US3054074A

US3054074A - Termination device with removable center conductor

Info

Publication number: US3054074A
Application number: US798727A
Authority: US
Inventors: James R Bird; Harold E Stevens
Original assignee: Bird Electronic Corp
Current assignee: Bird Electronic Corp
Priority date: 1953-02-04
Filing date: 1959-03-11
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11
Also published as: US3095545A; GB753989A

Description

Sept. 11, 1962 J. R. BIRD ETAL TERMINATION DEVICE WITH REMOVABLE CENTER CONDUCTOR Original Filed Feb. 4, 1955 2 Sheets-Sheet 1 0 wwmm R5 E m N m E ww W50 w IEL A Sept. 11, 1962 .1. R. BIRD ETAL 3,054,074

TERMINATION DEVICE WITH REMOVABLE CENTER CONDUCTOR Original Filed Feb. 4, 1953 2 h t 2 |NVENTOR5 JAMES P. B/PD HAQOLD E. 57'EVEN5 50M,5W,

HMMMM ATTORNEYS 3,054,074 Patented Sept. 11, 1962 j free 3,054,074 TERMINATION DEVECE WITH REMOVABLE CENTER CONDUCTOR James R. Bird, Chagrin Falls, and Harold E. Stevens,

Lyndhurst, Ohio, assignors to Bird Electronic Corporation, Cleveland, Ohio, a corporation of Ohio Original application Feb. 4, 1953, Ser. No. 335,118, new Patent No. 2,884,603, dated Apr. 28, 1959. Divided and this application Mar. 11, 1959, Ser. No. 798,727 21 Claims. (Cl. 33322) This invention relates to high frequency electrical devices and has particular reference to coaxial line components of the reflectionless termination type used either alone for attenuation or absorption of wave signal energy or in conjunction with suitable detector, sampling, pickup or voltage dividing devices as a measuring instrument or the like. Reference is made to co-pending parent application for United States patent, Serial No. 335,118, filed February 4, 1953, now Patent 2,884,603, of which this is a division.

The transmission, absorption and measuring of high frequency electrical energy is more difificult in many respects than the corresponding treatment or handling of low frequency or direct current electrical energy because of capacitive and inductive effects, reflections and other phenomena. High frequency energy is satisfactorily transmitted on coaxial lines and it is known that a coaxial transmission line can be terminated substantially reflectionlessiy by a device which incorporates coaxial inner and outer conductors, one of which is tapered and one of which is resistive, the tapered conductor desirably taking the form of a tubular metal horn surrounding a cylindrical insulator of ceramic or like material on which is deposited or otherwise formed a film of carbon, or equivalent, the latter constituting the inner conductor of the line termination. In such arrangement the smaller end of the outer horn conductor makes direct electrical connection with resistive carbon film at one end of the inner conductor, thus completing the circuit.

Electrical energy fed into a line termination of the character mentioned is absorbed all along the resistive inner conductor, resulting in heating of the carbon film. At low energy levels the energy is satisfactorily dissipated into the atmosphere as by blowing air over the resistive film or by permitting air to circulate over the resistive film through the action of convection currents. It has also been proposed to employ a liquid dielectric coolant in the annular tapered dielectric space which separates the inner and outer conductors of the termination for forced flow or convective circulation of such coolant through the dielectric space either axially of the device or transversely thereof.

By reason of the geometry of the reflectionless device, requiring close proximity of the inner and outer conductors at one end of the device and wide separation thereof at the other end, and the need for substantially uniform heat absorption all along the length of the resistive conductor, servicing, checking and repairing such devices present numerous problems. The present invention is therefore concerned primarily with and has for one of its principal objects the provision of a new apparatus for reflectionlessly terminating a coaxial transmission line which incorporates novel manufacturing, assembling and servicing advantages. More particularly, the device combines inner and outer coaxial conductors arranged as a rcflectionless termination with the inner conductor axially withdrawable from and reinsertable into the outer conductor. As a refinement, the inner and outer conductors are separated by an insulator and operative means is provided for stressing and deforming the insulator to grip the conductors to hold them against axial shifting relative to the insulator and to one another, the operative means being actuatable to relieve the stress on the insulator and the parts being proportioned and arranged for axial withdrawal of the inner conductor from and reinsertion of the same or a similar inner conductor into the outer conductor when the insulator is so relieved.

Another and more specialized object is to provide such a device having an inner conductor withdrawable from and reinsertable into a coaxial outer conductor with which it forms a reflectionless termination in which the coaxial termination is contained in a housing from which it is removable and reinsertable axially as a unit without disturbing the relative positions of the inner and outer conductors.

Cooling of the circulating coolant which has been heated by flowing over the hot resistive conductor is effected preferably, though not necessarily, in a zone wholly removed from the termination, this also being an objective. The coolant may, for example, be passed through a heat exchanger separate from the termination and thereafter returned to the resistor. The coolant thus com. pletes a closed circuit in which the flow may be induced by convection but preferably is accomplished by powerdriven pump means which is more effective in obtaining the high flow rate desired to secure, in sectional area, preferably uniform'along the length of the resistive conductor and, in the case of a device having a resistive center conductor of circular cross section, surrounding such resistive conductor..

Another object of the invention is to provide a combination which comprises a coaxial line component or termination of the character mentioned in association with a casing or housing for holding a suitable liquid dielectric coolant, the line termination being immersed in the liquid dielectric coolant contained in the casing. In the arrangement preferred as an embodiment of this aspect of the invention thecasing is included in a fluid coolant circuit which also includes a heat exchanger connected by suitable conduits or tubes for the serial flow of coolant as by means of a power driven pump also included in the coolant circuit. In flowing through the casing the coolant absorbs heat by direct contact with the resistive element of the coaxial line component or termination; in flowing through the heat exchanger the coolant gives up heat, say to a circulating refrigerant such as water passed through pipes or tubes immersed in a body of the circulating liquid dielectric contained in the heat exchanger receptacle. This separation of the line termination casing from the heat exchanger receptacle and the forced serial flow of coolant therethrough is an objective of the invention.

In a specialized version of the apparatus wherein the coaxial device is in the form of a reflectionless termination and the liquid dielectric coolant is contained in a casing which encloses or houses the termination and wherein the coolant is forced to flow over a closed circuit, the present invention also contemplates a further refinement wherein the flowing coolant is brought into the casing through an entrant tube, preferably in the bottom of the casing and is confined and directed to flow from such entrant tube directly into the dielectric space separating the inner and outer conductors of the termination, this being an objective of the invention.

It is a further objective of the invention to provide a combination of tubular circular sectioned casing and contained termination or coaxial device wherein the latter is coaxial to the casing and acts as a partition or flow barrier controlling the movement of liquid dielectric coolant through the casing. In the preferred embodiment contemplated the coaxial termination device is axially withdrawable from and reinsertable into the casing and has a tapered outer conductor having a portion of maximum cross sectional area or diameter intermediate its ends which maximum section portion engages or has substantially sealing relation with the cylindrical casing wall by which it is surrounded to divide the casing chamber and constrain the flowing dielectric coolant to flow through the interior of the termination.

Other objects and advantages pertain to certain novel combinations of parts and features of construction, including capacitance compensation at the small end of the termination, the arrangement of the termination on a vertical axis with provision for axial withdrawal of the inner conductor structure, provision for telescopic assembly of the several component parts of the termination device and casing with advantageous locating and guiding relationships and positive securement of the inner conductor structure to resist shifting and turning in use. Such and still other objectives and advantages are apparent in the following detailed description of a preferred embodiment of the invention, its description being made in connection with the accompanying drawings forming a part of the specification.

In the drawings:

FIGURE 1 is an elevational view, partly diagrammatic and with parts broken away and removed, showing a high frequency electrical meter instrument which incorporates a reflectionless termination for a coaxial transmission line embodying the principles of the present invention;

FIG. 2 is a fragmentary elevational view, partly in section, partly diagrammatic and with parts broken away and removed, showing the casing containing the line termination component of the device of FIG. 1, this view being enlarged with respect to that figure;

FIG. 3 is a transverse sectional view, with parts removed, taken substantially in the plane designated by the line indicated at 33 of FIG. 2;

FIGS. 4 and 5 are fragmentary sectional views taken longitudinally through the upper and lower portions respectively of the reflectionless termination component and the casing for such component, these views being enlarged with respect to FIG. 2;

FIG. 6 is a sectional detail in the plane designated by the line indicated at 6-6 of FIG. 4, being enlarged with respect to that figure;

FIG. 7 is a longitudinal sectional detail showing an expansible section of the center conductor and the manner in which an implement is inserted axially into the movable element or expander of such section to turn such element in effecting expansion;

FIG. 8 is a transverse sectional detail taken substantially in the plane designated by the line indicated at 8-8 of FIG. 5 and enlarged with respect to that figure; and

FIG. 9 is an enlarged sectional detail, diagrammatic in character, showing the terminal contact band of thin brass soldered about the copper plated end of the resistive inner conductor at the lower or small end of the termination.

The high frequency electrical meter device illustrative of the present invention comprises a reflectionless termination T received in an elongated casing C, the latter preferably taking the form of a cylindrical metal tube 1 of brass or steel, although other cross sectional shapes can be used. The top and bottom ends of the casing are closed by circular metal plates 10 and 11, respectively, the latter being permanently secured in place as by peripheral welding 12. The top or cover disc 10 is peripherally grooved and held in place by clamping ring 14. An interposed rubber O-ring effects a fluid tight seal between the casing flange and the cover it).

At its upper end the body tube 1 of the casing C is connected to and supported by a heat interchanger or receptacle R comprising a body 16 closed at the bottom by a disc similar to the disc 11 of the casing C, and at the top by a cover 17 bolted to a flange 19 formed or welded in place about the upper end of the body tube 16. The bottom of the receptacle R rests on a pedestal or base 20 4 which also serves as a support for an electrical motor 21 that in turn supports and drives a coolant circulating pump 8.

The connection between the casing C and the receptacle R at their upper ends comprises aligned metal coupling tubes 22 welded into aligned openings in the body tubes and attached together by flanged joint 23 sealed by a suitable ring or gasket. At the bottom end of the casing C connection is made to the lower part of the receptacle R through the pump 8. The inlet of the pump is connected by a metal tube 24- to the bottom of the receptacle 16, a flanged joint 25 being interposed to facilitate assembly and disassembly. The tangential outlet of the pump, indicated at 26, is connected by aligned

tubes

27 and 28 to the lower end of the casing C, a flanged joint 29 being provided between the tubes. A liquid coolant having suitable dielectric properties fills the casing and receptacle for serial flow therethrough in a closed circuit.

In operating the device the motor 21 is energized to drive the pump 8, which forces the liquid dielectric coolant upwardly into the bottom of the casing C. As shown in FIG. 5, the tube 28 extends into the bottom of the casing through a circular opening 30 in the bottom closure 11. In the receptacle which constitutes a heat exchanger to cool the liquid the flow of the liquid dielectric coolant is generally downwardly, liquid coolant entering the top of the receptacle from the casing C displacing liquid from the bottom of the receptacle and forcing the latter to flow out the bottom discharge tube 24 of the receptacle into the intake of the pump, thus completing the liquid coolant cycle.

As indicated in FIG. 1, the receptacle R is much larger than the casing C and has a volumetric capacity many times that of the casing to promote tempering and provide for adequate cooling of the circulating liquid. The cooling of the dielectric liquid occurs principally during its downward flow in the receptacle R, such cooling being effected by any suitable arrangement familiar to the heat exchanger art, such as heat transfer by conduction through the metal walls of the body tube 16 and dissipation into the atmosphere by radiation and convection, the heat transfer, if desired, being a cooling medium such as cold water from a conventional pressurized water supply system that is circulated in direct heat exchange rel tion to the liquid dielectric in the receptacle R, the water being passed through a coil or coils 33 disposed within the receptacle and having inlet and

outlet tubes

34 and 35, respectively, projected through the top closure 17.

The inlet 34 is connected as to a city water supply system by suitable conduits and valves (not shown), one valve being an electrically operated or solenoid valve preferably of the water pilot type responsive to a thermostatic switch immersed in the liquid dielectric coolant in the receptacle R and carried as by a boss on the receptacle top. The switch is arranged to open the water or coolant supply valve when the temperature of the liquid dielectric coolant becomes heated to a predetermined temperature, say about 35 centigrade in the case of the diphenyl, diphenyl oxide mixture mentioned, and to close the valve when the liquid dielectric coolant is cooled to a predetermined temperature, say about 30 centigrade when using such material, the electric valve thus automatically supplying the cold water or other refrigerant so as to maintain the circulating liquid dielectric coolant within predetermined temperature limits. The energization of the pump drive motor 21 is governed manually to be turned on each time before electrical energy is fed into the device or, preferably, the pump is operated automatically to circulate the liquid dielectric coolant Whenever energy or power is fed into the termination T and simultaneously with such feeding.

A further control refinement comprises a pair of series connected thermostatic switches responsive to the temperature of the dielectric coolant in the receptacle R. These switches act through suitable relays or other controls to prevent operation of the equipment with which the present instrument is associated, say for example, a television transmitter, when such temperature is objectionably high, say above about 50 centigrade for the diphenyl, diphenyl-oxide mixture mentioned, and when such temperature is objectionably low or close to the freezing point of the liquid coolant, say below about 12 centigrade for such mixture. Still another thermostatic switch immersed in the liquid in the receptacle and responsive to the liquid temperature controls the energization of an electrical immersion heater, not shown, which is regulated in this manner to keep the temperature of the liquid coolant above the freezing point. The latter thermostatic switch may project upwardly through a port in a boss in the receptacle top 17, the boss and the upper end of the switch assembly being enclosed in a cover 38. The switches interlocking the signal generating equipment are mounted in other bosses under similar covers, not shown, on the top 17.

The termination T extends downwardly into the casing C through the top opening in the latter, in fact, being carried by the top 17 in suspended relation and inserted into the casing through such top opening in assembly. The general construction and geometry of the termination T follow well known principles enunciated, for example, in United States Patents 2,552,707, dated May 15, 1951, and 2,556,642, dated June 12, 1951, and application for United States Patent Serial No. 72,782, filed January 26, 1949. There are, however, certain improvements in the combination of parts and refinements in the structure of the termination that are features and objectives of the present invention, as will appear.

The termination has an inner resistive conductor in the form of a carbon film 44 or equivalent, deposited or otherwise formed on the outer cylindrical surface of a ceramic tube 41. Surrounding the inner resistive conductor in coaxial relation thereto is an outer tapered conductor 42 which may take the form of a metal horn spun or stamped from brass or similar thin metal. The horn is curved or shaped in accordance with the known principles referred to above so as to provide a characteristic impedance at any point or section which is substantially equivalent to the resistance of that portion of the resistive inner conductor 40 which lies between the point or section of reference and the small end of the termination where the inner and outer conductors are mechanically and electrically joined.

At its upper or large diameter end the tapered horn outer conductor 42 is formed with an integral cylindrical extension or connector section 44 received telescopically within a matched cylindrical socket opening through the bottom end of a body member 45 which is of circular section and may be in the form of a spinning or, as shown, a turning of brass or other metal. The conductive parts of the device are machined from brass stock, except as otherwise indicated or implied. The circular body 4'5 has an external surface 46, here cylindrical, that is complemental to and has a freely sliding fit in the cylindrical body tube 1 of the casing or, as shown, in cylindrical reinforcing band 47 previously press fitted into the body tube of the casing to reinforce the walls of the latter. The upper open end of the circular body 45 is formed with a shallow cylindrical socket 49 axially aligned with the socket that receives the connector 44. One end of a cylindrical relatively thin walled metal connector tube 55 is received in the shallow socket 49 and extends upwardly therefrom through the upper portion of the casing in coaxial relation and through a central opening 51 in the top closure 10. The connector tube 5%, of brass or copper, is secured in the shallow socket 49 as by soldering or brazing and additionally by a plurality of radial set screws 52 threaded through the termination sealing ring 127 comprising an element of a tubular guide for the flowing liquid dielectric coolant.

A ring 54 is formed on or welded at 55 against the underside of the top closure 10 about the center opening that receives the connector tube 50. Radial set screws 56 are threaded through the ring 55 and are received through openings in the connector tube so as to bear radially against and become interlockingly embedded in an annular block or insulator 60 of polytetrafiuoroethylene or other suitable dielectric plastic material, this insulator block constituting a support for the center conductor assembly of the termination, as well appear. Rubber 0-ring 59 of circular section is received in an annular groove formed in the external cylindrical surface of the insulator block 69 and engages the internal surface of the connector tube 50 in the provision of a fluid tight seal. A number of axially elongated circumferentially spaced openings or slots 61 are formed in that portion of the connector tube 50 which lies between the circular section body 45 of the termination and the annular insulating block 60, these apertures placing the interior chamber of the connector tube in communication with an upper annular casing chamber 6 2 which is above the circular body 45 and in communication with the heat exchanger receptacle R through the connecting tube 22.

The lower end of the ceramic tube 41 is embraced by the small end of the outer or horn conductor 42; the upper end of the ceramic tube is connected to a center conductor connector 64 within and coaxial to the connector tube 50. The metal center conductor 64, which is of circular section, is formed at its lower end, which is the same diameter as the ceramic tube 41, with an internal thin walled cylindrical socket 65 that receives reduced diameter upper end portion 66 of the ceramic tube 41, the latter being preliminarily turned or ground down to the desired diameter and coated with silver or other conductive metal paint or plated with copper to provide a terminal band 67 Which extends onto and makes annular electrical connection with the end portion of the deposited carbon film coating. The joint is preferably soldered.

High frequency electrical energy from a signal generator such as a television transmitter or other source, which energy is to be absorbed and converted into heat by the termination T, is conducted to the termination over inner and outer conductors 71 and 72 of a suitable coaxial transmission line, indicated diagrammatically in FIG. 1. The coaxial transmission line, conventional in character, is provided with terminal fittings by means of which the inner and outer conductors 71 and 72 are respectively connected to inner terminal 73 and the portion of the connector tube 50 which projects through the top 10 of the casing and constitutes the connector terminal for the outer conductor of the termination T.

The inner terminal 73 is of circular cross section and desirably may comprise a turning of brass or similar metal formed at its upper end with a cylindrical cup 74 which is adapted to receive a connector plug of the quick disconnect fitting (not shown) on the coaxial transmission line. This terminal is formed with a reduced diameter shank portion 75 that extends axially and downwardly through center opening or bore 76 in the insulator 60, the reduction in diameter from the outer projecting portion of the terminal 73 which contains the terminal socket 74 to the diameter of the shank portion 75 compensates for the difference in the dielectric constant of the air in which the socket portion of the terminal is located and the polytetrafiuoroethylene or other insulating material in which the shank portion 75 is located, thereby maintaining substantially the same characteristic im pedance axially along the length of the device.

A strong frictional grip may be obtained between the walls 74 of the terminal cup and the center terminal plug of a coaxial line fitting attached to the present de vice. Accordingly, unless provision is made for a strong grip between and anchorage of the internal parts of the present device, the center cenductor structure or assembly, including the center connector 64 and the ceramic tube 41 which carries the resistive film 4b, is likely to be objectionably disturbed or shifted axially when the transmission line is uncoupled. By reason of the relatively greater area of contact between the connector tube 56 and the outside of the insulator on as compared to the inside bore of the insulator and the outside of the center terminal elements 73, slipping and shifting normally are more likely to be encountered between the latter parts. Thus, special provision is made in the form of an expanded and interlocked structure for anchorage of the inner terminal element within the surrounding insulator. The shank 75 of the terminal element 73 is expanded radially outwardly against the walls of the bore 76 in the solid insulator 60 and an interlock established. The insulator is in turn circumferentially embraced by the cylindrical walls of the connector tube Sit and thus capable of strongly resisting the expansion of the terminal element shank 75 to maintain a lasting permanent grip of one part on another. To distend the shank 75 a pluglike expander 8% (FIG. 7) is forced axially through a center bore in the terminal element, the expander having a tapered end 81 which engages an internal shoulder or shoulders 82 formed at the juncture of axial inner bore 83 and an outer threaded counterbore 84 which extends into the terminal element through the bottom of the cylindrical cup 74. Other types of expanders may, of course, be employed and the expander may be variously forced into place, a preferred arrangement being the use of the internal threads in the counterbore 84 of the terminal element 73 which cooperate with external threads 85 on the expander 80 to shift the expander axially relative to the terminal element upon relative turning so as to force the tapered end 81 against the shoulder 82. The expander is turned as by a hex or other noncircular tool or instrument, indicated at 86, inserted temporarily and for the purpose axially through the cup 74 and into a matching socket in the expander 80.

As a further refinement of the structural combination that holds the center conductor assembly or structure in place the terminal element shank 75 is formed with axial slots 87 which extend through the shoulder 82 in the provision of a number of tines or fingers 88. The shoulder 82 thus comprises a circumferential series of arcuate shoulders concentric to the axis of the terminal element and spaced axially from both ends of the slots. At its end opposite the terminal cup 74 the element 73 is formed with a reduced diameter end portion 89 receivable in matching socket 90 of intermediate element 91 that has a telescoping connection with the center conductor connector 64. The embracement of the ends of the tines 88 by the walls of the socket 9t) prevents expansion of the lower end of the slotted shank 75 under the radial pressure of the expander 89 so that the expansion of the terminal element takes the form of an outward or radial bowing of each of the tines or fingers 88, with the maximum radial distention occurring in the region of the shoulder or shoulders 82 engaged directly by the tapered end 81 of the expander. The relative movements of the parts such as the expander and the tines of the terminal element in such expansion may be small dimensionally and, in fact, are not shown in the drawings, the relatively stiff plastic block 60 strongly resisting distortion. Rubber O-ring 93 is received in an annular recessed groove formed in the wall of the bore 76 in the plastic insulator and engages the cylindrical external surface of the intermediate element 91 to seal the bore 76.

The insulator 60, which, as previously mentioned, is preferably a relatively stiff plastic material such as polytetrafiuoroethylene, while incompressible, or substantially so, is sutficiently deformable so that under the expanding pressures exerted by the bowed tines 88 it tends to fiow slightly into the slots 87, thereby providing an interlock mechanical in nature between the terminal element 73 and the insulator which resists turning of the terminal element relative to the insulator. The outward bowing of the tines 88, which may of course result in slight axial swelling of the plastic insulator 6%, also provides an interlock mechanical in nature between the terminal element 73 and the insulator which resists relative axial shifting of the parts. Thus inner terminal element 73 is both frictionally gripped and mechanically interlocked by and with the surrounding annular plastic insulator 60 in such a manner as effectively to prevent both relative turning and objectionable axial displacement or shifting of the center conductor structure of the device under such forces as are encountered in normal use or incidental to connecting and disconnecting a coaxial transmission line.

Besides effecting a strong grip and interlock between the insulator and the terminal element 73 by expansion of the latter, the expanding pressure is transmitted radially through the walls of the insulator 60 to the embracing cylindrical walls of the connector tube 50, which thus maintains a tight grip on the insulator to resist relative turning and axial shifting of the parts. To further insure against axial shifting and turning of the insulator in the connector tube 50 an interlock is provided in the form of the radial set screws 56 threaded through aligned openings in the connector tube 50 and in the surrounding ring 54, the openings being suitably tapped to receive the set screws. As shown in FIG. 6, the set screws bite into the periphery of the insulator 60.

At the small end of the termination the tapered outer conductor 42 may be curved into tangential contact with the deposited resistive film coating 40 of the center conductor or, and this is the preferred arrangement, may include a relatively short integral cylindrical end section or portion 95 to provide an annular radially shallow clearance space 96 of uniform circular section surrounding the resistive film 40 of the center conductor. This annular clearance is more effective for the flow of liquid coolant than the tapered clearance space resulting from tangential contact between the curved horn and the cylindrical film resistor, as called for by theoretical considerations governing the design of reflectionless terminations for coaxial lines. To compensate for the departure from such theoretical considerations resulting from use of the cylindrical end section 95, a capacitance compensating inductive metal tube 102 is disposed inside the end of the resistive conductor tube 41 and electrically connected to the small end of the conductor horn 42.

Contact is made between the horn conductor 42 and the resistive inner conductor 40 by a reduced diameter cylindrical end 97 which is integral with and extends as an axial continuation or extension of the cylindrical portion 95. The small cylindrical end portion or section 95 of the horn conductor 42 is formed with apertures such as axially elongated slots 93 for admitting liquid coolant to the dielectric space between the termination conductors, as will be described later. These slots extend the full length of the cylindrical portion 95 and are spaced uniformly about the circumference of such cylindrical portion. At least one of the slots 93 is continuous through the reduced diameter cylindrical end portion 97, as indicated at 123, FIG. 9; to permit expansion and contraction of the latter in yieldingly gripping the end of the inner conductor. Electrical connection may be made directly between the carbon film coating 40, comprising the inner conductor, and the cylindrically curved inner surface of the extreme end or terminal portion 97 of the metal horn conductor 42. Suitable yielding clamping means such as a plurality of axially spaced parallel split spring rings 99 is provided to contract resiliently about the cylindrical end portion 97. The cylindrical terminal end of the horn conductor is thus held or compressed conformatively against the inner conductor for good electrical contact with the latter.

A preferred arrangement for connecting the compensating tube 102 to the horn 42 is described in copending application Serial No. 798,728 filed March 11, 1959. According to such arrangement a conductive metal band 100 in the form of a strip of thin sheet brass is wrapped about the end portion of the carbon film 40 on the ceramic tube 41 and permanently secured by solder 94. The solder bonds to a conductive film or band coating 1195 of copper electroplated on the end portion of the carbon film. The brass terminal band 100 extends axially beyond the end of the ceramic tube 41 and embraces a brass ring 101 located against the end of the ceramic tube. The ring 161 is soldered to the metal terminal element or band 1% and at 113 to the brass tube 102 which is telescoped within the end of the ceramic tube 41.

The metal capacitance compensating tube 102 is of such length that its upper or innermost end 1113 is disposed approximately at the radial plane defined by the juncture indicated at 109 between the cylindrical end portion 95 and the tapered portion of the outer horn conductor 42. Capacitance between the conductive metal sleeve 1% and the film conductor 40 compensates for loss in capacitive coupling between the tapered horn conductor 4' 2 and the resistive film conductor 40 resulting from using the cylindrical portion 95 at the small end of the horn conductor instead of continuing the curvature of the tapered horn into tangential contact with the cylindrical surface of the resistive film conductor as called for by the theoretical considerations previously referred to which govern the design of refiectionless terminations.

The termination T is aligned axially with the entrant tube 28 through which the circulating liquid dielectric coolant is introduced into the casing C, the inflowing liquid being thus directed to flow axially against the small end of the termination. To guide and confine the fiow of the liquid a funnel 106 embraces both the ends of the termination and inlet end 1117 of the entrant tube 28. The funnel has a stem portion 103 received about the small end of the horn conductor 42, the funnel stem being soldered to and making substantially annular sealing contact with the external surface of the horn conductor at a circular line 104 above or spaced toward the large end of the termination from upper ends of the

axial slots

98 and 116 which admit the liquid dielectric coolant into annular space 6 between the horn conductor and the inner resistive film conductor 41?. The interior of the cylindrical stern portion 108 of the funnel is of larger diameter than that portion of the external surface of the horn conductor 42 surrounded thereby to define annular clearance space 110 extending the full length of the

axial conductor slots

98 and 116. This space provides a passage for axial flow of entering liquid coolant in the form of a tubular sheath so that such coolant may enter the annular dielectric space 96 along the full length of each of the

slots

98 and 116.

At its other or lower end the funnel 106 is formed with a bell end 111 which surrounds the end 1ti7 of the entrant tube 28 in embracing but slightly spaced relation, the annular clearance thus provided being indicated at 112. The bell end 111 is formed with a flared lip 114 which acts as a pilot to guide the funnel over the tube end 107 in assembling the parts into the telescoped relation shown. The infiowing liquid is confined by the entrant funnel 106 and constrained to fiow into the annular dielectric space between the resistive inner film conductor 40 and the tapered outer conductor 12 at the small end of the termination.

The liquid dielectric coolant surrounding the tapered outer or horn conductor 42 is in a quiescent state, or substantially so, the flow through lower outer portion 115 of the casing chamber being relatively small or nonexistent and resulting from permissible leakage between the body 45 of the termination and the casing walls for reinforcing ring 47.

Equalization of pressure between the interior or dielectric space of the termination and the outer casing chamber 115 is obtained through the annular clearance 112 between the funnel 106 and the end 107 of the tube 28.

In circulation of the liquid dielectric coolant about its circuit the flow through the casing C is confined substantially to the annular dielectric space separating the inner and outer conductors of the termination. The termination body 45 constitutes, in effect, a partition or barrier across the path of the circulating liquid and the liquid entrance and exit openings of the casing are located near corresponding entrance and

exit slots

98, 116 and 61 in the outer conductor of the termination to constrain the flow of the coolant within the casing substantially to the annular dielectric space between the coaxial conductors of the termination.

The liquid dielectric coolant is desirably maintained in a path closely surrounding the resistive inner film conductor 40 as by a tubular guide 118 which surrounds the inner conductor. The guide tube 118 is formed of a suitable dielectric material such as a plastic or, as here shown, of glass.

At its end adjacent to the small end of the termination T the glass guide 118 is telescoped into collar 120 of plastic dielectric material formed with a tapered external surface which fits the internal tapered contour of the outer conductor 4-2. An opening or passage 122 through the wall of the collar 120 permits pressure equalizing flow of the coolant.

At its other or upper end the tubular glass guide 118 is formed with an integral flared end 125 received in a locating and sealing ring 127 formed of suitable plastic material.

To insure a small fluid flow through the chamber 124 that surrounds the guide 118 the sealing ring 127 is formed with an axial passage 128 which thus connects the chamber portion 124 with the space between the center conductor connector 64 and the connector tube 51 The passage 128 in the plastic ring 127 and the passage 122 in the plastic collar or thimble 121) are respectively located substantially at the extreme upper and extreme lower ends of the chamber portion 124 to result in a limited flow of liquid dielectric coolant through such apertures or openings into and out of the tapered portion of the dielectric space of the termination that has a scavenging effect which carries occluded air or other gas. The annular dielectric block 611 sealing the upper end of the connector tube 5d extends downwardly at least to the tops (as shown) or even below the upper ends of the slots 61 and also below the top of the port or opening in the pipe or tube 22 through which the coolant is discharged from the casing C into the receptacle R to prevent entrapment of air or gas in the dielectric space at the upper end of the termination.

The maximum diameters and cross sectional areas of the guide tube 118 and of the plastic sealing rings 12% and 127 are each less than the diameter and cross sectional area of the interior opening or passage of the connector tube St} so that in assembling the guide tube 118, collar or thimble 1211 and the sealing ring 127 into the outer conductor structure of the termination, the guide tube may be inserted axially into place through the open terminal end of the connector tube 50 prior to insertion therein of the annular insulator block 60 and the inner conductor assembly. In commercial PllO- duction of the device the circular body 45, the connector tube 50 and the tapered horn conductor 42 are conveniently assembled together in the telescoped relation shown while outside of the casing body tube 1. The guide tube 118 is also moved into place prior to assembly into the line of the inner conductor components and while the outer conductor components are outside the casing tube 1. The annular insulator block 60 is assembled about the inner terminal element 73 by sliding it axially over the inner conductor 41 to the desired location about the shank 75 of the inner terminal element 73, the block being axially located in such assembly by a plastic dielectric washer 13! interposed between the block and the shoulder provided by the relatively large diameter head end of the inner terminal element 73. The center conductor structure of the termination, comprising the ceramic tube 4-1 with its terminal band 100, the capacitance compensating tube 1&2, the connector 64, the terminal 73, and the dielectric insulating block 66, is then assembled with the outer conductor structure by relative axial telescoping movement to the position shown in FIGS. 2, 4, and 9. The top closure 10, including the ring 54, is placed about the connector tube Sti, secured as by brazing or welding and the holes for the set screws 56 drilled and tapped in a preliminary sub-assembly procedure.

Prior to the insertion of the termination T or the outer conductor 42 thereof into the casing C the funnel element 1% is assembled onto the small end of the outer conductor by telescoping such element into place and soldering or razing the end of the stem portion 1% to the external surface of the outer conductor 42. The spring clamping rings 99 are assembled about the axially split cylindrical end 97 of the outer conductor either before or after the inner conductor structure has been moved into place. The clamping force of the split conductor end 97 about the terminal band 1% on the inner conductor is insufficient to prevent axial adjusting movement of the inner conductor structure relative to the outer conductor structure. In telescopically assembling the tubular guide 118 and the inner conductor structure with the outer conductor structure prior to the insertion of the later into the casing body 1, the parts may be easily and accurately placed by telescopic movement in desired predetermined relative axial positions, as by means of suitable assembly jigs. In such initial assembly outside the casing C the set screws 52 and 56 may also be advanced or adjusted into engagement with the plastic sealing ring 127 of the guide tube 118 and with the annular dielectric block 60 to secure these plastic components in place. Thus the termination T, including the inner and outer conductor assemblies, the guide tube 118, and with the casing tube closure attached to the connector tube 543, is insertable by axial movement as a unit into the casing C, the engagement between the upper rim of the casing body tube 1 and the periphery of the top closure 10 serving to locate the line assembly in the casing. During the movement into position of the insertable line unit the bell end 111 of the funnel element 106 serves as a pilot to guide the lower or small end of the termination T into axial alignment with the discharge or inlet end 107 of the entrant tube 28, the funnel element being rigidly secured to the outer conductor 42 as by the soldered joint mentioned.

The permissible axial slipping or shifting of one conductor structure relative to the other, mentioned above, is a desirable feature not only because of the accommodation of manufacturing variations which permits greater tolerances and the ability of the device to expand and contract differently upon temperature changes encountered in practice but because of further advantages incident to service and repair in the field. It may occur, for example, that one of the inner conductor components such as the resistive film 4t? or the ceramic tube 41 becomes damaged in use or the instrument may appear to be functioning improperly so that it becomes desirable to inspect the interior of the line or the inner conductor to determine the existence of a defect in or injury to one of the component parts or elements.

The structure of the present invention provides for optional removal and replacement of the inner conductor assembly without disturbing the outer conductor assembly and without even draining or removing the liquid dielectric coolant from the casing C. To effect such removal, the main coaxial transmission line comprising the inner and outer conductors 71 and 72 previously mentioned in connection with FIG. 1 is first disconnected from the terminal end or" the connector tube and from the socket or cup 74 of the inner terminal element 73 so as to disconnect the device or instrument from the signal generator. Thereafter the interlock and grip of the insulating block 6% on the shank 75 of the terminal element 73 is released or relieved by backing oif the expander 84 which is turned relative to the terminal element by an implement such as a hex end bar 86 inserted axially through the cup 74 of the terminal element and into nonrotative interfitting engagement with the expander. The tines 38 being of resilient spring material such as brass, of which the terminal element '73 is formed, spring back to their normal unstressed shape when relieved of the expanding support provided by the expander 30, thereby reducing the size of the terminal element shank and withdrawing it from interlocking engagement with the walls of the bore 76 in the insulator block 6 3. The interlock and grip between the insulator block as and the terminal element shank '75 being thus released, the inner conductor assembly is no longer held against relative turning or relative axial movement of the insulating block 66 and can be withdrawn bodily from within the outer conductor assembly, the inner conductor structure or assembly being lifted vertically in this operation. The bore 7e in the insulating block 60 is, of course, slightly larger in diameter than the withdrawn parts such as the resistive coating 4% on the cylindrical ceramic tube 41 and the brass terminal band or element on the lower end of the inner conductor so that these parts may be withdrawn axially through the insulating block 60 in lifting the inner conductor assembly up and out through the top of the conductor tube 50 while the insulating block 69 remains permanently assembled and secured in the latter through the interlocking action of the set screws 56.

Upon replacement of the same or a duplicate substitute inner conductor assembly the brass terminal band 100 bears the frictional load imposed by the split clamping end 97 of the horn conductor which, under the resilient squeezing action of the spring rings 99 and by reason of the inherent resilience of the brass or other metal stock from which the horn is formed, must be slightly distended by the terminal band 1% to admit the latter in the automatic establishment of electrical connection between the ends of the conductors at the remote or lower end of the termination.

The termination T can be used to absorb the energy from a high frequency electrical signal generator such as a television transmitter. It may be combined with a suitable signal responsive system including a detector connected and arranged, say, to sample the wave signal from the transmitter in accordance with known principles. In such an instrument a pickup device or detector D, like the unit assembly D described in application Serial No. 99,474, filed June 16, 1949, is combined with the termination T so that the parts function together in accordance with the principles described in the application referred to.

The unit D includes a chambered body member 70 of brass or similar metal formed with a cylindrical pilot extension 133 through which probe 132 and plastic cap 134 project. A flat mounting plate 135 is formed with a central aperture which receives the cylindrical extension 133 of the body and is abutted against a shoulder of the latter, being soldered to the body and to the cylindrical extension 133.

A circular opening 137 to receive the pilot extension 133 is formed through the wall of the casing 1, through the reinforcing band or ring 47, and through the telescoped body 45 and connector section 44 of the termination outer conductor. This opening through the juxtaposed parts is of such size as to provide a sliding fit with the pilot extension 133 received therein, the pilot thus keying the parts together. Rubber O-ring 136 is received in a circular groove formed in the external cylindrical surface of the extension 133. A flat spot face 138 on the outside of the casing body 1 about the opening 137 receives the mounting plate 135, the latter being attached to the casing as by screws 139 threaded into tapped holes that extend into the reinforcing ring 47. Reference is 13 made to copending application for patent Serial No. 798,777 filed March 11, 1939, now Patent No. 2,973,479, covering features related to the interfitting of the pick-up device D with the casing 1 and the termination T.

The present invention thus provides useful improvements in specialized apparatus for converting high frequency electrical energy into heat and dissipating such energy.

In accordance with the patent statutes the principles of the present invention may be utilized in various ways, numerous modifications and alterations being contemplated, substitution of parts and changes in construction being resorted to as desired, it being understood that the embodiment shown in the drawings and described above is given merely for purposes of explanation and illustration without intending to limit the scope of the claims to the specific details disclosed.

What we claim and desire to secure by Letters Patent of the United States is:

1. A'high frequency electrical line terminating device comprising an elongated tubular casing open at one end, a coaxial line section comprising an inner conductor and an outer conductor surrounding the inner conductor in spaced relation, a closure disposed across said open end of the casing, one end of the line section projecting through the closure and having inner and outer terminals for connection to the inner and outer conductors of a coaxial transmission line, means detachably securing the closure to the casing for facile removal and replacement of the closure and the line section from and into predetermined position in the casing as a unit, conduit means connected to the casing for supplying and withdrawing liquid coolant, said conduit means having an entrant element at the other end of the casing, means carried by the line section registered with the entrant element to receive liquid coolant from such element and conduct the received coolant directly to the space between the conductors, said liquid receiving means being fast to the line section and readily separatable from the entrant element for removal with the line section, and the liquid receiving means and the entrant element automatically registering upon replacement of the line section to said predetermined position.

2. A terminating device as in claim 1 in which the entrant element comprises a tube projecting into the interior of the casing and the liquid receiving means comprises a tube disposed in interfitting relation with the entrant tube, said tubes being readily separable by relative axial movement in one direction for removal of the line section and being readily interfittable by relative axial movement in the reverse direction for replacement of the line section.

3. In a high frequency electrical device of the character described, a line section comprising an inner conductor and a tubular outer conductor arranged coaxially with an annular dielectric space surrounding the inner conductor, an expandable insulator having a central opening with a wall of circular section closely embracing the inner conductor, said insulator extending radially outwardly from the inner conductor into engagement with the outer conductor to locate and support the inner conductor in fixed relation to the outer conductor, said inner conductor including axially spaced end portions and a central holding portion between such end portions, the central holding portion being located wholly between and spaced toward the center from the axial limits of the insulator and readily expandable radially relative to the end portions, said holding portion of the inner conductor comprising a plurality of axially elongated conductive elements of resilient spring material disposed in symmetric relation about and equally spaced from the axis of the line section, said elements being fast to and mechanically and electrically connecting the end portions and in engagement with the insulator wall, an expander supported within the inner conductor and adapted to be actuated for coaction with the inner conductor for relative axial shifting,

said expander upon actuation in one direction being adapted to bear radially outwardly against the elongated elements upon such axial shifting to thereby expand the central portion of the inner conductor and force the elements strongly against the insulator wall and the insulator against the tubular outer conductor in the establishment of strong frictional grips between the insulator and the conductors for holding the conductors in fixed relation, and, upon actuation of the expander in a reverse direction, the inherent resiliency of the spring elements being adapted to contract the central portion of the inner conductor to thereby release the insulator and the conductors.

4. In a high frequency device as in claim 3 the inner conductor being formed with a threaded axial bore, the expander being threaded into the bore and located wholly between the axial limits of the inner conductor, and the inner conductor having an axial passage adapted to admit a tool for engagement with the expander to turn the latter in effecting said axial shifting.

5. In a high frequency device as in claim 3 one of the end portions of the inner conductor having a cylindrical surface located axially beyond the elongated elements, the insulator having a cylindrical surface portion surrounding said cylindrical surface of the inner conductor, and a resilient deformable sealing ring recessed into said cylindrical surface of the insulator and closely embracing the inner conductor in sealing relation.

6. In a high frequency device as in claim 3 the tubular outer conductor and one of the end portions of the inner conductor having cylindrical surfaces, the insulator having cylindrical surface portions one surrounding the cylindrical surface of said one end portion of the inner conductor, another surrounded by the cylindrical surface of the outer conductor, and resilient deformable sealing rings recessed into the cylindrical portions of the insulator and sealingly engaging the conductors.

7. In a high frequency electrical device of the character described in which an inner conductor and an outer conductor are arranged as a coaxial line and in which an annular insulator surrounds the inner conductor to 10- cate and support the latter in the outer conductor, an improved inner conductor structure comprising an elongated tubular member having a central portion embraced by the annular insulator and formed with axial slots for radial expansion, said slotted central portion termination at both of its opposite extremities short of the axial limits of the insulator, the inner conductor having end portions mechanically and electrically connected to the extremities of the slotted central portion and restraining said extremities against radial expansion, an expander receivable within the tubular member, the expander and the tubular member being formed with means and the expander being adapted for actuation to coact with the tubular member to effect relative longitudinal adjusting movement of the expander and to retain the expander in adjustment, the tubular member having an internal formation and the expander having an external formation adapted to cooperate to effect expansion of the tubular member against the insulator upon relative axial movement therein of the expander, and means on the opposite ends of the tubular member for connecting such tubular member to inner conductor components of the line in coaxial relation thereto, one of said connecting means being formed with an axial aperture through which to insert an implement for engaging the expander to effect axial movement of the latter relative to the tubular member.

8. A high frequency electrical device comprising a casing adapted to contain a body of liquid dielectric coolant and having a top access opening, a coaxial line section disposed within the casing so as to be immersed in such a liquid body, the line section comprising an inner conductor and an outer conductor surrounding the inner conductor in spaced relation, a closure disposed across the access opening and formed with a central aperture, the line section including inner and outer terminals separated by an annular dielectric space, said terminals being electrically connected to the inner and outer conductors, respectively, and projecting upwardly through the aperture in the closure, the outer terminal being secured to the closure to support the line section therefrom, an insulator filling the space between the terminals and thereby preventing loss of dielectric liquid out the aperture in the closure through such space, means interlocking the insulator and the outer terminal preventing axial movement of the insulator relative to the outer terminal, said insulator having a central through opening in which is received the inner terminal, the inner conductor comprising an elongated resistive member electrically connected at one end to the inner terminal and, at its other end, having a terminal band, the outer conductor comprising an elongated tubular member electrically connected at one end to the outer terminal and, at its other end, having a radially yieldable terminal portion resiliently embracing the terminal band in the provision of an electrical connection between the conductors which permits relative longitudinal shifting of the conductors, the inner conductor throughout its length from the insulator to and including the terminal band being receivable through the insulator opening to permit vertical axial withdrawal and reinsertion of the inner conductor from and into the casing and the outer conductor with the liquid dielectric body remaining in the latter and while the outer conductor and the closure remain in place, the terminal portion of the outer conductor being adapted automatically to re-establish electrical connection with the terminal band of the inner conductor upon reinsertion of the latter, the closure together with the inner and outer terminals and the inner and outer conductors fast together as a unit being axially removable from and replaceable on and into the casing with the liquid dielectric body remaining in the latter.

9. A device as in claim 8 having means actuatable to lock the inner terminal in the insulator and prevent axial movement of such inner terminal relative to the insulator.

10. \A device as in claim 8 in which the outer conductor a is tapered toward its terminal portion and guides the end of the inner conductor having the terminal band into predetermined coaxial relation during said reinsertion.

11. In a high frequency electrical device of the character described an inner conductor and an outer conductor arranged coaxially, the inner conductor comprising an elongated relatively resistive member having a substantially cylindrical terminal on one end and on the other end an axially extending connector, the other conductor comprising an elongated tubular member surrounding the inner conductor in generally spaced relation and at one end having a terminal portion closely and y-ieldingly embracing the terminal end of the inner conductor to effect electrical conection therewith while permitting relative axial sliding of the terminal end within said terminal portion, an insulator in the space between the conductors and spaced axially from the terminal end and the terminal portion to locate the inner conductor in coaxial relation to the outer conductor, the inner conductor being insertable into the outer conductor and withdrawable therefrom through the insulator by endwise movement, and means for releasably securing the connector of the inner conductor in the insulator to resist withdrawal of the inner conductor.

12. In a high frequency electrical device comprising a casing having an opening and, projecting into the casing through such opening, a coaxial line section, the line section comprising a tubular outer conductor and an inner conductor extending through the outer conductor in spaced coaxial relation, a plastic insulator surrounding the inner conductor in supporting relation and extending radially outwardly from the inner conductor into engagement with the outer conductor, said outer conductor comprising a relatively thin metal tube in sur rounding contact with the insulator and a body of relatively thick section encircling the tube and comprising a closure member extending radially beyond the thin metal tube, the closure member at its outer periphery being detachably secured to the casing for removal and replacement of the closure member and the line section as a unit, and a locking element extending radially through both the thick body and the thin tube and having an inner and embedded in the plastic insulator.

13. In a line section as in claim 12 the outer conductor being formed with a tapped radial bore and the locking element comprising a set screw threaded into such bore.

14. A high frequency electrical line terminating device comprising in combination an elongated hollow casing having an access opening in one end, a coaxial line section having an inside end within and an outside end without the casing, said line section comprising an elongated inner conductor and a tubular outer conductor, the outer conductor surrounding the inner conductor in spaced coaxial relation and including a member of circular section tapered from a large diameter end to a small diameter end, said small end embracing and being electrically connected to one end of the inner conductor at the inside end of the line section, the outer conductor including a body member at the large end of the tapered member, said body member being relatively short axially and located intermediate and spaced from the ends of the line section, said body member being axially slidable relative to and, at a point spaced axially from said end opening, closely embraced by the casing to locate the line section in predetermined relation to the casing, the outer conductor including a connector tube having a portion extending into the casing with one end fast to one side of the body member, said connector tube portion being surrounded by an annular clearance space separating the connector tube from the casing, the inner conductor extending axially through the body member and the connector tube and having on its outer end a terminal for connection to the inner conductor of a coaxial transmission line, a closure disposed across said end opening, the connector tube projecting through and being fast to the closure and at said outside end having a terminal for connection to the outer conductor of a coaxial transmission line, said tapered member at its large end being fast to the other side of the body member and projecting axially therefrom cantilever fashion and in coaxial relation into the interior of the casing, the tapered member being wholly supported from and by the body member, means securing the closure to the casing for facile disconnection and reconnection, the closure together with the line section as a unit being adapted for easy axial removal from the casing upon such disconnection and for easy axial replacement, and locating means on the closure and on the casing adapted to bear one against the other automatically to limit relative axial movement of the line section into the casing and thereby position the line section in predetermined axial relation to the casing in such replacement.

15. A device as defined in claim 14 in which the casing is of uniform section and has a cylindrical internal surface, the closure has an inside locating portion received within the casing and peripherally engaged against such cylindrical surface, and the locating means on the closure comprises a radial flange portion adapted to bear axially against the casing.

16. A high frequency electrical line terminating device comprising in combination an elongated hollow casing having an access opening in one end, a coaxial line section having an inside end within and an outside end without the casing, said line section comprising an elongated inner conductor and a tubular outer conductor, the outer con ductor surrounding the inner conductor in spaced coaxial relation and including a member of circular section tapered from a large diameter end to a small diameter end, said small end embracing and being electrically connected to one end of the inner conductor at the inside end of the line section, the outer conductor including a body member at the large end of the tapered member, said body member being relatively short axially and located intermediate and spaced from the ends of the line section, said body member being axially slidable relative to and, at a point spaced axially from said end opening, closely embraced by the casing to locate the line section in predetermined relation to the casing, a closure disposed across said end opening, the line section projecting through and being first to the closure and at said outside end having inner and outer terminals for connection to the inner and outer conductors of a coaxial transmission line, said tapered member at its large end being fast to the body member and projecting axially therefrom cantilever fashion and in coaxial relation into the interior of the casing, the tapered member being wholly supported from and by the body member, the closure together with the line section as a unit being adapted for easy axial removal from and replacement in the casing, means for supplying liquid coolant including an entrant tube connected to and having a discharge opening into the casing, said line section also including liquid conducting means having an internal passage continuous with the space between the conductors, said conducting means having a receiving opening into the passage, and said eating of the line section also serving to register the receiving opening of the line section liquid conducting means with the discharge opening of the entrant tube during such replacement.

17. A device as defined in claim 16 in which the entrant tube has an inner end formed with said discharge opening and projecting into the interior of the casing and the liquid conducting means is telescopically interfitted With said inner end of the entrant tube.

18. In a high frequency electrical device of the character described comprising an elongated inner conductor and an elongated tubular outer conductor arranged as a coaxial line and separated by a dielectric space, an annular one piece insulator in said space surrounding the inner conductor and supporting the latter in the outer conductor, the inner conductor having an axial bore and including means located wholly intermediate and spaced axially from both ends of the one piece insulator expandable radially to lock the inner conductor and the insulator together against relative axial shifting, an expander of less axial length than the inner conductor dis- 18 posed in the bore and guided therein for relative axial shifting, and threaded means actuatable to effect such axial shifting of the guided expander in the bore, the expander being adapted upon such shifting to expand said expandable means and effect locking together of the inner conductor and the insulator.

19. In an electrical device as claimed in claim 18 the threaded means comprising mating threads formed in the inner conductor and on the expander, and said shifting of the expander being effected by and upon rotation of the expander within the inner conductor.

20. In an electrical device as claimed in claim 18, the conductors having at one end of the line means for connecting them to terminal fittings on the conductors of a coaxial transmission line, the inner and tubular outer conductors at their other ends comprising elements of an attenuating line section, the latter elements being retained in predetermined positions relative to one another by said locking together in resisting forces tending to shift one such element axially relative to the other resulting from axial loads imposed on the inner and outer conductors at said one end of the line in connecting and disconnecting a transmission line.

21. In an electrical device as claimed in claim 20, the attenuating line section element of the inner conductor being withdrawable axially from the outer conductor and through the insulator upon contraction of said expandable means and unlocking of the inner conductor and the insulator.

References fitted in the file of this patent UNITED STATES PATENTS 1,981,753 Pearson Nov. 20, 1934 2,057,242 Mautsch Oct. 13, 1936 2,395,196 Roberds Feb. 19, 1946 2,399,930 Keister May 7, 1946 2,453,283 Tiley et al Nov. 9, 1948 2,551,611 Kuhner May 8, 1951 2,552,707 Bird et a1 May 15, 1951 2,556,642 Bird June 12, 1951 2,663,753 Bird Dec. 22, 1953 2,752,572 Bird et a1 June 26, 1956 FOREIGN PATENTS 617,699 Great Britain Feb. 10, 1949