US1945546A

US1945546A - Oscillator

Info

Publication number: US1945546A
Application number: US400489A
Authority: US
Inventors: Clarence W Hansell
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1929-10-18
Filing date: 1929-10-18
Publication date: 1934-02-06
Anticipated expiration: 1951-02-06
Also published as: NL35065C; FR699497A; DE537198C

Description

Feb. 6, 1934. w HA EL 1,945,546

OSCILLATOR Filed Oct. 18, 1929 ("I "6"" ""6656 ll QNTENNQ INVENTOR CLARENC E W. HANSELL' BY vf dm ATTORN EY Patented Feb. 6, 1934 PATENT oFEicE oscmm'roa 1 Clarence W. Hansell, PortJeifer-uon, N. Y., as-

aignor to Radio Corporation of America, a eor-' porationof Delaware Application October 1S, 1929. Serial No. 400,489 2': Claims. (01. 250-36) l lators of which the most effective have been mechanical oscillators, such as tuning forks and piezo-electric quartz crystals, which control the output frequency of a generator through a chain of amplifiers. However, these schemes offer the disadvantages that they-are expensive, difficult to adjust and add greatly to the probability of failures in service due to the increase in the number of tubes, circuits etc., the failure of any one of which may interrupt the operation of the equipment.

In order to eliminate the foregoing difficulties, another object of this invention is to provide an oscillator in which low power frequency control devices such as crystals and their associated low power amplifiers and circuits may be eliminated, and wherein frequency stabilization may be applied directly to a relatively high power generator of oscillations.

Broadly, to accomplish this object I make use of a sharply tuned circuit coupled to the high frequency oscillator which reacts upon the oscillator in a way which tends to hold the oscillator frequency near to the resonant frequency of the circuit. For the purpose of obtaining a very sharply tuned circuit, and to have afrequency control circuit which shall be independent of the load taken from the oscillator, I make use of a long resonant line having substantially uniformly distributed inductance and capacity.

Further, I cause such a line to have standing waves built up thereon depending solely upon the frequency and the length of the line and independent of any reaction caused by external circuits or loads, and, according to my invention, I apply the standing waves produced on the line to the generator, which I preferably make a tube oscillator, for controlling the frequency of oscillation thereof. In this way, not only does the long line act as a resonant circuit to pull the oscillator into step therewith; but, in another aspect it can be considered as a phase shifter, waves from the oscillator being sent over the line to the far end and reflected back to the oscillator, arriving back with a phase which shifts rapidly with change of frequency and which tends to modify the oscillator frequency to make zero difference in phase between the ingoing and reflected waves at the input end of the line. That is to say, the long line acts to pull the oscillator. into phase with its own oscillations whenever there is a shift in phase caused by shift in the oscillator frequency.

Still other objects of my invention are to provide a frequency stabilizer which improves in accuracy as the frequency at which it is operated '65 is increased, and to provide a frequency. stabilizer which shall be independent of variations in temperature humidity and barometric pressure. These objects are also fulfilled by the provision of' a long line for frequency control. As frequency increases, the length of any particular line, expressed in wave lengths, increases in pro-, portion to frequency. Since the rate of phase shift in the reflected waves with change of frequency is proportional to the number of wave 76 lengths in the line it follows that the theoretical percentage accuracy obtainable with any particular line increases in proportion to the frequency at which it is operated.

With reference to the last mentioned objects, 80 they are accomplished by temperature controlling the line; or, by designing the line so as to have constant electrical length regardless of temperature, by using materials not affected by humidity and placing the line in a sealed container. The effect of barometric pressure which may have considerable effect on the frequency of a crystal has practically no effect on a line. The effect of vibration is made negligible by using a rigid line construction.

Still another object of my invention is to provide a frequency stabilizer which may be utilized to stabilize an oscillator at more than one frequency, or in other words, to provide a stabilizer readily adapted to frequency changeover. This object is also accomplished by the use of a long resonant line, for, by simply varying the length of the line, the wave length of the standing waves thereon may readily be changed. Or, if desired, the line may be made to resonate at and to have not only standing waves of a fundamental frequency thereon, but also waves corresponding to harmonic frequencies relative to its fundamental.

The invention may best be understood by referring to the accompanying drawing in which I have shown a few embodiments of my invention which, of course, are to be taken only by way of illustration and not by way of limitation.

In the accompanying drawing, Figure '1 .indi-' no cates a resonant line inductively coupled to a tube oscillator for frequency control thereof,

Figure 2 indicates similar apparatus to tha shown in Figure 1 but wherein the line is capacitively connected or coupled to an oscillator,

Figure 3 shows by way ofexample a pushpull transmitter having, according to my invention, a long line directly connected or coupled thereto for frequency control, and,

Figure 4 is similar to Figure 3 but shows, in addition, an amplifier after the frequency controlled oscillator.

Tuming to Figure 1 I have indicated a high power tube oscillator 1 having in its output circuit a tunable circuit 2 tuned to approximately or as nearly as possible to a desired frequency, In this manner, the tuned circuit acts as a relatively rough controlfor the oscillator frequency. The control electrode 3 of tube 1 is regeneratively connected to the output circuit. Resistance 4 is provided to insure a correct biasing potential and choke 5 helps prevent radio frequency losses in the resistance. Condenser 6 acts as a radio frequency path to ground. Condenser '7 is the usual blocking condenser. Anode potential is supplied through a choke 8 to the anode 9.

The arrangement as shown is self starting and produces oscillations of a frequency corresponding to that to which circuit 2 is tuned. However, as so far described, due to a change in load upon the oscillator or due to some external reaction upon the circuits thereof, or due to a'change in voltage applied to some of the elements thereof,

. or for some other reason, the oscillation frequency of the oscillator will vary. Consequently, circuit 2 only approximately controls the frequency of oscillation. I

In order to prevent variation in frequency I inductively couple to the output circuit 2 of the oscillator by means of a coil12, a resonant line 10 whose effective length may be adjustably varied by means of a slider 11. By means of slider 11 the line 10 having substantially uniformly distributed inductance and capacity is caused to resonate very sharply at the desired frequency. As a resonant circuit, the line pulls the oscillator constantly into step with itself, and, as the line will not resonate at, but discriminates against, wave lengths other than that to which it is tuned, the oscillator 1 becomes frequency stabilized and will have very-much less variation in frequency with changes already referred to which ordinarily produce large undesired frequency changes.

Due to reflection from points 13 and 14, standing waves are produced upon the line of constant wave length, depending upon the fixed length of the line.

As the standing waves on the

wires

15, 16 of the line 10 are opposite in phase, the standing wave potentials applied to the control electrode and anode of the oscillator will have the correct phase relationship for sustained oscillation generation; and further, these potentials of opposite phase on

lines

15 and 16 will pull the alternating poj as tentials on the grid and plate of tube 1, into phase with themselves, whenever there is a tendency for a shift in phase thereof due to a shift in frequency.

- If, after the line 10 is adjusted for a certain.

frequency, tuning condenser 32 is changed so that 5 quencies are desired, an additional adjustment of slider 11 must be made.- In either case, frequency changeover is relatively extremely simple.

In Figure 2, the long line 10 has its elements or

conductors

15 and 16 coupled or connected to the oscillator 1 by means of condensers i7, 18. These condensers will usually have suflicient dielectric capacity to act as continuous connections or short circuits for the oscillator frequency but if they have appreciable reactance this may easily be corrected by making the wires 15, 16 a little longer, than would be otherwise necessary for the production of standing waves of correct lingltlli, by means of slider or adjustable mem- As already pointed out, the long line 10 comprising

conductors

15, 16 having uniformly distributed inductance and capacity acts as a very sharply tuned circuit coupled tothe oscillator and locks the oscillator into step with the standing waves produced upon the conductors.

In Figure 3 I have shown my invention applied to a transmitting system utilizing pushpull connected

electron discharge devices

19, 20. The output circuits thereof are broadly tuned by varying the amount of inductance included-between the plates of the tubes. The capacity for the output resonant circuits of these tubes is furnished by the

interelectrode capacities

21, 22 indicated by dotted lines on the drawing. If desired, the tuning may be altered by paralleling the tube capacities by

variable condensers

60, 62 or by paralleling a portion of the inductance 23 with a condenser 64.

The long resonant line for stabilizing the frequency of the pushpull oscillator is directly connected to the control electrodes or grids of the tubes. In other words, as in Figures land 2, the long line is closely coupled to the oscillator and carries a relatively considerable amount of high frequency energy.

Modulation or keying is accomplished by a suitable device 24 operated either directly or remotely. Device 24, of course, may be replaced by a telephone or a resistance through which voice or other signalling currents are made to flow, or, the anode potential of the oscillator tubes may be varied in accordance with methods already well known in the art.

As indicated on the drawing when keying device 24 is closed, negative bias is removed from '30 prevents short circuiting of the source of biasing potential 31 at that time also. Between the control electrodes or grids of

tubes

19, 20 there is connected a high frequency choke coil or impedance 66, whose mid-point is grounded through a by-passing condenser 68.

In Figure 4 I have shown an arrangement similar to that disclosed in Figure 3 but wherein the modulating currents are in the form of voice currents. Voice currents from telephone 50 may 7 be amplified as desired by any suitable amplifler 51 before causing the modulation of currents in the

oscillator

19, 20. The output of the oscillator may be amplified in any suitable way by any desired number of amplifier stages; and, in this case I have shown by way of example a single high power pushpull amplifier stage 52, 53 which amplifies the modulated oscillatory currents before transmission over the antenna system 28.

To prevent radiation from the long line, it, of course, may be, as already stated, shielded or, the

wires

15, 16 may be placed very close together, parallel, and, side by side as illustrated so that there is mutual radiation cancellation.

Still another way of preventing radiation would be to make -

wires

15 and 16 concentric. This scheme would also offer the advantage that the external conductor could be grounded and in this way any radiation is simply and effectively eliminated. A line controlled system making use of concentric conductors is described more fully in my copending application Serial Number 534,255, filed May 1, 1931 in the United States Patent Office.

Preferably the long resonant control line is placed indoors and temperature controlled so as not to vary in length. It may as already indicated, be made of material having zero coefficient of expansion whereby changes in length are avoided.

Although in the drawing the long line, (which is termed long because it is ordinarily a number of half wave lengths long) has been shown in connection with a single thermionic device or oscillator, or in connection with a single power stage, it should be apparent that, if desirable, a plurality of electron discharge devices or stages may be connected in cascade and the line applied to only the first one of them.

As the line is simple in construction and can handle large currents, it can be applied to the last stage or nearly the last stage of a power amplifier which was not possible by the use of any frequency stabilizer heretofore known. Of course, the invention is not limited to a high power amplifier or oscillator but may also be utilized to good advantage in low power equipment.

In actual construction, the resonant line may be an ordinary transmission line. It is preferable, however, to keep the line indoors to prevent variations in its electrical properties due to changes in temperature, wind, etc. Such a line is not affected by changes in barometric pressure and humidity and, therefore, presents for frequency control, marked advantage over other types of frequency control devices which are sensitive to pressure and moisture changes.

Another desirable construction is one in which the line is coiled on a dielectric of high strength. In this manner the line may be placed within an enclosure and easily temperature controlled. Also, if found advisable, such a line may be inclosed within a hermetically sealed container which may be evacuated to any desired degree or filled with any suitable gas. Shielding of this embodiment may be accomplished by the use of a grounded metallic cylinder about the coiled line, which may, if desired be split.

Having thus described my invention, what I claim is:

1. In combination, an oscillatory circuit having inductance and capacity, an electron discharge device having an anode a cathode and a grid, connections from said anode cathode and grid to points of different alternating current potential on said oscillatory circuit whereby oscillations are set up in said circuit at a frequency corresponding approximately to the resonant frequency of said circuit, and, a sharply resonant circuit coupled to said oscillatory circuit for maintaining constant the frequency of oscillations generated in said oscillatory circuit, said sharply resonant. circuit comprising a pair of conductors having substantially uniformly distributed inductance and capacity and arranged so as to be substantially radiationless.

2. In combination, an electron discharge device having an electron-emitting cathode a cold electrode spaced therefrom and maintained at a relatively positive potential and a grid intermediate said cold electrode and said cathode, a circuit having inductance and capacity, connections from said electrodes to points of different alternating current potentials on said circuit whereby oscillations are set up at a frequency corresponding approximately to the resonant frequency of said circuit having inductance and capacity, and, a pair of conductors, forming a sharply tuned circuit coupled to said first mentioned circuit for maintaining the frequency of oscillations in said circuit having inductance and capacity substantially constant, said conductors having uniformly distributed inductance and capacity and being adjusted so as to have standing waves of a desired operating wave length built up thereon and being arranged so as to be substantially radiationless.

3. In combination, a pair of electron discharge devices each having an electron emitting cathode, a cold electrode spaced therefrom and a grid intermediate said cold electrode and said cathode, a circuit having inductance and capacity connected across said cold electrodes, means 10! supplying relatively positive potentials to said cold electrodes whereby oscillations are set up in said circuit having inductance and capacity at a frequency corresponding approximately to the resonant frequency of said circuit having inductance and capacity, and, a pair of conductors having substantially uniformly distributed inductance and capacity adjusted so as to have standing waves of a desired operating wave length set up thereon coupled to said grids whereby the oscillations in said circuit having inductance and capacity are substantially locked into step at a frequency corresponding to the wave length of the standing waves set up upon said conductors.

4. A constant frequency system comprising a pair of electron discharge devices each having an anode a cathode and a grid, a circuit comprising an inductance coil and a condenser connected across said anodes whereby said anodes fluctuate 180 degrees out of phase, an impedance connected between said grids whereby saidgrids fluctuate 180 degrees out of phase, and, a pair of substantially linear conductors having substantially uniformly distributed inductance and capacity connected to said grids, said conductors being adjusted so as to have standing .waves set up thereon at a wave length corresponding substantially precisely to a desired frequency of operation and being arranged so as to be substantially radiationless.

5. A vacuum tube oscillator comprising an oscillator having input and output circuits at least one of which is tunable and, a long line long, relative to the operating wave length having standing waves thereon of a. desired wave length, coupled. to the oscillator so that potentials of the standing waves are applied thereto in such phase relationship as to pull the oscillator into step therewith.

6. A pushpull tube oscillator comprising a plurality of tubes, input and output circuits therefor, one of said circuits having a reactive elelea ment therein, and a long line several half wave lengths long at the desired operating frequency resonant at a desired oscillation frequency, coupled thereto for controlling the frequency of 'oscillaticr. of the pushpull tube oscillator.

1 7. Radio signalling apparatus comprising a pair of pushpull connected electron discharge devices oscillating at a desired frequency,.and means, coupled to the control electrodes of said devices comprising along line several half wave lengths long at the desired operating frequency having standing waves thereonof a wave length corresponding to the desired oscillation frequency, for stabilizing the oscillation frequency of said oscillator.

8. A generator of constant frequency oscillations comprising a multi-electrode device having cathode grid and plate electrodes, means for subjecting said grid electrode to a potential such that it is negative with respect to said cathode electrode, means for maintaining said plate electrode at a positive-potential with respect to said cathode electrode, a high frequency circuit connected between said grid and cathode electrodes; a high frequency circuit connected between said anode and cathode electrodes, one of said circuits being tuned to approximately a desired frequency ofoperation, said circuits being coupled together to generate oscillations of a frequency corresponding to the tuning of said tuned circuit, and a substantially radiationless resonant transmission line comprising a pair of straight conductors substantially parallel to one another and arranged close'together coupled to a pair of electrodes of said device for accurately frequency stabilizing the oscillations generated by said device.

9. A system for generating constant frequency oscillations comprising a pair of devices each having anode cathode and grid electrodes, a high frequency circuit connected between said anode electrodes, a high frequency circuit connected between said grid electrodes, means for subjecting said grid electrodes to a negative potential with respect to said cathode electrodes, said cathode electrodes being connected together, means for subjecting said anode electrodes to a positive potential with respect to said cathode electrodes, one of said high frequency circuits being tuned to approximately a desired operating frequency, both of said high frequency circuits being coupled together whereby oscillations are set up and generated at a frequency corresponding to the tuning of said tuned high frequency circuit, a substantially radiationless resonant transmission line comprising a pair of substantially linear conductors arranged parallel to each other and close together coupled to a pair of electrodes of said devices for frequency stabilizing the oscillations generated by said devices, and, an output circuit, independent of said line, coupled to the circuit connected between said anode electrodes.

10. In apparatus for generating high frequency oscillations of substantially constant frequency, a pair ofelectron discharge devices each having anode cathode and grid electrodes, a circuit having induc'ance and capacity and exhibiting parallel resonance phenomena at approximately a desired operating wavelength connected between said anode eletrodes whereby 'said anode electrodes fluctuate out of phase at the desired operating frequency, a circuit connected between said anode and cathode electrodes for subjecting said anode electrodes to a suitable operating potential with respect to said cathode electrodes, a circuit connected between said grid electrodes and said cathode electrodes for subjecting said grid electrodes with respect ranged as to be substantially radiationless, said conductors being adjusted in eflZetive electrical length so as to have standing waves of a desired operating wavelength thereon and said conductors being'dimensioned as to be of low loss and adapted to handle relatively large amounts of circulatory frequency controlling currents, and, a load output circuit, independent of said pair of conductors, coupled to said circuit connected between said anodes. v

11. A pushpull electron discharge device oscillating system comprising a pair of electron discharge devices each having an anode a cathode and a control electrode, an inductance coil connected between said anodes, an impedance connected between said control electrodes, a connection to ground from a point intermediate said impedance, said connection including a'resistance, and, a pair of conductors having uniformly distributed inductance and capacity conductively connected to said control electrodes, said conductors being adjusted so as to have standing waves of a wave length corresponding to a desired operating frequency built up thereon and 11( acting to pull the oscillations generated by said electron discharge devices into step with said standing waves.

12. In apparatus for amplifying or sustaining undulatory high frequency currents, the combi- 115 nation of an electron discharge device having input and output electrodes, a rough frequency controlling circuit having inductance and capacity regeneratively coupling said electrodes together, and, a long transmission line long relative to the operating wave length closely coupled thereto, said line comprising a pair of linear conductors having uniformly distributed inductance and capacity, being sharply resonant to a desired operating frequency and having standing waves 13-5 thereon, for frequency stabilizing the undulatory currents regeneratively amplified or sustained by said device.

13. In combination a pair of electron discharge devices each having an anode a cathode and a 3 grid, an inductance coil connected between said anodes, capacities between said anodes and grids acting to cause regenerative production ofoscillations at an approximately constant frequency, and, a pair of substantially linear conductors connected to said grids, said conductors having substantially uniformly distributed inductance and capacity, said conductors being adjusted so as to have standing waves set up thereon at a wave length corresponding exactly to a desired frequency of operation and acting to pull the frequency of oscillations setup by said capacities into step with the standing waves set up thereon.

14. A constant frequency system comprising a pair of electron discharge devices each having an anode a cathodeand a grid, an inductance coil connected between said anodes, a condenser connected to said inductance coil, an impedance connected between said grids whereby said grids fluctuate substantially 180 degrees out of phase, and,

a pair of substantially linear conductors having substantially uniformly distributed inductance and capacity connected to said grids, said conductors being adjusted so as to have standing waves of a desired operating wave length set up thereon and acting to pull the oscillations generated by said devices into step with the standing waves.

15. In a system for the production of sustained high frequency oscillations of substantially constant wave length, an oscillator for the generation of high frequency oscillations comprising an electron discharge device having regeneratively coupled input and output electrodes, a tuned circuit for controlling the frequency of oscillations generated to approximately a desired value, and, a two wire radiationless transmission line long, relative to the operating wave length having standing waves thereon of a wave length corresponding to a desired frequency of oscillation, closely coupled to said oscillator for pulling the oscillations generated by said oscillator into step with the standing waves on the transmission line.

16. In a system for the production of high frequency oscillatory energy, a regeneratively acting electron discharge device utilizing interelectrode capacity for the production of sustained oscillations, reactive tuning means for roughly controlling the frequencv of oscillations generated by said electron discharge device, and, a long resonant transmission line, long relative to the operating wave length having standing waves thereon of a wave length corresponding to a desired frequency of oscillation, coupled to said oscillator so that the oscillations generated thereby are pulled into step with the standing waves on said resonant long line.

17. In a system for the generation of sustained high frequency undulatory electrical currents, a

' pair of pushpull connected electron discharge devices utilizing for feed back the grid-plate capacities of said devices, a rough frequency controlling circuit connected across the plates of said pushpull connected devices, said circuit comprising an .inductance coil and a variable condenser connected in shunt with a portion of said coil, and, a long resonant radiationless transmission line -long, relative to the operating wave length having standing waves thereon, coupled thereto so that the undulatory currents generated by said pushpull connected electron discharge devices correspond in frequency to the standing waves on said line.

18. A constant frequency oscillation generator comprising an electron discharge device having an anode a cathode and a control electrode, a tuned circuit comprising an inductance coil and a condenser, means coupling said anode cathode and control electrode to said tuned circuit whereby oscillations are set up, and, a long transmission line, long, relative to a desired wave length, closely coupled to said oscillating system com-prising said tuned circuit and said electron discharge device, waves fed into the line being reflected back with a shift in phase corresponding to the number of waves contained in the line whereby the reflected waves force the oscillator to oscillate at a frequency for which there is zero difference in phase at the input end of the line for the reflected wave and the ingoing wave.

19. An oscillatory system for generating oscillations of constant frequency comprising an electron discharged device having within an hermetically sealed container -an anode a cathode and a control electrode, a parallel tuned circuit comprising an inductance coil shunted by a variable condenser, connections from said anode cathode and control electrode to points of different alternating current potentials on said variable tuned circuit whereby oscillations corresponding roughly in frequency to a desired frequency of operation are generated by said electrondischarge device, and, a long transmission line, consisting of a pair of conductors, having uniformly distributed inductance and capacity and being sharply resonant to a desired operating frequency closely coupled to electrodes-of said oscillating device, whereby standing waves on said line pull the oscillatory system into oscillation at a frequency corresponding substantially exactly in a desired frequency of operation.

20. Means for generating oscillations compris-. ing a reactance, an electron discharge device having an anode a cathode and a control electrode, connections from said reactance to said electrodes whereby oscillations corresponding roughly in frequency to a desired frequency are set up by said electron discharge device and reactance, and, a long transmission line, long, relative to a desired wave length, closely coupled to said oscillatory system comprising said electron discharge device and reactance, whereby standing waves on said long transmission line pull said oscillatory system comprising said electron discharge device and reactance into step with the standing waves on said long transmission line.

21. Means for generating oscillations comprising an inductance coil, an electron discharge device comprising anv anode a cathode and a control electrode coupled to said inductance coil whereby oscillations are generated by said electron discharge device, and means, comprising a long resonant transmission line, long, relative to a desired operation wave length, closely coupled to said oscillatory system comprising said inductance coil and electron discharge device, whereby standing waves on said long transmission line pull said oscillatory system into step therewith.

22. An oscillatory system comprising a pair of electron discharge devices each having an anode a cathode and a control electrode; inductors connected between the anodes and control electrodes of said devices, whereby oscillations are generated by said electron discharge devices, and, a long transmission line, long, relative to the operating wave length coupled to the control electrode circuit of said electron discharge devices, whereby standing waves upon said long resonant transmission line cause said devices to oscillate at a frequency corresponding to the wave length of the standing waves upon said long resonant transmission line.

23. An oscillatory system comprising an elec- 'tron discharge device having an anode a cathode and control electrode, a parallel tuned circuit comprising an inductance coil and a variable condenser connected to said anode cathode and control electrode whereby oscillations are generated by said electron discharge device, and, a long transmission line, long, relative to a desired operating wave length, inductively coupled to the inductance of said parallel tuned circuit, standing waves set up upon said line by virtue of the close coupling, pulling the oscillations generated by said device into step with the standing waves on the line.

24. Apparatus as'claimed in the preceding claim wherein an intermediate point of said inductance coil forming part of said tuned circuit is grounded for high frequency currents and connected to said cathode, and points on said coil opposite said grounded point being connected to said control grid and anode, and, means comprising the series combination or a choke coil and resistance connected between said cathode and control grid, for maintaining suitable biasing potential on said grid with respect to said cathode.

25. In an oscillating system comprising an electron discharge device having ananode a cathode and a control electrode, a tunable circuitcomprising an inductance coil and a variable condenser connected in parallel therewith, the coil to said tunable circuit being connected at an intermediate point to said cathode and at points on both sides of said point to said control grid and anode, whereby oscillations are generated by said electron discharge device, means for grounding said' point and said cathode for high frequency currents, means for establishing suitable grid bias upon the control grid of said electron discharge device, and, a long resonant transmission line, long, relative to a desired operating wave length, closely coupled to said parallel tuned circuit through relatively large blocking condensers offering no appreciable impedance tooscillatory energy of a frequency generated by said electron discharge device whereby standing waves set up on said resonant long line due to its close coupling with the electron discharge device oscillator, pulls the oscillator into step in frequency at a frequency corresponding to the wave length of the standing waves on the long line.

26. A pushpull electron discharge device oscillating system comprising a'pair of electron discharge devices each having an anode a cathode and a control electrode, an inductor connected between said anodes, another. inductor connected between said control electrodes, means for grounding the midpoint oi said last mentioned inductor, and, a long transmission line, long, relative to a desired wave length, conductively coupled to said control electrode inductor at points on both sides of said grounded midpoint, whereby standing waves on said long resonant transmission line pull the oscillations generated by said electron discharge devices into step therewith.

27. Apparatus as claimed in the preceding claim wherein a unidirectional potential path to ground from the midpoint of said control electrode inductor is provided, and wherein the effective resistance of said path is altered in accordance with desired modulation, whereby the output of said oscillator is modulated in accordance with said modulation.

' CLARENCE W. HANSELL.