said screen grid and said anode.

3. A mixing circuit arrangement for mixing a rst wave and a second wave to produce an intermediate frequency wave, comprising an electron discharge tube having a cathode, a first control grid, a screen grid, a second control grid and an anode, a first impedance network tuned to the frequency of said intermediate frequency wave and coupled between Vsaid anode and said cathode, a second impedance network tuned to the frequency of said second wave interposed between said iirst impedance network and said cathode, means to capacitively couple the end ofsaid lirst impedance network remote from said l anode to said screen grid, a tapped inductive element inductively couplied to said second impedance network and having one endv thereof coupled to said -irst control y grid to apply said secondwave to said control grid-iu positive `feed-back relationship, a third impedance net- Ywork intercoupling the other end of said inductive ele-` ment and ground potential, means to apply said Vfirst wave to the tap on said inductive element, and means to apply a control voltage to said second control grid to vary the current distribution between said screen grid and said anode.

4. A mixing circuit arrangement for mixing a rst wave and a second wave to Lproduce an intermediate frequency wave lcomprising an electron discharge tube having in successive disposition a cathode, a rst control grid,v

a-screen grid, a second control grid and an anode, a first impedance network tuned to the frequency of said intermediate frequency wave and coupled betweensaid anode and ground, a second impedance network tuned to the frequency of Ysaid second wave and connected between said cathode and ground, means to connect the end'of said first impedance network remote from said anode to said screen grid, a tapped inductive element inductively coupled to said second Vimpedance network and having one end thereof connected to said first control grid in regenerative relationship at the vfrequency of said second wave, a balancing impedance` connecting the other end of said element to ground, means to apply said rst wave between the tap of. said element and ground, and means to apply a control voltage to said second control grid to vary the current distribution between said screen grid and said anode. Y

.References Cited in theV le of this patent UNITED STATES PATENTS Dammers Ian. 15, 1952

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