WO1997023925A1

WO1997023925A1 - Screening enclosure

Info

Publication number: WO1997023925A1
Application number: PCT/GB1996/003011
Authority: WO
Inventors: Ray Malkowski
Original assignee: Fringe Electronics Ltd.
Priority date: 1995-12-21
Filing date: 1996-12-05
Publication date: 1997-07-03
Also published as: GB9526164D0; AU1038597A; GB2308511B; GB2308511A

Abstract

A screening enclosure (20) and connection assembly for a circuit board (40) which enables simple and effective connection of coaxial cables (50) thereto. Coaxial cables having a core conductor (55) for connection to a circuit board (40) within a screened enclosure (20), and having an outer screen conductor (53) for connection to the walls of the screened enclosure are directly connected without the use of plug and socket arrangements. The sheathed core conductor of the coaxial cable is passed through an aperture (26) in the screening enclosure wall (23) to a connection point inside the enclosure, while an exposed portion of the outer screen conductor is clamped (70) directly to an adjacent portion of an outer wall of the screening enclosure. Preferably, the connection point inside the enclosure is a screw terminal (60) and an access port (28) is also provided in the screening enclosure to allow direct screwdriver access to the screw terminal.

Description

SCREENING ENCLOSURE

The present invention relates to methods and apparatus for the electrical and mechanical connection of screened coaxial cables to electronic circuits housed in screened boxes and the like.

Prior art techniques for connecting screened cables to circuits in screened enclosures typically include the use of intermediate connecting assemblies such as screened coaxial plugs and corresponding screened coaxial sockets such as BNC, TNC and standard UHF connectors.

To effect such connections, typically the coaxial cable end is stripped and prepared for soldering of the core to a pin of the coaxial plug, or male connector. The outer screen of the cable is soldered or compression fitted to the barrel of the plug. The screened enclosure is prepared with an aperture in which is mounted the coaxial socket, or female connector. The socket projects through the aperture to allow the outer screen housing or barrel of the socket to be directly connected to the walls of the screened enclosure. The socket generally includes a receptacle for receiving the pin of the coaxial plug, and the gauge of the barrel of the socket is sufficiently large to receive the barrel of the plug therein, or vice versa.

A number of different configurations of plug and socket (eg. TNC and BNC connectors) also provide locking devices which prevent the plug from being inadvertently withdrawn from the socket, eg. by way of screw- threaded barrels or bayonet type barrels.

Although these types of connectors are robust, provide good screening performance and enable easy connection and disconnection of the coaxial cable to the screened enclosure, they use a large number of individual components which must be prepared and soldered or mechanically fixed in place prior to final assembly.

It is an object of the present invention to provide a low cost, reliable and effective method and apparatus for electrically and mechanically connecting a coaxial cable to a screened enclosure.

According to one aspect of the present invention there is provided a connection assembly, for connecting a coaxial cable having an outer screen conductor and at least one core conductor to, respectively, a screening enclosure and an electrical connection housed therein, the connection assembly including: a screening enclosure having an aperture in a wall thereof, for passage of said at least one core conductor therethrough into the screening enclosure; a clamp assembly outside the screening enclosure and coupled thereto adjacent to the aperture, adapted to grip a portion of the coaxial cable and to make a direct electrical connection to the outer screen conductor thereof.

According to another aspect of the present invention, there is provided a screening enclosure for a circuit board comprising: top, bottom and first and second side walls defining a cavity therebetween, and having a rebate along a corner edge defined by first and second recess walls in substantially orthogonal relation to one another, and lying between the top and first side walls; at least one aperture in the first recess wall and an access port adjacent thereto in the top wall; a first channel, in the second side wall approximately coplanar with the second recess wall, adapted to receive an edge of a circuit board.

According to another aspect of the present invention there is provided a method of connecting a coaxial cable, having at least one core conductor and an outer screen conductor, to an electrical connection housed within a screening enclosure and to a wall of the screening enclosure, including the steps of: preparing the coaxial cable such that a portion of the core conductor projects longitudinally beyond an exposed end of the outer screen conductor; passing the projecting portion of the core conductor through an aperture in the walls of the screening enclosure and electrically connecting the core conductor to the electrical connection within the screening enclosure; clamping the exposed end of the outer screen to an outer conductive surface of the wall of the screening enclosure.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a screening can according to one aspect of the present invention;

Figure 2 shows an end view of the screening can of figure 1 ;

Figure 3 shows a schematic cross-sectional view of the screening can of figures 1 and 2, with a circuit board installed therein, and a coaxial cable connected to the circuit board and screening can; Figure 4 shows a front view of the screening can, circuit board and cables of figure 3; and

Figure 5 shows a perspective view of a screening can according to another aspect of the present invention.

With reference to figures 1 and 2, a presently pre! ^"erred embodiment of a screening can 10 will be described. The screening can

10 comprises, broadly speaking, four walls defining a screening enclosure 20. The walls are, for convenience, described herein as a top wall 11 , bottom wall 12, first side wall 13 and second side wall 14. It will be understood that the screening can may be in any particular orientation, and the use of the expressions "top", "bottom" and "side" in connection therewith do not limit the orientation.

A rebated corner 22 is formed along one edge of the enclosure, by way of first and second recess walls 23,24 extending between the top wall

11 and the side wall 13. First recess wall includes a number of apertures 26 which are preferably of such a diameter as to provide a loose fit for a coaxial cable core and its insulating sheath, as will become clear later. Top wall 1 1 includes a corresponding number of access ports 28 which are preferably each in lateral alignment with a corresponding aperture 26, as shown in figure 1.

Preferably, the first and second side walls each include a channel

30,31 or groove which is adapted to receive an edge of a printed circuit board installed in the screening can. In the preferred embodiment as shown, the channels 30,31 are positioned so as to define a plane which the circuit board occupies and which is immediately below the second recess wall 24. A circuit board being installed in the screening can may conveniently be slid into place from one end of the screening can. End caps (not shown) may be provided to completely enclose a fully screened cavity or enclosure 20.

In the second recess wall 24 there are a number of fixing holes 33 which may be used to allow a clamp assembly to be screwed, bolted or otherwise attached to the outer surface of the second recess wall 24, to be described later.

With reference to figures 3 and 4 there is shown a screening can 10 with a printed circuit board 40 which is mounted in the channels 30,31. Components (not shown) would typically be mounted on either side of the printed circuit board 40.

A coaxial cable 50 comprises a core conductor 51 , a core conductor sheath 52, an outer screen conductor braid 53 and an outer insulating sheath 54 in accordance with commonplace coaxial cables. The coaxial cable is prepared by: stripping away the outer sheath 54 to a point A; folding back or compressing the outer screen conductor braid 53 to provide a braid connection area between points A and B; leaving a projecting portion 55 of core conductor 51 which is preferably protected by core conductor sheath 52 at least as far as point C.

A side entry terminal post 60 of known type is soldered into place in circuit board 40 such that it is substantially in alignment (in the direction of cable entry) with the aperture 26. The projecting portion 55 of core conductor 51 extends through the aperture 26 and into the terminal grip where it is clamped by screw 61. Screw 61 is located directly below the access port 28 to facilitate the tightening of screw 61 by a screwdriver inserted from above. The point C preferably lies inside the screening enclosure 20 such that there is no risk of electrical contact between the projecting portion 55 of core conductor 51 and the screening can first recess wall 23.

A clamp assembly 70, best viewed in figure 4, is placed over the exposed portion of outer screen conductor 53 (ie. that lying between points A and B; figure 3) and is screwed into place using suitable means such as bolt 71 and nut 72. The bolt 71 preferably passes through the printed circuit board 40 thereby providing an additional fixing point to the screening can 10. With this arrangement, the channel 31 may well be dispensed with if desired.

The clamp assembly 70 is preferably formed from an electrically conducting material such as copper strip, to provide a good electrical contact to the outer screen conductor braid 53. The nut and bolt can thereby form a connection to a suitably positioned track of the printed circuit board, and also the pressure contact of the clamp assembly and a part of the conductor braid 53 directly to the second recess surface 24 can provide an electrical connection to the screening can.

With reference to figure 5 a simplified arrangement comprising a screening can 100 and connection assembly is described. Features in figure 5 which have the same or similar function as features in figures 1 to 4 are numbered with the same reference numerals with the addition of one hundred. In this arrangement, the screening can 100 provides a top wall 111 , side walls 1 13 and 114, and end walls 116 and 117. End walls 116 and 117 include projecting lugs which extend through appropriately positioned holes 141 in a printed circuit board 140. These can provide a friction fit, or the lugs can be bent on the underside of the circuit board, to prevent detachment. Where required, the lugs can be soldered into place to provide an electrical connection to tracks on the board 140.

A clamping assembly 170 is provided in similar manner to that described in connection with figures 3 and 4. In figure 5, an alternative arrangement of separate clamps for each coaxial cable is illustrated. Electrical connection of the outer screen conductor braid 153 may be made to a ground plane 124 which fulfils an analogous function to the second recess wall 24 in figure 1. This ground plane may be provided as a metallized area on the printed circuit board 140, or alternatively as an extension of the screening can wall 113 which is bent at right angles thereto.

The coaxial cable 150 is prepared and connected in exactly the same way as previously described in connection with figures 3 and 4.

It has been determined that the connection assemblies herein described provide a screening performance equal to that of prior art separate plug and socket assemblies.

The screening cans 10, 100 may be formed from any suitable electrically conductive ferrous or non-ferrous material. A removable lid may take the place of top wall 11, 1 11 , in which case, the access ports 28, 128 may be omitted.

Although the clamping assemblies have been shown as simple screw-down shaped bars 70, 170, it will be understood that there are a number of other clamp and connect systems that may be readily applied.

For example, a slotted block having electrically conductive knife blades which pierce the outer sheath 54, 154 to make electrical contact with the conductor braid and which grip the cable 50, 150 may be mounted onto the ground plane 124 or recess surface 24. This arrangement would further simplify connection of the cable.

Although side entry terminal posts 60, 160 have been illustrated, it will be understood that a number of other connector systems could be used, such as spring loaded posts, further simplifying the connection of the cable. Alternatively, a direct soldered connection of the core conductor to the printed circuit board in the screening can could be made.

The relationship between the ground plane 124 or recess second wall surface 24 to the aperture 26, 126 has been shown as substantially orthogonal, although it will be understood that this need not be so.

Claims

1. A connection assembly, for connecting a coaxial cable having an outer screen conductor and at least one core conductor to, respectively, a screening enclosure and an electrical connection housed therein, the connection assembly including: a screening enclosure having an aperture in a wall thereof, for passage of said at least one core conductor therethrough into the screening enclosure; a clamp assembly outside the screening enclosure and coupled thereto adjacent to the aperture, adapted to grip a portion of the coaxial cable and to make a direct electrical connection to the outer screen conductor thereof.

2. A connection assembly according to claim 1 in which the screening enclosure includes a recess in the outer walls defined by at least a first recess wall incorporating the aperture and a second recess wall providing a mounting surface for the clamp assembly.

3. A connection assembly according to claim 2 in which the first and second recess walls are at substantially right angles to one another.

4. A connection assembly according to claim 3 in which the first and second recess walls form a rebate along a corner edge of the screened enclosure.

5. A connection assembly according to claim 3 or claim 4 in which the screening enclosure includes a third wall, adjacent to the recess and defining a plane substantially parallel to the plane of the second recess wall, the third wall including an access port allowing access for a tool to a location, within the screening enclosure, which is adjacent to the aperture.

6. A connection assembly according to claim 5 further including a side entry terminal post within the screening enclosure, positioned to receive a core conductor of a coaxial cable as it passed through the aperture, and also positioned to receive a screwdriver blade passed through the access port, for effecting connection of the coaxial cable to the terminal post.

7. A connection assembly according to any one of claims ] to 4 wherein the screening enclosure includes an access cover.

8. A connection assembly according to any preceding claim in which the clamp assembly comprises an electrically conductive bar with a shaped portion having a profile approximately corresponding to the outer radial profile of the coaxial cable, positionable immediately adjacent to the aperture.

9. A connection assembly according to claim 8 in which the screening enclosure includes a plurality of apertures substantially in alignment in said wall, and in which the clamp assembly bar is adapled to simultaneously clamp a coaxial cable corresponding to each aperture.

10. A connection assembly according to any preceding claim in which at least one wall of the screened enclosure is formed by a printed circuit board.

1 1. A connection assembly according to claim 10 in which a number of walls of the screening enclosure include projecting lugs for engagement with holes in the printed circuit board.

12. A connection assembly according to claim 1 1 in which the clamp assembly is mounted onto the printed circuit board adjacent to the apertures and making electrical connection to the screened enclosure via the printed circuit board.

13. A connection assembly according to any preceding claim in which the screening enclosure further includes at least one internal groove or channel adapted to receive one edge of a printed circuit board and retain it in position within the screening enclosure.

14. A connection assembly according to claim 13 in which the clamp assembly is adapted to engage with a portion of the printed circuit board to further retain it in position within the screening enclosure.

15. A screening enclosure for a circuit board comprising: top, bottom and first and second side walls defining a cavity therebetween, and having a rebate along a corner edge defined by first and second recess walls in substantially orthogonal relation to one another, and lying between the top and first side walls; at least one aperture in the first recess wall and an access port adjacent thereto in the top wall; a first channel, in the second side wall approximately coplanar with the second recess wall, adapted to receive an edge of a circuit board.

16. A screening enclosure according to claim 15 further including a second channel, extending along or proximal to the edge defined by the first side wall and the second recess wall, and adapted to receive a second edge of the circuit board.

17. A screening enclosure according to claim 15 or claim 16 in which the ends of the screening enclosure are open.

18. A screening enclosure according to claim 15 or claim 16 further including at least one end wall.

19. A screening enclosure substantially as described herein and with reference to the accompanying drawings.

20. A connection assembly substantially as described herein and with reference to the accompanying drawings.

21. A method of connecting a coaxial cable, having at least one core conductor and an outer screen conductor, to an electrical connection housed within a screening enclosure and to a wall of the screening enclosure, including the steps of: preparing the coaxial cable such that a portion of the core conductor projects longitudinally beyond an exposed end of the outer screen conductor; passing the projecting portion of the core conductor through an aperture in the walls of the screening enclosure and electrically connecting the core conductor to the electrical connection within the screening enclosure; clamping the exposed end of the outer screen to an outer conductive surface of the wall of the screening enclosure.

22. A method according to claim 21 including the step of protecting the projecting portion of the core conductor by an electrically insulating core conductor sheath at least as far as a point at which the conductor enters the screening enclosure.

23. A method of connecting a coaxial cable, having at least one core conductor and an outer screen conductor, to an electrical connection housed within a screening enclosure and to a wall of the screening enclosure substantially as described herein with reference to the accompanying drawings.