US2173193A

US2173193A - High-frequency oscillator

Info

Publication number: US2173193A
Application number: US159616A
Authority: US
Inventors: Vladimir K Zworykin
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-08-18
Filing date: 1937-08-18
Publication date: 1939-09-19
Anticipated expiration: 1956-09-19

Description

Sept. 19, 1939. v, K. ZWORYKIN ,1

' HIGH-FREQUENCY OSCILLATOR Filed Aug. 18, 1937 v INVENTOR y K. Izzy/0N BY ATTORN EY snares pron-mos os'ron nu Er Z, 3''- too Qorporatlon In; invention relates to an improvement in hih frequency, oscillators.

Heretofore, plezo electric crystals have been used to stabilize a tube oscillator and such practice is feasible when-oscillations oi a relatively low frequency are d. The highest frequency for which a r at the present time can be around without w. encessive precautions is around 100 meters, which corresponds to approately one u so thickness of the quartz crystal. A further decrease of the wave length or what amounts to a decrease inthe thickness oi the crystal involves excessive iragility oi the crystal and the lowest possible limit is considered 80 meters or about 3.? megacycles.

At the present time, frequencies up to 30 megacycles and in some cases even higher are employed. There is, or course, a method or stopplug up the frequency oi a crystal controlled oscillator by a series of frequency doublets or multipliers, each being an oscillator or a frequency two or more times as high. as the preceding one. Such systems involve ccnsiderahlc clificulty due to energy losses andare expensive and hard to maintain in proper running condition.

The invention is a means and methotlto a plify the frequency multiplication and to pelt an absolute control of frequencies higher than is possible with frequency doublers. The p -;.;ple of this method involves a cathode ray beam moving over a mask having a series of perforations or apertures and the electrons which pass through these apertures are collected by a collector anode positioned hehincl the mash. The stream of electrons is interrupted by the mask and consequently the collector supplies a number of impulses whose frequency depends upon the velocity of the beam movement and the number of apertures. If these apertures are positioned in a circular path and the beam is moved over them with a constant velocity the frequency supplied by the collector will correspond to the angular velocity of the be multiplied lay the number of apertures.

One of the disadvantages of this system is that only one-half of the energy of the cathode ray beam is utilized, the second half being absorbed by the mask. In order to overcome these losses the following arrangement may be-nrade:

It is well known that when a cathode ray beam strikes a substance it evolves a secondary sion which sometimes has a greater number of lectrons than the primary beam. The velocity of the secondary electrons is a function of the velocity. or the primary in and the nature of any 091.00

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13, 3193?, Serial No. 159,816

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the substance bombarded. is present in most of our thermlonics and is usually a very undble iactor. In the present invention, however, the secondary electrons are collected by the matter being emitted from the collector, and in most cases the mask should be at a potential slightly positive with respect to the collector anode. The time of propagation of the secondary electrons from the collector to the mask depends upon the velocity of the secondary electrons and the-distance between the two electrodes, together with the potential difierence existing between the collector, anode and the mask. If we arrange that this velocity and distance are such that the time of second emission propagation between the two electrodes correspondsfto the time of one-half cycle of the pro rlucecl oscillations; a source of resonant oscillations willbe setzup-lcctween the collector plate and the mashpandthe secondary con will supply the missinghali or the hireouency wave being generated;

an object of my invention, therefore, is to provide a high frequency oscillator which f1; pro== duce oscillations of'the order of so megacycles aucl'upward without the use or the usual crystal. Another object of my invention is to provide an oscillator in which both halves of the alternatlng current cycle will be supplied by the oscillator.

A further object of my invention is to pro= vltle an oscillator wherein an electron stream is utilized and wherein secondary eons set up by the electron stream will also he utilized.

Further objects of my invention he more apparent to those smiled in the art from the following description and from an itlon ofthe drawing wherein:

in Fig. l, and

Fig. 3 is an application or the device to a tetrode, discharge tube.

Referring to the drawing, Figure 1 shows a cathode ray tube having the convenmonal cathode or emitter 5 and deflecting plates t, ti, and l, l. Two anodes are shown, one of which operates as a mask 9, while the other operates as a collector anode and secondary electron enusslve surface iii. A source of potential it is connected between the emitter 5 and the anode t and in this connection, a choke coil 85 is inserted to improve the operation oi the oscillator. e two anodes are connected externally oi the tube by way of an inductance l3 and a capacitance l2, while the anode potential is applied to the conductor M.

It will be noticed that the mask 0 is provided with a plurality of openings or apertures Ii, through which the electrons of the produced cathode ray may pass in order to contact the anode III. A suitable source of alternating current is applied to the deflecting plates I, in order that the cathode ray may be caused to move along the perforated mask 0. This tube construction is similar to the construction used in cathode ray tubes when used as frequency multipliers. In the case of such tubes, however, only half of the cycle of the output frequency is supplied and these half cycles or impulses must be applied to a transformer or some other apparatus in order that a full wave alternating current may result.

This invention, however, operates to supply also the missing half wave of the produced frequency and to do this the secondary emissions which result from the impact of the cathode ray against the anode iii are utilized. The distance between the anodes 9 and i0 is such that the time required for the secondary electrons to pass from the anode ill to the anode 9 is equivalent to the time transpired in a hall cycle of the resulting high frequency oscillations. Under such conditions, as the cathode ray is moved to such a position that it will strike the mask, the secondary electrons 25, as a result of the previous impact of. the ray with the anode in, will have reached the anode 9 and a full wave alternating current cycle will result. One half cycle later the cathode beam will again be directed against the collector anode in through the next succeeding opening in the mask anode 9. The inductance i 3 and the capacitance ii are so chosen as to form a series resonant circuit for 'the particular frequency developed by the device so that the current produced-may oscillate freely within the circuit connecting the two anodes.

The output circuit of the oscillator may be connected in any known manner, as by an inductive coupling to the inductance l3, or by connection to opposite sides of the condenser II or by any other desirable means.

If a sinusoidal wave form is applied to the deflecting plates 1, it is necessary that the openings in the mask 9 be spaced in such a manner as to produce an alternating current of a uniform frequency. Ii, however, it is desired to rotate the cathode ray rather than move the ray in only one plane, the same may be done by applying proper alternating voltages in proper phase relationship to the deflecting plates 6, 6 and 'I, I and in which case an annular mask 2i and collector 22 maybe used as shown in Figure 2. The anodes 2i and 22 may be connected to a circuit in a manner similar to the connection shown in Figure 1. The paths of the secondary emission from the anode 22 areshown by the arrows 25.

The present invention may also be applied to a tetrode discharge tube as shown in Figure 3. The tube is indicated generally at 3|, and comprises a cathode or emitter 32, a grid or control electrode 33, a screen grid or auxiliary control electrode 34 and an anode 35. A source of potential is connected between the emitter and the anode by way of an inductance 31. It is sometimes preferred that the screen grid 34 be operated at a slightly higher potential than the primary electron collector or anode 35 in order that the secondary electrons which originate at the anode will be drawn to the grid 34. Such an arrangement is shown in Figure 3. The screen grid 34 of the discharge tube 3! is inductively connected to the grid 33 by means of a transformer 36 and

condensers

38 and 39 are placed between the anode and the screen grid and between the screen grid and the grid respectively. The operation of this tube is similar to the operation as described with respect to Figure 1 insofar as the secondary emission is concerned, and the control grid 33 being inductively coupled with the screen grid or electrode 34, causes the tube to oscillate at a frequency dependent upon the values of the external elements connected to the tube.

From the above it will be seen that a high frequency oscillator capable of producing of the order of megacycles and upward and having a high efliciency has been produced since the secondary emission from the primary beam impact is utilized, and since both the positive and negative half cycles of the desired frequency are supplied.

Various modifications or alterations may be made in the oscillator without departing from the scope or spirit of my invention and it is desired that only such limitations be placed thereon as are imposed by the prior art or the appended claims.

I claim as my invention:

1. A high frequency source comprising means for supplying a stream of electrons, a pair of electrodes, a source of current for maintaining one of the electrodes positive with respect to the source of electrons, means for permitting the electrons to strike the other of the electrodes intermittently whereby secondary electrons emitted therefrom may be intermittently supplied to the said one electrode, circuit means comprising a series resonant circuit connecting the electrodes, the resonant frequency of said circuit corresponding to the frequency of the oscillations being produced and the electrodes being spaced apart a-distance such that the time required for the secondary electrons to pass from said one electrode to said other electrode will correspond to one half cycle of the produced frequency. 1

2. A high frequency source comprising means for producing a stream of electrons, a collector anode for said electron stream, an electron mask of conducting material positioned between the said collector anode and the source of electrons said mask having a series of apertures, means for moving the electron stream across said mask, means connecting the mask and the collector anode comprising a series resonant circuit only, the resonant frequency of the resonant circuit corresponding to the frequency produced, the mask and the collector being so spaced that the time required for secondary electrons to pass from said collector to said mask corresponds to one half cycle of the produced frequency, and means including a part of said series resonant circuit for maintaining said electron mask positive with respect to said means for producing the stream of electrons.

3. In a high frequency oscillator, means for producing a source of an electron stream, means for moving the electron stream over a predetermined path, a pair of electrodes positioned in the path of the electron stream, one of said electrodes being perforated in order that the electron stream may strike the other electrode, a

series resonant circuit means including an inductance and a capacitance member connecting the electrodes, the resonant circuit being tuned to the frequency generated by the oscillator, the electrodes being so spaced that the time required for secondary electrons which arise at the said other electrode as a result of the impact of the electron stream thereon to pass to said one e1ec-.