FR2698477A1 - High frequency signal transmission cable. - Google Patents

Abstract

The present invention relates to a high frequency signal transmission cable comprising at least two conductors or sets of conductors (5, 5 '), each of the conductors (3) being insulated by a first insulating sheath (4), the conductors or sets of conductors (5, 5'). conductors located inside a second sheath of an insulating material surrounded by a metal screen (7, 7 ') itself protected by an outer casing (9), characterized in that the second sheath (6, 6 ') consists of a thin envelope of a material chosen from low or medium density polyethylenes, polyolefins, polypropylenes, elastomeric thermoplastics and fluorinated resins, this envelope surrounding the conductors or sets of conductors (5, 5' ) without the latter being embedded in the sheath (6, 6 ') that it constitutes.

Description

HIGH FREOUENCY SIGNAL TRANSMISSION CABLE

  The present invention relates to a high-frequency signal transmission cable. It relates more particularly to such a cable intended to be used in the computer field for the transmission of data. These cables generally have an outer shape called flat, that is to say they have an oval-shaped section

  very flattened or eight very flattened as appropriate. A flat computer cable is described for example in the PCT patent application published under the number WO 86/05311.

  It has two pairs of insulated conductors Each of these pairs is surrounded by a sheath of an extruded insulating material so that the conductors of each pair are embedded in this sheath. The insulating sheath of each pair is surrounded by a shielding metal screen. Finally, the two shielded pairs are held and protected together by an outer sheath made of an insulating material. The structure thus obtained has a shape of eight very flattened, with two large opposite substantially planar faces (called flats) and two rounded sides joining together. the flats The electrical function of the intermediate insulating sheath is to move the metal screen away from the conductors, in order to reduce the linear capacitance of the cable.25 The material constituting the insulating sheath is a polyvinyl chloride (PVC) having a high resistance to the compression to allow the cable thus realized to be installed on the ground and thus to undergo without damage For example, it is important to note that the PVC sheath is intended for

  keep the conductors parallel to each other, regularly spaced and at precise distances from the cable edges.35 Such a cable is not entirely satisfactory.

  Indeed, the Applicant has observed that, during the extrusion of the PVC sheath which drowns the conductors, they move relative to each other because of the forces to which they are subjected Therefore, even if the 5 Although the conductors are effectively held by the PVC sheath in fixed and precise positions during the use of the cable, the fact remains that these positions are incorrect initially. However, the strict respect of the positions of the various conductors inside the cable is very important because it makes it possible to obtain the electrical characteristics of the cable

  and, in particular, the impedance, the attenuation and the crosstalk This results in particular that the attenuation at 1 M Hz, instead of being of the order of 15 23 d B / km, as provided in the document mentioned previously, is 40 d B / km.

  In addition, the cable obtained according to the previous document is not very flexible because drowning drivers

  in the sheath has the effect of giving the latter20 a large volume that does not achieve the desired flexibility.

  The object of the present invention is to provide a cable for the transmission of high frequency signals, and in particular a flat cable for data processing, the electrical characteristics of which are not liable to vary due to a bad positioning of the conductors at the moment of manufacture, and which has a greater flexibility than the cables of the prior art. The present invention proposes for this purpose a high-frequency signal transmission cable comprising at least two conductors or sets of conductors, each of said conductors being insulated by a first insulating sheath, said conductors or sets of conductors being gathered inside a a second sheath made of a dielectric material surrounded by a metal screen itself protected by an outer casing, characterized in that said second sheath is constituted by a thin casing made of a material chosen from low or medium density polyethylenes; polyolefins, polypropylenes, elastomeric thermoplastics and fluorinated resins, said envelope surrounding said conductors or sets of conductors without these being embedded in the sheath it constitutes. Thanks to the invention, and particularly to the use of a sheathing envelope instead of a massive sheath in which the conductors or sets of conductors are embedded, the latter are not likely to move

  during the installation of the duct The electrical characteristics of the cable obtained are therefore those expected.

  In addition, the choice of material constituting the second sheath allows the latter to be both rigid to ensure accurate and reliable maintenance conductors or sets of conductors relative to each other, and fine to reduce clutter Flexibility of the cable 20. Advantageously, the outer casing may be PVC, polyethylene, polypropylene or polyurethane, and more generally in a halogen-free and fire-resistant material. On the other hand, sets of drivers can

  for example pairs or quads of twisted conductors.

  According to one possible embodiment, the cable according to the invention comprises four quads of conductors, these quads being grouped in pairs so that each set of two quads is inside a second separate sheath and the second sheaths are

  both surrounded by a metal screen, the outer casing being arranged around the two sets of two quads side by side so that the cable has a flattened eight-shaped section having substantially two opposite flats joined together by two sides rounded.

  A screen continuity wire may be installed parallel to the conductors between the second sheath and the screen. Moreover, to facilitate the stripping of the conductors, the second sheath can be split longitudinally over all or part of its length. In addition, the second sheath can be extruded around the conductors or sets of conductors so as to

  The outer casing may be extruded around the second casing.

  Finally, the material constituting the second sheath does not adhere to the material constituting the first sheath.

  Other features and benefits of this

  invention will become apparent from the following description of a particular embodiment given as a

  illustrative and in no way limiting. In the following figures: FIG. 1 is a perspective view with partial detachments of a flat cable according to the invention,

  Figure 2 is a partial enlargement of Figure 1.

  In these figures, the common elements bear the same reference numbers.

  FIG. 1 shows a flat cable 1 according to the invention.

  The cable 1 comprises four quads 2 Each of the quads 2 consists of a twist of four solid conductors

  in copper 3, the conductors 3 being each insulated by a first insulating sheath 4 of a material having a low dielectric constant, such as expanded polyethylene or polypropylene, for example.

  The diameter of the solid conductors 3 is 0.643 mm

  (+ 3%), and the diameter of the conductors 3 isolated by means of sheaths 4 is 1.35 mm.

  The quads 2, arranged side by side, are grouped in two sets of two, referenced 5 and 5 'The sets and 5' are surrounded by a second insulating sheath 6 and 6 'respectively According to the invention, the sheaths 6 and 6 ' are

  consisting of a thin envelope with a thickness of 0.25 to 1 mm polyethylene.

  The quads 2 are not embedded in the material constituting the sheaths 6 and 6 ', and these latter simply constitute a thin envelope around the quads 2, this envelope allowing a rigid and reliable holding of the quads 2 relative to each other and guaranteeing a small footprint of the cable 1.10 Moreover, the material constituting the sheaths 6 and 6 'has both sufficient rigidity to maintain the quads in a determined position during the various manipulations of the cable (winding on a drum during manufacture, pulling, installation, possible repacking15), which guarantees the conservation of the characteristics of the cable, and a sufficient elasticity for

  allow these different manipulations (unlike the bulky sheaths of the prior art that do not allow such manipulations) without the sheaths 6 and 6 '20 may tear.

  A screen 7, 7 'in the form of a thin metal foil is disposed respectively around the sheaths 6 and 6'. This screen serves as a shield to prevent disturbances of the signals conveyed by the cable by radiation.

external electromagnetic

  A screen continuity wire 8, 8 'is respectively disposed between the sheath 6 and the screen 7 and between the sheath 6' and the screen 7 ', parallel to the quads 4. Finally, the two groups 5 and 5' isolated and shielded quads are joined side by side in a protective outer casing 9 and PVC, extruded around the assembly The casing 9 gives the cable 1 a "flat" structure, that is to say that the cable 1 has a section of eight very flattened, with four flats 91, 92, 9335 and 94 and two rounded sides 95 and 96 The length of this section in the plane of Figure 2 is 18.3 mm ( 5%), and its height of 5.7 mm (5%). In order to facilitate the stripping of the conductors 3 of the cable 1, in particular with a view to connecting the latter to another cable or to any device, the sheaths 6 and 6 'may be incised longitudinally (see FIG. 2), as shown in FIG. 10 'In addition, the material

  6 and 6 'are chosen so as not to adhere to the material constituting the sleeves 4 of the conductors 3, always in order to facilitate the stripping of the latter.

  The cable 1 according to the invention can in particular be used in the computer field to connect the

  different peripherals of a computer to the central unit15 of the latter for example.

  A table is given below in which the characteristic impedance Z (in Ohms) has been reported,

  the linear attenuation A (in d B / km) and the crosstalk P (in d B) of the cable 1 as a function of the frequency of use f (in M Hz).

f (M Hz) Z (Ohm) A (d B / km) P (d B)

0.772 125 + 15% 67

1 123 + 15% 18 65

4 120 + 15% 30 60

8 120 + 15% 41 58

120 + 15% 45 55

16 120 + 15% 54 52

120 + 15% 59 50

120 + 15% 67 48

31.25 120 + 15% 75 45

62.5 120 + 15% 110 40

120 + 15% 140 35

  Due to the constitution of sheaths 6 and 6 ', the values given, which are those observed on the cable,

  correspond to those provided, that is to say that the installation of sheaths 6 and 6 'did not cause variation of these values, contrary to what was observed in the prior art.

  Of course, the invention is not limited to the embodiment just described.

  In the first place, the material constituting sheaths 6 and 6 'can be chosen from low or medium density polyethylenes, polyolefins, polypropylenes, elastomeric thermoplastics or fluorinated resins. On the other hand, the cable made according to the invention may be a cable comprising only a pair of isolated conductors arranged side by side. More generally, a cable according to the invention may comprise at least two conductors or sets of conductors (pairs , fourths,) intended to be arranged and held side by side so that the section of the cable has for example a flattened shape of eight or

oval flattened.

  A cable according to the invention does not necessarily have a dual structure (i.e. a structure divided in two

  groups as described above) and flat or flattened, and is not necessarily intended for use in the computer field It can be used for example in telephony.

  Finally, we can replace any means by a means

  equivalent without departing from the scope of the invention.

Claims (4)

  1 / High frequency signal transmission cable comprising at least two conductors or sets of conductors (5, 5 '), each of said conductors (3) being insulated by a first insulating sheath (4), said conductors or sets of conductors being inside a second sheath made of an insulating material surrounded by a metal screen (7, 7 ') itself protected by an outer casing (9), characterized in that said second sheath (6, 6') consists of a thin envelope made of a material chosen from low or medium density polyethylenes, polyolefins, polypropylenes, thermoplastic elastomers and fluorinated resins, said envelope surrounding said conductors or sets of conductors (5, 5 ') without these are embedded in the sheath (6, 6 ') that it constitutes.   2 / Cable according to claim 1 characterized in that said outer casing (9) is made of a material chosen from PVC, polyethylene, polypropylene or polypropylene.   polyurethane. 3 / Cable according to one of claims 1 or 2 characterized in that said sets of conductors (5, 5 ') are   pairs or quads (2) of twisted conductors (3).   4 / Cable according to one of claims 1 to 3 characterized in that it comprises four quads (2) of conductors (3),   said quads (2) being grouped two by two so that each set (5, 5 ') of two quads (2) is inside a second separate sheath (6, 6') and said second sheaths (6, 6 ') are both surrounded by a metal screen (7, 7'), said outer casing (9) being arranged around the two sets (5, 5 ') of two quads placed side by side so that said cable (1) has a   flattened eight-shaped section having substantially two opposite flats joined together by two rounded sides.   Cable according to one of Claims 1 to 4, characterized in that a screen continuity wire (8, 8 ') is installed   parallel to said conductors between said second sheath (6, 6 ') and said screen (7, 7'). 5 / cable according to one of claims 1 to 5 characterized in that said second sheath (6, 6 ') is slotted   longitudinally (10 ') over all or part of its length. 7 / Cable according to one of claims 1 to 6 characterized in that said second sheath (6, 6 ') is extruded around   said conductors or sets of conductors to form a thin envelope around them.   8 / Cable according to one of claims 1 to 7 characterized in that said outer casing (9) is made of a material   insulation and is extruded around said second sheath 15 9 / Cable according to one of claims 1 to 8 characterized in that the material constituting said second sheath (6, 6 ').   does not adhere to the material constituting said first sheath (4).