US2303484A - Modulated continuous-wave operation - Google Patents

Description

Dec. 1, 1942. M D N 2,303,484

MODULATED CONTINUOUS-WAVE OPERATION Filed Aug. 13, 1940 I WITNESSES: INVENTOR Z,MW (W/ J m; (/5811.

Patented Dec. 1, 1942 MODULATED CON TINUOUS-WAVE OPERATION Carl J. Madsen, Woodlawn, Md., assignor to Westinghouse Electric & Manufacturing Company,

Ealsita Pittsburgh, Pa., a corporation of Pennsyl- Application August 13, 1940, Serial No. 352,348 4 Claims. (01. 179-1715) My invention relates to continuous-wave generating systems often employed for communication and direction-finding purposes and, in particular, relates to a system which can be employed at will either for generating continuous waves of substantially constant amplitude or for producing continuous waves which are modulated in accordance with the frequency of a local generating source.

One object of my invention is to provide a system which may be changed from modulated continuous-wave generation to constant amplitude continuous-wave generation with a minimum number of alterations in the circuit connections.

Another object of my invention is to provide a system which can be altered from modulated continuous-wave to straight continuous-wave operation without switching operations in the grid circuits of the audio oscillator and which will operate without such circuit changes while still maintaining substantially the same output wave form in each of the above-mentioned modes of operation.

Other objects of my invention may become apparent upon reading the following specification taken in connection with the single figure of drawing, which is a circuit diagram of an interconnected radio-frequency amplifier and audiofrequency oscillator adapted to form a portion of a continuous-wave transmitting system and embodying the principles of my invention.

In the drawing, a radio-frequency amplifier I, which may be of the pentode type, has its anode 2 and cathode 3 supplied with voltage from a direct-current source 4 of the variable potentlometer type well known in the radio art. The plate circuit of the tube I is provided with a variable capacitor 5 and an inductor 6 for coupling it to a load or to other amplifiers in a manner conventional in the radio art. A capacitor 8 is provided which has one terminal grounded and thereby connected to the grounded negative end of the voltage source 4 to bypass radio-frequency currents in a manner conventional in the art. The tube I may likewise be provided with a screen grid 9 grounded through a capacitor II and connected through an inductor I2 to an appropriate point of voltage on the source 4. The tube I is likewise provided with a control grid l3 which is connected through an input source I4 to a proper bias potential point on the direct-current source 4 in a manner conventional in the radio When any desired carrier wave, which may, when desired, vary in accordance withsignals to be transmitted, is impressed upon the input element I4, the output circuit connected 0 the plate 2 will transmit an amplified replica of the voltage impressed on the input element I4 as a result of th connections so far described, and is adapted to operate for continuous-wave transmission.

In order to provide for modulated continuouswave transmission when desired, a second tube 2|, which may have a cathode, an anode and a control grid, is arranged to derive current from the voltage source 4 througha winding 22. The control electrode of the tube 2| is connected to a suitable bias point on the voltage source 4 through a resistor 23 and an anti-resonant circuit comprising a capacitor 24 connected across the terminals of a winding 25 which is in inductive relation to the winding 22. A capacitor 26 may be provided to connect the cathode end of the winding 25 to ground, and a capacitor 21 be provided to connect the positive end of the winding 22 to ground to form alternating-current bypasses in accordance with practice well known in the radio art. By proper poling and adjustment of the windings 22 and 25, the tube 2| may, in a manner well known in the radio art, be made to generate audio-frequency oscillations of the frequency at which it is desired to modulate the continuous-wave output of tube I. To impress the audio-frequency oscillations of the tube 2| upon the radio-frequency amplifier I, the grid of tube 2| is connected to the suppressor grid I5 of the tube I When the tube 2| is rendered operative by raising its cathode to an electron-emitting temperature, the tube 2| will generate oscillations of the desired frequency for modulation of the output of radio-frequency amplifier and impress them upon the output thereof. The system is thus arranged for modulated continuous-wave operation. When now it is desired to operate the system as a straight continuous-wave device, a switch 28 in the cathode circuit of the tube 2| may be opened, thereby deenergizing it; when this is done, it may be found that the radio-frequency amplifier continues to operat with a good output and an undistorted wave form.

With a source of 2000 volts impressed upon the anode circuit of radio-frequency amplifier I,

a source of 1000 volts impressed upon the plate art. The tube i is likewise provided with a suppressor grid I5 which is connected to ground in a conventional manner through a capacitor I8.

of the oscillator tube 2|, and from 300 volts to 600 volts impressed upon the grid 9 of radiofrequency amplifier I, I have found that a maximum output is obtained from the radio-frequency amplifier l during continuous-wave operation if the control grid of the tube 2| is biased to a 3 positive potential or from .zero to 60 volts.

voltage on the grid I! in radio-frequency amplifier I, may be varied to obtain the most desirable wave form and amplitude of the output current from the circuit of plate 2 or the radioirequency amplifier.

While the radio-frequency amplifier tube I has been described as having a screen grid 9, it will be recognized that a tetrode in which this screen grid is omitted'may be usefully employed for certain conditions. Likewise, it will be recognized by those skilled in the art that, while the audioirequency oscillator 2| has been described as a triode, a tetrode or a pentode arranged for audioirequency oscillation in accordance with connections well known in the radio art may replace such a triode.

While in accordance with the patent statutes I have described a specific embodiment of the principles 01 my invention, it will be recognized that they are capable of broader application in ways which will be evident to those skilled in the art.

I claim as my invention:

1. In a carrier-wave modulation system, a radio-frequency amplifier tube having an anode, a cathode and at least two control electrodes, an input circuit adapted to impress a carrier wave upon one of said control electrodes, an output circuit connected to said anode, an oscillation generator tube comprising a cathode, an anode and at least one control electrode, a bias resistor connected between the last-mentioned cathode and the last-mentioned control electrode, a connection conductive to direct current from a second control electrode of the first-mentioned tube to a point on the circuit of said resistor, and means for selectively rendering said generator operative and inoperative while said amplifier is maintained operative.

2. In a carrier-wave modulation system, a radio-frequency amplifier tube having an'anode, a cathode and at least two control electrodes,

an input circuit adapted to impress a carrier wave upon one of said control electrodes, an output circuit connected to said anode, an oscillation generator tube comprising a cathode, an anode and at least one control electrode, a bias resistor connected in a circuit between the last-mentlonedcathode and an anti-resonant circuit connected to the last-mentioned control electrode, and a connection from a second control electrode of the first-mentioned tube to a point on the circuit including said bias resistor remote from said last-mentioned cathode.

3. In a system for transmitting carrier waves, an amplifier tube having an anode, a cathode and at least two control impressing a carrier wave on one of said control electrodes, a vacuum-tube oscillation generator comprising an anode, a cathode and a control electrode, means for coupling the circuit otthe lastmentioned control electrode and the last-mentioned anode to cause said oscillator to generate a modulating-frequency current, a connecting channel between the first-mentioned cathode and the second-mentioned cathode, a bias resistor between the second-mentioned cathode and its associated control electrode, and a connection from a second control electrode in the first-mentioned tube on the circuit of said resistor, and means for selectively rendering said generator operative and inoperative while said amplifier is maintained operative.

4. In a system for transmitting carrier waves. anamplifier tube having an anode, a cathode and at least two control electrodes, means for I impressing a carrier wave on one of said control electrodes, a vacuum-tube oscillation generator comprising an anode, a cathode and a control electrode, means for coupling the circuit of the last-mentioned control electrode and the lastmentioned anode to cause said oscillator to generate a modulating-frequency current, a connecting channel between the first-mentioned cathode and the second-mentioned cathode, a bias resistor provided with bypass capacitance between the second-mentioned cathode and its associated control electrode, and a connection from a second control electrode in the first-mentioned tube to a point on the circuit of said resistor, and means for selectively rendering said generator operative and inoperative while said amplifier is maintained operative.

ARL J. MADSEN.

electrodes, means for

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