DE1041120B - Method for keeping diameter changes of the outer conductor of coaxial cables small when bended - Google Patents

Description

The invention relates to a method for keeping the size that occurs when bending coaxial cables relative changes in the effective diameter of the outer conductor.

It is known to make coaxial cables flexible in that their outer conductors have ribs or grooves is provided. It is also known that in order to achieve a specific characteristic for the desired characteristic impedance required effective diameter when determining the diameter of the Outer conductor cylinder the expanding or narrowing influence of the ribs or grooves is taken into account.

When the cable is bent, the ribs or grooves are deformed on the outside of the cable arch widened and narrowed accordingly on the inside of the arch. This deformation should disappear again when the cable is bent straight. But it has been shown that the ribs and Grooves retain permanent deformations, so that the effective diameter of the outer conductor is opposite the new condition of the cable and thus also its wave resistance has changed. Because in general Such permanent deformations are unevenly distributed over the cable lengths, such are suitable Cables are not used for purposes that require a great deal of longitudinal uniformity. One uses therefore z. B. for television cables, where double and multiple reflections at small wave impedance irregularities can lead to significant image disturbances (ghosting), smooth Outer ladders without grooves and ribs. Such cables are relatively stiff and subject to excessive bending stress the outer conductor, which in this embodiment does not support the flexibility Contains imprints, buckle spontaneously.

The relative changes in the effective diameter D of coaxial cable outer conductors with embossed transverse ribs or grooves can be kept sufficiently small by the method according to the present invention. The method is characterized in that the rib or groove depth, width and spacing are selected so that the relative change

of the effective diameter —- = - the relationship

JD

d ~

2-n-t-b d

3.5

is sufficient, where η is the number of ribs per m, t is the effective rib depth in mm, e.g. B. with a semicircular rib shape 0.75 X maximum depth, b is the rib width in mm, d is the inner diameter of the cylindrical conductor part in mm.

Using a numerical example and the curve shown in the drawing, the inventive method to keep it small

of changes in the diameter of the

Outer conductor of coaxial cables

at bends

Applicant:

Telefunken GmbH,
Berlin NW 87, Sickingenstr. 71

Dr. phil. Lothar Krügel, Nuremberg,
has been named as the inventor

thought to be explained. A cable with a clear diameter of the outer conductor of d = 9.5 mm contains rib or groove-shaped embossments with a width of b = 0.8 mm and an effective depth of t = 0.2 mm. If, in this cable, the number of impressions per m, indicated by η , or the mutual spacing of the impressions in mm, indicated by α, is varied, the relative change in the effective diameter changes according to the curve shown. It can be seen that with a large distance between the ribs, that is to say with a small number of impressions per m, the curve is flat (right), whereas with a small distance it is steep (left). The curve breaks off for a very small distance between the indentations, since the distance here is of the order of magnitude of the rib width. The shape of the curve is retained if the width and / or depth of the embossments is varied instead of the distance between them.

When the cable is bent, the ribs or grooves are now deformed, as shown above, and thus the relative diameter changed. If such a bend occurs in a cable with a depth The width and spacing of the embossing are chosen so that

that - = - lies on the left, steep part of the curve, so is due to the deformation of the imprints

when bending, too

AD

according to the steep

Change the course of the curve relatively strongly, and since the changes are mostly localized, Differences in wave resistance occur along the cable. On the other hand, the dimensions are about the number

AD

of the imprints chosen so that

on the

right, flat part of the curve is like this

809 658/303

only small changes in the effective diameter occur when the cable is bent. According to the Invention are intended to measure the dimensions of the embossments

be chosen so that --j- <Ξ 3.5.

It is known per se, tubular conductors with a cross section deviating from the circular shape, as they are for Dielectric tubular cables are used to transmit magnetic hollow waves, such at intervals to be provided with Ouerrillen that the attenuation of the cable is only slightly increased by the grooves.

In contrast, the method according to the invention is not concerned with keeping the attenuation small, but with keeping changes in the effective diameter of the outer conductor of coaxial cables small in the event of bends. By embossing ribs or grooves in the outer conductor of coaxial cables, an increase in attenuation occurs in principle due to the lengthening of the current paths, which can easily be calculated from the size of the detour, but is retained when the cable is bent. If one considers the extension of the current path represented by the ribs discussed in the example given above, and if one assumes that the impressions are roughly in the form of flat circular arcs with a chord length of i) = 0.8 mm and a height of t = 0.2 mm, one finds that the current through each indentation has to travel a distance that is about 15% longer than that of the tendon. Since the meter of cable may contain a maximum of 100 impressions in the rib dimensions selected in the example, and the mutual distance between the ribs may be a minimum of 10 mm in order to achieve the A-effect of the method according to the invention, the extension through the ribs converted to the meter is only 1, 2%. If you consider λνεϊΐεΓ that about 70% of the attenuation of a coaxial cable is caused by the resistance of the inner conductor, while the resistance of the outer conductor only accounts for about 30% of the attenuation, the indentations mean an increase in attenuation of the entire cable by less than 0.5%, a value that is practically impossible to measure and z. B. in a cable made of copper by a temperature increase of a good 1 ° C is also caused.

In the case of a cable, which contrary to the teaching of the invention per m with 200 impressions of the above If the rib dimensions were selected for the example, this would result in an otherwise identical rib shape an increase in attenuation of about 1%. a value that is also not taken into account in practice would be set.

If both cables are bent, the size of the increase in attenuation is retained. Against this is The last-mentioned cable with 200 ribs per m shows the relative change in the effective diameter greater than 3.5, so that dangerous wave resistance differences can occur, while in the inventive Cable with a maximum of about 100 ribs

per m ~ j— changes so little that the

Cb

no longer disturb possible wave resistance differences.

Claims (1)

Claim: A method for keeping the relative changes in the effective diameter of the outer conductor of coaxial cables occurring during bends small, in which the outer conductor is made up of one or more longitudinally bent strips which are provided with transverse ribs or grooves, characterized in that ribs or grooves. Groove depth, width and spacing are chosen so that the relative change in the effective AD Diameter —- ^ - the relationship JD 2-n-t-b ^ 3.5 is sufficient, where η is the number of ribs per m, t is the effective rib depth in mm, b is the rib width in mm, d is the inner diameter of the cylindrical conductor part in mm. Considered publications:
German patent specification No. 885 738. 1 sheet of drawings © 809 658/303 10.58