US2879487A - Tube mounting method and apparatus - Google Patents

Description

March 24, 1959 S. R. FITZMORRIS TUBE MOUNTING METHOD AND APPARATUS Filed May 18, 1956 INVENTOR. $7'AA/)"R./77ZMORRIS M/Mb... 41?

United States Patent TUBE MOUNTING METHOD AND APPARATUS Stanley R. Fitzmorris, Baldwinsville, N.Y., assignor to the United States of America as represented by the Secretary of the Air Force Application May 18, 1956, Serial No. 585,915

Claims. (Cl. 333-98) The present invention relates to a tube mounting device, and is concerned more particularly with a means for mounting electronic tubes which employ R.F. energy in a manner which will prevent damage due to sparking and other undesirable conditions.

In mountings of the type wherein a coaxial transmission line is formed by a portion of a tube and a metal wall of the member on which such tube is mounted, it has been found that damage frequently occurs due to sparking across said line at the point of mounting. As a result of such damage the useful lives of both the tube and the mounting are greatly diminished. One of the proposed solutions to this problem was to provide better insulation between the tube and the metal wall at the mounting point. This technique has proved to be unsuccessful since it is extremely difiicult to eliminate air gaps between the tube and the mounting bushing, and also between the latter and the metal wall. The high gradient across these gaps allows corona to form and sparking to take place. Further, by increasing the spacing between the tube and the metal for the purpose of adding insulation, the impedance of the coaxial line is raised causing higher voltages to be generated thereacross. Although actual tests of this solution showed improvements, these were neither substantial nor sufficient.

My invention provides a method and apparatus for solution of the problem by lowering the impedance of the coaxial transmission line. This is done by establishing a relatively high capacitance, low reactance path from the tube to the metallic wall of the member mounting the tube, thereby providing a controlled impedance path for the R.F. energy and thus minimizing the danger of spark damage.

Thus, it is a primary object of this invention to provide a new and improved method for controlling energy flow in coaxial transmission lines constituted by R.F. tubes of the character indicated.

It is another object of the invention to provide a tube so constructed as to tend to reduce tube and mounting damage to a minimum in tubes of the type heretofore mentioned.

A further object of this invention is to provide a simple and inexpensive tube mounting arrangement which will materially increase the lives of the tube and the mounting bushing.

Still a further object of the invention is to provide a means for reducing damage to conductors in coaxial transmission lines caused by high potential differences between such conductors.

The above and still further objects, advantages, and features of the invention will become apparent upon consideration of the following detailed description of a single embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is an isometric view of a waveguide having a portion broken away to show the duplexer tubes therein;

Fig. 2 is a sectional view of one of the duplexer tubes mounted in accordance with the invention;

Fig. 3 is an exploded view showing a portion of a duplexer tube and the several elements of its mounting arrangement; and

Fig. 4 is an enlarged view, partially in section, of contact area between a tube and gasket.

Although the specific embodiment to be described involves a duplexer tube mounted on a waveguide of a type used in radar equipment, it should be recognized at the outset that the instant invention is susceptible of use in conjunction with other and different tubes and structures on which such tubes are mounted, and also in conjunction with coaxial transmission lines in which the conductors are separated at intervals by spacing means.

Referring now to the drawings in which like characters of reference indicate like parts, Fig. 1 shows a waveguide generally indicated at 10. The specific details of the waveguide form no part of the instant invention and, therefore, will be only briefly described. Waveguide 10 is of the twist type having rectangular connecting portions at opposite ends joined by a circular twist section 12. Heat dissipating fins 14 are mounted on the twist section 12, and a receiver arm 16 enters thereinto. Mounted on the twist section in uniformly varying angular positions is a series of capillary TR tubes 18. These tubes extend through the waveguide walls and a pressure sealing cap 20 covers each protruding tube end.

In Figs. 2 and 3 it can be seen that the wall of the twist section is formed with apertures for the reception of the tubes, each of such apertures being surrounded by an upstanding boss 22. Although the bushing 26 is shown as a separate part, it should be clear that it may also be formed integrally with members 12 and 22. Within the boss the wall of the twist section extends slightly to form an annular shoulder 24. The boss 22 is internally threaded, and receives an externally threaded metal bushing 26 therein. The bushing 26 is T-shaped, and the vertical leg of the T extends into the central bore through the shoulder 24. The cross arm of the T is seated against said shoulder, and a central passage is formed through the bushing. An annular metal-mesh gasket 28 is seated on bushing 26 within the boss. A clamping nut 30 is threaded into boss 26 atop the gasket 28,

' and the sealing cap 20 closes the upper end of said boss.

The threaded portion of said cap is reduced for reception in said boss, and an O-ring 32 is compressed between the upper end of the boss and the shoulder formed by said reduced portion of the cap. Both the clamping nut 30 and the cap 20 have central through bores. The bore in said cap receives a metalized glass head 34 which is soldered into said bore and forms a seal therefor. This bead permits an observer to ascertain whether the gas in the tube is ionized and eliminates the need for unscrewing the cap 20.

One of the tubes 18 passes through the central apertures in members 26, 28 and 30. That portion of the tube which is in contact with the metal-mesh gasket is silvered at 36. The silver coating surrounds the tube, and the coated area is preferably at least twice the width of gasket 28. In this manner the coated area of the tube will remain in contact with said gasket in the event of slight slippage or misalignment.

In choosing the proper material for the metal-mesh gasket, the primary consideration is to have a minimum contact resistance between said gasket and the silver coating. Optimum results were obtained using a gasket of silver plated brass which showed contact resistance of .072 ohm as compared with .164 ohm for stainless steel. The significance of these figures becomes apparent when contrasted with the contact resistance of a gasket of aluminum mesh which was 340 ohms.

In assembling the mounting, the nut 30 will be adjusted to compress the metal-mesh gasket against the bushing 26. In this way a good contact can be assured between said gasket and the coated portion of the tube 18. The ionized gas column of the TR tube forms the inner conductor of a coaxial line. The members 22, 26, 28, 30 and 36 form the outer conductor of said line. Since the capacitance across the tube wall between the gas column and the coating is high while the reactance of the coating, gasket and metal wall is low, it is clear that a low impedance path has been provided between said conductors. The tendency toward sparking therebetween is accordingly reduced, and the damage problem is avoided.

It is to be understood that the above-described arrangement is merely illustrative of the applications ofthe principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

1. Mounting structure for RF. energy conductors comprising a hollow electrical conducting member having an internal projection, apertured metallic gasket means disposed within said member, adjustable means in said member for radially deforming gasket means, second conducting means passing through the aperture in said gasket means, said second means comprising a central portion of non-electrically-conductive material and a coating of electrical conducting material on said portion, operation of said adjustable means forcing said gasket 4 means into contact with said coating to produce a low impedance path between said conducting members.

2. A tube mounting arrangement for preventing damage due to sparking comprising a mounting base having a boss, a deformable annular metal-mesh gasket in said boss, an annular clamping nut adjustable in said boss to compress said gasket, non-conductive-tube means in said boss extending through said gasket and said nut and in circumferential contact with the former, and a metallic coating on said tube means at its area of contact with said gasket whereby a low impedance path is formed between said boss and said tube means.

3. A device as defined in claim 2, in Which the metalmesh gasket is formed of a material having low contact resistance, and the metallic tube coating is of silver.

4. Mounting structure as defined in claim 1, wherein said gasket is formed from a metal-mesh material having low contact resistance.

5. Mounting structure as defined in claim 1, wherein said non-conductive material is glass, and said conductive coating is silver.

References Cited in the file of this patent UNITED STATES PATENTS 718,607 Costello Jan. 20, 1903 1,779,225 Bausman Oct. 21, 1930 2,557,180 Fiske June 19, 1951 2,557,961 Goldstein et al. June 26, 1951 2,594,732 Cork Apr. 29, 1952 2,624,858 Greenlee Jan. 6, 1953 FOREIGN PATENTS 722,406 Great Britain Ian. 26, 1955

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