Patent Application
20050126817
1. Field of the Invention
The instant invention relates to an overhead or underground telephone lead-in cable for VVDL-type services (voice, video, data and lead-in) permitting the connection of the users to the public telephone system with high speed digital services link besides offering analog services. This is made possible through the integration of a balanced circuit to the original design of two elements made of metal, plastic of kevlar fibers, in parallel, also serving as self-supporting elements in overhead installation. Said cable is characterized because its core is protected by a moisture resistant film and is thus highly convenient for overhead or underground installation.
2. Previous Art
Generally, the overhead lead-in lines of the unitary telephone services have been limited with regard to their bandwidth and resistance to radio interferences because of their design. The demand for transmission means able to support a bandwidth large enough to meet the growing demand for digital services in the coming years also requires designs that do not increase the costs or limit the ease of installation of the current products. With regard to the cables used for the connection of the users to the telephone network, the design is a decisive factor. The cable should be light and economical and permit high-speed data transmission above 155 Mbps. It should also have an adequate response in frequencies above 100 Mhz and be self-supporting over distances spanning more than 100 meters. Moreover, the cable should be weather-resistant and in windy and icy conditions, it should permit its reinforcement without being necessary to modify its shape, so that the same anchorage elements usually used in this type of services can be utilized.
Among the known techniques used to solve the above-mentioned problems, in U.S. Pat. No. 4,467,138 a “conductive cable for plural communications” is described, the design of which is related to a flat communication conductor. Said flat communication conductor has two o more communication ports, polyolefin insulated cables united throughout its length arranged in groups on opposed and parallel sides of a conductive steel wire.
Even though cables presenting stranded pairs of conductors are known, not all of them have the same application, i.e. depending on their use, the design varies in each case and even the number of pitches of the stranded pair presents differences. For example, in U.S. Pat. No. 6,064,008 a communication cable having two pair of stranded conductors is described, the main characteristic of which it is not the stranded pairs but the insulating filling material based on a chemical product of fluorinated polymer with a blowing agent. In U.S. Pat. No. 6,509,526 D, anteriority of the instant invention, a telephone lead-in cable is described for ordinary voice service and high performance Data and Video transmission services. Said cable is based on a thermoplastic sleeve, with a data transmission circuit having two metal wires helically united within a thin protective band resisting to temperatures up to 240° C. At the center of said thermoplastic sleeve a circuit element for voice transmission based on two parallel metal conductors is arranged. Each one of said metal conductors is opposed to the helical union of the first circuit.
Thus, for example in U.S. Pat. No. 4,761,053 an overhead lead-in cable is described which includes a rectangular cross-section sleeve with two tension members based on various filaments impregnated with a sleeve compatible material. Each said member is arranged opposite a pair of conductors and at least one of them is made of optic fiber and vertically aligned, in parallel.
In U.S. Pat. No. 5,180,890 a cable is described which is also of a rectangular type, including two tension members, one placed at each end of the sleeve and two copper conductors separated and horizontally aligned, in parallel.
In U.S. Pat. No. 5,155,304 an overhead lead-in cable is described with an embodiment of 4 or more tension members based on intertwined filaments impregnated with a plastic material forming a reinforcement thread for the catenary elongation tension. Said overhead lead-in cable also has two or more insulated copper conductors placed in the center of the thermoplastic sleeve, vertically aligned and in parallel or in the shape of a cross forming and interstice between the insulated conductors.
The applicant has developed an improved VVDL-type lead-in cable for overhead or underground installation, based on a design of self-supporting elements for overhead lead-in lines and a dedicated circuit permitting a high-speed digital signal transmission without interfering at all with the voice service signals or the use of additional electronic circuits to separate the signals. The design that is also highly resistant to diaphony, is characterized because it has a core of two insulated conductors impregnated with a surrounding layer of moisture absorbing swelling powder.
The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the instant invention.
The main object of the new Voice, Video and Data (VVDL) telephone lead-in cable is to prevent moisture penetration into the core of the VVDL cable, when it is used in overhead service and exposed to moisture penetration from rain, or when said cable is installed in underground ducts and directly exposed to extremely moist environments. The core formed by two insulated conductors is characterized because it incorporates outside around the conductors a moisture absorbing powder film of swelling material preventing water penetration inside said core.
The film is applied alternately through an electrostatic system when the external cover of the cable is applied. Said system permits the distribution of the film in a controlled way, and the deposit of the swelling material in a quantity that is proportional to the required thickness of said film. The VVDL-type (Voice, Video, Data, Lead-in) lead-in cable (A) includes two self-supporting metal elements for overhead lead-in lines 10, 11 and can also transmit voice signals when the members are made of metal because, between them, they create an additional circuit dedicated to the transmission of analog signals. It also includes a circuit permitting the transmission of data at relative high speed formed by two metal wires 12 and 13 individually insulated with a polyolefinic material, polyethylene or polypropylene, and stranded together, forming a balanced circuit of 100 ohms impedance 15,
Lead-in Cable (VVDL) FIGS. 1 to 3
The cable object of the instant invention (A), is a rectangular elongated body at the ends of which corner pieces are placed 19, which are rounded for better installation handling. Said cable also presents recesses 20 in its lateral ends, in the middle part, to create a semi-rectangular geometrical shape submitted to lower tensile stress.
The lead-in cable (A) has, equidistantly distributed in its structure 18, one or several transmission circuits, which do not require for their installation any special type of fittings for fixing them onto the terminal distribution post or box of the telephone network and the house of the consumer or user of the telephone services. The voice circuit elements are preferably placed in the stranded pair of wires 12 and 13 of the central core 15, but can also been incorporated in the tension members 10, 11 when they are made of metal conductors acting as self-supporting elements. In this case, said elements 10, 11 are made of metal cylindrical conductors, without limitation as to their composition and cross section, i.e., the elements can be of metal alloys or composition of two metals tempered with a treatment permitting a high rupture strength. This is because said elements are self-supporting and are also supporting the other elements conforming the cable. However, the thermal treatment must be between 45° C. and 550° C. Through a treatment of this type, said conductors or self-supporting metal elements do not substantially lose their resistance characteristics to the passage of electrical current. Said elements 10, 12 are placed longitudinally in parallel between them and are separated by a 4 to 6 mm distance permitting the placement of the second transmission circuit 15 between them. Said elements are arranged to offer an appropriated means for transmitting digital signals 12 at relatively high speeds (155 Mbps). They are made of quasi cylinder mild copper metal conductors, 100% pure and stranded with a smooth surface of a diameter of 0.5 to 0.64 mm, permitting spans on distances of up to 150 meters and with relatively low losses of 22 Db/100 at 100 MHz. Each one of the conductive elements is individually insulated with a thermoplastic compound layer 14 applied continuously and highly uniform insuring a concentricity of the wall of insulating material with regard to the conductor above 90%. Said insulating layer can be applied in only one layer or in various layers and each one of the insulating layers is colored to facilitate its identification. The material used for layers can be solid, expanded through physical or chemical action or can have compounds delaying or inhibiting flame propagation. The insulated conductors are stranded 15, forming a pair or balanced circuit the distance between each strand of the conductors being such that it permits to minimize the diaphony effects caused by the proximity of other element emitting electromagnetic signals and to reduce the exit of energy towards the other circuit. The stranded pair 15 shows an optimum performance because the control of the wall thickness and the helix of each one of the stranded conductors to form the pair insure the stability of the characteristic impedance at relative high frequencies. Moreover, the circuit remains in an excellent electrical balance minimizing in this way the interference of external agents. The balance circuit or stranded pair 15 is optionally covered by a thin tape protecting against melting, made of temperature resistant material, 16 applied helicoidally or longitudinally onto said protective cover when it is required for the installation. The tape prevents a melting of the insulation material among themselves and/or among the compound of the cover during the application of the outer cover 18 through an extrusion process, and because of heat transfer from the compound to the insulated conductors. Moreover, this tape also acts as a barrier to prevent the invasion of the transmission area of the balanced circuit by the compound of the cover. It also acts as a barrier to prevent the modification of its dielectric constant and in turn its characteristic impedance that increases the circuit loss because of a higher capacitance. It also presents a cover reinforced by its design based on a thermoplastic compound 18 forming an integral body and maintaining the self-supporting elements on each side and diametrically parallel opposite to the stranded pair.
The space between the protection tape 16 and the core of the strand 15, is impregnated through electrostatic means with a layer of swelling powder material which is a poly(sodium acrylate) homopolymer commercial product.
The cover 18 protects both elements against mechanical damage that could be caused during the storage, transportation and installation. The compound of the cover is weather resistant according to the installation area and protects also the circuits against premature aging through the action of sun, water or any other external agent. This compound can also be flame retardant if it is required where the cable is installed.
The design of the cable body has a rectangular geometrical shape with trimmed edges 19, and recesses 20 permitting the product to be installed using any of the fixing fittings currently designed. Moreover, it is possible to avoid that the components be damaged by the tensile and compression stresses to which they are submitted during installation and daily functioning.
The advantage of the cable design is the tensile strength, i.e. the increase of the installation span distance that can be solved through the change of the cross section of the support elements or the type of material used in their manufacturing.
The use of swelling powder on the paired core permits the direct use of the cable in underground installations because the absorbing material prevents the penetration of the moisture usually found in underground installation areas.
VVDL Cable Characteristics
Additionally, the cable withstands a crushing test of 1000 lb/f (14.88 kg/cm) which meets the underground conditions. The cable of U.S. Pat. No. 6,509,526 B2 includes 24 AWG conductors as components of the conductive core of the VVDL cable while the instant invention permits the development of new cable constructions from 16 to 26 AWG cables.
The electrical performance of the new VVDL cable of two 24 AWG conductors fulfils the following electrical characteristics.
The self-supporting members, i.e. the tensile members 10, 11 are made of conventional glass fibers impregnated with polymers or kevlar tapes when the lead-in cable includes only one transmission circuit.
It will be apparent to those skilled in the art that various modifications and variations can be made in the lead-in cable of the instant invention without departing from the spirit or scope of said invention. Thus, the present invention is not limited by the foregoing descriptions but is intended to cover all modifications and variations that come within the scope of the spirit of the invention and the claims that follow.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA/A/2003/011491 | Dec 2003 | MX | national |
