US2041830A - Signaling system - Google Patents

Description

May 26, 1936. c w. HANSELL SIGNALiNG SYSTEM Filed May 20, 1933 2 Sheets-Sheet 1 INVENTOR C W. HANSELL ATTORNEY y 1936- c. w. HANSELL I 1,830

I SIGNALING SYSTEM Filed May 20, 1933 2 Sheegs-Sheet 2 mo /:55 (WM/mm;

ATTORNEY Patented May 26, 1936 UNITED STATES PATENT OFFICE SIGNALING SYSTEM notation of Delaware Application May 20, 1933, Serial No. 672,034

4 Claims.

This invention relates to the production of ultra high frequency alternating currents such as are employed in radio signaling in the ultra short wave field, and to methods of and apparatus for modulating such currents by means of signals. The invention particularly concerns a novel type of magnetron oscillator circuit for the generation of oscillations of the order of 300,000,000 cycles and higher, and is a continuation in part of my copenoling application Serial No. 471,309, filed July 28, 1930.

Magnetron oscillators in the past have been known to comprise electron discharge devices in v which the generation of oscillations has been controlled by a magnetic field. The usual type of magnetron consists of a cylindrical envelope within which is an elongated electron emitting element in the form of a filament and surrounding the element an anode, either of the solid or split type. On the outside of the envelope it is customary to provide a coil for generating a magnetic field. It is known that when the filament of the magnetron is maintained at suitable incandescence by a source of heating current and a suitable voltage is impressed upon the electrodes, a current will flow in the output circuit connected to the anode. With no modifying magnetic field, the value of this current is determined by various factors, among which are the impressed voltage, the filament temperature, the size andgeometrical relations of the electrodes, and the resistance of the output circuit. The electrons which carry or constitute this current travel outwardly in straight radial paths from the cathode to the surrounding anode. When a magnetic field is applied substantially parallel to the cathode and hence substantially at right angles to the electric field between the electrodes, then the electrons are deflected and caused to travel in a spiral path about the filament on their way to the anode. As the field strength is increased the sprial path of the electrons becomes longer until finally at a critical magnetic field strength, characteristic of any particular device, some of the electrons fail to reach the anode by reason of this deflection, thereby resulting in a decrease of current. When the field strength is still further increased, above this critical value, the electron current rapidly falls and is finally reduced substantially to zero. It has been usual in these magnetrons to control the current flowingfrom the filament to the anode entirely by varying the strength of the magnetic field.

The present invention has for one of its objects -to provide a novel type of magnetron circuit which is capable of generating with high efiiciency and small cost ultra short Waves of the order of one meter and less, and wherein the magnetic field is not used as a control element as in the past, but only to produce conditions under which the moving electrons themselves may constitute their own control. A most important characteristic of the present invention, therefore, is that the magnetic field remains substantially constant throughout the period of a cycle.

Another object is to enable the generation of much, greater amounts of power in the form of the very high frequencies than has heretofore been possible, and the modulation of the oscillations of such high frequencies.

A feature of the present invention is the solid type of anode construction which is utilized within the envelope itself in order to increase the efficiency and amount of power obtainable from the magnetron.

Other features and objects will appear in the subsequent detailed disclosure, wherein Figure 1 shows partly in section and partly diagrammatically a circuit arrangement for producing ultra high frequencies and modulating these with signals in accordance with the present invention, and Figure 2 illustrates a modification of the system of Figure 1. Figure 3 illustrates schematically and in simple form a view of the magnetron oscillator by itself showing, for purposes of illustration, the paths of the electrons under different conditions of field strength. v

Throughout the several views like figures will be used to indicate like parts.

Referring to Figure 1, there is shown a magnetron oscillator for obtaining the desired ultra high frequency oscillations in accordance with the present invention. This magnetron comprises a cylindrical anode 22 within a glass envelope 20 at the longitudinal axis of which is an electron emitting filament 23. Surrounding the envelope of the device is a field coil 24 which, when energized, sets up a strong magnetic field coaxial with the filament and at right angles to the plane of the figure. For heating filament 23 there is provided a source of current, such as is illustrated by the battery 25, and for applying a suitable potential to the anode 22 a source of high voltage, which may be illustrated by battery 26 which connects with the anode through a telegraph key or relay 2! and lead 28. Power source 25 may also serve to energize the field coil 24 which is arranged to set up a magnetic field which is substantially constant throughout the period of a cycle of oscillation.

Coupled to lead 28 in any desired manner may be a utilization circuit such as 29 which is herein shown for purposes of illustration as a transmission line extending to an antenna circuit 30. There may be provided, if desired, tuning elements in the transmission line such as trombone slides 31 and 32 for tuning the line to the output circuit. A condenser 33 provided with a movable slider 34 is shown connected to lead 28 for effecting the tuning in the anode circuit. For modulating the oscillations generated, there is shown a telegraph key or relay 21 which interrupts the circuit extending from the anode to source 26 in accordance with the signals to be transmitted.

In the operation of the device, when the filament is energized, electrons will be emitted which will be attracted toward the anode 22 and tend to travel directly thereto. These electrons in motion constitute an electric current and are subject to the same laws as any current carrying conductor. The electrons moving across the magnetic field set up by the coil winding 24 will have a force exerted upon them at right angles to their direction of motion and in proportion to their velocity and to the strength of the magnetic field. It will thus be evident that the electrons will be forced to follow a curved path, as shown in Figure 3, and if the field is of sufficient strength will not reach the anode at all, but will return to the filament, following the image of their outward path and giving up their kinetic energy in so doing. This condition is commonly known as cut-01f in a magnetron tube.

At a critical plate voltage for a definite field strength the electron stream will just skim the surface of the anode 22 and some of the electrons will strike the anode while others will return in a similarly shaped path to the filament. The complete path of the electronic stream from filament to plate and back to filament will be approximately that of a cardioid, as is shown in Figure 3. If the anode voltage is increased, all of the electrons will be attracted to the anode, and if the field strength is increased none of the electrons will reach the anode. At a critical rela tion between the anode voltage and the magnetic field some of the electrons will return to the filament as previously described, a condition which will increase the space charge near the filament and decrease the flow of electrons from the filament toward the anode. This increase in space charge will, in turn, decrease the number of electrons refiected back from the anode a short time later, and thereby the space charge near the filament will decrease. Such action will again allow the flow of electrons from the filament toward the anode, and the process will be repeated periodically. The frequency will depend chiefly on the anode 'voltage and will increase when the voltage is increased. In other words, it may be said to be determined by the time taken for an electron to travel from the filament through its path back to the filament, an interval equal to approximately the length of time of such travel for a complete period. The strength of the magnetic field, it will be understood, determines the amplitude of the oscillations and the efiiciency, but has relatively little to do with the frequency.

The wave form of the electronic current which fiows to the anode will ordinarily be quite far from a sine wave and will be more nearly rectangular in shape. Such a wave form is rich in harmonics and the useful output from the tube may be obtained at harmonics of the fundamental frequency by tuning the circuits between the filament 23 and the anode 22 to the harmonics, as shown, for example, by tuning condenser 33 which is arranged to glide over lead 28 to obtain the desired frequency. Experiments have so far produced oscillations having a wave length of thirty centimeters and it is possible to obtain waves of ten centimeters or less.

The oscillations generated are modulated telegraphically by key or relay 21 which interrupts the anode circuit in accordance with the signals to be transmitted. Of course, a vacuum tube or other device capable of current control may also be used.

It is also possible to make the tube produce its oscillations directly at harmonic frequencies by having groups of electrons traversing the space between the filament 23 and the anode 22 rather than a continuous stream, and in practice it is diflicult to determine which eifect predominates in producing energy at harmonic frequencies.

Figure 2 is a modification of Figure 1 and shows one manner of modulating the output high frequency currents in the anode circuit fying the diagram. The speech waves are amplified by an amplifier 36 and the audio components impressed through a transformer 31 upon the grid of an electron discharge device 38 whose output is connected to the anode lead 28. As will be noted, tranmission line circuit 29 connected to the antenna 30 is herein shown as coupled to the anode 22 through a transformer 39 instead of the straight conductor leads illustrated in Figure 1. Other means of coupling will readily suggest themselves to those skilled in the ar In the arrangement of Figure 2 the ultra high frequency magnetron oscillator has its anode to filament voltage modulated by the Heising method of modulation. Obviously, the oscillations may also be modulated by impressing the output of an audio amplifier such as 36 upon the anode to filament circuit by connecting the secondary of the amplifier output transformer 31 in series with the anode to filament voltage supply circuit. The modulating energy may be applied to amplifier 38 over any telephone circuit and may come from a source of audio or low radio frequency modulating energy, such as 39, or from a phonograph record, phonofilm or any other sound recording and reproducing device. If desired, the modulation applied may come from a television pick-up device. For disconnecting microphone 35 and connecting source 39 to the magnetron, a double pole-double throw switch 40 may be employed.

In many cases the keying system illustrated in Figure 1 may be combined with the modulating system of Figure 2 in order to transmit interrupted continuous waves or modulated telegraph signals. For this purpose a telegraph key 4| is shown in the lead extending from the field coil 24 to its source of high voltage energizing current. Condenser 42, which is shunted across the telegraph contacts, merely serves to reduce sparking.

In the circuit of Figure 2 it is proposed to use a separate modulation reactor 43 instead of using the field coil as a reactor in the manner indicated in Figure 1.

While the theory of operation outlined above is believed to be a correct explanation of the principles underlying applicants invention, further investigation may lead to a modification of this theory. It is tobe distinctly understood, however, that the invention is independent of any theory which may be advanced to account for the results obtained.

I claim:

1.' High frequency transmitting apparatus comprising-a magnetron oscillator having a cylindrical anode of continuous form and a filament positioned along the axis of said cylindrical anode, both being located within an envelope, a magnetic field which is substantially constant throughout the period of a cycle for influencing the electrons accelerated from said filament toward said anode located substantially parallel to the filament, a source of potential, a connection from the positive terminal of said source to said anode, a condenser movably adjustable over the path of said connection for tuning the oscillations in said anode connection to a desired frequency, a transmission line and an antenna inductively coupled to said connection, and a telegraph key serially connected between said source of potential and said connection for modulating the oscillations in said anode connection in accordance with telegraphic signals to be transmitted.

2. In combination, a magnetron oscillator comprising an envelope within which there are located a cylindrical anode and a filament positioned along the axis of said cylindrical anode, a magnetic field which is substantially constant throughout the period of a cycle for influencing the electrons which are accelerated from the filament to the anode surrounding said envelope, at source of potential for heating said filament, a capacity in shunt with said heating source, a source of positive potential and a connection therefrom to said anode, a condenser one plate of which is grounded and the other plate of which is adjustably connected with said anode connection for tuning the oscillations produced by said magnetron to a desired frequency, a connection from the electrical midpoint of said shunt capacity to ground, a utilization circuit coupled to said anode connection, and means in circuit with said anode connection. for modulating the oscillations I generated by said magnetron.

3. In combination, a magnetron oscillator comprising an envelope within which there is located a cylindrical anode and a filament positioned along the axis of said cylindrical anode, a magnetic field which is substantially constant throughout the period of a cycle for influencing the electrons which are accelerated from the filament to the anode surrounding said envelope, a source of potential for heating said filament, two serially connected capacities in shunt to said heating source, a connection from ground to a point between said two capacities, a source of potential and a connection from the positive terminal of said source to said anode, a variable condenser one plate of which is connected to ground and the other plate of which is adjustably movable over said anode connection for tuning the oscillations produced by said magnetron to a desired frequency, a utilization circuit coupled to said anode connection, and means in circuit with said anode connection for modulating the oscillations generated by said magnetron.

4. In combination, a magnetron oscillator comprising an envelope within which there is located a cylindrical anode and a filament positioned along the axis of said cylindrical anode, a magnetic field which is substantially constant throughout the period of a cycle for influencing the electrons which are accelerated from the filament to the anode surrounding said envelope, a source of potential for heating said filament, two serially connected capacities in shunt to said heating source, a connection from ground to a point between said two capacities, a source of potential and a connection from the positive terminal of said source to said anode, a variable condenser one plate of which is connected to ground and the other plate of which is adjustably movable over said anode connection for tuning the oscillations produced by said margnetron to a desired frequency, a utilization circuit comprising a transmission line inductively coupled to said anode connection and an antenna connected to said line, and means comprising a telegraph key in circuit with said anode connection for modulating the oscillations generated by said magnetron.

CLARENCE W. HANSELL.

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