US2075379A - Time delay oscillator - Google Patents

Description

ch 30, 1937a R. H. VAREAN TIME DELAYOSCAILLATOR 2 sheets-Sheet 2 Filed Marh 13, 19535 INVENTOR.,

RUSSELL H.' VAR/AN. BY

Patented Mar. 30, 1937vv UNITED STATi-:s PATENT emes' TIME 'DELAY oscmm'ron Russell H. Varian, San'Francisco, Calif., assignor to Farnsworth Television Incorporated, a cor- 1 poration of California Appiication March 1a, 1935, serial No. 10,890

s claims. (on. 25o-3 6) of flight of an electron; to provide .a cathode'ray -v oscillator wherein the means for deiiecting a cathode ray beam are, also the means for colu lecting the electrons in said beam; to provide a cathode ray tube wherein the electrons are deflected by the charge on the collecting anodes;

to provide a cathode ray tube of simple construction and which is an automatic oscillator; to provide a cathode ray tube oscillator having a minis mum of leads associated with the oscillating circuit; and to provide a cathode ray oscillator operating by virtueof the time elapsed during the passage of an electron through a predeter- 25 mined path.

Other objects of my invention will be apparent or will bespeciflcally pointed out in ,the description-forming al part of this specification, but I [do not' limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawings:

Figure 1 is a perspective view, in elevation, of a preferred form of cathode ray tube of my invention wherein the envelope walls have been cut away to show the internal elementa t. -Figure 2 fis a diagramindicating thevarious positions of the beam during a complete cycle.

Figure 3 is a diagram, reduced to lowest terms, 40 of a simple circuit in which my invention may be utilized.

Figure 4 is a perspective View similar to Figure 1, showing a modification oi.' my invention wherein the impact area oi the received beamis ofi- 45 In broad terms Iof method, my invention comprises generating a beam of cathode rays, defleeting said beam near the source, projectingv said beam into space, and causing said beam to .n return to a position close to the plane oi' deection, there to be collected. r I prefer to cause the potentials produced by the collection of the beam v to deiiect the beam. Due to the time .delay ci the electron during its travel i'romthezone of 55 deflection back to the zione ol' collection, I am able to create an oscillating current in an external circuit. The operation of the tube depends upon the time delay between the deflectionand the collection, and also [on the fact that a deiiection velocity received close to the: source 5 produces avmuch greater deiiection than an equal velocity received as the electron returns to be i collected.

In broad terms of apparatus, my invention comprises a pair of anodes and means for passing 1o an electron beam through an aperture between them. I then provide means -for imposing a -retarding potential on said beam to cause it to change its course and return to be collected by the anodes. The potentials imparted to the two anodes by collection of the electrons causes deflection totake place. Proper adjustment of the time of ight `will cause the beam to automatically oscillate from one anode to the other.

A tuned circuit is preferably connected across the anodes. y. v

l The method and' details of construction of my vinvention may be easily gathered from the fol.

lowing description: Y Y

Referring to Figure 1, showing a preferred vform of myinvention, a cylindrical envelope i is provided at one end with a reentrant stem 2. A press 3 of this stem carries a pair of cathode leads 4l supporting a linear cathode 5. An accelerating anode 8 provided with a linear aper- 30 ture 1 is held by means of accelerating anode leads 8so that the, aperture 1 is immediately over and parallel with the linear cathode 5. In Figures 1 and 4 the electrodes have been sepa-z rated more than they'would be in actual prac- 35 tice, this larger separation being here shown for the sake of' clarity in illustration. This combina'- tion of linear cathode and linear anode aperture I will produce an electron beam collimated in such a way that the long dimension oi the beam will 40 be at right angles yto the cathode and the slot, a's described in the application above referred to.

Slightly above the accelerating anode I prefer to position a pair of semi-circular collecting an- @des 9A and 9B. These anodes are provided with 45 opposing up-turned lips i0, are in the same plane, and are positioned with thelips spaced slightly apa#v to form a beam slit II at right angles to the of the cathode and so Icentered as to allow the collimated beam to pass between the two anode lips. The anodes 9A and 9B are supported by anode leads l2 sealed through the side Iwalls of the tube. l At the other end .of the tube I prefer to mount a held forming bar Il mounted on an electrode 25 lates.

lead I5. I prefer to make this electrode of relatively small wire and mount it so that the bar will extend at right angles to-the beam slit II between the anodes and parallel with the aper- 5 ture 1 and the cathode 5. This comprises all the structure necessary inside the tube for the proper operation of the device.

As the structure shown in `Figure 4 is very similari to that shown in Figure 1, it utilizes the same principle of operation and the same circuits,

it Will be described at this time.- Here the envelope lIv is provided with the same accelerating anode 6 and linear cathode 5, with the exception that the cathode and accelerating anode assembly are oli-set slightly toward one side of the tube. The two anodes 9A and 9B in this case are slightly overlapped and the lips I0 are short and extend only part Way across the overlap, thus providing an off-center beam slit. Then, by means of a focusing electrode IS supplied by a constant potential source Il, a small continuous bias is placed on the beam causing it to return in a position on the anodes where it does not have to pass over the slit II as the beam oscil- In all other respects the two tubes are identical, and their operation will be described later. In both Figures 1 and 4 I have diagrammatically indicated the path of the beam by broken lines I'I, and theimpact area, covered by the beam as it returns to the anodes 9A and 9B, by a dotted line I6.

A circuit in which this tube may be utilized is shown, reduced to lowest terms, in Figure 3. An inductance 20 is shunted 'by a capacity 2l to yform a tuned circuit, one end of which is connected through wire 22A to the anode 8A, and the other end is connected through wire 23B to the anode 9B. A center tap 24 of the inductance 26 is connected by means of wire 25 to the accelerating anode, and the two together are connected by wire 26 to a source of positive potentia12l, the negative end of which goes directly through wire '29 to the bar electrode I and also through a resistor 30 to the cathode E. As is quite customary in diagrams of this sort. no

source oi current is shown for the cathode E.

It is belived that the operation of the device may be more readily understood by reference to the anodel 6, and through the beam slit II. The

electrons in the beam travel out toward the bar I4 against the retarding negative potential thereon, and turn at the top of their trajectory and return to the plane of the 9A and 9B anodes.

It will be obvious, of'course, thatv the retarding potential shall be such that the electrons do not quite reach ie bar I4; and that the length of path should be adjusted either by the potential on the bar or by the physical spacing of the 7 0 bar from the anodes, in combination with the initial velocity of the electrons, so that the time required for the beam electrons to travel the distance of their course is either 1/2, 3/2, 5/2 etc. of theperiod of the oscillator.

75 At` theV instant of the iirst return of the electrons to the 9Al and 9B anodes, more electrons will be bound to fall on one than on the other.

In diagram A of Figure 2 I have shown more electrons falling on 9B than on 9A. 9B therefore acquires a negative charge and 9A an equal and opposite `positive charge. The lips of the anodes then act as deflecting plates, and the beam will be thrown to the left, as shown in diagram B.

'As soon as the returning electrons, however,

start to arrive on 9A, the anode 9A changes from positive to become highly negative, as shown in diagram C. This change immediately deflects the beamtoward 9B, but electrons are still re turningvto' 9A. The stream, however, has been given the inclination toward 9B and as the intensity of charge rises, due to the full collec- Ation of the stream by 9A, maximum deflection is obtained in diagram C and the returning electrons start to move back' again toward 9B. When they begin to arrive on 9B, as Shown in diagram D, 9B accumulates the negative charge which immediately starts the deflection in the direction of 9A, asl Shown in diagram E, and the cycle is repeated as indicated in diagram F.

As plates 9A'and 9B are connected to anY oscillating circuit the oscillationsset up therein .by the collection of the electrons will be continuous, and all that is necessary for maximum output of sustained oscillations is that the time of ilight be so regulated that the electrons will fall on one plate while being deflected near the source toward the other plate. The action might be compared in physical analogy to the result which would be obtained if a garden hose nozzle were held in the hand, directing a stream of water therefrom straight in the air. A slight horizontal oscillation given to the -nozzle would cause the returning water to land on one side or the other of the nozzle, and it would be quite possible to reproduce the entire action with water if the water collected could be made to oscillate the nozzle, and the time of flight of individual drops of water be properly adjusted. f

It will be noted that in the device shown in Figure 1 the returning electrons pass directly across the slit II and intermingle with the outgoing electrons, and that due to this fact there lwill be a slight time gap in the output energy as some returning electrons will pass back through the slit. I have avoided this action in the construction shown in Figure 4 by overlapping the plates and causing the returning electrons to .travel in a path toone side of the slit. In this manner there is no loss of returning electrons nor do they, except at thebend in the path, intermingle with the outgoing electrons.

While both the outgoing and returning electrons are subject, in varying degrees, to the deflection potentials, the deiiection velocity vreceived as the electrons leave the accelerating anode produces a much greater deilection than an equal velocity received as the electrons return to a collecting anode. The displacement of the beam may thus be' accomplished without difculty.

The frequency produced by the device will vary as the square root of the voltage between the cathode 6 and the accelerating anode A, provided the bar electrode ,I4 is only slightly negative with respect to the cathode 5.- If, however, the bar electrode I4 is made considerably more negative with respect to the cathode 5, by means of a battery or other arrangement, the frequency will vary in the reverse direction if a large dat plate is used instead of the bar I4. If, however, a eld,

due tothe electrode I I, which varies in strength directly as the distance from the accelerating anode 6 c an be set up, the repelling force on the electron is directly proportional to the distance 5 from the accelerating anode. lA ileld of this type can be closely approximated by the use of the narrow bar electrode as shown. The difference of potential between this bar and the cathode may be adjusted by means of the resistance 30 to l give the best compromise possible.

When these factors have beentaken care of, we have the law of the spring pendulum fulfilled in which the resisting force is proportional to the displacement; and the period is independent of l the amplitude. These conditions would make the frequency of .the loscillator substantially independent of voltage. It is not, however, necessary that this law be exactly fullled in order to make the frequency independent lof voltages over a small range. It is entirely practical to so arrange the elds and the potentials in the tube that the frequency will be constant over the normal range of the line fluctuations when the potentials even- I tuate from converters attached to current mains. It will be apparent to all those skilled in the art that by proper adjustment of the resistance 30,

to change the bias between the cathode 5 and -the Y bar. electrode i4, and using the proper travel distance and the proper voltage on the anodes to correspond with the frequency desired and fixed by the constants of the tuned circuit, that ordinary line voltage fluctuations will not change the frequency to an extent which would, in any way, .be inimical to the-practical operation of the device. If the bias on the bar Il be tied in with the potential of the anodes, some compensation will occur. l

The uses and advantages of the invention are obvious. It would of course be possible to build 40 a device wherethe bea'm traversed a long tube, eventually landing on collecting anodes. Leads from these anodes, however, would have to be brought back along the 'tube to deecting plates positioned near the source. The existence of these leads would immediately destroy the ability of the tube to oscillate at ultra high frequencies and for that reason deiiecting the stream and collecting the electrons 'therein in substantially the same plane allows such leads to become non-v existent, the deflecting means and collecting means being the same piece of metal.

To carry the application of this device to its ylogical conclusion for the production of ultra high frequencies, the, anodes 9A and 9B may be directly connected to the respective ends of a L radiating dipole,the size of which will control, in conjunction with a properly coordinated travel time, the frequencyof oscillation. Furthermore,

- it is easily possible to modulate this oscillator by 60 the useof a grid tocontrol the current ofthe cathode ray beam. This grid would effect the amplitude of oscillation of the beam, giving a req generative effect on the modulation, but lt would not changel the frequency. c5 As the time delay b etween deflection and collection determines the frequency, mit will be obvious the frequency varies4 as I4. AS this cult to maintain a very accurate fixed potential upon it by other means, as this electrode d'raws no current. Other means of stabilization will also be apparent to those skilled in the art.

As the frequency can be changed bythedirect current .potential of bar I4, it is quite obvious that the oscillator can be synchronized with other `devices utilizing the charge on the bar I4 as a frequency control.

` The actual physical dimensions of a tube necessary to obtain a given frequency should next be considered. The velocity V of an electron:

where E is themelectrostatic voltage, C is the charge on the electron in electrostatic volts, and

M is the mass of theelectron. .If the anode po# As D=VT where V is velocity and T time; the

total distance travelled by an electron is 12.4 cm. The distance one way is 6.2 cm. or 2.44 inches.

It will be seen, therefore, that the tube is entirely practical and compact in its structure.

QA tube such as the one shown in the drawings may be operated-.at one, three or ve times the fundamental frequency, but is probably limited practically to the lower harmonics unless the region of deflection can be limited to a very exn ceptionally short distance from the accelerating anode. The shorter this distancevthe easier the tube will work on the higher harmonics.

Since the frequency which can be handled by this tube is determined to a degree by the time spent by the electrons between the deflecting plates, and the sensitivity to deflection goes up as the total time of flight of an electron increases, it is not advantageous toshorten the tube in denitely for excessively high frequency operation. It has been found, however, that tubes of the construction shown with practical spacings will operate satisfactorily lbetween 30 and 200' megacycles.

It is also possible vto adapt the tube to produce much lower frequencies, and in case it is desired to use such lower frequencies I prefer to put a screen grid above the anodes 9A and 9B which is negative thereto but positive tothe cathode. This will produce a long electron path at relatively low averagevelocities, and greatly increase the tine of flight. It will be obvious that with this latter arrangement the deflection sensitivity will also be increased. It is possible by the use of such a grid to g'o below 10 megacycles.

It is therefore seen that my invention is limited in its'production of high frequency oscillating current only bythe loss of deflection `sensitivity with very short paths, and in the production of low frequencies only by the ability to lay out a sufficiently long path. The limitation on the high frequencies may be, in certain desirable cases, removed by some sacrifice of emciency, and the device may be used to supply a small oscillating current at an extreme high frequency where most of the energy is needed for deflection.

The limited output may then be amplied by other means.

Within its wide range in the ultra high band,

therefore, the device is an eflicient and' what might be termed an easy oscillator. It starts at a long distance from the power supply, as on masts. The circuit is exceptionally simple, and

the device, when attached to a di-pole, needs only' filament vand anode supply wires with no necessity for complicated circuits. The physical dimensions of the tube for extraordinary high frequencies may be made relatively large; accuracy of construction may thereby be obtained. No critical adjustments are necessary, and the device may be readily modulated. V

I claim: l

1. The method of producing sustained oscillations which comprises generating a beam of electrons, projecting said electrons into space, returning said electrons to a plane adjacent the source, collecting the electrons substantially in said plane, and applying the charge produced thereby in the same plane to said beam to produce deflections thereof.

2. The method of producing sustained oscillations in a cathode ray tube having an electron source and a pair of collecting electrodes which comprises positioning said `electrodes adjacent said source, directing electrons between said elecmove said beam to cause electrons to return to the other of said electrodes.

3. In a cathode ray tube'comprising an envelope containing a cathode and an anode, for

. producing a cathode ray beam, a pair of collectdelectors when charged by collection.

4. In a cathode ray tube comprising an. envelope containing a. cathode and anode adapted to produce a cathode ray beam, a pair of electrodes separated to allow said beam to pass therebetween into space, means for returning said beam to the plane of said electrodes for collection,

the charge imparted to said electrodes thereby acting to deflect said beam, means for regulating the time of flight, and means for stabilizing velope containing a cathode and anode adapted to produce a cathode ray beam, a pair of electrodes separated to allow said beam to pass therebetween into space, means for returning said beam to the plane of said electrodes for collection, the charge imparted to said electrodes thereby acting to deflect said beam, means for regulating the timev of flight, and means including a tuned circuit connecting said electrodes for stabilizing the deflections.

6. In a cathode ray tube comprising an envelope containing a cathode and .anode adapted to produce a cathode ray beam, a pair of dual purpose electrodes separated to allow said beam to pass therebetween positioned close to the source of -said beam, means for producing an alternating deflection charge on said electrodes by collection of electrons from said beam, and means for regulating the frequency of deection.

7. In a cathode ray tube comprising an envelope containing a cathode andl anode adapted to produce a cathode ray beam, a pair of electrodes separated to allow said beam to pass therebetween positioned close to the source of said beam, means for producingan alternating deflection charge on said electrodes by collection of electrons from said beam, means for regulating the frequency of deflection, and means for utilizing the excess of electrons over the power necessary for deflection.

8. In a cathode ray tube having an envelope containing a cathode and anode adapted to project a beam of cathode rays into space, a pair of electrodes positioned close to the source of said beam and separated to allow said beam to pass therebetween, meansl for returning said beam to 4the plane of said electrodes, means for regulating the time of flight oi the electrons in said beam, a tuned circuit connecting said electrodes, and means for offsetting the beam in space so that it will describe a path across said electrodes during collection apart from the region wherein electrons are passing outwardly between said electrodes. l

RUSSELL H. VARIAN..

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