CS274064B1 - Coaxial cable for car aerials - Google Patents

Abstract

Improvement of the construction of coaxial cable for automobile antennas that enables to achieve the minimum working electrical capacity, which conditions achieving minimum interference of a car engine with AM and FM radio signals. The principle of the solution consists in double-layer insulation coating of the core /1/ made of metal wire. The first layer /2/ is made of full non-polar plastic insulation with hardness above 50 Shore and the second layer /3/ applied on the first layer /2/ is made of expanded polyethylene with relative electric permittivity epsilon /r/ < 1.6. The thickness of the full insulation layer /2/ in relation to the minimum semi-diameter of the coaxial cable bending corresponds to the following condition: d1>= 3d./D1/d0/,where d1 is the diameter above the full insulation, d is the diameter above the inner core, D1 is the resulting diameter above the insulation and d0 is minimum semi-diameter of the coaxial cable bending and of an insulation layer of expanded polyethylene applied on it, with a relative electrical permittivity epsilon /r/ < 1.6.<IMAGE>

Description

The invention relates to an improvement in the construction of high-frequency coaxial cables used to transmit AM and FM radio signals from car antennas to car radios. The purpose of the invention is to achieve the smallest tram service capacity, a low value of which is of great importance in order to minimize the impact of determining motor reception as well as saving media in the production of these cables.

The construction of known coaxial cable solutions for autoanthenes, which are intended to have as little electrical operating capacity as possible for their use, is based on various variations of the attachment of the very thin core forming inner core in the center of the coaxial cable. The outer insulation consists of a thin-walled hard plastic tube, in which the wire must be crimped in order to avoid ripple or tooth spacing on the wire at the electrical length of the transmitted signal. Functionally, the wire can then be considered to be axially guided. Another way of centering the wire is to place it in the insulation in the form of various beams, most often a star cross-section, which results in a low relative electrical permittivity along with the required cable flexibility. The transmission part of the cable is enclosed by the outer core, in which case braiding by wires. In other types of coaxial cable design over auto-antennas, foam insulation of low relative electrical permittivity is applied to the inner core, using which it is also possible to achieve a low value of operational electrical capacity.

Cylindrical polyethylene foam insulation ensures high cable homogeneity at low electrical relative permittivity, resulting in the required low electrical operating capacity, but a thin steel wire cuts at very low bends and in some cases conductively shortens the inner and outer core of the coaxial cable. A significant disadvantage that exists with existing solutions is the relatively high labor intensity 'and low productivity of their production. In addition, the corrugated or serrated wires impart unwanted inhomogeneities in the cables, which are more pronounced especially in the transmission of very short waves. Signal reflections from impedance changes along the cable reduce the gain from the antenna dipole on the car. A further disadvantage is that for insulation that does not have a cylindrical surface, e.g. in various beam construction solutions, a new way of manufacturing outer cores by coating metallized plastic foils and contact wires cannot be applied. The use of an outer core of wire braid not only achieves higher production productivity, but also a substantial higher cable shielding efficiency at increasing levels of electromagnetic interference.

The above-mentioned disadvantages of the prior art are eliminated by the solution according to the invention, which consists in that the core insulation consists of two layers, namely a layer of full nonpolar plastic insulation of hardness above 50 Shore and a second layer of polyethylene foam insulation with relative electrical permittivity _. x 1.6. The thickness of the full insulation in relation to minimum bend radius of a coaxial cable satisfies the condition ^D 1 ^D and ^3D π ^1> a where d ^ is the diameter of the full insulation, d is the diameter of the inner core, the final diameter of the membrane d _Q minimum bending radius of the coaxial cable .

The design of the coaxial cable with double-layer insulation ensures the resistance of the foam insulation against the cutting of the insulated wire into the foam insulation. Compared to cables with wavy and serrated wires, impedance inhomogeneity at 100 MHz is reduced by up to 2 orders.

Such an outer core cable comprised of foils and wires, which may be used, has a shielding efficiency, expressed as a coupling impedance at 30 MHz, of less than 20 Mohm / m as opposed to 150 to 200 Mohm / m for cables using a wire braid. This feature shall be applied in an environment of increased electromagnetic interference by a useful signal to interference interference level of more than 60 dB.

CS 274 064 DL 2

In the accompanying drawing, a cross-sectional cross-sectional view of a single core coaxial cable for outoanthones 6 is insulated with a layer 2 filled with insulators, over which an insulating layer of foamed polyethylene is embossed. Above the insulation, the outer core 6 and the sheath 6 are folded.

The essence of the solution is further illustrated by two variants of a particular embodiment of the invention.

Example 1

Low capacity coaxial cable with inner core £ of steel wire diameter d =

0.2 mm, insulated thin film 2 of full high density polyethylene insulator / type KO

2-29 / for diameter d ^ = 0.6 mm. The second layer of insulation 6 is of polyethylene foam (type KB 2-37) of < 5 _r = 1.54 and is embossed to a diameter of ^ = 3.7 mm. Above the second insulation layer 6 there is an outer core 6 of two metallised foils with metal to each other and contact wires therebetween and above the outer core 6 is a sheath 6 of dark gray PVC sheath stabilized mixture. Mi, nimáliiy polonnr bend ύθ of this cable hol 3,7 mm.

Example 2

Low-capacity coaxial cable with an inner core 6 of copper-plated pricrner steel wire d = 0.1 mm, insulated with a thin layer 2 of polyamide (type PA 12) to a diameter d = 0.3 mm.

The second layer of insulators is made of polyethylene foam (type KB 2-37) of about 1.54, embossed with a diameter of 0 ^ = 2.95 mm, above it is an outer core 4 of two metal-plated foils together and contact wires between them and above the outer core 6 is a sheath 6 of dark gray PVC sheath stabilized composition. The coaxial cable thus formed had a minimum bending radius d = 3.00 mm. about '

Application of the solution comes into consideration in the production and ultimately in the assembly of car antennas in cars.

Claims (2)

OBJECT OF THE INVENTION Single core insulated coaxial cable with insulated outer composite core and sheath, characterized in that the core insulation (1) formed of metal wire consists of two layers (2, 3), namely a solid layer (2). nonpolar plastic insulation of hardness above 50 Shore, whose thickness in relation to the minimum bending radius of the coaxial cable corresponds to the condition ^d i> ^3d ΐΓ> o where dj jc the diameter above the full insulation, d is the diameter above the inner core, 0 ^ is the resulting diameter above the insulation and dg the minimum bend radius of the coaxial cable, and the polyethylene foam insulation layer (3) deposited thereon, having a relative electrical permittivity δ. Z, 1.6.