Abstract:
A coaxial connector mountable on an end of a coaxial cable having a central conductor (cc) and an exterior conductor (ce), the connector comprising a first conductive contact element ( 2; 27; 38; 40 ) for contacting the central conductor (cc), a second conductive contact element ( 4; 21; 302; 411 ) for contacting the exterior conductor (ce) electrically isolated from the first contact element, a clamping member ( 5; 22; 42 ) opposing the second contact element for clamping the exterior conductor against the second contact element and a force applying member ( 6; 23; 441 ) for forcing the clamping member and the second contact element towards each other, wherein the second contact element and/or the clamping member comprise at least one deforming member ( 502; 222 - 223; 423 - 424 ) for deforming the exterior conductor (ce) under influence of the force applying member, wherein each deforming member ( 502; 222 - 223; 423 - 424 ) is constructed in a material with a predetermined hardness above that of the material of the exterior conductor and has a predetermined shape for hardening a portion of the exterior conductor to such an extent that it becomes substantially fully elastic.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to coaxial connectors mountable on an end of a coaxial cable having a central conductor and an exterior conductor.  
         [0003]     All the materials which are used in fabricating coaxial cables, the metals as well as the plastics, are non-elastic materials. The fixing onto the cable, the sealing and the electric contacts are functions which are realised by forces between the elements of the cable and the elements of the connector during the mounting of the latter on the cable. The majority of existing connectors use rigid elements for applying the necessary forces for realising one or more of the functions, which leads to a material flow which consists of a cold deformation for eliminating mechanical stress. The forces diminish to an extent which is insufficient for the respective function. An other problem of existing connectors is the use of an internal threaded part for holding the exterior conductor of the cable. Such internal threaded part creates grooves in the outer conductor which can break the connection. For certain cables with a fragile exterior conductor, for example a braid of metallic strands, rigid contact systems are used which press the fragile conductor against the dielectric on the interior thereof, with the same risk of possible breakage. Furthermore, the deformation of the cross-section of the cable by this type of gripping can modify the impedance of the cables and disturb the transmission of the signal. All these disadvantages of rigid contact elements are increased in the field as a result of temperature variations and vibrations.  
         [0004]     2. The Prior Art  
         [0005]     From EP-A-897 202 a coaxial connector is known, comprising a head portion having a recess which has one end formed with a first ring surface for establishing a contact from inside with an end zone of an outer cable conductor of a coaxial cable, and a restraint for the coaxial cable. The restraint is formed by a clamp bushing having a head portion side end formed with a second ring surface for clamping the end zone of the outer cable conductor from outside, and a pressure-applying member enclosing the cable and fastened to the head portion for forcing the clamp bushing in the axial direction against the first ring surface and to thereby clamp the end zone of the outer cable conductor between the first and second ring surfaces. At least one of the ring surfaces is formed with at least one annular bead which projects in the direction of a respective area of the end zone of the outer cable conductor and is defined by a height of approximately 5 to 30% of a wall thickness of the outer cable conductor. Upon tightening of the connector around the cable, this annular bead causes a plastic deformation of the outer conductor.  
         [0006]     The coaxial connector known from EP-A-897 202 however has the disadvantage that the electrical contact between the outer cable conductor and the head portion may deteriorate in time.  
         [0007]     It is a first aim of this invention to provide a coaxial connector in which the deterioration in time of the electrical contact with the outer cable conductor can be reduced.  
         [0008]     It is a second aim of the invention to provide a coaxial connector with enhanced cable retention.  
         [0009]     It is a third aim of the invention to provide a coaxial connector with an enhanced seal against penetration of moisture.  
       SUMMARY OF THE INVENTION  
       [0010]     The first aim is achieved according to the invention with a coaxial cable conductor comprising a first conductive contact element for contacting the central conductor, a second conductive contact element for contacting the exterior conductor electrically isolated from the first contact element, a clamping member opposing the second contact element for clamping the exterior conductor against the second contact element and a force applying member for forcing the clamping member and the second contact element towards each other, wherein the second contact element and/or the clamping member comprise at least one deforming member for deforming the exterior conductor under influence of the force applying member, wherein each deforming member is constructed in a material with a predetermined hardness above that of the material of the exterior conductor and has a predetermined shape for hardening a portion of the exterior conductor to such an extent that it becomes substantially fully elastic.  
         [0011]     In other words, the connector of the invention has elements for compressing a portion of the exterior conductor, thereby deforming it beyond its plastic deformation capability. This leads to a local hardening of the material of the exterior conductor in such a way that any further compression, however limited, is reversed when the contact is released, i.e. that the material can only be elastically further compressed and has the intention to return to its original shape. This has the advantage that the electric contact at this hardened portion can adapt itself to pressure changes and remain excellent over a longer period in time. Due to the elasticity which is gained, any material flow which entails a reduction of the contact pressure is overcome by an expansion of the hardened, elastic part of the exterior conductor. Furthermore, due to the hardening of the material, this portion of the exterior conductor is less susceptible to material flow, so that an excellent electric contact over a very long period of time is achievable.  
         [0012]     In a preferred embodiment, one deforming member is formed by a step edge between a first and a second contact surface of the second contact element or the clamping member, the step edge having a predetermined height corresponding to at least one third of a wall thickness of the exterior conductor. Alternatively, one deforming member may also be formed by a narrow shoulder which has a predetermined height corresponding to at least one third of a wall thickness of the exterior conductor. The local reduction of the wall thickness of the exterior conductor by at least one third of its original wall thickness, which is more than the 5 to 30% known from the prior art, can assure that this portion of the exterior conductor is hardened to the desired extent.  
         [0013]     The first aim of the invention is furthermore achieved with a connector comprising a first conductive contact element for contacting the central conductor, a second conductive contact element for contacting the exterior conductor electrically isolated from the first contact element, and a clamping member for clamping the exterior conductor against the second contact element, wherein the clamping member is constructed in an elastically deformable, substantially incompressible material.  
         [0014]     By constructing the clamping member in such a material, the same principle as with the local hardening of the exterior conductor as has been described above exists, namely that the electric contact between the exterior conductor and the second contact element is under the influence of an element, here the clamping member, which is elastically deformed and has the intention to regain its original shape. As a result, the contact can adapt itself to pressure changes which may for example be caused by material flow and an excellent electric contact over a very long period of time is achievable.  
         [0015]     In a preferred embodiment, the second contact element comprises a groove for accommodating a deformation of the exterior conductor under the influence of the clamping member. This has the advantage that the exterior conductor is deformed into the groove, which can contribute to cable retention.  
         [0016]     The second aim of the invention is furthermore achieved in that the connector comprises a permanently deformable split ferrule with conical outer surface complementary to a conical inner surface of a ring and is axially slidable for tightening the split ferrule around the cable, wherein the conical surfaces are directed such that a pull force on the cable causes a further tightening of the ferrule. In this way a pull force on the cable increases the grip of the connector onto the cable, so that excellent cable retention is achievable.  
         [0017]     The third aim of the invention is achieved with a coaxial cable comprising one or more O-rings for sealing the interior of the connector against penetration of moisture, wherein the O-rings are compressed both radially and axially upon mounting the connector onto the cable. The compression of the O-rings in these two orthogonal directions can substantially enhance the seal which is formed by them.  
         [0018]     It is furthermore an aim of this invention to provide a connector for each of the different types of available coaxial cables, in which the principles of the invention are applied. This and further aims will become apparent from the detailed description given below.  
         [0019]     The invention will be further elucidated by means of the following description and the appended figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  shows a cross sectional view of a first embodiment of a coaxial connector according to the invention.  
         [0021]      FIG. 2  shows a cross sectional view of the embodiment of  FIG. 1 , mounted on a coaxial cable.  
         [0022]      FIG. 3  shows a cross sectional view of a second embodiment of a coaxial connector according to the invention.  
         [0023]      FIG. 4  shows a cross sectional view of the embodiment of  FIG. 3 , mounted on a coaxial cable.  
         [0024]      FIG. 5  shows a cross sectional view of a third embodiment of a coaxial connector according to the invention.  
         [0025]      FIG. 6  shows a cross sectional view of the embodiment of  FIG. 5 , mounted on a coaxial cable.  
         [0026]      FIG. 7  shows a cross sectional view of a fourth embodiment of a coaxial connector according to the invention.  
         [0027]      FIG. 8  shows a cross sectional view of the embodiment of  FIG. 7 , mounted on a coaxial cable.  
         [0028]      FIG. 9  shows a detail of  FIG. 8 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     The coaxial connectors shown in the figures are intended for mounting on a coaxial cable which comprises a central conductor cc, a dielectric d surrounding the central conductor cc, an exterior conductor ce, cet, cef surrounding the dielectric d and an outer insulation g. As appears from the figures, solutions are presented for different types of coaxial cables which may be used in telecommunication, television distribution and other applications, particularly for connectors whose mounting cannot be effected by welding. In this case a plurality of categories exist: connectors which are mounted in the field, connectors for cables of large dimensions, connectors for cables with conductors whose metal is unsuitable for welding or for cables whose dielectric cannot resist the temperature of welding etc.  
         [0030]     The coaxial connectors have to fulfil one or more of the following conditions: decent fixing on the cables, resistance to corrosion, and assuring good electric contacts. Their quality and life are directly linked to these parameters and particularly to the quality of the electric contact. The coaxial cables are very different from a viewpoint of utilised materials, constructional options and types of application. It is impossible to achieve a good connection with connectors having the same type of fixing, sealing and contact for all existing types of cables.  
         [0031]     The first coaxial connector of  FIG. 1  is intended for mounting on a coaxial cable having as exterior conductor ce a tube in extruded aluminium. The connector comprises a body  1  with a central bore comprising a first portion  100  at the front, which widens into a second portion  101  and further to a third portion  102  at the rear of the connector. In the interior of the first portion  100  of the central bore, a central elastic contact  2  is mounted, which is intended for making an elastic contact with the central conductor cc. For the purpose of clarity, the location of the central contact  2  is here called the “front” of the connector and the opposite side of the connector which faces the coaxial cable is called the “rear”. A guide  3  for guiding the central conductor cc upon insertion into the central contact  2  is mounted in the second portion  101  of the central bore, in which portion also a mandrel  4  is fixed. This mandrel  4  extends towards the rear into the third portion  102  of the central bore and is provided for electrically connecting the exterior conductor ce to the body  1 . In this third portion  102  of the bore, a ring  6  is mounted which is held in position by an O-ring  7 , seated in a groove  103 . Behind the groove  103 , the body is provided with an internal thread which is complementary to an external thread on a rear part  8  of the connector, which is shown in a position in contact with the O-ring  7 . The ring  6  has a conical entrance  601  facing the front of the connector. This conical entrance  601  is in contact with a corresponding conical outer surface  501  of a split ferrule  5 , which is mounted on the interior of the ring  6 . The ferrule  5  is on its interior provided with two narrow shoulders  502  which protrude towards the inside and are provided to be pressed into the outer surface of the exterior conductor ce. Behind the conical entrance  601 , the ring  6  further comprises a cylindrical portion  602  which forms a passage for the outer insulation g of the coaxial cable.  
         [0032]     The connector of  FIG. 1  is a so-called monoblock connector, which means that the rear part  8  does not have to be removed from the body  1  for mounting the connector on the cable. For mounting the connector, one first places a reference mark on the prepared cable at a distance L measured from the front plane of the exterior conductor ce. This distance L is the distance between the end of the rear part  8  and the mark  104  which is provided on the outside of the body  1  and indicates the transverse plane of the surface  401  of the mandrel  4  against which the front plane of the exterior conductor ce is to abut. One places the connector on the cable and pushes it over the cable until the end of the rear part  8  arrives at the reference mark placed on the cable. In this way, it can be ensured that the cable is in the correct position on the inside of the connector, before the connector is fixed onto the cable by screwing the rear part  8  into the body  1 . The use of the reference mark  104  avoids the need for dismantling the connector for verifying if the cable is in the correct position.  FIG. 2  shows the connector of  FIG. 1  mounted and fixed on the cable.  
         [0033]     The first connector of  FIG. 1  functions as follows. By screwing the rear part  8  into the body  1 , it dislodges the O-ring  7  from the groove  103  while compressing it radially and pushing it into the third portion  102  of the central bore against the ring  6 . The ring  6  is thereby moved towards the front and cooperates by means of its conical surface  601  with the conical surface  501  of the split ferrule  5  for tightening the latter against the exterior conductor ce of the cable. The angle of the two conical surfaces  601  and  501  being small, the tightening of the split ferrule  5  is caused with great force. The exterior conductor ce of the cable is deformed and pressed against the mandrel  4 , which is fixed in the second portion  101  of the bore in the body, by the radial tightening force transferred via the two small shoulders  502  of the ferrule  5 . These shoulders  502  break the aluminium oxide film, which forms an insulation, and as a result ensure a good electric contact. Moreover, by the large tightening force the exterior conductor ce is locally hammer-hardened to the extent that it becomes substantially fully elastic, so that an elastic contact is created between the exterior conductor ce and the mandrel  4  which can adjust itself to stress changes and thus can assure a good contact over a very long period of time. The hardening of the exterior conductor ce makes it also less sensible to cold metal flow. The exterior conductor ce is hardened by the shoulders  502 , but it is not cut by them. Cuts are to be avoided since they could lead to breakage upon occurrence of vibrations.  
         [0034]     From a mechanical point of view, the tightening of the exterior conductor ce by the split ferrule  5  around the mandrel  4  can assure the fixing of the connector and the retention of the cable. Since the shoulders  502  enter into the exterior conductor ce when the ferrule  5  is tightened for the first time and the ferrule  5  remains in position when the tightening force is released, i.e. when the rear part  8  is screwed out, the ferrule  5  fixes the connector on the cable. When the rear part  8  is screwed out, the connector becomes axially rotatable around the cable end but is advantageously held in position on the cable end. The conical entrance  601  of the ring  6 , which is provided for tightening the ferrule  5 , has a diameter which shortens from the front towards the rear of the connector. This has the effect that in the tightened state, i.e. with the rear part  8  screwed into the body  1 , any pull force on the cable tightens the ferrule  5  even more around the exterior conductor ce, so that excellent cable retention is achieved.  
         [0035]     The O-ring  7  also has both a mechanical and an electric function. In the tightened state, the O-ring  7  substantially completely fills the space between the third portion  102  of the bore, the ring  6 , the rear part  8  and the outer insulation g of the cable, and functions like the joint of a stuffing box, assuring an excellent seal between the cable and the connector which can adapt itself to variations in the thickness of the insulation g of the cable. A seal is also obtained between the exterior conductor ce and the insulation g of the cable, which penetrates into the passage  602  of the ring  6 , which is very important for preventing the entrance of moisture into the connector which can be located between a damaged part of the insulation g and the exterior conductor or the penetration of compound in case the cable is of the compound containing type. The pressure of the O-ring  7  onto the insulation g of the cable is of such an extent that it is transferred onto the exterior conductor ce which is in turn tightened and deformed around the mandrel  4 . Thus the O-ring  7  contributes to the electric contact between the exterior conductor ce and the mandrel  4 . Since the elastomer of the O-ring  7  is elastic but substantially incompressible, it has a tendency to regain its original form in cross-section as does any elastic element, so that the O-ring exerts a self-adjusting pressure on the cable and creates a second elastic contact between the exterior conductor ce and the mandrel  4 , which can compensate a possible flow. Due to the double elastic contact created by on the one hand the hammer-hardened part of the exterior conductor ce and on the other hand the elastic O-ring  7 , which can both compensate for material flow, as well as due to the large contact forces, an excellent long term electric contact is achievable.  
         [0036]     The second coaxial connector of  FIG. 3  is intended for mounting on a coaxial cable having as exterior conductor ce a fine malleable tube in welded aluminium. The connector comprises a body  20  with a central bore comprising a first portion  200  at the front, which widens into a second portion  201  and further to a third portion  202  and a fourth portion  204  at the rear of the connector. In the interior of the first portion  200  of the central bore, a central elastic contact  27  is mounted, which is intended for making an elastic contact with the central conductor cc. Again a guide  28  is provided for guiding the central conductor cc upon insertion into the central contact  27 . In the second portion  201  of the central bore, a mandrel  21  is fixed, which is provided for electrically connecting the exterior conductor ce to the body  20 . This mandrel  21  extends towards the rear into the third portion  202  of the central bore where it comprises an outer groove  212 . In this third portion  202  of the bore, a ring  23  is mounted which is held in position by an O-ring  25 , seated in a groove  203 . Behind the groove  203 , the body is provided with an internal thread which ends at the fourth portion  204  of the bore. The internal thread of the body  20  is complementary to an external thread on a rear part  24  of the connector, which is shown in a position in contact with the O-ring  25 . The rear part  24  comprises an outer groove  243  in which a further O-ring  26  is seated for forming a seal in the fourth portion  204  of the body  20 . The ring  23  has a conical entrance  231  facing the front of the connector. This conical entrance  231  is in contact with a corresponding conical outer surface  221  of a split ferrule  22 , which is mounted on the interior of the ring  23 . The ferrule  22  is on its interior provided with two central bore portions  222  and  223  which have a different diameter, forming a step of about one third of the thickness of the exterior conductor ce. This step edge and the front edge of the wider diameter portion  222  are provided to be pressed into the outer surface of the exterior conductor ce upon tightening the ferrule  21 .  
         [0037]     This second connector is also a monoblock connector whose rear part  24  does not have to be removed for mounting the connector on the cable. This is done by placing a reference mark on the prepared cable on a distance L 1  measured from the front plane of the exterior conductor ce. This distance L 1  is the distance between the end of the rear part  24  and the mark  205  which is provided on the outside of the body  20  and indicates the transverse plane of the surface  211  of the mandrel  21  against which the front plane of the exterior conductor ce is to abut. One places the connector on the cable and pushes it over the cable until the end of the rear part  24  arrives at the reference mark placed on the cable. In this way, it can be ensured that the cable is in the correct position on the inside of the connector, before the connector is fixed onto the cable by screwing the rear part  24  into the body  20 . The use of the reference mark  205  avoids the need for dismantling the connector for verifying if the cable is in the correct position.  FIG. 4  shows the connector of  FIG. 3  mounted and fixed on the cable.  
         [0038]     The second connector of  FIG. 3  functions as follows. By screwing the rear part  24  into the body  20 , it dislodges the O-ring  25  from the groove  203  while compressing it radially and pushing it into the third portion  202  of the central bore against the ring  23 . The rear part  24  is screwed further so that the O-ring is moved into an entrance  241  for containing the O-ring  25  which is provided in the rear part  24 . This entrance  241  has a slightly smaller diameter than the third portion  202  of the bore, so that the O-ring  25  is further radially compressed when it is pushed into this entrance  241 . By further screwing the rear part  24  into the body  20 , the O-ring  25  is axially compressed between the ring  23  and the rear part  24  and the ring  23  is also moved towards the front. The ring  23  cooperates by means of its conical surface  231  with the conical surface  221  of the split ferrule  22  for tightening the latter against the exterior conductor ce of the cable. The angle of the two conical surfaces  231  and  221  being small, the tightening of the split ferrule  22  is caused with great force. This causes the ferrule  22  to slightly tilt, so that both the front edge of the wider bore  222  and the front edge of the narrower bore  223  of the ferrule  22  come into contact with the exterior conductor ce and are pressed into it, breaking the aluminium oxide film. As a result, the exterior conductor ce of the cable is again deformed and pressed against the mandrel  21  by the radial tightening force transferred via the two sharp interior edges of the ferrule  22 . By the large tightening force the exterior conductor ce is locally hammer-hardened to the extent that it becomes substantially fully elastic, so that an elastic contact is created between the exterior conductor ce and the mandrel  21  which can adjust itself to stress changes and thus can assure a good contact over a very long period of time. The hardening of the exterior conductor ce makes it also less sensible to cold metal flow.  
         [0039]     From a mechanical point of view, the tightening of the exterior conductor ce by the split ferrule  22  around the mandrel  21  can again assure the fixing of the connector as well as the retention of the cable. Since the edges on the interior of the ferrule  22  enter into the exterior conductor ce when it is tightened for the first time and the ferrule  22  remains in position when the tightening force is released, i.e. when the rear part  24  is screwed out, the ferrule  22  fixes the connector on the cable. When the rear part  24  is screwed out, the connector becomes axially rotatable around the cable end but is advantageously held in position on the cable end. The conical entrance  231  of the ring  23 , which is provided for tightening the ferrule  22 , has a diameter which shortens from the front towards the rear of the connector. This has the effect that in the tightened state, i.e. with the rear part  24  screwed into the body  20 , any pull force on the cable tightens the ferrule  22  even more around the exterior conductor ce, so that excellent cable retention is achieved.  
         [0040]     The O-ring  25  again has various functions. In the tightened state, the O-ring  25  substantially completely fills the space between the entrance  241  of the rear part  24 , the ring  23  and the outer insulation g of the cable, and functions like the joint of a stuffing box, assuring an excellent seal between the cable and the connector. A seal is also obtained between the exterior conductor ce and the insulation g of the cable, which penetrates underneath the ring  23 , which is very important for preventing the entrance of moisture into the connector which can be located between a damaged part of the insulation g and the exterior conductor or the penetration of compound in case the cable is of the compound containing type. The sealing between the rear part  24  and the body  20  of the connector is assured by the second O-ring  26 . The pressure of the first O-ring  25  onto the insulation g of the cable is of such an extent that it is transferred onto the exterior conductor ce which is in turn tightened and deformed by entering into the groove  212  in the mandrel  21 . Thus the O-ring  25  contributes to the electric contact between the exterior conductor ce and the mandrel  4  and also to retention of the cable. Since the elastomer of the O-ring  25  is elastic but substantially incompressible, it has a tendency to regain its original form in cross-section as does any elastic element, so that the O-ring exerts a self-adjusting pressure on the cable and creates a second elastic contact between the exterior conductor ce and the mandrel  21 , which can compensate a possible flow. Due to the double elastic contact created by on the one hand the hammer-hardened part of the exterior conductor ce and on the other hand the elastic O-ring  25 , which can both compensate for material flow, as well as due to the large contact forces, an excellent long term electric contact is achievable.  
         [0041]     An important advantage of the monoblock construction of the two connectors described above exists if the connectors are provided with standard screwable heads or interfaces (not shown) for connecting the cable to further equipment. When it is desired to remove the cable from said equipment, one unscrews the rear part  8 ,  24  for releasing all the tensions or pressures onto the cable. At that moment, the connector can be unscrewed from the equipment since an axial rotation of the connector around the cable is enabled, as has been described above. This rotation does not damage the surfaces which provide the electric contacts, since the tensions are released. But the connector remains in position on the cable end. For remounting the cable on the equipment it is then sufficient to screw the connector head back on and then to screw the rear part  8 ,  24  back into the body  1 ,  20  for retightening the connector on the cable. The result is substantially identical to the result after the first mounting.  
         [0042]     The third coaxial connector shown in  FIG. 5  is intended for mounting on a coaxial cable having as exterior conductor cet a braid of very fine metallic strands. This connector is however also suitable for cables whose exterior conductor is composed of two layers, respectively a metal strip cef below the braid cet. The connector again comprises a body  30  with a central bore with a front portion  300  in the interior of which a central elastic contact  38  is mounted, which is intended for making an elastic contact with the central conductor cc. Again, a guide  39  is provided for guiding the central conductor cc upon insertion into the central contact  38 . The body  30  ends in an externally threaded portion, in front of which an outer groove  301  is provided, holding an O-ring  31  for forming a seal with a rear part  34 . A rear portion  302  of the central bore, extending in the interior of the externally threaded portion of the body  30 , is provided for accommodating a ring  32 . This ring has an external groove  323  in which an O-ring  33  is held, which functions to hold the ring substantially in the centre of the rear portion  302  of the bore in the body. The ring  32  has at its rear end an upstanding contact surface  321  for contacting the end surface  303  of the body  30 . When these surfaces  321  and  303  are in contact, a narrow gap is formed between the ring  32  and the front wall  304  of the rear bore portion  302 . The connector further comprises the rear part  34  which has a central bore successively comprising an entrance portion  341  for surrounding the body  30  at the O-ring  31 , an internally threaded portion corresponding to the externally threaded portion of the body  30 , a first rear portion  342 , a slightly narrower second rear portion  343  and a further narrower third rear portion  344 . In the first rear portion  342  of the rear part  34 , a split ferrule  35  is held with its outer surface  351  in contact with the inner wall of the portion  342 . The ferrule  35  again has an outer conical surface  353  at its rear end, cooperating with an inner conical surface  361  of a ring  36 , which is located in the second rear portion  343 . Behind the ring  36  in the same bore portion  343  another O-ring  37  is located for sealing purposes. All these parts are held in place in the rear part  34  by the ferrule  35 . The ferrule  35  furthermore has an outer conical surface  354  at its front end which cooperates with an inner conical surface  322  of the ring  32 .  
         [0043]     For mounting the connector of  FIG. 5  on the cable, the rear part  34  is taken and placed on the prepared cable. Then the ring  32  is taken and slid over the braid cet until it is in contact with the front of the insulation g, after which the braid cet is folded back over the O-ring  33  on the outside of the ring  32 . The cable with the ring  32  is pushed into the body  30  for insertion into the rear bore portion  302  of the body  30 . Finally the rear part  34  is screwed onto the body  30  and tightened.  FIG. 6  shows the connector of  FIG. 5  mounted on the cable.  
         [0044]     The third connector of  FIG. 5  functions as follows. The O-ring  33  on the outer groove  323  of the ring  32  presses the braid cet of the cable against the wall of the rear bore portion  302 , assuring an electric contact between the braid cet and the body  30 . This electric contact is furthermore elastic due to the elastic properties of the elastomer of the O-ring  33 , but entails substantially no modification in the diameter of the cable so that its impedance remains substantially the same. Providing the electric contact by means of the O-ring also has the advantage that the connector body  30  is axially rotatable around the cable without damaging the exterior conductor cet (as long as the rear part  34  is not tightened), since the friction between the braid cet and the O-ring  33  is above that between the braid cet and the body  30 . By screwing the rear part  34  onto the body  30 , the split ferrule  35  is tightened around the cable as a result of being pressed between the rings  32  and  36 . The orientation of the corresponding conical surfaces  322  and  354  at the front of the ferrule  35  and the cooperating conical surfaces  361  and  353  at the rear is such that both rings  32  and  36  contribute to the tightening of the ferrule  35 . The ferrule has an interior shoulder  352  which penetrates into the insulation g of the cable, thereby assuring retention of the cable. This shoulder is short and has a height of about one third of the thickness of the outer insulation g, so that the deformation in cross-section of the latter is insignificant. By the same movement, the ring  36  pushes the O-ring  37  into the third rear portion  344  of the bore in the rear part  34 , which compresses the O-ring  37  radially. Afterwards, the O-ring  37  is also axially compressed so that it exerts a large pressure on the outer insulation g of the cable, thereby assuring a tight seal between the cable and the rear part  34 . The seal between the body  30  and the rear part  34  is assured by the O-ring  31  which is tightened between the groove  301  and the entrance portion  341 .  
         [0045]     The fourth coaxial connector shown in  FIG. 7  is intended for mounting on a coaxial cable having a corrugated exterior conductor ce. The connector comprises a body  41  and a rear part  44 . The body is provided with a central bore, in the interior of which a central elastic contact  40  is mounted, which is intended for making an elastic contact with the central conductor cc. The central bore has an internally threaded portion followed by a rear portion  412  which are respectively intended for receiving a corresponding externally threaded front portion of the rear part  44  and a sealing O-ring  43  which is seated in an outer groove  443  of the rear part  44 . The body  40  further comprises a conical surface  411  for contacting the inside of the front end of the exterior conductor ce of the cable. The rear part  44  has an entrance bore portion  442  which is followed by an annular projection  441 . A ferrule  42  is held in the rear part  44  by the projection  441  and is axially slidable along the projection  441 . This ferrule  42  comprises a cylindrical crown  422  onto which a plurality of forwards projecting elastic fingers  426  are attached, which can be elastically bent from a neutral position  426   a  shown in  FIG. 7  and in dashed lines in  FIG. 9  to a position under stress  426   b  shown in  FIG. 8  and in full lines in  FIG. 9 . Each finger  426  has a head  421  which has outer surfaces  427  and  425  abutting the entrance bore portion  442  and the annular projection  441  of the rear part  44  and two inner conical surfaces  423  and  424  for contacting the outside of the front end of the exterior conductor ce of the cable. An annular step edge is formed by a sudden decrease in diameter from the first, more frontal conical surface  423  and the second, more rearward conical surface  424  of the ferrule  42 . This step edge has a height of about one third of the thickness of the exterior conductor ce. This step edge as well as the front edge of the first conical surface  423  are provided to penetrate into the exterior conductor ce, in a similar way as was described for the ferrule  22  of the connector of  FIG. 3 , when the ferrule heads  421  are tightened under the action of the projection  441  onto the abutting surface  425 . To this end, the conical surfaces  423  and  424  are substantially parallel to the contact surface  411  on the body  41  when the fingers  426  are in the neutral state  426   a.    
         [0046]     For mounting the connector, first the rear part  44  is placed over the prepared cable. Then the body  41  is placed at the front of the cable with its surface  441  in contact with the inside of the exterior cable ce. Finally, the rear part  44  is screwed onto the body  41 , thereby tightening the ferrule  42  and clamping the front end of the exterior conductor ce between the contact surface  411  of the body  41  and the ferrule heads  421 . The result is shown in  FIG. 8  and in detail in  FIG. 9 .  
         [0047]     The functioning of the fourth connector is as follows. By screwing the rear part  44  onto the body  41 , the ferrule  42  slides along the projection  441  until the upstanding outer surface  425  of the heads  421  abuts the projection  441 . Further screwing has the effect that the projection  441  exerts a tightening force onto the heads  421 , causing them to pivot slightly until the front edge of the first conical surface  423  comes into contact with the exterior conductor ce. This pivoting puts a given stress onto the fingers  426 , causing them to take their position  426   b . Next, the force exerted by the projection  441  onto the heads  421  causes the front edge and the step edge to penetrate into the material of the exterior conductor ce, thereby breaking the oxide film and locally hammer-hardening the exterior conductor ce to the extent that it becomes substantially fully elastic. As a result, an elastic contact is created between the exterior conductor ce and the body  41 , which is enhanced by the stress on the elastic fingers  426 . Thus, the elastic contact can adjust itself to stress changes and overcome material flow as a result of the achieved elasticity of the exterior conductor ce as well as the elasticity of the fingers  426 . Since the front edge and the step edge of the ferrule  21  have entered into the material of the exterior conductor ce, again also an excellent cable retention is achievable.  
         [0048]     In order to provide a seal also at the rear end of the rear part  44 , a further O-ring  45  is seated in a groove  445 . Behind this groove  445 , the rear part  44  is provided with an internal thread which is complementary to an external thread on a further rear part  46  of the connector. By screwing the further rear part  46  into the rear end of the rear part  44 , the O-ring  45  is dislodged from its groove  445  and moved to a narrower bore portion  444  and compressed radially around the outer insulation g of the cable.  
         [0049]     In all the above described embodiments, the contact with the central conductor cc is achieved by introducing the latter possibly through a guide  3 ,  28 ,  39  into an elastic central contact  2 ,  27 ,  38 ,  40 . This central contact  2 ,  27 ,  38 ,  40  is formed by a tightened tulip in elastic metal, whose petals are spread by the introduction of the central conductor cc, so that an elastic contact force is achieved. This assures electric contact without gripping the central conductor. This type of contact is very good over a long period of time and furthermore enables the rotation of the connector around the cable.