JPH03181209A - Rapial coaxial cable - Google Patents

Abstract

PURPOSE: To improve an water resistance characteristic by absorbing also water or moisture infiltrated into an output protection jacket by an water protective barrier tape and restricting the movement of the absorbed water or moisture in the radius direction or the longitudinal direction. CONSTITUTION: A moisture protective barrier tape 15 is formed on a corrugated outer conductor 13 and an outer jacket 16 is extruded and molded on the surface of the tape 15. In this case, the tape 15 is functioned as an water-protective barrier, so that the intrusion of moisture, i.e., water, and the contact of moisture with the conductor 13, especially a radiation slot 16 and foaming dielectric 12, can be restricted. Even when the completeness of the jacket 16 is lost by mechanical cut of break, the barrier tape 15 restricts water infiltration in the radius direction or the longitudinal direction and a change in the electric characteristic of the cable due to water action to the foaming dielectric can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to coaxial cables used in communication systems. More particularly, the present invention relates to radial coaxial wires formed from expandable dielectric materials and exhibiting improved water resistance properties.

PRIOR ART AND PROBLEMS THEREOF The use of foamed material and air dielectric type coaxial cables is widespread for antenna feed systems in communication systems.

Typical applications include antenna systems for terrestrial microwave systems, small scale terrestrial mobile radio broadcasting, broadcast transmission antenna systems, ground station antenna systems, and high frequency communication systems. It functions to transmit it to some form of antenna that sends this signal. Broadcast coaxial cables are also designed to function as continuous antennas, transmitting electrical or radio signals directly from the cable rather than through the antenna. Such a radiating or leaky coaxial cable is
It serves as an effective and economical medium for transmitting radio signals in cases where it is impractical to use a conventional antenna. Radiant cable systems support two-way mobile radio, radio call broadcasts and regular centralized VHF
It is particularly essential for local communication services in applications involving extended underground facilities such as railways, mines and tunnels, and where UHF communication systems cannot be used.

A common problem with electrical cables in general, and coaxial cables in particular, is that the transmission characteristics are significantly degraded by water penetration into the cable. Such cables have a severe impact on electrical and mechanical properties that are important for high humidity environment operation. In particular, water present between insulated conductors in the cable greatly increases the capacitance and forms, among other things, leakage paths. Water penetration into the area between the conductor and the jacket of an insulated cable also increases the potential for signal attenuation, noise and conductor corrosion.

Therefore, an important requirement for coaxial cables in many applications is to have a high degree of protection against water or moisture penetration. Even if some water enters the cable by radial water penetration, it is important to limit the movement of water along the longitudinal axis of the cable from the point of damage. This prevention of longitudinal migration ensures that even if some water penetration does occur due to unavoidable external causes such as cuts or tears in the outer cable jacket, it will prevent deterioration of the electrical properties and repair length of the cable. It is important to limit the

Traditional approaches to water infiltration into telecommunications and power cables, especially radiated coaxial cables,
Various high viscosity fillings/flashings are used to fill the space between the outer conductor and the surrounding protective skin or jacket.
g) using a compound, this compound is:
Mineral oil, Aqualock (registered trademark),
Examples include Teleflock (registered trademark). The filling compound is generally pumped into the free space inside the cable and, when uniformly distributed over the length of the cable, serves as an effective water barrier layer.

However, this flushing method is complicated and expensive to implement because it is difficult and time consuming to apply the flushing compound. It is difficult to distribute the flashing compound uniformly in the longitudinal direction of the cable, and if the flashing compound is not uniformly distributed, it cannot perform its full effect as a water protection layer. Also, filling the cable with flushing compound in situ during the cable installation process is a cumbersome and cumbersome task that requires considerable skill. Moreover, because of the viscosity of the flushing compound, the protective compound cannot be easily removed from the cable afterwards, making the connection of the cable impracticable.

A major problem encountered in using flashing compounds to provide moisture protection to coaxial cables is that these compounds generally degrade the fire resistance properties of the cable.

In various power transfer and communication applications, coaxial cables also require high protection against flame propagation. Fires occur when cables overheat due to overload current or associated equipment failure.

More importantly, if the electrical equipment is already exposed to fire, the cables used in the electrical equipment themselves contribute to the flame propagation and generate harmful soot and smoke.

By wrapping with a halogen-containing material such as polyvinyl chloride or other fluoroplastic materials, coaxial cables can resist the spread of fire even in severe thermal conditions. However, when exposed to fire, the halogen-containing materials within the envelope generate toxic fumes and form toxic and corrosive gases. Flame-protected cables with cable jackets of cross-linkable halogen-free compounds and technical plastics with inherent flame protection are fairly expensive and are generally stiff and difficult to flex.

The problems inherent in foamed dielectric type radiating cables arise precisely from the construction of such cables. In radiating cables, a slot or other opening is formed in the outer conductor to allow the transmitted RF multiplied signal controlled portion to radiate, thus creating a natural source of radiation along the entire length of the cable. be done. The outer conductor itself encloses an assembly consisting of a foam core extruded over the inner conductor. The entire coaxial cable assembly is coated with a flame-protective material.

When subjected to high temperature conditions, the intumescent material inside the cable melts and bubbles out of the openings in the outer conductor, penetrating the softened outer jacket and exposing it to fire. Therefore, the flame propagates rapidly along the cable and destroys the entire cable.

U.S. Patent No. 4.800 issued to the inventor.
The improved flame-proof radial coaxial cable disclosed in the '351 patent avoids the above-mentioned problems.

In this coaxial cable, a layer of inner barrier tape with high flame protection is used between the outer conductor and the outer jacket of the cable. The tape is a material that has good thermal protection properties while at the same time having sufficiently low dielectric loss and good transmission properties that the radiated electromagnetic field around the slot or aperture in the outer conductor is substantially unaffected by the barrier tape itself. is selected to be. The barrier tape effectively contains the foam dielectric inside the cable, thereby preventing flammable foam material from fueling a fire. The combination of the flame resistant barrier tape and the flame resistant thermoplastic material of the jacket provides a non-toxic, flexible radiating cable with high flame protection.

For flame-protected radiant cables of the type described above,
Furthermore, significant problems arise when attempting to provide a high degree of resistance to water penetration. That is, the use of a flame-protecting barrier tape is not compatible with the use of a flashing compound around the outer conductor to provide moisture protection. As explained in the above-mentioned U.S. Pat. It is necessary to provide it between the outer conductor and the outer jacket. This is important to prevent the tape from completely covering the radiating aperture and melting the dielectric into penetrating contact with the jacket material, especially if the jacket softens considerably in high heat conditions.

When using flashing compounds, the flame-protecting structure with the above-mentioned advantages cannot be easily modified. This is because sufficient water protection is achieved only when the flushing compound is applied directly over the openings of the outer conductor. Therefore, it becomes completely impractical to wrap a flame-protective tape over a coating layer of flashing compound. Also, the flashing compounds commonly used in such coaxial cables are themselves flammable to at least some extent, thus inhibiting the flame protection provided by the barrier tape.

OBJECTS OF THE INVENTION The basic object of the invention is to provide a foamed dielectric type radiating coaxial cable with improved water protection properties.

In this regard, a related object of the present invention is to provide a radiant cable with a high degree of water protection, which has properties that locally absorb water and limit longitudinal water movement.

Another object of the invention is to provide a radiating cable having all the above-mentioned characteristics and also convenient for storage and flexible in use.

Yet another object of the invention is to provide a radiant moisture-protective cable of the above-mentioned type which is adapted to readily exhibit a high degree of fire protection properties.

Objects and advantages of the invention will become apparent from the following description of the embodiments taken in conjunction with the drawings.

EXAMPLES While the present invention will be described with respect to certain preferred embodiments, it will be understood that there is no intent to limit the invention to these embodiments. On the contrary, the intention is to cover all alternatives, modifications, and equivalent constructions falling within the principle and scope of the invention as claimed.

As shown in FIG. 1, a radiating cable, generally designated 10, has a central conductor 11 at the center of the cable. Center conductor 11 is a generally smooth or corrugated conductive material such as copper, aluminum, or copper-clad aluminum. The central conductor is surrounded by a layer of lossy material 12. The outer conductor 13 surrounds a foamed dielectric material,
It is generally formed by a corrugated piece of copper provided with a series of slots or apertures 14 arranged along the axial length of the conductor. The slot is preferably oval in shape as shown in FIG. 1, but may have any other shape. The radiating aperture in the corrugated copper outer conductor allows a controlled portion of the radio frequency signal propagated through the cable to be radiated from the source along the entire length of the cable, allowing the coaxial cable to actually act as a continuous antenna. allow to do so. The structure described so far is conventional and commonly used in radiating cables. In such cables, the outer conductor 13 is provided with an outer skin or jacket 16, typically made of a suitable thermoplastic material, which serves as an outer protective layer for the cable. fulfill. Traditionally, cables of this type have been made impermeable to water by filling the space between the outer conductor 13 and the outer jacket with a water-protective compound (generally mineral oil). The processing procedure includes applying a filler compound onto the outer conductor by some form of pumping mechanism, followed by extruding an outer jacket over the coated structure.

Filling compounds necessarily have high viscosities and pumping is difficult and cumbersome.

In order to make this type of radiant cable permeable to water valves while eliminating the problems mentioned above, at least one layer of moisture-protective barrier tape 15 (FIG. 1) is applied on the corrugated outer conductor 13. establish. The outer jacket 16 is then extruded onto the barrier tape 16. In fact, the tape 15 acts as a watertight barrier between the outer jacket 16 and the outer conductor 13, which allows moisture or water to enter the conductor 13, especially the radiating slots 16 and the foam dielectric 1.
2. Contact is restricted. Even if the integrity of the jacket 16 is compromised, for example by mechanical cutting or rupturing, the barrier tape will limit water penetration in the radial and longitudinal directions, thereby preventing the cable's electrical loss due to the action of water on the foam dielectric. This sufficiently reduces the possibility that the characteristics will change.

The method described above is advantageous because effective water protection can be obtained without the need for any filler compounds. Conveniently, barrier tape is wrapped over the outer conductor as part of standard cable manufacturing operations.

Conveniently, the outer jacket is extruded onto the barrier tape. Additionally, such radial cables are easy to cut and connect because the barrier tape layer can be easily cut and the ends of the cable rejoined.

Preferably, the water-protective barrier tape is formed from a dynamic barrier tape, which is provided with a coating of water-swellable material between the core and the outer screen layer of the tape. The coating material has a high swelling response to water and expands considerably upon contact with water. As a result, substantially all the capillary spaces and air gaps between the core and the screen are sealed, thereby limiting water penetration in both the radial and longitudinal directions. In fact, the area between the outer conductor 13 and the outer jacket 16 becomes sealed when water comes into contact with the barrier tape provided in this area.

The coating material is generally in powder form, and the powder is formed from a natural water-absorbing material such as cellulose or a water-swellable synthetic resin material such as sodium polyacrylate.

The preferred properties required for a barrier tape are adequate swelling height, swelling rate, and gel strength to effectively localize water penetration and provide a stable water penetration depth. The swellable powder must be tightly bonded inside the tape (i.e. within the core and screen layers) to minimize dust generation during cable manufacturing, termination or connection operations. This tight bond also ensures even distribution of powder over the circumference and length of the cable. It is important that the barrier tape exhibit adequate swelling and water retention over repeated wet/dry cycles.

In terms of physical properties, it is desirable that the barrier tape have sufficient mechanical strength and flexibility so that it can be easily applied and does not compromise the overall flexibility of the cable. The surface of the screen on the side of the tape exposed to water is preferably an open-structure fabric so that water can easily access the water-swellable powder underneath.

In terms of chemical properties, the barrier tape is preferably electrically insulating, at least semiconducting with low resistivity.

Water-protective tapes that meet most of the above requirements are commercially available from Xable Tapes Ltd., Indiana, USA, and Lantor Bv., Netherlands, under the trade names "K-Block" and "FIRE," respectively.
There is a T.

"K-BLock" tape uses natural cellulose-based powder for the water-absorbing layer. On the contrary, “FIRET”
The tape uses an absorbent layer made of synthetic material. For long-term use, tapes with a coating of synthetic resin are preferred, since such coatings do not deteriorate due to bacterial or mildew attack.

The manufacturing process for producing the water-resistant radiating cable of the present invention begins by depositing a foamed dielectric core 12 (see FIG. ref.).

A strip of the desired material, usually copper or aluminum, is then formed into a tube around the assembly and then welded to form the continuous outer conductor 13. The outer conductor is arranged coaxially with the center conductor 11, and the inside of the outer conductor except for the center conductor is almost completely filled with foam dielectric. The outer conductor is annularly or spirally corrugated to provide flexibility to the cable, and each longitudinal portion thereof has alternating peaks 13A and troughs 13B,
A radiation aperture 14 is formed in each peak. With the above-described configuration, the material of the outer conductor 13 bites into the dielectric core near the corrugated troughs 13B, ensuring a sufficient gripping action between the outer conductor and the dielectric it surrounds, and Different elongations between these two materials can be accommodated. The metal piece forming the outer conductor can be formed with a radiating aperture of the desired shape and size before being corrugated around the core assembly. Conversely, the outer conductor may be placed around the core assembly and corrugated prior to machining the radiating aperture in the outer conductor.

At this stage, a water-tight barrier tape 15 is wrapped around the outer conductor 13 so that all radiating apertures 14 are completely covered by the barrier tape. The barrier tapes are preferably wrapped with 50% overlap, effectively providing a double layer of barrier tape over the radiating aperture 14. A desired thermoplastic protective material 16 is then extruded onto the assembly to jacket the entire assembly.

Providing barrier tape is a simple additional step in the overall cable manufacturing process. The tape is flexible and can be easily bent, so -4
Convenient for wrapping around the side conductor. The flexibility of the tape also ensures that the entire cable assembly remains flexible.

Depending on the actual application, virtually any mechanically strong polymeric material can be used to form outer jacket 16. However, for flame protection, it is preferred that the outer jacket material be flame-protective, non-halide, self-extinguishing, and have low dielectric loss. These properties are particularly advantageous in radial type cables. A jacket material having the above characteristics is commercially available from General Electric Company under the trade name "N0RYL-PX 1766".

In conventional radiating cables, the outer jacket on the copper outer conductor is itself flame protective. When such cables are subjected to extreme thermal conditions, the jacket material, although flame protective, softens at high temperatures. In addition, the foamed dielectric material 12 housed in the outer conductor is exposed to high temperature radiation through the radiation opening 14 and surrounded by the outer conductor 13. It comes out on the outside. The foam dielectric presses against the softened outer jacket and eventually passes through the jacket and is exposed directly to the fire. The dielectric material fuels the fire and allows the flame to propagate freely, eventually leading to complete destruction of the cable.

An example of an attempt to improve the fire protection of radiant coaxial cables is the use of an inert, flame protection material on the corrugated outer conductor, as described in the above-mentioned U.S. Pat. No. 4,800.351. Barrier tape was sometimes installed. An outer skin or jacket formed of a flame-protective non-halide thermoplastic material is then provided over the barrier tape. The tape acts as a barrier between the outer jacket and the outer conductor, thereby effectively retaining the foam dielectric within the conductor and preventing it from melting and contacting the bleed jacket material. Even if the material of the outer jacket softens considerably in high temperature conditions, there is no risk of the foam penetrating the jacket.

As disclosed in the above-mentioned U.S. Pat. No. 4,800,351, barrier tapes are composites that can act as an insulating barrier even when exposed to flames of sufficiently high temperatures. Selected. The tape composite is chemically inert, non-toxic and halide-free. The composite is also preferably water impermeable, radiation resistant, acid resistant and alkali resistant. The barrier tape also needs to be dry, non-adhesive, flexible and fully applicable. A preferred composite for the barrier tape is an inorganic refractory material such as electrical grade mica, impregnated with a heat resistant binder and combined with a suitable carrier material such as fiberglass. It is important that the refractory material, when used in the cable, exhibits a suitably low loss factor at the frequencies at which radiant coaxial cables normally operate. This results in
Ensure that the presence of barrier tape does not significantly affect the electrical properties of the cable. A tape that satisfies the above requirements is manufactured by Cogebi of Belgium under the trade name "F IR".
OX” commercially available.

However, this effective method of using flame-protective barrier tapes is not compatible with the conventional method of using filler compounds to provide water-protective properties to radial coaxial cables. As mentioned above, the filler compound is coated onto the outer conductor of the cable using some form of pumping mechanism to form a slippery layer. It is extremely difficult and cumbersome to wrap a layer of flame-protective tape over a slippery layer of filler compound. Because there is no frictional surface on the underside of the tape, there is no gripping action required to first wrap the tape according to the desired shape and then to secure the wrapped tape. As a result, the water-tight tape becomes easily slippery both during and after wrapping, thereby failing to achieve the purpose of watertightly covering the radiating aperture. As a result, it is impractical to combine filler compounds and flame-protective barrier tapes.

The structure according to the principles of the invention shown in FIG. The design and construction of radial coaxial cables has been made viable. After wrapping the water-resistant barrier tape onto the outer conductor, a flame-protective barrier can be wrapped over the water-resistant barrier tape in the same manner. This combination has the advantage that the water-protective tape does not in any way contribute to the propagation of the flame, and the flame-protective tape does not compromise the water protection of the cable. This type of arrangement is shown in FIG. 2 in accordance with another embodiment of the invention. The embodiment of FIG. 2 is similar to the embodiment of FIG. This embodiment differs from the embodiment shown in FIG. 1 above in that the embodiment shown in FIG. Preferably, the second layer 17 is wound with a 50% overlap. Layer 17 serves to supplement the effect of primary layer 15 in sealing radiation aperture 14 . More importantly, layer 17 provides flame protection without significantly affecting the water protection properties, transmission properties or flexibility of the cable.

A sample of a radiant cable constructed as described above using a combination of layers of water-protective tape and flame-protective tape was tested for its flame spread characteristics by uL 1581/
IEEE 383 particle tray frame
Test Protocol (UL 1581. Reference Standard for Electrical Wires, Cables and Flexible Cords, 1983, IJnderwri, North Pruck, Illinois, USA)
ters Laboratories Inc.;
I E E E383-1974, Standard for Type Testing of Class IE Electrical Cables, Field Splicing and Connections for Nuclear Power Plants, 1974, Institute of Electrical & Co., New York, USA.
Electronics Engineers) and its water infiltration properties were tested according to the U.S. Rural Electrification Administration Test Protocol (RE^; PE-39, 5ection 28).
) 1: Both tests yielded good results.

From the foregoing, it can be seen that the present invention provides a foam dielectric type radiant cable with greatly improved water protection properties that overcomes many of the problems commonly associated with the use of filler compounds. It would be obvious to provide. Also, such cables are advantageously made to exhibit high flame protection without economic loss or deterioration of electrical properties, and this high flame protection is achieved by incorporating dielectric layers and/or
or by the conventional use of cross-linked polymeric materials in the outer protective jacket. Radiant cables formed in accordance with the present invention exhibit a high degree of water protection and limited radial and longitudinal water movement, do not propagate flame, are easily manufactured by conventional procedures, and
Also, its excellent flexibility makes it convenient for installation.

[Brief explanation of drawings]

FIG. 1 is a cutaway side view showing the various layers that make up a radial coaxial cable in accordance with the principles of the present invention. FIG. 2 is a cutaway side view of a radial coaxial cable according to another embodiment of the present invention. [Explanation of main symbols] 10: Coaxial cable, 11, Center conductor 12: Dielectric material, 13: Outer conductor, 13A: Peak, 13B: Valley, 14: Opening, 15: Barrier tape, 16. Outer jacket, 17 , flame-protective tape. (4 other people)

Claims (10)

[Claims] 1. A foam dielectric type radial coaxial electrical cable with improved water protection, comprising: a center conductor; a layer of porous foam dielectric surrounding the center conductor; and a layer of porous foam dielectric in direct contact with the foam dielectric layer. and a single enclosing this,
an outer conductor having a continuous waveform, the outer conductor having an opening provided at a peak of a corrugated portion formed along the longitudinal direction of the outer conductor for passing electromagnetic radiation; at least one layer of water-protective barrier tape wrapped onto an outer surface to cover each of the radiating apertures of the outer conductor; an outer protective jacket extruded over the wrapped layer of tape; wherein the barrier tape is comprised of a layer of water-swellable material adapted to swell upon contact with water to effectively confine the contacted water to localized areas; A radiant cable characterized in that it acts as an absorbent barrier that absorbs any water or moisture that penetrates the jacket and limits the radial and longitudinal movement of the absorbed water or moisture. 2. A radiating cable according to claim 1, characterized in that the water-protective barrier tape comprises a layer of water-swellable natural polymeric material, such as cellulose powder. 3. A radial cable according to claim 1, characterized in that the water-protective barrier tape comprises a layer of water-swellable synthetic polymeric material, such as sodium polyacrylate. 4. 2. The radiating cable of claim 1, wherein a layer of flame-resistant tape is wrapped over the layer of water-resistant barrier tape to effectively cover the radiating aperture, and wherein the barrier tape is heat-resistant. A radiant cable characterized in that it comprises particulate refractory material adhered to a carrier material with a binder. 5. 5. A radiant cable according to claim 4, characterized in that the fire-resistant material provided on the flame-protective tape is dielectric grade mica and the selected carrier material is fiberglass. cable. 6. a center conductor; a layer of porous foam dielectric surrounding the center conductor; a single continuous corrugated outer conductor surrounding the layer of foam dielectric, the outer conductor having a conductor extending along its length; , and the troughs of the corrugated portion of the outer conductor cut into the dielectric layer to extend the longitudinal direction between the outer conductor and the dielectric layer. the outer conductor adapted to limit relative movement in direction;
a radiating coaxial cable comprising: an outer jacket surrounding the outer conductor; a water-protective barrier wrapped over the outer surface of the outer conductor and covering all of the radiating apertures of the outer conductor; at least one layer of tape, said barrier tape comprising a layer of water-swellable material adapted to swell upon contact with water to effectively confine the contacted water to a localized area; , radial type, characterized in that it acts as an absorbent barrier to absorb any water or moisture that penetrates the extruded jacket and to limit the radial and longitudinal movement of the absorbed water or moisture. coaxial cable. 7. The radiation type coaxial cable according to claim 6,
Radiating coaxial cable, characterized in that the water-protective barrier tape comprises a layer of water-swellable natural polymeric material, such as cellulose powder. 8. The radiation type coaxial cable according to claim 6,
Radiating coaxial cable, characterized in that the water-protective barrier tape comprises a layer of water-swellable synthetic polymeric material, such as sodium polyacrylate. 9. The radiation type coaxial cable according to claim 6,
A radiating coaxial cable characterized in that a layer of flame-proof tape is wrapped over said layer of water-proof barrier tape to effectively cover said radiating aperture. 10. 7. The radiant coaxial cable of claim 6, wherein the flame-protective tape is made of an inorganic material, such as electrical grade mica, impregnated with a heat resistant binder and combined with a carrier material such as fiberglass. A radiating coaxial cable characterized by being formed from a fireproof material.