DE2306995A1 - PROCEDURE FOR ADJUSTING THE WAVE RESISTANCE OF COAXIAL CABLES - Google Patents

Description

DR. MÜLLER-BORE DJPL-PHYS. DR. MANITZ DIPL-CHEM. DR. DEUFEL DlPL-ING. FINSTERWALD DlPL-ING. GRÄMKOW 2306995

PATENT LAWYERS

Munich, the ti FEB. 1973 Ks / Sö - N 11OQ

HORTHEHN ELECTRIC COMPANY, LIMITED 1600 Dorchester, Boulevard West, Montreal, Que., Canada

Procedure for setting the wave resistance of

Coaxial cables

The invention relates to a method for adjusting the wave resistance of coaxial cables and specifically relates to a method of reducing the characteristic impedance of an insulating washer Set coaxial cable during manufacture.

Jjie fluctuations between the minimum and the maximum value of the characteristic impedance Z of a coaxial cable are generally limited to about 1 fo ; for a coaxial cable with a characteristic impedance of the nominal value (nominal characteristic impedance) 75 ohms, the design tolerance is +0.5 ohm, for example. i) This represents the absolute limits for the wave resistance of the cable, but nowadays even tighter tolerances are often necessary in order to achieve an optimal wave impedance adjustment between joined cables and thus to keep the reflections small, which can be very disruptive when they are not extremely

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be kept weak. In the case of a cable with a nominal characteristic impedance of 75 ohms, an actual tolerance of around +0.2 ohms is therefore preferable, while remaining completely within the tolerance of 75 +0.5 ohms.

With the known manufacturing processes, it is not possible to Control wave impedance with the required degree of accuracy. "

Up to now, the wave resistance was usually checked empirically according to the so-called "trial and error method", i.e. a length of cable was made and immediately tested for its wave impedance. Corrections were made by changing the dimensions either the inner conductor or the outer conductor of the next cable length to be produced. This procedure is both time consuming as well as very costly, because you have to wait before making the next cable length until the necessary adjustments, for example, the replacement of the die for the fine pulling of the inner conductor have been made. In addition, so far have been common further readjustments are necessary for several consecutive cable lengths before the value of the characteristic impedance is within was within the prescribed tolerance.

The present invention is based on the knowledge that the wave resistance a coaxial cable provided with disk-shaped insulating holders can be influenced by the distance between adjacent insulating washers on the inner conductor changed. The invention thus provides a practical method for permanent Checking the wave resistance of a coaxial cable during its Manufactured by changing the distance between the insulating washers on the inner conductor. This is done either by changing those Speed at which the slices are fed to an inner conductor, which is fed at a constant feed rate to a slice

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application station passes, or by changing the feed speed of the inner conductor with constant application speed of the discs.

To explain the invention, the following is based on drawings a method for arranging the panes at a certain distance is described.

FIG. 1 shows a longitudinal section through a typical coaxial cable with insulating washers;

FIG. 2 schematically shows part of a device for applying the insulating disks to an inner conductor.

The coaxial cable 10 shown in FIG. 1 consists of an inner conductor 12, the coaxial inner halo of a tubular outer conductor 14 by means of Thinner insulating washers 16 is held at intervals one behind the other sit on the inner conductor 12. Usually there is such a thing Inner and outer conductor made of copper, but the outer conductor can also consist of a combination of copper and steel. That the preferred material for the insulating washers Io is polyethylene.

The characteristic impedance Z of the cable shown in FIG. 1 is a function of the inner diameter (D) of the outer conductor 14, the outer diameter (d) of the inner conductor 12 and the effective dielectric constant (S) of the insulation. It has been found that the effective dielectric constant of the insulation depends on the distance between the disks 16 and the inner conductor 12, so that the characteristic impedance Z of the cable is also influenced by this distance, ο

The relationship found between the wave resistance Z and the distance between the disks is as follows, using FIG. 1 derive mathematically:

The change in the wave resistance Z _n with the spacing L

j »O

can be expressed as - ^ e and is:

dL

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double room άϊΓ

ο =

dL

(D

where d £ = effective dielectric constant of the mixed dielectric

kums polyethylene - air in a coaxial cable with insulating washers.

The relationship between the "effective". Dielectric constant
g and the dielectric constant £ of the polyethylene alone is:

£ _e = i + | (ε-ι)

with t = slice thickness. From equation (2) it follows:

d £

dT

e =

d F ^{1 +} *

Sl L l

(2)

and after differentiation of this equation one obtains:

Ife = - (f-1) tL ~ ² dL

The standard formula for the wave impedance Z is:

rj __

log.

10

with D = inner diameter of the outer conductor d 5s outer diameter of the inner conductor.

(3)

(4)

From this it follows

dZ

0 = β

138

log.

10

fs)

Equation (5) differentiated results in: ^ o = 138 log ₁₀

D d

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(5)

(6) - 5

Substituting equations (3) and (6) into equation (1), we get man:

• ζ / ο ο

dZ _ 69

dL "

With equation (7), the characteristic impedance is in ohms per unit of distance expressed by the known parameters of the cable.

Take a 0.375 coaxial cable with insulating washers as an example, in which

D = 3.75 t = 0.085 inch = 2.159 mm ^d L = 1.0 inch = 25.4 mm

6 _e = 1.095

ε = 2.28
The solution to equation (7) is then:

f ^ o = 3.73 ohm / inch * 1.47 ohm / cm dL

or in other words:

dZ = 3.73 x dL 0hm (with dL in inches)

O / Q \

= 1.47 x dL Ohm (with dL in cm) ^KJ

For example, if the distance between the slices is changed by $ 5, then is

dL = 0.05 inch = 0.127 cm

dZ = 3.73 x 0.05 or 1.47 x 0.127

dZ _Q = 0.1865 ohm

From equation (8) it can be seen that in the case of a high wave resistance of a cable length, a reduction in the distance between the panes to one Reduction of the wave resistance leads and that on the other hand

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with a low wave resistance an increase in the distance between the panes leads to an increase in the wave resistance.

In Figure 2 a part of a device is shown, with --which Insulating washers can be applied to a conductor. A full description of this device can be found in U.S. Patent 3,634,606 entitled "Method of and Apparatus for Applying Insulating Discs to Conductors," which issued Jan. 11, 1972 was issued. This disc applicator is with the coupled to the linear feed rate of the conductor, so that the panes are applied with an even and predetermined spacing The distance between the panes can be adjusted with such a device change by increasing or decreasing the feed rate of the conductor, while the speed, with which the discs are applied to the conductor, constant holds. Another possibility is to increase or decrease the frequency or speed of the slice feed, while the feed rate of the conductor remains constant. Although both possibilities are feasible, in the present If the latter is preferred in order to obtain constant production speeds.

Located in the disk application device shown in FIG two application wheels 18 and 18 on both sides of a conductor 19, which moves forward at a constant speed. Every application wheel is provided with several retaining teeth 20 or 2Q ^, which in uniform Are arranged spaced around the edge of the wheel and feed individual slotted disks 16 onto the inner conductor 12. The slotted disks 16 can be supplied by a suitable feed device be brought up, for example as they are in the U.S. Patent No. 3,634,6o6 referred to above. the Application wheels rotate at the same peripheral speed V and are synchronized so that the disks 16 always alternate sit on the ladder 12.

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The device is designed for a nominal speed at which the peripheral speed of the application wheels is equal to the feed speed of the conductor 12. This and the diameter of the wheels determine the number of retaining teeth 20 and 20, which are used to apply disks to the conductor 12 at the nominal distance are necessary. To implement the present invention, such a device can be provided with a variable speed drive, with. which the speed of the application wheels to change the Seheiben distance on the conductor 12 can be varied.

Such an arrangement is a simple means of adjusting the Characteristic impedance of a coaxial cable constructed with insulating washers, with excessive downtimes of the cable manufacturing machine can be avoided, as was previously necessary for changing or replacing parts. A first cable length can produced and examined for their wave resistance. In the meantime, the production of a further length of cable can begin. As soon as you have determined from the first cable length that a change in the wave impedance is necessary, during the production of the second cable length a corresponding change in the pulley spacing can be brought about by simply changing the peripheral speed the application wheels are adjusted.

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Claims (4)

Claims 1. Procedure for adjusting the wave impedance of an insulating washer built-up coaxial cable during the manufacture of the cable, characterized in that a) an elongated conductor (12) - at a disc application station (18, 1β ', · 20, 2θ') is moved past; b) that at this station washers (16) -placed on the conductor will; c) and that the application speed of the disks relative to Feed rate of the conductor is changed to the distance between successive slices on the conductor to change. 2. The method according to claim 1, characterized in that the change of the distance between successive disks (16) the speed at which the disks are changed can be applied to the conductor (12) advancing at a constant linear feed rate. " 3. The method according to claim 1, characterized in that the characteristic impedance of a finished cable length is measured and that the distance between successive disks (16) required to correct the wave resistance is determined - is, and that the speed of application of the disks for transfer this change is adjusted to the following cable lengths. 4. The method according to claim 3 * characterized in that the relationship between the wave resistance and the distance between the panes from the following Formula is won? 309834/0898 69 log ₁₀ / D (i.e. where dZ is the change in characteristic impedance and dL is the change in the distance between the pulleys and where D, d, £ , E, t and L are known parameters of a given cable. 309834/0895 Blank page