US2073454A - Pentode heterodyne detector - Google Patents

Description

March 9, 1937. H. 0. PETERSON ET AL 2,073,454

PENTODE HETERODYNE DETECTOR I AM L lF/fl? 04 75670 III! OSC/LLATOR INVENTOR M48010 0. P572350 fL E 0ND ATTORNEY Patented Mar. 9, 1937 UNITED STATES PATENT OFFICE PENTODE HETERODYNE DETECTOR Application March 1, 1933, SerialNo. 659,090 Renewed September 4, 1936 4 Claims.

This invention relates to detector circuits for radio receiving apparatus.

An object of the present invention is to obtain improved heterodyne detection in multi-electrode vacuum tubes, free from undesired reactions between closely related circuits.

Heretofore in the use of multi-electrode tubes for heterodyne detection purposes, it has been customary to impress the local oscillator voltage 1 either upon the control grid or the screen grid of the tube, and, in some cases, upon the plate circuit or even the cathode thereof. This mode of coupling the local oscillator to the incoming signal circuit has been found to upset the balance of the circuit and to lead to undesirable capacitive efiects. In the case of the control grid connection the local oscillator circuit has been known to aifect, to some extent at least, the tuned signal circuit, in consequence causing the latter circuit to have an undesirable reaction upon the oscillator frequency and amplitude. This result has also been experienced when the cathode is connected to the local oscillator. If the screen grid is coupled to the oscillator, the impedance path to ground of the screen grid for the radio frequency currents is caused to fluctuate and undesired capacitive effects are thus produced; again, reactions occur which affect both the signal input circuit and the oscillator circuit. As for 3 the plate method of coupling, this also has been found to be highly inefficient, but for another reason, since it requires very high oscillator voltages to obtain any appreciable heterodyne efiect; consequently, increasing the expense of the circuit and the tendency of the arrangement to radiate.

According to the present invention the foregoing difliculties are overcome, and the operation of the oscillator and the tuned signal input cirl0 cuit rendered substantially independent of each other. Specifically, this is accomplished by utilizing a five electrode tube, commonly known to the art as a pentode vacuum tube, and applying to the suppressor grid or fourth electrode thereof,

which is interposed between the screen grid and the anode, the local oscillator voltage.

A better understanding of the invention may be had by referring to the following detailed description which is accompanied by a drawing showing, diagrammatically, a radio receiving circuit having heterodyne detection apparatus in accordance with the present invention.

In the drawing, there is shown a pentode vacuum tube first detector comprising a cathode I3 of the indirectly heated type, a signal control grid I2, a positive screen grid ll, an auxiliary or suppressor grid 5, and a plate or anode 1. Connected to the control grid I2 is tunable signal input circuit 3 comprising a variable condenser i4 and an inductance l5, the latter, in turn, being inductively coupled to a signal energy collector l6 through a coil l'i. Suppressor grid 5 is interposed between the plate and screening electrode 1 l and is maintained at a suitable fixed negative potential by a biasing battery 18 which supplies the suppressor grid through resistor 6. In the suppressor grid circuit is shown a local vacuum tube oscillator 2 which is coupled to grid 5 through a coupling condenser 4. In the output circuit and connected to the plate I through a suitable amplifying and detecting system 9 and a filter circuit Bis any desired type of utilization circuit H], which is herein exemplified as a pair of headphones. If desired, system 9 may comprise the intermediate frequency selective amplifying circuit of a superheterodyne type of receiver. The network 8 comprises an inductance and two condensers serially connected from each side of the inductance and to ground. The network transmits only the intermediate frequency, and the network 9 may amplify and demodulate the intermediate fre-.

quency energy. a

In the operation of the circuit, signals received over energy collector l6 will be induced into tuned circuit 3 and impressed upon the control grid I2 of the first detector tube. At the same time, excitation voltage from local oscillator 2 upon suppressor grid 5 will cause a combination of signal voltage and local oscillator voltage within the first detector tube which will produce a beat note in the plate circuit 1 equal to the sum or difference of the oscillator frequency and the incoming signal frequency. This beat note appearing in the plate circuit 1 will be carried off through filter circuit 8 to amplifying and detecting system 9 which feeds utilization circuit Ill.

By virtue of the shielding provided by screen grid ll interposed between the suppressor grid 5 and control grid l2, coupling'is prevented between these latter two circuits thereby rendering the operation of local oscillator circuit 2 and tuned signal input circuit 3 independent of each other. It is this isolation which makes the present arrangement a highly advantageous one.

The values of the voltages applied to thevarious elements of the first detector tube are, of course, made such as to give proper heterodyne detection.

Obviously, various other types of output circuits and utilization circuits than the one shown in the drawing may be associated with the output circuit.

What is claimed is:

1. In a superheterodyne type of radio receiver, in combination, a first detector network comprising a tube having at least a cathode, a signal grid, an anode, a local oscillation grid, and an auxiliary electrode between the two grids, a tunable signal input circuit connected between the signal grid and cathode, an intermediate fi'e=- quency transmission network connected to the anode of said tube, means for maintaining the said auxiliary electrode at a positive potential with respect to said cathode, signal grid and oscillation grid, means for maintaining said oscillation grid at a negative potential with respect to said cathode, a resistor connected in circuit with said cathode and oscillation grid, and a tunable local oscillator network comprising a tube connected to produce local oscillations, said oscillator tube being coupled to said negative oscillation grid across said resistor to impress thereupon said local oscillations, said oscillator grid being disposed between the positive auxiliary electrode and the anode, and the signal grid being disposed between the cathode and auxiliary electrode.

2. In combination, a tube provided with at least a cathode, anode, signalelectrode, screen electrode, and auxiliary electrode, means to apply a signal to the signal electrode, means to bias the latter negative with respect to the cathode, means to bias, the screen at a. positive potential, means to bias the auxiliary electrode negative with respect to the cathode, the negative auxiliary elec trode being disposed between the screen and anode, and means, including an electron discharge tube having its circuits arranged to produce local oscillations, reactively coupled to said auxiliary electrode to vary the potential thereof at the frequency of said oscillations, a direct current connection, including a resistor between the cathode and the negative auxiliary electrode, said oscillation means being coupled across said resistor, said screen being disposed between the. two

negative electrodes and acting as an electrostatic screen therebetween.

3. In a heterodyne type of radio receiver, in combination, a detector network comprising an electron discharge tube provided with at least a cathode, a signal electrode, an anode, a local oscillation electrode, and an auxiliary electrode between said two electrodes, a tunable signal input circuit connected between the signal electrode and cathode, an intermediate frequency transmission network connected to the anode of said tube, means for maintaining said auxiliary electrode at a positive potential with respect to the said cathode, signal electrode and oscillation electrode, a resistor connected in circuit between said cathode and oscillation electrode, a tunable local oscillator network including a tube connected to produce local oscillations, said oscillator tube being coupled to said oscillation electrode across said resistor to impress thereacross said local oscillations, said oscillation electrode being disposed between the positive auxiliary electrode and' the anode, and the signal electrode being disposed between the cathode and auxiliary electrode.

4. In combination, an electron discharge tube provided with at least a cathode, anode, signal electrode, screen electrode, and auxiliary electrode, means to apply a signal to the signal electrode, means to bias the latter negatively with respect to the cathode, means to bias the screen at a positive potential, said auxiliary electrode being disposed between said screen electrode and anode, and means, including an electron discharge tube having its circuits arranged toproduce local oscillations, reactively coupled to said auxiliary electrode to vary the potential thereof at the frequency of said oscillations, a direct current connection including a resistor between the cathode and said auxiliary electrode, said oscillationa means being coupled across said resistor, and, said screen electrode being disposed between said signal and auxiliary electrodes and acting as: an electrostatic screen therebetween.

HAROLD O. PETERSON. ELMER F. BOND.

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