US2492168A - Modulator - Google Patents

Description

Dec. 27, 1949 MARKER 2,492,168

MODULATOR FiledApril 3, 1948 SQUARE WAVE PULSE AMI? IFECWF/tn mrm k i km J5 m E k k as /55 l a Q E I & k 8 RfFLfCTR V/ V2 v 0 o WME VOLTAGE I l l EEFZEC'TO/P VI 0 5 JNVENTOR. VOLT/76E THU/VA r. MARKER TTOFNEY Patented Dec. 27, 1949 I MODULATOR Thomas F. Marker, Bloomfield, N. J., alsignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application April 3, 1948, Serial No. 18,812

'lClalms. 1

My invention relates generally to modulators and more particularly to means for applying si nal voltages to regulated or steady direct currents in a communication system.

Electronic oscillator, amplifiers, and modulators invariably require a high voltage direct current source and, generally, this source must supply a fairly steady voltage to prevent undesired frequency drift, changes in gain, and the like. Some systems are so sensitive to these voltage changes that voltage regulators are placed between the source and the load. One regulator comprises a discharge device with the grid-controlled space of the device connected in series with the load and source, and with a feed-back circuit to apply voltages to the grid in phase opposition to voltage changes at the source to neutralize and hold steady the voltage at the load. Obviously, signal voltages cannot be impressed on the direct current voltage of such a regulated source because the signals would be opposed and neutralized by the regulator.

One object of my invention is, accordingly, a signaling system in which signals may be effectively impressed on regulated direct current.

The generator of microwaves requires particularly well regulated direct current sources, the frequency of operation usually being responsive to small changes of electrode potential. The output of the so-called reflex oscillator, for example, will vary in frequency or even stop with small changes of potential of the reflector electrode and must be connected to a voltage regulator that will effectively protect the reflector from voltage changes. When rectified alternating current of commercial power lines is used, both gradual and rapid fluctuations of line voltage must be reckoned with and regulators as well as the usual filters must be used. Yet, it is sometimes desirable to modulate the amplitude of direct current supplied to such oscillators while maintaining steady the unmodulated or reference value of the voltage.

Accordingly, a more specific object of my invention is a system for modulating with signals the amplitude of regulated voltages to oscillators, a still more specific object being the modulation .of the direct current voltage applied to the refiection electrode of a reflex oscillator.

One embodiment of my invention comprises, essentially, a voltage source and a load such as an oscillator with a voltage regulator therebetween. The regulator contemplated comprises a gridcontrolled electron discharge device with the anode-cathode space connected in series with the source and with the grid coupled to the line and responsive to voltage changes at the load so that the impedance of the anode-cathode space may be changed to compensate for changes in voltage at the source. A signal source is also connected to the grid, and to prevent neutralization of the signal modulation intended for the load, a low pass filter is inserted between the grid and the point on the line from which the grid receives its degenerative energy. Hence, the grid may respond to the slow line variations or low frequency changes below the cut-oil frequency of the low pass filter, but will not respond to signal frequencies feed-back from the line.

The above-mentioned and other featuresand objects of this invention and the manner of attainin them will become apparent and the invention itself will be best understood, by reference to the following description of an emb0diment of the invention taken in conjunction with the accompanying drawing, wherein:

Fig. 1 is a circuit diagram of one modulator of this invention, and

Fig. 2 are graphs showing the functional relation of important variables of the circuit of Fig. 1.

For illustrating the principles of this invention, the simple rectangular signal wave is first considered, and the oscillator on which the signals are impressed is of the reflex type. It will be understood as the description proceeds that both the signal source and the type of oscillator may be changed in many ways without departing from the scope of the invention. Further, the details of the voltage regulator circuits may be changed in various ways by those skilled in the art within the teachings here set forth. The oscillator l comprises a cathode 2, a control grid 3 and a pair of grids 4 and 5 in aligned openings in a resonant cavity structure 6. The cavity walls are toroidal and are symmetrical about the aligned openings. The reflector electrode 1 is parallel to and is spaced a measured distance from the grids on the side opposite th cathode. A relatively high voltage on the grids accelerates the electrons from the cathode to and through the grid openings. As the electrons traverse the space between and near the grids, certain of the electrons are accelerated still more and others are decelerated depending on th times of arrival with respect to the time phase of the alternating electric field between the grids. This later effect tends to bunch the electrons. The bunches of electrons approaching the reflector are decelerated by the negative reflector field, are stopped, and are returned to the grid so that for a given initial velocity and electrode spacing the reflector voltage may be adjusted to cause the electron bunches to return to the grid at the proper time phase to give up much of their kinetic energy to the electric field. Experience has shown that oscillations may be maintained at a number of distinctly different reflector voltages, the oscillations, always at or near cavity frequency, being known as voltage modes. The range of tuning by the reflector voltage within any voltage mode is quite narrow and the oscillator is inactive at intermediate values of reflector voltage.

The voltage source and voltage regulator for the reflector, hereinafter more fully described, may be adjusted to hold the reflector at precisely the desired mode voltage, and the signal source in combination therewith will vary the reflector voltage, in spite of the regulator for the voltage source. Undulating and voice signals will frequency modulate the oscillator over a limited range, but with pulse signals of the proper amplitude, the reflector voltage may be made to swing abruptly into and out of the mode voltage to turn the oscillator on and off. The pulses, further, may be modulated as to phase, frequency, or duration.

A commercial alternating current power source I is assumed and since the rectifier and filter 9 may be any of the known types they need no specific description. The positive and negative output leads I and H of the rectifier are connected, respectively, to the cathode 2 and reflector electrode 1 of the oscillator. In one lead, for example In, is serially connected the anodecathode space l2l3 of the electron discharge device It, the grid IS in the device conveniently controlling the anode-cathode impedance of the device. The voltage applied to the load is sampled by the sliding contact it of a potentiometer i1 directly across the load, or if desired directly across the source. For greater sensitivity, the voltage at the contact i6 is first amplified in the pentode l8 and then applied to the grid I of the impedance device It. The pentode includesan anode IS, a cathode 2n and control grid 2| as well as a screen and suppressor. The gaseous discharge tube 22 is connected in the cathode circult of the amplifier to establish a fixed potential for the cathode so that voltage changes at the grid of the amplifier will appear in amplified form at the anode and hence at the grid of the impedance device. With the plate load resistor 23 connected as shown the amplified voltages are inverted so that increased current through the impedance tube and increased voltage at the potentiometer contact l6 and grid 2| means reduced voltage at the plate I9 of the amplifier and at the grid ii of the impedance tube.

According to a further and important feature of this invention, signal voltages are also applied to the grid 15 of the impedance device. The particular signal source shown comprises a signal oscillator 24, of say 900 to 1100 cycles per second, and a one or two stage amplifier 25 for squaring the wave followed by a conventional pulse amplifier 28. The signal output of the last amplifier is applied, through the coupling condenser 21, directly to the grid l5 of the impedance device. A diode 28 and parallel resistor 29 are connected across the input of the impedance device to hold constant the reference level of the pulses.

Now, a low pass filter 30 comprising the resistor II and the condenser 32 is connected between the output of the amplifier I8 and the input of the impedance device, and the time con- 4 stant or cut-oflfrequency of the resistance-capacity combination is chosen intermediate the signal frequency and the probable frequency of variation of the line voltage. Since voltage variations at the oscillator attributable to line voltage disturbances and drift or due to load changes are usually quite low in frequency, the cut-off irequency may be made lower than any usable signal frequency. Hence, all regenerative voltages of signal frequency may be blocked by the low pass filter to permit signal modulation of current passed by the impedance device without altering the voltage regulating function of the device.

While the impedance of tube It has been described in series between the source and the load, it will appear to those skilled in the art that the impedance of the tube could be connected in shunt to the lines it and i I to perform the voltage regulating function. The phase of the degenerative energy would of course then be reversed.

The functional relations of the reflector voltage, time, and amplitude of oscillator output are depicted in the graphs of Fig. 2. The curve 33 indicates how the high frequency output of a refiex oscillator drops off to zero as the reflector voltage varies to either side of the optimum mode voltage VI. At other reflector voltages, such as V3, the oscillator will recommence oscillations. The direct current pulse voltage represented by the line 34 is applied to the grid of the impedance device and if adjusted to such a value as to repetitiously change the reflector voltage between the two values Vi and V2 corresponding, respectively, to reflector voltages for full-on and full-oil oscillations, pulses 35 of high frequency appear in the oscillator output. If the pulse signals 34 are substantially square and the slope of the sides of the pulses approach infinity, the frequency transition of the oscillator becomes so short frequency modulation components may be neglected. The envelope of the high frequency oscillator output is then correctly represented by the rectangular forms 35. Modulation of the phase, frequency or duration of the direct current pulses produce, obviously, corresponding changes in the high frequency pulses.

While the modulated voltage regulator of this invention has been specifically applied to a reflex oscillator, it may be applied to more conventional oscillators or to high frequency modulators where the reference voltage must be maintained as a predetermined value. The terminals of my regulator may for example supply the steady voltage and the signal to the anode or to the grid of a cotnventional feed-back or electron-coupled oscilla or.

That is, while I have described the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

I claim:

1. In combination an unregulated direct current voltage source, a load, a grid-controlled electron discharge device, the anode-cathode space of said device being connected between said source and said load, means responsive to voltage changes of said source applying a voltage to said grid to oppose current changes in said space, a signal source connected to said grid, and a low pass filter with a cut-oi! frequency below the signal frequency of said source connected between said grid and the voltage responsive means.

2. The method of modulating a steady direct current comprising varying the impedance of the circuit between the current source and the load for said source in response to changes in voltage of said source of a predetermined range of frequencies, the impedance changes being of such phase as to neutralize changes in magnitude of said direct current, and modulating said impedance at signal frequencies outside said predetermined range of frequencies.

3. In combination, a voltage source, an electronic device connected to said source, said device being responsive to voltage variations of said source, an impedance device including an anode, a cathode and a grid, the anode and cathode being serially connected between said source and said electronic device, means applying degenerative energy to said grid from said source, and a signal source coupled to said grid.

4. In combination, a voltage source, an electronic device connected to said source, said device being responsive to voltage variations of said source, an impedance device including an anode, a cathode and a grid, the anode and cathode being serially connected between said source and said electronic device, means applying degenamplifier tube, the input circuit of said amplifier 85 voltage regulator inoperative to voltage changes of signal frequency.

'7. In combination, a reflex oscillator containing a reflection electrode, a voltage source connected to said reflection electrode; a voltage regulator in circuit with said source responsive to voltage changes at said reflection electrode, a signal source coupled to said reflection electrode, and means to exclude signal voltage variations from said voltage regulator.

THOMAS F. MARKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,120,884 Brown June 14, 1938 2,393,785 Leeds Jan. 29, 1946 2,403,716 Goldberg et al July 9, 1946

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