JPS5911163B2 - shielded cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to coaxial and other shielded cables.

As is well known, coaxial cables with two or more braided wire screens as outer conductors surrounding a dielectric have better high frequency shielding properties than coaxial cables with only one braided wire screen, i.e. It has good unrelated frequency shielding characteristics.

Moreover, it is also known that inserting a layer of magnetic material between those braided wire screens 5 improves their radio frequency shielding properties. The degree to which the radio frequency shielding properties are improved is a function of the magnetic permeability and thickness of the magnetic material used and the effective air gap in the magnetic path provided by the magnetic material. Of course, it is important that the addition of magnetic material does not significantly inhibit the inherent cable flexibility of the cable construction, and therefore it is important that the addition of magnetic material does not significantly inhibit the flexibility of the cable inherent in the cable construction, and therefore Fifteen magnetic materials were actually used.

It has been found that the manner in which the tape layer is applied can have a significant impact on the mechanical and electrical properties of the finished cable. For example, if you wrap magnetic tape 20 times with the side edges of the tape butted between turns (to minimize air gaps), the tape will tend to twist when the cable is bent. thus resulting in a deterioration of mechanical and magnetic properties. This drawback can be eliminated by winding the tape with gaps between successive turns, which create larger air gaps than 25 butt turns, but this first layer of tape The second tape layer may be applied in a different relationship to the tape layer. Yet another construction example, which is directly related to the present invention, is one in which 30 wraps of tape are wrapped with considerable overlap to minimize voids. Under these conditions, the rear edge of the tape should be stretched by an amount proportional to the thickness of the tape.
Continuous winding operations must be possible without increasing diameter. Difficulties 35 arise in winding the tape in this manner. That is, annealing (
If an annealed tape is wound with such high tension that it is stretched beyond its elastic limit, the edges of the tape will stretch unless the tension is very carefully controlled. The trailing edge of the tape being applied to the cable must be wrapped onto the cable with an increased radius equal to the overlap thickness of the immediately preceding tape, so that the trailing edge is slightly more stretched than the leading edge. . Unfortunately, this stretching cools the magnetic properties and creates a cable that is somewhat stiff due to the tight constraint it creates. According to the invention, a shielded cable includes a braid of wires and a continuous longitudinal flexible metal wire surrounding this braid without applying radial stress to the underlying wire braid. have.

The absence of radial pressure is favorable, as evidenced by the presence of a small annular gap between the metal tube and the underlying braid. Preferably, the metal tube is formed by wrapping a metal tape inside a rotating tubular die in a series of overlapping helical turns. When the rotating tubular die is wound with a metal tape to form a flexible metal tube, the inner portion of the cable, e.g., at least one portion covered with insulation and one or more wire braids, is
It may also include the dielectric material of the book.

Additionally, there may be no conductive portion of the screen within the die during such a tape winding process. If desired, a flexible metal tube formed by overlapping turns of helical tape may be formed in a die to allow later insertion of the inner portion of the cable. In any case, the "tube" of the tape increases in diameter during overlap until it comes into contact with the inner surface of the tubular die and can no longer grow in size. The trailing edge of the tape compresses the leading edge of the preceding turn of tape inwardly, creating a swage effect that causes significant damage to the trailing edge of the tape being applied. This is achieved without significant stretching.
Thus, said table comprises at least one electrical conductor electrically insulated from the surrounding wire braid and a metal tape wound in the form of a flexible metal tube located over said wire braid. is a shielded cable in which each turn of the tape layer overlaps the immediately preceding turn by a significant amount, but is wound so that it does not exert any confining pressure on the wire braid, so that the magnetic properties of the tape are not degraded. is provided. The finished cable has one or more electrical conductors electrically insulated from the outer shield and covered entirely by a protective jacket, the outer shield preferably having a first conductive braid. It consists of a screen of wire, a magnetic layer created by a single helix of magnetic tape, and a screen portion of a second conductive braided wire, with the single helix of tape underneath. No confining pressure is applied onto certain first braided wire screen sections.

Additional magnetic layers and braided wire screens may be provided. In either case, the magnetic tape layers are preferably applied in a continuous overlapping manner and with an inner diameter larger than the braided wire screen immediately below. Although this tape layer is not actually air insulated from the first braided wire screen and is separated during manufacturing, the tape layers are spaced apart along the length of the screen. You will find that it comes into contact with. It is important to avoid stretching the magnetic tape during winding, and care must be taken to ensure that the magnetic tape layer is not unduly stressed when applying overlapping layers of braiding or protective coatings. It is.

Otherwise, even careful application of the magnetic tape layer would be of no use. Also important is the flexibility to allow the shielded cable to bend at a small radius without degrading the magnetic properties of the screen. In the case of a screen wrapped around a table, 50 and 8
It is desirable to maintain the tape feed angle between 5° and 60°, preferably between 60° and 80°. The method of applying the helically wound tape layer described above is such that the underlapping edge of the tape turn is pushed radially by the tape tension exerting a restraining pressure against the underlying wire braid. not,
``The edges are radially pressed by the inner surface of the die, so that the gap formed under the tape layer can be easily bent without stressing the layer.

The shielded cable of the present invention is constructed by passing a magnetic metal tape through a limited length axial slot in a rotating tubular die through which the cable is axially threaded.
applying a first magnetic tape layer over the conductive wire braid;
This tape is wound over the cable in a plurality of partially overlapping helical turns, and the overlapping edges of the tape are stretched very lightly and passed through a die section leading from the axial slot. by maintaining a substantially uniform diameter of the wound tape. Preferably, a special winding head and die combination is provided for winding the tape into layers as described above.

Primarily, the combination includes a tubular body having an end portion for engaging the rotating head and a free end portion. A tape supply and a tape guide are located between these two portions of the tape supply to feed the tape into a slot of limited axial length in the free end portion. The slot is fan-shaped and is cut so that one surface is tangential to the hole in the tube and the other surface is radial, and the slot is cut in a plane that intersects the tangential surface in the hole of the tubular die. positioned. This causes the tape to be inserted into the slot along the perforation plane and wrapped around the hole in the die. For the size of the holes in the tubular die, measure the outside diameter of the unfinished cable that is going to be screened by tape;
Add this dimension to 4 times the tape thickness plus a fraction of a millimeter for the air gap (air gap between the tape and the underlying braid).
is determined by adding the sum of This void is 0
．． 1m1t and 0.4mm, typically
．． 2mm is selected. A die for applying a screen to a coaxial cable has a tubular body with an aperture substantially equal to the diameter of the screened cable, an elongated fan-shaped slot in the tubular body, and a slot in the die. It has a leading surface that is substantially tangential to the hole and a trailing surface that is substantially radial to the hole in the die, the tangential surface and the radial surface being in contact with the leading surface and the trailing surface with respect to the direction of rotation of the die. It is the posterior aspect.

Furthermore, a carrier device is provided which is rotatable with the die and which supports the supply of screen tape and which is arranged in a plane substantially parallel to the tangential plane or at a slight angle to the tangential plane. The tape is guided into the hole of the die along the plane formed. In order that the present invention may be better understood, preferred structures and methods will now be described with reference to the drawings. Referring to FIG. 1, the cable of the invention in the illustrated form has an internal electrical conductor 1 which is covered by a layer of insulation 2 of plastic material and has a shield. The shield comprises a coaxial layer of wire braid 3 and a layer 4 of superimposed helical turns of conductive metal tape, with layer 4 forming an air gap 7 therebelow. The wrapped tape layer 4 effectively forms a longitudinally flexible metal tube, without exerting significant restraining pressure on the underlying wire braid when wrapped around the unfinished cable. is wound around.

The effect of this new method of application in making the new cable can be seen from FIGS. 2 and 3.

FIG. 2 shows how the tape layer 4a is compressed because in conventional application methods each turn exerts a strong confining pressure on the underlying braid 3a resulting in a very tight contact between the tape layer 4a and the braid. Indicates whether it is undergoing significant stretching. In contrast, FIG. 3 shows that in the cable of the present invention, the tape layer 4 is applied without significant stretching and without applying confining pressure to the underlying braid 3, so that the tape layer 4 and the braid 3
This shows that a gap 7 is left between the two. The air gap 7 is shown exaggerated in the drawing, but this is caused by the absence of confining pressure. This results in a separate construction sequence according to the invention, in which the layer 4 is formed as a longitudinal flexible tube without conductive parts of the screen inside it.
FIG. 3 shows just one example, in which the layer 4 is in the form of a longitudinally flexible conductive metal tube.

Furthermore, the shield comprises a second screen 5, which also consists of a wire braid to which a tape layer 4VC has been applied. The screen 5 is placed in an outer non-conductive power bar 6. This cable is designed for high frequencies, in which the inner conductor forms the first conductor;
The braid and tape wrap layer 4 forms the second electrical conductor.
Layer 4 is applied to the cable after insulation 2 and inner wire braid 3 have been applied to inner conductor 1. Figures 4 and 5
As shown, the cable is fed axially through the bore of the tubular rotating die 10.

The die 10 has a rearwardly extending handle 11 which is adapted to be placed in a chuck such that by rotating the chuck the entire die can be rotated relative to the cable. The forwardly extending part 12 of the die has holes 12a of a diameter equal to the desired diameter of the screen to be applied with the air gap 7. Portion 12 has one quadrant cut away to form a sector-shaped slot 13 of limited axial length. This slot has a leading surface 13a in a plane tangential to the bore 12a and a trailing surface 13b in a radial plane, the surface 13b intersecting the tangential plane as described above. Here, the terms "leading plane" and "tracing plane" refer to the direction of rotation of the die, and the terms "radial direction" and "tangential direction" refer to the hole in the die. A subur 14 supporting the metal tape for layer 4 is mounted between flanges 14a on die 10 and rotates therewith. The metal tape is made of Mumetal, an alloy with high magnetic permeability, and its width is adapted to the diameter of the cable to which it is applied. Although the tape is conventionally annealed and can be stretched without breaking for practical general handling purposes, this property is rarely exploited. Not done. The bent portion 8 of the tape is pulled out from the drum;
Information bar 15VC. Therefore, it is guided in a plane that is substantially parallel to or coincides with a plane that includes the tangential plane 13a of the slot 13. The tape is guided into the slot 13 and wrapped around the unfinished cable located in the hole of the die. Of course, some tension must be applied to the tape, but this tension is only that necessary to ensure continuous smooth feeding of the tape and to press against the leading edge 1 of the previous turn. is insufficient. This tension is
It is made adjustable by a tensioning device. This tension device is 1
The nut 16 is located between the two flanges 14a and the nut 17, and the axial position of the nut 17 with respect to the flange 14a can be adjusted by screwing into the threaded portion of the body of the die. The guide bar 15 is supported by an arm 18 extending radially from the spool.

The angular position of the guide bar relative to the axis of the die can be adjusted in rotation by means of a thumbscrew connection 19. In operation, the die is fixed in the chuck of a suitable rotary head, and the cable to be screened is fed from the back of the chuck through the hole in the die and exits through the open-ended front section 12.

The tape for layer 4 is withdrawn from spool 14 and passes over guide bar 15 into die slot 13.
The tape has a leading surface 1 in the tangential direction as shown in FIG.
Approach 3a and enter the slot. The tape is given a first turn around the cable into frictional engagement with the braid 3, and once rotation of the die begins, the cable is pulled through the die at a constant speed without rotation. When the tape 4 leaves the leading surface (or in close proximity to the leading surface) of the slot 13 and enters the hole in the die body, this is defined where the wall of the hole in the die intersects the trailing surface 13bVC of the slot. Contact the other edge 20 of the slot. Edge 20 thus exerts radially inward pressure on the tape, so that
The overlapping edges of the tape press the edges of the lower turns of tape radially inward toward the screen of braided wire, leaving a small annular gap. Thus, as shown in FIG. 3, the tape material can be processed without undue cold working.
Partially overlapping helical turns are thus created while preserving their magnetic properties. The pitch of the helical layers of tape is preferably such that there is an overlap of about 25q6.
Adjustment is made by adjusting the speed at which the cable is drawn through the die. Because of the shape of the die, and because the die and tape supply rotate as a unit, the pressure exerted on each turn of the tape is the radial force exerted by the die through the overlap of the next sequential turn. Only inward pressure results in the upper winding portion 21 of each turn.
When applied, this part 21 becomes the lower winding part 22 (
Figure 3) is compressed.

At the same time, the diameter of the cable that comes out is equal to the diameter of the hole in the part 12 of the die, so that a cable of the correct size comes out. Additionally, the cable has tape layers applied with a small air gap. The tab enters the slot at an angle of approximately 70 layers to the axis of the die. In other words, this method reduces deformation of the tape that would degrade its magnetic properties.

When the upper wound portion of the tape engages the lower portion, the deformation necessary to produce a uniform diameter is divided into upper and lower layers, but unevenly.

The lower layer is compressed radially inward to a greater extent than the upper layer is stretched. The cable construction is completed by adding yet another braided wire screen and applying an external jacket thereon.

Both of the braided wire screens together with the intervening tape constitute the outer conductor.

To improve the screen, further magnetic tapes and braided wire screens can be applied as well, in which case the three braided wire screens and the two intermediate magnetic tapes constitute the outer conductor. To test the effectiveness of the invention, we compared the transfer impedance of cable A screened with a tape wound according to the invention and with a tape wound with conventional equipment. A comparative test was conducted to compare the transfer impedance of the cable 6 provided with a screen.

The same test was carried out on cable A. designed to produce maximum cooling of the shield in terms of transfer impedance. It was given to both B.

Transfer impedance is a property of all shielding circuits and is generally defined as the voltage present in the shielding circuit divided by the current flowing through the shielding body. As is known, in order to have sufficient radio frequency shielding properties, a cable shield must have a low transfer impedance from the beginning and be able to maintain this low transfer impedance over time. Must be. The test selected here was a test in which a shielded cable was subjected to cold working and changes in its transfer impedance were sequentially monitored.

This process consisted of winding each cable onto a 50 mm diameter mandrel, unwinding it again, and repeating this process. For each direction of bend, the cable was reversed. In FIG. 5, the number of times the cable is wound onto the mandrel and unwound again is scaled along the horizontal axis, and the transfer impedance at 100 K pressure (ZmΩ/m) is scaled along the vertical axis.

Both are logarithmic scales. Transfer impedance was measured. In each case, the cable was removed and straightened to make measurements. After the measurement, the cable was wound again, but in the opposite direction. This graph shows that not only did cable A of the present invention initially have a lower transfer impedance than cable B, but also that the magnetic properties of the metal screen of cable B degraded more rapidly than cable A. It is shown that. In fact, as a result of repeated bending in opposite directions, the change in transfer impedance of cable A was extremely small. As is known, a low transfer impedance characterizes good radio frequency shielding properties. Although the above examples relate to coaxial cables, the invention is equally applicable to triaxial or twin-type cables, and to cables with multiple conductors within the same outer protective cover.

Additionally, a method of forming a flexible tube selected by way of example includes wrapping the inner surface of a tubular die through which the cable is threaded, the tube being a cable internal element inserted into the flexible tube. may be created separately. In this case, the tape layer is wound onto a removable mandrel, which is then removed and a cable inner element inserted in its place.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a cable embodying the invention, in this example the cable is a coaxial cable. FIG. 2 shows a conventional method of applying a wound tape screen. FIG. 3 shows a method comparable to FIG. 2 for applying a rolled tape screen according to the invention. Figures 4 and 5 are side and end views, respectively, of a winding device for applying a winding tape screen to a cable. FIG. 5a is an enlarged view of a portion of FIG. 4 viewed in the direction of arrow A. FIG. 6 is a graph showing changes in transfer impedance when an equivalent cable is repeatedly bent. 1... Internal conductor, 2... Insulator, 3
, 3a... wire braid, 4, 4a... tape layer, 5
...Second screen (wire braid), 6...Cover 7...Gap, 8...Bending portion, 10...Dice 11...Handle, 12...Portion extending forward ,1
2a... Hole, 13... Slot, 13a... Leading surface, 13b... Trailing surface, 14... Spool, 14a
...Flange, 15...Guide bar, 16...Spring, 17...Nut, 18...Arm, 19...
... Connecting portion, 20... Edge, 21... Lower turn portion, 22... Upper turn portion.

Claims (1)

[Claims] 1 at least one inner conductor electrically insulated from the surrounding wire braid; a longitudinal flexible metal tube surrounding said wire braid leaving an annular gap therebetween; and another wire braid covering a gold-enhanced tube, wherein the flexible metal tube is made of a continuous magnetic tape wound in a helical manner so as to partially overlap.