US2190515A - Ultra short wave device - Google Patents

Description

ULTRA SHORT WAVE DEVICE Filed July 15, 1958 Fig.1.

- r0 0071 anal/ MR A lhvenbor: i William C. Hahn,

e His Attorney- Patented Feb. 13, 1940 ULTRA SHORT WAVE DEVICE William C. Hahn, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application July 15, 1938, Serial No. 219,386

6 Claims.

The present invention comprises improvements in ultra short wave devices of the general type described and claimed in my prior application, Serial No. 153,602 which was filed July 14, 1937,

and of which this application is a continuation in part. This invention relates particularly to converters or mixing tubes which can be used at wave lengths on the order of from five meters to five centimeters or less.

As was pointed out in the aforesaid application, an electron stream may be modulated either as to electron velocity or as to charge density. The first type of modulation involves the production of systematic irregularities in electron velocity from point to point along the beam. The second involves the production of charge density variations, such variations being manifested as systematic irregularities in the electron grouping.

In the conventional design of electronic discharge devices no distinction is made between these two types of modulation. In connection with ultra short-wave devices, however, it is advantageous to utilize electrodes which are capable of producing velocity modulation without simultaneously causing appreciable charge density varations. For reasons which need not be elabarated here this expedient avoids the objectionable decrease in input impedance which is observed with conventional prior art devices when they are operated at extremely high frequencies. Velocity modulation produced as above specified may be subsequently converted into charge density modulation of a higher order of magnitude to obtain amplification effects.

The foregoing matters are explained in detail in my prior application, Serial No. 153,602. It is an object of the present invention to provide means whereby the principles described in such application may be applied to so-called converters or super-heterodyne detectors in which signal oscillations are mixed or combined with 10- cally generated oscillations of fixed frequency to produce other oscillations of intermediate frequency.

The novel features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 represents a sectional view of a converter suitably embodying the invention; Fig. 2 shows a modified embodiment; Fig. 3 il- 5 lustrates a further application of the invention in connection with a device which is adapted to serve both as a converter and a super-regenerative detector, and Fig. 4 is a graphical representation useful in explaining the invention.

Referring particularly to Fig. 1, there is shown an elongated sealed metallic envelop l0 closed at one end by means of a base portion II. The envelope encloses an electron gun for producing a relatively concentrated beam of electrons. In the particular case illustrated, the gun includes a cathode which is constituted of a heater l3 (shown in dotted outline) and an emitting cylinder l4 surrounding the heater. A conducting cylinder I5 surrounds the cathode and when properly biased with respect to it, serves to focus the emitted electrons into a beam of appropriately small dimensions. The cylinder I5 is supported directly by an insulating sleeve 16 and indirectly by a second metallic cylinder H. The latter in turn is supported by being mechanically connected to an apertured barrier l8 which extends transversely across the envelope.

The elements so far referred to are energized by means of lead-in connections connected with a series of bayonet contacts 20, 2| and 22 mounted on the base of the envelope. Through these contacts the cathode heater I3 is energized by means of a low voltage potential source shown as a battery 24, while the cylinder I5 is maintained at a desired potential by means of another potential source 26. A third potential source 21, capable of developing from one to sev eralhundred volts, serves to maintain the envelope l0 and especially the barrier l8 at a high positive potential with respect to the cathode so as to produce considerable acceleration of the electrons emitted by the latter. If desired, magnetic or electrostatic focusing means may be provided in connection with the device in order to prevent undue spreading of the electron beam.

In operation, means must be provided for modulating the electron beam so as to produce variations therein corresponding to the variations of a received signal. Furthermore, as explained in my aforesaid prior application, for satisfactory use at high frequencies such variations should comprise a maximum of velocity modulation with a minimum of attendant charge density modulation produced in the vicinity of the modulating electrode structure. This result may be obtained by the use of a modulating space which is sufiiciently shielded from the electrode source or cathode so that the application of potentials adapted to produce velocity modulation does not necessarily react on the cathode to produce corresponding charge density variations. In the particular case illustrated such a modulating space is provided between the transverse barrier l8 and a similar barrier 30 which is spaced therefrom. These barriers are respectively provided with openings 3| and 32 which permit the electron beam to pass through the modulating space. They are directly maintained at the same potential by being connected directly to theenvelope l0.

Within the modulating space there is provided a control electrode in the form of a hollow tubular conducting member 34 which is adapted to be traversed by the beam. As explained in my aforementioned prior application, if the otential level of this electrode is caused to rise and fall cyclically with respect to the boundary potentials of the modulating chamber (that is the potentials of the barriers l8 and 30) longitudinal velocity modulation of the beam is produced. This effect is a maximum when the length of the electrode 34 in the direction of the beam axis is I such that the electron transit time therethrough corresponds to a half cycle of the control potential or to an odd number of such half-cycles. Under these conditions, an electron which enters the modulating space at a time when the poten-- tial level of the electrode 34 is maximum is twice accelerated; once as it approaches the electrode, and again as it leaves the electrode. Similarly, an electron which enters the modulating chamber one half-cycle later is twice decelerated as it traverses the chamber. As a consequence of these successive accelerations and decelerations the electron beam issuing from the modulating space is velocity modulated in the sense of being characterized by successive variations in electron velocity from point to point along the beam.

The potential applied to the electrode 34 may comprise a modulated signal derived, for example, from an antenna 40. This is coupled to the electrode through a tuned circuit comprising an inductance 4| and a condenser 42. A battery 43 serves to maintain the average potential level of the electrode 34 in a desired relation to that of the barriers l8 and 30. Although such a relationship is not necessary, it is generally convenient to have the electrode and the barriers at approximately the same average potential.

With an arrangement such as that described. the velocity modulation of the beam issuing from the aperture 32 will have frequency components corresponding to those of the signal impressed on it. For converter operation, it is necessary additionally tomodulate the beam by means of a fixed frequency having a desired relationship to the signal frequency. This further modulation may be accomplished in a second modulating chamber similar to the chamber already described.

The second modulating chamber may be formed, for example, between the transverse barrier 3D and another barrier 46 which has a central opening 41. A tubular electrode 49, generally similar to the electrode 34, is enclosed within this chamber and is excited by connection to an oscillatory circuit comprising an inductance 50 and a variable condenser 5|. Assuming this circuit to be maintained in a condition of oscillation at a fixed frequency (by means hereinafter to be described), secondary modulation ofthe beam is produced. within the chamber so that the beam issuing from the opening 41 has modulation components of the fixed frequency as well as of the signal frequency; For converter operation, means must mixing these frequencies, preferably under conditions adapted simultaneously to produce amplification effects.

This is accomplished in accordance with my present invention by the use of a retarding field for reversing the lower velocity elements of the modulated beam. As explained in my aforemenapplication, Serial No. 153.602, this procedure is effective to convert the velocity modulation of the beam into charged density modulation of a higher order of magnitude. This is due to the fact that the reversed portion of the beam is constituted of spaced groups of lower velocity electrons, The higher velocity electrons are collected by a collecting anode.

The beam-reversing function isaccomplished inthe present case by an electrode arranged in the beam path and maintained at a potential not far from that of the cathode I 4. The relationship between the velocity modulatiton of the random velocity beam, and may be very high for practical tube constructions.

For straight amplification purposes it is desirable to operate under change in charge density modulation. tion, on the other lize some element ing non-linearly to the electron velocity variations which are produced in the beam.

Non-linearity is obtained in the present case by so biasing the electrode 55 as to assure operation at one of the curved portions of the charhand, itis necessary to uti- To obtain converter or mixer acwhich is capable of respondsignal and oscillator frequencies but also the sum 5 frequencies (i.e., the intermediate frequency) this may be done by providing in energy-exchanging relation with the reversed component of the beam a resonant system which is tuned to such frequency. In the present case I employ an oscillatory circuit connectedto the electrode 55 and adjusted to oscillate at the intermediate frequency. This circuit, which is shown as'comprisinga condenser 58 and an inductance 59 connected in parallel, is excited by the reaction or the reversed component of the electron beam on the electrode. The intermediate frequency voltage which is thus nal 60 and ground ing tube or to some other utilization device.

be provided for In order to maintain the local oscillator cir- If, as isdeveloped between the term'imay be applied to a succeedcuit 50, 5| in sustained oscillation, this also is caused to be affected by the reversed component of the beam. This is done by permitting the returning electrons to retraverse the electrode 49. In passing through this electrode, the charge density variations of the beam will induce corresponding current variations in the electrode and in its associated circuit. Since this circuit is tuned to a fixed frequency and since a component of this frequency appears also in the returning beam, there is obviously a tendency for free oscillations of the circuit to occur. If the length of the beam path from electrode 49 to electrode 55 and return is properly correlated with the beam velocity, these oscillations are selfsustaining. That is to say, the charge density variations of the returning beam, it correctly phased, produce voltage swings of the grid effective to maintain the system in continuous oscillation. This condition may be obtained for a particular case by properly adjusting the tube dimensions and the beam velocity.

It is not desired that the returning beam shall reenter the first modulating chamber, since to permit it to do so would result in an objectionable reaction on the electrode 34 and the associated input circuit. This may be avoided by tilting the electrode 55 to cause the reversed component of the beam to travel at an angle to the main beam path as indicated by the dotted line a. By this means the beam is caused to impinge on the solid portion of the barrier 30 and to be collected thereby. (The feature of a tilted electrode used as a beam reversing means is the prior invention of Harry C. Thorson and is fully described and claimed by him in his application S. N. 264,877, filed March 30, 1939, and assigned to the same assignee as the present application.)

In Fig. 2 I have shown an alternative embodiment of the invention. In this arrangement the elements of the electron gun and of the first modulating chamber are similar to those described in connection with Fig. l and are, therefore, similarly numbered. The modulated beam issuing from the opening 32 traverses a series of further chambers formed by a succession of transverse barriers 65, 66 and 61. These chambers respectively enclose electrodes 69, 10 and H, of which the last is connected to a local oscillator circuit comprising a condenser 12 and an inductance 13.

After traversing the oscillator electrode H the beam approaches an electrode 14 which is so biased by means of a battery 15 as to return the lower velocity components of the beam. In accordance with the principles already described, the operation of this electrode is to produce mixer action.

The reversed portion of the beam, containing components corresponding to the signal and oscillator frequencies as well as to their sum and difference, is caused to traverse both the chamber bounded by the barriers 61 and 66 and that bounded by barriers 66 and 65. In the former of these it acts to excite the electrode H so as to maintain the associated tuned circuit in a state of oscillation. In the latter it traverses the electrode 10 which is connected to a condenser 11 and an inductance 18, these constituting an intermediate frequency tank circuit. Output terminals 19 for the intermediate frequency circuit are provided in connection with an inductance which is coupled to the tank inductance 18. After its passage through the electrode 10 the reversed component of the beam is collected by being allowed to impinge on the barrier 65.

The charge density variations of the reversed portion of the beam tend to produce corresponding current variations in the electrode 10 and in its associated circuit. Due to its tuning, the latter is selectively responsive to stimulation by the intermediate frequency component of these variations and, therefore, oscillates at such frequency.

For best operation, the impedance of the intermediate frequency circuit should be high, which condition is attained only if the reaction of the circuit on the beam is relatively slight. In order to assure this result means are provided to minimize the tendency of the electrode 10 to velocity modulate the main beam-as it normally tends to do. In the present instance, this is accomplished by the provision of a complementary or neutralizing electrode 69 which is directly connected to the electrode 10. With this arrangement, potential variations of the electrode Ill are communicated directly to electrode 69 and cause a corresponding variation of its potential. If the length of each of these electrodes in the direction of the beam axis is such that the electron transit time through each corresponds approximately to a half cycle of the intermediate frequency, the modulating effect of the electrode 10 is offset by the equal and opposite effect produced by the electrode 69. That is to say, a given electron, which is to be accelerated a given amount by the electrode 10, is decelerated a precisely equal amount by the electrode 69. Consequently, any electron which traverses both electrodes experiences no net change in velocity. As a result, the impedance of both electrodes is high as far as their reaction on the beam is concerned.

The modification shown in Fig. 3 comprises an arrangement by which frequency mixing and super-regenerative detection can be accomplished in a single device. In this figure, elements which have been previously described in connection with Figs. 1 and 2 bear the same numerals in Fig. 3.

In the use of the combination shown, the signal modulated beam issuing from opening 32 is additionally modulated by means of an electrode 80 which is coupled to a local oscillator (not shown) through a tuned circuit comprising an inductance 82 and a condenser 83. Thereafter the beam is caused to traverse another modulate ing chamber which is bounded by transverse diaphragms 85 and 86 and which contains a tubular electrode 81. After leaving this chamber the lower velocity components of the beam are returned to it by the action of a retarding field provided by an electrode 89.

In accordance with the principlesexplained in connection with the oscillator electrode 49 of Fig. 1, the reaction of the returning component of the beam on the electrode 81 is such as to maintain the tuned circuit with which it is connected in continuous oscillation. This circuit, which comprises a condenser 9| and an inductance 92, is tuned to the intermediate frequency which corresponds to the difference between the signal frequency and the frequency developed by the local oscillator. In operation, it reacts on the-portion of the beam proceeding toward the electrode 89 to increase the velocity modulation thereof. (Since the electrode 8'! is not in this case used as an output electrode, the considerations mentioned in connection with Fig. 2 concerning the need for limiting the reaction of the electrode H! on the beam do not apply.)

In order to obtain super-regenerative operation, means are provided for intermittently interrupting the Oscillations of the intermediate frequency circuit. Such intermittent interruption may be accomplished by applying either to the'electrode 89 or to some other part of the system, quench oscillations having a super-audible frequency appreciably lower than the intermediate frequency. The quench is provided in the present case by means of a tuned circuit comprising a condenser 94 and an inductance 95, the latter being coupled to a source of quench oscillations (not shown). I

As a result of the arrangement specified, intermittent oscillations of the intermediate frequency circuit will occur, the instantaneous magnitude of such oscillations being a functionof the magnitude of the intermediate frequency component of the returning beam. Since this latter quantity is in turn proportional to the 0 modulation or audio component of thesignal applied to theelectrode 34, it is apparent that super-regenerative operation may be obtained. The amplified audio or modulation component may be selectively detected by the provision of a low frequency circuit connected to electrode 89, or to a separate electrode coupled with some portion of the beam in which it appears. In the present case such a circuit is provided by a signal translating device (shown diagrammatically as a head phone set 98) connected in series with a choke coil 99. This latter element serves to prevent the quench oscillations from passing through the head phone set. A blocking condenser I00 the quench circuit. I

The device described in the foregoing combines the advantages of high sensitivity and high amplification. It is, furthermore, characterized b a high degree of noise suppression.

0 While I have described my invention in con- P u e velocity variations in the electron ts, connected with one *such electrode to produce electron velocity variations in the stream corresponding to a signal frenection with particular embodiments thereof, it will beunderstood that various modifications may be made-by those skilled in the art without departing from theinvention. I, therefore, aim in the appended claims to cover .of structure and use as fall within the true spirit of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A converter'comprising means including a cathode for developing an electron stream, a pair of successively arranged electrodes operable to stream, said electrodes being sufiiciently shielded from the cathode so .as to be incapable at normally applied potentials of producing appreciable chargedensity variations in the stream, means of said electrodes for causing quency, means connected with the other electrode for causing such electrode to produce electron velocity variations in the stream at a fixed frequency different from the signal frequency, means reacting on the stream in a manner which varies non-linearly with the velocity of the stream, thereby to obtain in the stream charge density variations having frequency components resulting from the mixing of the said signal and fixed frequencies, and means selectively responsive to a particular frequency resulting from such mixing for abstracting energy from the stream.

2. In combination, means including an electron gun for producing a concentrated beam of electrons, a series of electrodes electrostatically of a potential having excludes the audio frequency from all such variations a partlcularirequency resulting from such mixing for abstracting energy from the beam.

3. A converter including means for developing an electron beam, means for producing velocity modulation of the beam by means of a potential of signal frequency, means for producing additional velocity modulation of the beam by means a selected frequency different from the signal frequency, means providing reversing at least a portion to the difference between the signal frequency and the selected frequency,

the beam at a fixed frequency'other than signal frequency, means reacting on the doubly modulated beam to produce mixing of the signal and fixed frequencies, an oscillatory circuit which is resonant at an intermediate frequency produced by such mixing, coupling means causing said cirtionof intermediate frequency oscillations in the said circuit, and signal translating means coupled to the beam afterits reaction with the circuit, said last-named means being selectively responsive to the modulation component of the signal.

6. In combination, means comprising an electron gun for producing a relatively concentrated beam of electrons, a series of electrodes arranged along the beam path and adapted to influence the beam successively, means connecting with one of said electrodes for producing variations in electron velocity at a frequency corresponding to that of a modulated signal, means connecting with another of said electrodes for producing additional electron velocity variations at a fixed frequency different from the signal frequency, means acting on the beam after its traversal of the said electrodes and effective to reverse at least the lower velocity components of the beam, thereby to produce mixing of the said signal and fixed frequencies, an oscillatory circuit which is tuned to an intermediate frequency produced by such mixing, said circuit being connected to one of said electrodes which is traversed both by the main beam and by the reversed components thereof, means including a source of quench oscillations for periodically terminating the oscillations produced in the said circuit by the reaction thereon of the reversed component of the beam, and signal translating means selectively responsive to the modulation component of the signal, said last-named means being in energy-exchanging relation with a portion of the beam affected by the intermediate frequency oscillations produced in the said circuit.

WILLIAM C. HAHN.

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