US2897313A

US2897313A - Coaxial cable switch

Info

Publication number: US2897313A
Application number: US711106A
Authority: US
Inventors: Edward S Burgess
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-01-24
Filing date: 1958-01-24
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28

Description

7 July 28, 1959' E. S. BURGESS COAXI'AL CABLE SWITCH Filed Jan. 24, 1958 IN VEN TOR. fowl/e0 5 fiulfifas ATM/Mfr COAXIAL CABLE SWITCH Edward :S. Burgess, Rutherford, NJ. Application-January 24, 1958, Serial'N'o. 711,106

9 Claims. or. 200-87) "This invention relates to high frequency electrical circuits, particularly to a switching circuit therefor, and has "for its primary object to provide a mechanism for switching from one coaxial cable to another coaxial cable, .whereby the transmission efficiency of said interconnected cables through said mechanism is maintained at substantially the same level as in the cables.

It is important, particularly in high frequency circuits, that the impedance of cables and interconnected circuits be equal. As is well known, a mismatch in impedance produces a reflected wave or bump having a magnitude determined bylthe extent of impedance mismatch. While the coaxial cables themselves have predetermined impedances that are readily matched, it has been found that irregularities are introduced into the circuit at switching points of the cables with consequent disturbances and lowered efficiency.

It is, therefore, another object of the invention to overcome the above disadvantages and to provide a constant impedance coaxial switch.

It is still another object of the invention to provide a switch that has a constant impedance regardless of mechanical tolerances in the construction of the parts thereof.

.It is a further object of the invention to provide a coaxial cable switch free of connectors, whereby coaxial cables of any length may be directly terminated in the switch and conductors of the cables used as switching components.

Yet a further object of the invention is. to provide such a constant impedance switch which is simple and economical in construction and practical and reliable in operation.

Other and further objects will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur .to one skilled in the art upon employment of the invention in practice.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawing, forming a part of the specification, wherein:

Fig. 1 is a front elevational view of a coaxial cable switch of the invention showing three coaxial cables directly terminated in the switch body and an electrical relay assembled thereto,

Fig. 2 is a sectional view taken along line 2-2 of Fig. l in the direction of the arrows showing the detailed construction of the switch with the inner conductor of the coaxial cable functioning as a switching contact,

Fig. 3 is a schematic view of the switch arrangement.

Referring 'now to the drawing, particularly Figs. 1 and 2., there is shown a switch body of any suitable conductive material, such as aluminum because of its lightness in weight, having a pair of open ended, intersecting grooves. 11, 12 formed therein. Both grooves .are of the samedepth and width, about A inch, for example, for use with a 52 ohm cable, groove 12 being off center Patented July .28, 1959 f. we

and adjacent the front edge 14 of the body and extending between side-edges 16, 17, and groove 11 being centrally disposed between side edges 16, 17 and extending between front edge 14 and rear edge 18. As seen in Fig. 2, the intersecting grooves are in the shape of an inverted 'T, groove 12 containing two spaced coaxial cable terminations 19, '21 and groove 11 containing a third coaxial cable termination 22.

The coaxial cables are conventional, each consisting of an outer insulating cover 24, an outer mesh conductor 26, a centrally disposed, inner conductor 27, and an insulating layer '28 between the two conductors '26, 27. It is to be noted that the

coaxial cables

19, 21, and 22 are terminated directly in the grooves of the switch block, the usual connectors being eliminated, and the inner conductors 27 being utilized as switching contacts, as will appearhereinafter. Inother words, the coaxial cable conductors are used as integralpartsof the switch and, by eliminating intermediate connectors, avoid troublesome impedance mismatch.

For terminating the cables in the switch body 10, each cable-is stripped to permit the inner conductor 27 to project a short distance, as seen in Fig. 2, and a sheathed contact piece 29 is rigidly secured thereto. The contact piece 29 is only long enough to befastened to the inner conductor 27, so that the same, constant impedance of the coaxial cable is maintained within the switch block. The outer insulation 24 is then removed for a slightly greater distance to expose the outer, braided conductor 26 and around this-latter conductor a collar 31 of conductive material, preferably brass, having a slot 30 on its face and having a square, outer configuration is rigidly secured, as by solder, the slot 30 assisting in making a good soldered connection. The cross-sectional dimensions of each collar 31 are of substantially the same width and .depth as the groove in which it is slid'able, in this example being about A 'inch for a 52 ohm coaxial cable. To adjustably secure each collar 31 and associated cable ina fixed position within the switch block, a set screw 32 for each of

cables

19, 21 adapted to penetrate into groove 12 and a set screw 33 for cable 22 adapted to penetrate into groove 11 are provided. As is evident, the set screws 32, 33 are in mesh engagement with threaded openings 34 in the body 10. Thus it seen that the outer conductors of all three cables are interconnected through the switch body 10.

The sheathed contact piece 29 of the central conductor "27 for cable 22 is shown slotted and in the slot is rigidly secured one end of a short, flat spring 36, preferably of beryllium copper, having a contact 37 intermediate its ends adapted to alternately engage the contacts 29 of cables '19, 21. In this example 'of a switch for a 52 ohm cable the spring 36 is about inch in length between slotted contact 29 and contact 37, inch in width and 0.005 inch thick, whereby a capacitance of about 29 micromicrofarads .per inch is maintained in the cavity formed in groove 11 and occupied byspring'36. At this point it may be mentioned that the shorter the length of spring 36 the less likelihood there is of impedance mismatch between cable 22 and either of

cables

19 and 21.

The spring 36 is shown initially biased to engage one of said contact pieces in order to provide a continuous connection, as between cable '22 and cable 21 in the present illustration, transfer of contact 37 from cable 21 to cable 19 being produced by electromechanical means, as will appear hereinafter. All three contact pieces '29 are held firmly to the respective outer conductors by insulating material 38, whichalso rigidifie's the central conductors '27 and assures good engagement between contacts 7 M 2 i In view of the'lzore'going constructiomaconstant 'ele'ctrical'impedance is maintained in the switch unit. This is brought about primarily by terminating each coaxial cable directly in the switch, so that the sheath contact pieces 29 of

opposing cables

19, 21 areat a relatively :short distance apart and the spring 36 forinterconnecting cable 22 to either of

cables

19, 21 is also relatively short. The cavity in which the spring 36 is located is also relatively short and is dimensioned to have the same electrical capacity per unit length as the coaxial cable terminals. The inherent shortness of the elements also enables the switch to be useful at shorter electric-wave lengths, since any variable impedance bump in an otherwise constant impedance circuit has less detrimental effect on the wave length, if the impedance bump is short in length compared with the associated electric wave length. As seen in Fig. 1, a cover 39 having a slot 41 in registration with the front end of groove 11 is provided as an upper closure for the switch body 10, the cover being secured to the body by screws 42 freely passing through openings 43 in the body and meshing with threaded openings 44 in the cover. On top of the cover is rigidly mounted a bracket 46 and to this bracket is fastened an electrical relay 47 having a winding 48, armature 49, and winding terminals 51. The armature 49 is shown formed with a depending arm 52 to which is rigidly secured a further depending arm 53, preferably of wire, having a right angle bend therein and being adapted to be movably disposed in said slot 41 and groove 11. A short tubular piece 54 of insulating material is shown around the lower end of the wire arm 53 to insulate it from the free end of the transfer spring 36 of the cable 22.

The operation of the switch will now be described. The coaxial cables with the hereinbefore described terminations are initially placed in their respective grooves and the collars 31 are slid to their proper positions in the grooves, after which set screws 32 and 33 are turned to secure them in place. Assuming that the transfer spring 36 is biased to the right, as viewed in Figs. 2 and 3, with contact 37 in engagement with contact piece 29 of cable 21, communication may then be had over both

cables

21 and 22. To change the circuit from cable 21 to cable 19 it is merely required to move transfer spring 36 to the left. For this purpose any suitable source 56 (Fig. 3) of electrical energy may be used and by closing switch 57 a simple energizing circuit for relay 47 through winding 48 is established. Upon energization of relay winding 48 armature 49 is attracted thereto and its depending arm 53 with insulated end piece 54 is moved to the left, as viewed in Figs. 1, 2, and 3, so that contact 37 separates from contact 29 of cable 21 and engages contact 29 of cable 19. Communication over

cables

19 and 22 may be had as long as relay 47 is operated, opening of switch 57 de-energizing the relay and causing the armature 49 to retract to its normal position, after which transfer spring 36 also retracts to its initially biased position to reestablish the originally described connection between

cables

22 and 21.

From the foregoing description, it will be seen that the present invention provides a simple, economical, and highly practicable switch which offers a constant impedance to interconnected coaxial cables, particularly since the cable conductors are utilized as component parts of the switch and since the transfer spring, cavity containing the transfer spring, and spacing between opposing cable conductors are all relatively short to meet the required impedance value. While the 52 ohm coaxial cable example has been described in detail hereinbefore, it is, of course, understood that applicant is not limited to this example.

As various changes may be made in the form, construction, and arrangement of the parts herein, without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be under- 4 stood that all matters are to be interpreted and not in any limiting sense.

What is claimed is:

1. A switch unit comprising a body of conductive material having a pair of intersecting grooves each of equal depth and width and having a cover over said grooves forming a cavity in one of said grooves, a pair of coaxial cables of predetermined characteristic impedance each having a central conductor and a spaced, sleeve conductor surrounding the central conductor, said cables having respective ends thereof disposed in said grooves, a contact at the end of one of said central conductors, a flat, movable element of conductive material having one end thereof secured to the other of said central conductors disposed in said one of said grooves within said cavity and having the other end thereof biased into engagement with said contact at the end of said one central conductor, said movable element being proportioned to the cavity dimensions to produce a constant capacitance per unit length of the cavity, whereby the characteristic impedance along said cavity is maintained substantially equal to the characteristic impedance of said coaxial cables, means for securing said sleeve conductors in said grooves to said body, whereby said body constitutes a common outer conductor for said cables, and means for separating said movable element from engagement with said contact.

2. A switch in accordance with claim 1, wherein said cavity is rectangular in longitudinal section.

3. A switch in accordance with claim 1, wherein said grooves are at right angles with respect to each other.

4. A switch unit comprising a body of conductive material having a pair of intersecting grooves each of equal depth and width and having a cover over said grooves forming a cavity in one of said grooves, a pair of coaxial cables of predetermined characteristic impedance each having a central conductor and a spaced, sleeve conductor surrounding the central conductor, said cables having respective ends thereof disposed in said grooves, a contact at the end of one of said central conductors, a flat,.movable element of conductive material having one endthereof secured to the other of said central conductors disposed in said one of said grooves within said cavity and the other end thereof biased into engagement with said contact at the end of said one central conductor, said movable element being proportioned to the cavity dimensions to produce a constant capacitance per unit length 'ofthe cavity, whereby the characteristic impedance along said'cavity is maintained substantially equal to the characteristic impedance of said coaxial cables, a collar of conductive material connected to each of said sleeve conductors, means for securing said collars in said grooves to said body, whereby said body constitutes a common outer conductor for said cables, and electrical means for separating said movable element from engagement with said contact.

5. A switch in accordance with claim 4, wherein said electrical means is constituted by a relay having attached to its armature an insulated end portion adapted to disengage the flat element from the contact.

6. A switch in accordance with claim 4, and insulating means interposed between said contact and said sleeve conductor for stiffening said one central conductor.

7. A switch unit comprising a body of conductive material having a pair of intersecting grooves each of equal depth and width and having a cover over said grooves forming a cavity in one of said grooves, three coaxial cables of the same predetermined characteristic impedance each having a central conductor and a spaced, sleeve conductor surrounding the central conductor, said cable having respective ends thereof disposed in said grooves with one of said cables disposed in said one groove and the remaining two of said cables oppositely spaced in the other of said grooves, a contact at the end of each of said centralconductors of said remaining two cables, a flat,

as illustrative movable element of conductive material having one end thereof secured to the other of said central conductors disposed in said one of said grooves within said cavity and having the other end thereof biased into engagement with said contact at the end of one of said central conductors of said remaining two cables, said movable element being proportioned to the cavity dimensions to produce a constant capacitance per unit length of the cavity, whereby the characteristic impedance along said cavity is maintained substantially equal to the characteristic impedance of said coaxial cables, a collar of conductive material connected to each of said sleeve conductors, means for securing said collars in said grooves to said body, whereby said body constitutes a common outer conductor for said three cables, and electrical means for transferring said movable element from said contact at the end of said one central conductor to the other contact at the end of the other central conductor of said remaining two cables.

8. A switch unit in accordance with claim 7, wherein said electrical means is constituted by a relay having attached to its armature an insulated end portion adapted for transferring said flat element from engagement with one to the other of said contacts of said central conductors of said remaining two cables.

9. A switch in accordance with claim 7, and insulating means interposed between said contact and said sleeve conductor of each of said remaining two cables for stif- 1 fenting said central conductors thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,472,274 Beleskas June 7, 1949 2,478,781 Reinschmidt Aug. 9, 1949 2,560,561 Ellis et a1. July 17, 1951