US2277638A

US2277638A - Ultra high frequency system

Info

Publication number: US2277638A
Application number: US280020A
Authority: US
Inventors: Ralph W George
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-06-20
Filing date: 1939-06-20
Publication date: 1942-03-24
Anticipated expiration: 1959-03-24

Description

March 24, 1942.

R. w. GEORGE 2,277,638 ULTRA HIGH FREQUENCY SYSTEM Filed June 20, 1939' s- Sheits-Sheet 1 20 m6 If i Ll ll 21 30 iii iE-m +raou T 36.3 M 5 L F. ourpuf w (30 MEGS.) .c -+9ou INVENTOR. RALP m GEORGE BY MM ATTORNEY.

March 24, 1942. w, GEORGE 2,277,638

ULTRA HIGH FREQUENCY SYSTEM Filed June 20,1959 3 Sheets-Sheet 2 I E OUTPl/T J 27 INVENTOR.

RALPH W GEORGE BY W A TTORN E Y.

March 24, 1942. w GEORGE 2,277,638

ULTRA HIGH FREQUENCY SYSTEM Filed June 20, 1939 3 Sheets-Sheet 3 V V 5mm? PLATES INVEN TOR. RA H W GEORGE BY MM ATTORNEY.

Patented Mar. 24, 1942 ULTRA HIGH FREQUENCY SYSTEM Ralph W. George, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 20, 1939, Serial No. 280,020

26 Claims.

This invention relates to ultra high frequency systems. It is particularly applicable to receivers suitable for receiving ultra short waves of 10 meters and below, and preferably to receivers adapted to receive ultra high frequency signals anywhere from 30 m'egacycles up to the order of 600 megacycles. 7

The invention includes novel mechanical and constructional details, and has for one of its objects to provide a simple and compact frequency converter to be used preferably with superheterodyne receiving apparatus, to receive ultra high frequency signals up to frequencies of the order of 500 megacycles and 600 megacycles, though not limited thereto.

Another object of the invention is to provide ultra high frequency detector and heterodyne oscillator circuits operating at maximum frequencies limited by the vacuum tube characteristics, and which are tunable by means of variable rotary type condensers.

Still another object is to provide an ultra short wave frequency converter of the type referred to above having an ultra high frequency oscillator circuit wherein means are provided for adjusting the inductance thereof.

A further object is to provide a tuned oscillatory' circuit for ultra high frequencies employing a variable condenser in which no leads or connecting wires are employed between the condenser and the associated circuit element of the oscillatory circuit,

A still further object of the present invention is to provide an ultra high frequency system utilizing a pair of concentric lines, or an equivalent U-shaped line, having uniformly distributed inductance and capacitance, with a single vacuum tube oscillator circuit connected across the inner conductors of said concentric lines or across the legs of said U.

Another object is to provide an ultra high frequency system utilizing several of the foregoing types of frequency converter units in a single receiver, any one of which can be selected and its output fed to a'high frequency amplifier, thus providing a wide range receiver.

A feature of the present invention lies in the use of a concentric line whose inner conductor constitutes an integral part of a rotary con-- denser employed for tuning said concentric line.

Another feature involves the use of a concentric line having an inner' conductor at whose high potential end there is provided a rotary condenser, the stator plates of which are connected to said inner conductor by extremely low inductance means, thus avoiding the use 'of leads or connecting wires from the condenser to the concentric line.

A further feature comprises an oscillatory circuit employing a coiled inductance having in series therewith a rotary condenser, certain of whose plates are connected tosaid line through extremely low inductance means. This inductance is coiled to obtain maximum inductance in as small a space as possible;

' Other objects,'features and their advantages will appear from a reading of the following description, which is accompanied by drawings wherein like parts are represented by like reference numerals throughout the figures. In the drawings:

Fig. 1 illustrates diagramatically the equivalent electrical circuit of an ultra high frequency converter unit embodying the principles of the present invention, particularly applicable to a superheterodyne receiver;

Fig. 2 shows an equivalent electrical circuit of the heterodyne oscillator shown in Fig. I;

Fig. 3a shows a front view and Fig. 3b the back view of the essential elements of a mechanical construction embodying the system of Fig.

Fig. 4 shows the essential elements of a mechanical construction of a modification of the system of Fig. 1 wherein there are employed coiled inductance elements for certain of the oscillatory circuits; Fig. 40 is' a front view of one of the coil inductance elements of Fig. 4 and shows, schematically, the f variable slider 'contacting the coil;

Figs. 5 and 5a respectively show bottom and side views, respectively, of the construction of the stator plates of the rotary condensers employed in the present invention: and

Fig.6 shows a side view of a novel type of oscillatory circuit for use in connection with the present invention, wherein one part of the inner conductor constitutes the'stator plates of a rotary condenser. This figure is taken along the lines 66 of Fig. '7, the latter of which shows a plan view of the arrangement of Fig. 6 along the lines l'l but with the shaft and rotor plates removed.

Referring to Fig. l inmore detail, there is shown a simple compact frequency converter unit comprising a detector unit '4 to whose grid there is coupled a tuned input circuit of the concentric inductance type and to whose cathode is coupled a heterodyne oscillator l3 which is controlled as to frequency by'a pair of rodlike inductance elements 9, ID. The tuned input circuit for'detector 4 comprises a concentric line having an inner conductor l and an outer grounded conductor l1 directly connected to said inner conductor at one end by means of end plate 28. The free or high potential end of inner conductor l is capacitively coupled to the adjacent end of the outer conductor I! by means of a variable rotary condenser 2 which will be described in more detail later. The received signals are collected on an antenna 21, shown herein by way of example as an unbalanced antenna system which is tapped across a portion of the inner conductor l of the tuned input circuit. The tuned input circuit 1, i1 is tuned to the signal frequency and energy therefrom is passed over tap 26 and lead 3 to the grid of the detector tube 4. At this time it should be noted that the tap 26 as well as the tap from the antenna circuit 21, are adjusted over the inner conductor 2 in order to obtain optimum impedance adjustments, the tap to the transmission line extending to the antenna 21 being adjusted to obtain an impedance match between the tuned input circuit and the antenna system.

The heterodyne oscillator l3 has its anode connected to the high potential end of inductance element 9 by means of a by-pass condenser 23, which is of low impedance to the oscillator frequency, while the grid of oscillator 13 is similarly connected to the high potential end of inductance element l by means of a by-pass condenser 22. The potential for the anode of the oscillator is supplied through a lead extending through the interior of the inductance element 9 to a source of voltage supply whose value as supplied to the anode can be adjusted by means of a tap 20, thereby also controlling the intensity of the excitation on the cathode of detector 4. The grid of the oscillator II! has connected thereto a grid-leak 29 directly connected across the grid input condenser 22. This gridleak condenser, if desired, can be located externally of the mechanical construction and connected to the grid through a lead extending in the interior of inductance element In, although this last arrangement is not preferred. The cathode of the oscillator is connected to ground through an impedance l4 which reduces the tendency for parasitic oscillations to occur and improves the efficiency of the oscillator by permitting the cathode to assume the most favorable potentials for maximum intensity of oscillation. This impedance l4 may be a resistor, and in some cases where it is desired to improve the efilciency of the oscillator it may constitute a small inductance, the size of which is preferably determined experimentally. In effect. inductance elements 9 and I0 may each be said to constitute a concentric line tuned circuit, the outer conductor of which is the shell I6 plus an imaginary shield extending symmetrically between and along the length of the inductance elements 9 and In. A modification showing such a concentric line arrangement is shown in Fig. 6 and described later in this specification. The total inductance between the anode and grid of oscillator Hi can be varied by slider I! which is connected between tubular elements 9 and I0, while the grid inductance l0 can be varied by slider 2| which is connected between element In and the outer grounded shield. If desired, inductance element 9 can also be varied independently by another slider in the same manner as inductance I0 is varied by slider 2!. The frequency of the oscillator is variable by means of tuning condenser 12 which comprises two rotary condenser elements bridged in series across the high potential ends of the inductances 9 and Hi. The stator plates of the two rotary condensers of i2 are directly and integrally connected to the ends of inductance elements 9 and Ill while the rotor plates are connected to a metallic shaft 32' in the manner indicated in Fig. 3b. Where a vernier adjustment of the oscillator circuit is desired, there may be provided a Vernier tuning condenser I5 which may be operated by suitable automatic control means over a shaft 30 and coupled to drive means, not shown.

The cathode of the detector tube 4 is energized by the heterodyne oscillator l3 via a tap 8 on the inductance element 9 through a coupling condenser 24 shunted with a self-bias resistor 25. The intermediate frequency output of the detector is derived from the anode circuit of tube 4 by means of the transformer 5, I, the primary coil 5 of which is tuned by the con densers l8 and 6. This intermediate frequency output is coupled to the intermediate frequency amplifier of the receiver, not shown.

Fig. 2 illustrates the equivalent electrical circuit for the heterodyne oscillator l3. It will be obvious that this circuit is generally of the Hartley three-point type, the grid being connected to one end of the tuned frequency controlling circuit, the anode being connected to the other end thereof, while the cathode is coupled to an intermediate point such as the center. Impedance Z, labeled 14, has been shown in box form, since it may constitute a resistance or an inductance whose values can be most readily determined experimentally. At lower frequencies, the impedance I4 is usually eliminated. It is not believed necessary to go into the operation of the circuit of Fig. 2, since it is believed to be apparent from an inspection thereof.

The mechanical construction of apparatus in accordance with Fig. 1 may take the form indicated in Figs. 3a and 3b, the former of which shows a front view and the latter of which a back view of the sarrie apparatus. Only the essential elements of the circuit of Fig. l have been shown in Figs, 3a and 3b in order to simplify the drawings. It should be noted that the tuned input circuit includes a square copper shield or outer conductor I! to whose low potential end an antenna 21 is connected. The antenna 21 is here shown as being a dipole which is connected through a balanced transmission line to both the inner conductor and the outer conductor. This manner of coupling the transmission line to the tuned input circuit is described in more detail in my application Serial No. 292,770, filed August 31, 1939, which has eventuated into United States Patent No. 2,234,- 556, granted March 11, 1941. It should be observed that the condenser 2 is of the multiplate rotary type comprising a plurality of stator plates and a plurality of rotary plates. The stator plates are directly connected to a metallic plate 3| of extremely low inductance forming part of or integrally mounted on the high potential end of conductor I, thus obviating the need for leads or conductors between the condenser 2 and the conductor l of the concentric line tuned circuit. The rotary plates are coupled to a shaft 32' which is grounded to the outer shell l1. It should be understood that the grounding of the rotary condenser plates is made with the introduction of no unnecessary inductance. The constructional details of the method of connecting the stator plates to the inner conductor l are shown in more detail in Figs. 5 and 5a. The oscillator I3 is located in a suitable rectangular shielded compartment I5 of its own (note Fig. 3a). The filamlent leads of this oscillator tube are shown connected to metallic plates 32" which are mounted on mica sheets to provide by-passing condensers to the partition wall of the compartment. In like manner, other by-pass condensers used in other parts of the circuit (not shown in Figs. 3a and 3b) are similarly constructed to obtain effective by-passing with no series inductance.

Referring to Fig. 31), it should be observed that the condensers I2 are also of the rotary type and of similar construction to the condenser 2 shown in Fig. 3a. More specifically, there is provided a rotary condenser for the high potential ends of the lines 9 and II], the stator plates of each rotary condenser being directly mounted on metallic plates 3| which are integral with the conductors 9 and I0, while the rotary plates of both condensers l2 are mounted on a single shaft 32'. Reference is made to Figs. 5 and 5a for a more detailed showing of the manner in which the stator plates of these rotary condensers are connected to the ends of lines 9 and ID. The shaft 32', which connects the rotary condenser plates of condenser I2 in series in the manner shown diagrammatically in Fig. 1, may or may not be grounded.

At this time it should be observed that the square shields or tubing for the conductor I1 and for the box I 6 affords a simple assemblage which enables the mounting of the various elements on. the walls thereof. It should be understood, how ever, that if desired these shields may also be cylindrical and have other forms without changing the desired characteristics of the circuit.

Fig. 4 shows an arrangement similar to Fig. 3b except that the straight inductance elements 9 and I have been replaced by small inductance tubular rod-like elements 9' and I0 each of about one and one-half turns. The size of this coil may, of course, vary with the desired amount of inductance and may comprise one turn, more or less. The additional inductance provided by the coils 9 and I 0' serves to reduce the size of the circuit elements for the lower frequencies to give a more compact structure. It should be noted that if straight linear inductance elements such as 9 and I 0 were employed instead of the coils 9' and ID to obtain the same inductance values, the lengths of the linear elements 9 and I0 would be inconvenient. It is preferred that coils 9 and Ill be small copper tubing through the interior of which leads (labeled 38 and 39) may extend from external sources of supply to the anode and the grid of the oscillator l3. Rotary condensers 12 (shown in Fig. 4) are similar in construction to the condensers l2 shown in Fig. 317. It should be observed that, except for the use of coils 9' and III, the arrangement of Fig. 4 is very similar to the arrangement of Figs. 3a and 3b.

Figs. 6 and '7 show a modification in construction of the heterodyne oscillator circuit l3 of the invention. In these figures the inductance elements 9" and I0" each constitute the inner conductors of a concentric line oscillatory circuit. The outer conductor of each concentric line oscillatory circuit of these figures constitutes the inner surface of a cylindrical hole formed from a solid block of metal 31, although it should be understood that, if desired, the outer conductor may also comprise a thin shell of material. The inner conductors 9" and I0 of the concentric line oscillatory circuits are each machined at their high potential ends to provide suitable stator plates integral with the inner conductors for the rotary condensers l2". In effect, each of the inner conductors 9" and I0" have a pair of flanges 34 at the free end thereof which are spaced from each other by a slot or groove cut into the inner conductor. These flanges form stator plates between which the rotary plate 35 of the condenser l2 moves. The rotary plates 35, 35 of both condensers are electrically connected together and controlled in unison by metallic condenser shaft 32'. In order to tune each concentric line including the inner conductors 9" and I0", there is provided a small padding condenser constituted by a movable metallic plate 36 which is adjustable in position over the free ends of the inner conductors adjacent the stator plates 34. This arrangement is clearly shown in Fig. '7, wherein the arrows indicate the direction of movement of the plates 36 between the inner and outer conductors of each concentric line oscillatory circuit. The ends of plates 36 which are immediately above the conductors 9 and ID" are separated therefrom by a suitable dielectric which may be air or some insulating material. The oscillator [3 may be mounted between the conductors 9" and I0 so that the anode and grid electrodes contact small metal plates 23' and 22' which form capacitors with those surfaces of the inner conductors 9" and ID" adjacent the flanges 34, thus providing anode and grid coupling condensers equivalent to

condensers

23 and 22, respectively, of Fig. 1. Putting it another way, the grid and anode of oscillator 13 of Figs. 6 and 7 are coupled to the elements 9" and H1" in the same manner as the oscillator I3 is coupled to the inductance elements 9 and ll) of Fig. 1. The arrangement shown in Figs. 6 and 7 has the advantage of giving extremely high frequency stability at the high frequency range around 500 megacycles for circuits employing lumped circuit elements for tuning the line.

It is proposed to employ several circuits of the type shown in the drawings to cover different ranges of signal frequencies. For example, one such circuit may cover a signal range greater than 250 to 500 megacycles while another such circuit may cover a signal range greater than 125 to 250 megacycles, while still a third circuit may cover a signal range greater than to megacycles. In this way the different units will overlap in frequency range to provide continuous frequency coverage capabilities. These three frequency converters may then be mounted side by side on a panel, any one of which can be connected with a common intermediate frequency amplifier by suitable switches, although, if desired, they could also be of the plug-in type. In this manner, there is obtained a simplified, extremely wide range, and compact ultra high frequency receiver.

What is claimed is:

1. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of rod-like inductance elements arranged parallel to each other and electrically connected to each other at one end and having a balanced tuning condenser arrangement coupling together the other ends of said inductance elements, a shield surrounding said inductance elements, a connection from said cathode to said shield, and paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said anode .and control electrode.

2. An oscillation generator in accordance with claim 1, characterized in this that said inductance elements are tubular, there being a lead extending within one of said tubular elements for supplying a polarizing potential to said anode.

3. An oscillation generator in accordance with claim 1, characterized in this that said inductance elements are tubular, there being leads extending within said elements for providing suitable bias potentials to said anode and grid.

4. An oscillation generator in accordance with claim 1, characterized in this that said inductance elements are coiled and tubular, there being leads extending within said elements for providing suitable bias potentials to said anode and grid.

5. The combination with an oscillation generator comprising an electron discharge device having an anode, a cathode, and a control elec trode; a pair of rodlike inductance elements arranged parallel to each other and electrically connected to each other at one end, and having a balanced tuning condenser arran einent coupling together the other ends of said inductance elements, a shield surrounding said inductance elements, a connection from said cathode to shield, paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said anode and control electrode, of a vacuum tube utilization circuit coupled to one of said inductance elements.

6. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode; a tuned circuit including a pair of straight tubular inductance elements of substantially the same diameter arranged parallel to each other and directly connected together at one end, and having a balanced condenser arrangement coupling together the other ends of said inductance elements, paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said anode and said control electrode, a connection from said cathode to the electrical center of said balanced condenser arrangement, and a slider for varying the effective lengths of said inductance elements with a consequent vari ation of the total inductance between the an ode and control electrode.

7. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit including a pair of spaced tubular inductance elements arranged parallel to each other and directly connected together at one end and capacitively coupled together at their other ends, paths of 10W impedance to energy of the operating frequency from said last ends of said inductance elements to said pair of cold electrodes, means for varying the total inductance of said pair of elements, and separate means for varying the inductance of one of said inductance elements.

8. A high frequency signalling system including an oscillation generator comprising an elec tron discharge device having a pair of cold electrodes, a tuned circuit including a pair of substantially identical, spaced, tubular inductance elements arranged parallel to each other and directly connected together at one end and capacitively coupled together at their other ends, paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said pair of cold electrodes, and vacuum tube utilization apparatus coupled to a point on one of said inductance elements intermediate its ends.

9. A high frequency signalling system including a vacuum tube oscillator having an anode and a grid, a tuned circuit comprising a pair of substantially identical inductance elements arranged parallel to each other and directly connected together at one end and capacitively coupled together at their other ends, capacitive paths of low impedance to energy of the operating frequency from said last ends to said anode and grid, and vacuum tube utilization apparatus coupled to a point on that inductance element which is capacitively coupled to said anode.

10. An ultra high frequency receiver comprising a high frequency detector having a grid, anode and cathode, a tuned input circuit coupled to said grid, an antenna coupled to said tuned circuit, an oscillator coupled to said cathode, and an intermediate frequency amplifier coupled to said anode, said oscillator including a vacuum tube having an anode, a cathode and a grid, a tuned circuit comprising a pair of rod-like inductance elements arranged parallel to each other and directly connected together at one end and capacitively coupled together at their other ends, capacitive paths of low impedance to en ergy of the operating frequency from said last ends to the anode and grid of said oscillator, and means for coupling said cathode of said oscillator to a point effectively intermediate said last ends of said inductance elements.

11. A receiver in accordance With claim 10, characterized in this that said first tuned circuit is a concentric line and the cathode of the detector is coupled to a point on the anode inductance element of said oscillator.

12. An oscillation generator comprising an electron discharge device having an anode and a grid, a tuned circuit coupled between said anode and grid and comprising a pair of tuned concentric lines whose inner conductors form linear inductance elements, said linear inductance elements being directly connected together at one end and capacitively coupled together at their other ends, and paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said anode and grid.

13. An oscillation generator comprising an electron discharge device having an anode and a grid, a tuned circuit coupled between said anode and grid and comprising a pair of tuned concentric lines whose inner conductors form inductance elements, said inductance elements being directly connected together at one end and capacitively coupled together at their other ends, paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said anode and grid, and means for individually tuning each of said concentric lines.

14. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit arrangement including a pair of spaced rod-like inductor elements arranged substantially parallel to each other and coupled together at one end by a path of low impedance to energy of the operating frequency, capacitive paths of low impedance to energy of the operating frequency from the other ends of said inductor elements to said pair of cold electrodes, shielding means surrounding said inductor elements, and means for varying the effective inductance of said rod like elements.

15. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit arrangement including a pair of spaced rod- "he inductor elements arranged substantially parallel to each other and directly connected together at one end, the other ends of said rod-like inductor elements being capacitively coupled together, and capacitive connections of low impedance to energy of the operating frequency extending from said last ends to said pair of cold electrodes, shielding means surrounding said inductor elements, and means for varying the effective inductance of said inductor elements.

16. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit comprising a pair of inductance elements which are similar in shape and size, each element having a low potential end and a high potential end, a connection of low impedance to energy of the operating frequency between the low potential ends of said elements, and capacitive connections of low impedance to energy of the operating frequency from the high potential ends of said elements to said pair of cold electrodes.

17. An oscillation generator comprising an electron discharge device having an anode, a cathode and a grid, a tuned circuit comprising a pair of inductance elements which are similar in shape and size, each element having a low potential end and a high potential end, a connection of low impedance to energy of the operating frequency between the low potential ends of said elements, means eiiectively coupling said connection to said cathode, and connections of low impedance to energy of the operating frequency from the high potential ends of said elements to said anode and cathode.

18. An oscillation generator in accordance with claim 8, including shielding means for said inductance elements and a connection from said shielding means to ground.

19. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit comprising a pair of inductance elements which are similar in shape and size, each element having a low potential end and a high potential end, a connection of low impedance to energy of the operating frequency between the low potential ends of said elements, a condenser arrangement having rotor and stator plates and coupling the said high potential ends of said elements together, and capacitive connections of low impedance to energy of the operating frequency from the high potential ends of said elements to said pair of cold electrodes.

20. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of rod-like inductance elements arranged in parallel planes and electrically connected to each other at one end and having a tuning condenser arrangement coupling together the other ends of said inductance elements, a shield surrounding said'inductance elements, a connection from said cathode to said shield, and electrically conducting connections from said last ends of said inductance elements to said anode and control electrode.

21. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of noncoaxial hollow tubular inductance elements arranged parallel to each other, a connection between one end of one inductance element and the adjacent end of the other inductance element, means effectively connecting said cathode to said connection, a condenser coupling together the other ends of said inductance elements, leads extending within said tubular elements for providing suitable bias for said anode and control electrode, and capacitive connections from the other ends of said inductance elements to said anode and control electrode.

22. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of noncoaxial hollow tubular inductance elements arranged parallel to each other, a connection between one end of one inductance element and the adjacent end of the other inductance element, means elTectively connecting said cathode to said connection, a condenser coupling together the other ends of said inductance elements, leads extending within said tubular elements for providing suitable bias for said anode and control electrode, capacitive connections from the other ends of said inductance elements to said anode and control electrode, and an output circuit coupled solely to one of said tubular inductance elements at a point intermediate the ends thereof.

23. An oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit arrangement including a pair of spaced rod-like inductor elements arranged in parallel planes and coupled together at one end by a path of low impedance to energy of the operating frequency, capacitive paths of low impedance to energy of the operating frequency from the other ends of said inductor elements to said pair of cold electrodes, and means engaging both inductor elements for varying the total inductance between said pair of cold electrodes.

24. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of rodlike inductance elements arranged parallel to each other and electrically connected to each other at one end and having a tuning condenser arrangement coupling together the other ends of said inductance elements, a shield surrounding said inductance elements, a connection from said cathode to said shield, and connections from said last ends of said inductance elements to said anode and control electrode.

25. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control electrode, a pair of rodlike inductance elements arranged parallel to each other and electrically connected to each other at one end and having a capacity frequency determining element coupled to the other ends of said indutcance elements, a shield surrounding said inductance elements, a connection from said cathode to said shield, and connections from said last ends of said inductance elements to said anode and control electrode.

26. A high frequency signalling system including an oscillation generator comprising an electron discharge device having a pair of cold electrodes, a tuned circuit including a pair of similar inductance elements arranged parallel to each other and electrically connected to each other at one end and capactively coupled together at their other ends, shielding means surrounding said inductance elements, paths of low impedance to energy of the operating frequency from said last ends of said inductance elements to said pair of cold electrodes, and vacuum tube utilization apparatus coupled to one of said inductance elements.

RALPH W. GEORGE.