COMMUNICATION CABLE
United States Patent 3636234
Communication cable with improved audio and radio frequency transmission and shielding characteristics uses a tinned annealed steel foil tape for shielding.
US Patent References:
Multiconductor cable
Hochstadter - February 1939 - 2147095
Composite shield for electric cables
Ronald et al. - January 1967 - 3300573
Shielded jacketed-pair communications wire
Cogelia - June 1967 - 3328514
ELECTRIC CABLE WITH ADHERED POLYMERIC INSULATION
Brown et al. - December 1969 - 3485939
Multiconductor cable
Hochstadter - February 1939 - 2147095
Composite shield for electric cables
Ronald et al. - January 1967 - 3300573
Shielded jacketed-pair communications wire
Cogelia - June 1967 - 3328514
ELECTRIC CABLE WITH ADHERED POLYMERIC INSULATION
Brown et al. - December 1969 - 3485939
Application Number:
04/882251
Publication Date:
01/18/1972
Filing Date:
12/04/1969
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
174/109, 174/105R
International Classes:
H01B11/00; H01B11/10; H01B11/18; H01P3/00; H01B11/02; H01B11/06
Field of Search:
174/36,102,103,105,106,108,109,113
Primary Examiner:
Kozma, Thomas J.
Assistant Examiner:
Grimley A. T.
Claims:
I claim
1. In a communication cable for transmitting electrical signals in audio and radio frequencies having a central metallic conductor, a layer of insulation surrounding the conductor, an outer metallic conductor surrounding the insulation, and a helically wrapped shielding tape surrounding the outer conductor, an improved shielding from external electromagnetic influences comprising a tinned annealed mild steel about 1-mil thick and about 0.50-inch wide lapped sufficient to provide complete outer conductor coverage when the cable is flexed in expected normal usage and having a general composition of from about 0.08 to about 0.13 percent carbon by weight, from about 0.30 to about 0.60 percent manganese by weight, up to about 0.04 percent phosphorous by weight, up to about 0.05 percent sulfur by weight and the balance iron.
2. In a communication cable for transmitting electrical signals in audio and radio frequencies having a pair of metallic conductors each surrounded by a layer of insulation and positioned next to each other in a generally longitudinal direction and a helically wrapped shielding tape surrounding the conductors, an improved shielding from external magnetic influences comprising a tinned annealed mild steel about 1-mil thick and about 0.50-inch wide lapped sufficient to provide complete conductor coverage when the cable is flexed in expected normal usage and having a general composition of from about 0.08 to about 0.13 percent carbon by weight, from about 0.30 to about 0.60 percent manganese by weight, up to about 0.04 percent phosphorous by weight, up to about 0.05 percent sulfur by weight and the balance iron.
1. In a communication cable for transmitting electrical signals in audio and radio frequencies having a central metallic conductor, a layer of insulation surrounding the conductor, an outer metallic conductor surrounding the insulation, and a helically wrapped shielding tape surrounding the outer conductor, an improved shielding from external electromagnetic influences comprising a tinned annealed mild steel about 1-mil thick and about 0.50-inch wide lapped sufficient to provide complete outer conductor coverage when the cable is flexed in expected normal usage and having a general composition of from about 0.08 to about 0.13 percent carbon by weight, from about 0.30 to about 0.60 percent manganese by weight, up to about 0.04 percent phosphorous by weight, up to about 0.05 percent sulfur by weight and the balance iron.
2. In a communication cable for transmitting electrical signals in audio and radio frequencies having a pair of metallic conductors each surrounded by a layer of insulation and positioned next to each other in a generally longitudinal direction and a helically wrapped shielding tape surrounding the conductors, an improved shielding from external magnetic influences comprising a tinned annealed mild steel about 1-mil thick and about 0.50-inch wide lapped sufficient to provide complete conductor coverage when the cable is flexed in expected normal usage and having a general composition of from about 0.08 to about 0.13 percent carbon by weight, from about 0.30 to about 0.60 percent manganese by weight, up to about 0.04 percent phosphorous by weight, up to about 0.05 percent sulfur by weight and the balance iron.
Description:
This invention relates to communication cables and, more particularly, to twin and coaxial communications cables with improved electromagnetic shielding having tinned annealed steel foil tape shielding instead of conventional copper braid.
Electrical cables used to transmit audio or radio frequency signals are often shielded to prevent electromagnetic fields from exterior sources from interfering with the transmitted signals and thus permit a high signal to noise ratio at the receiver. A copper braid is often used for the shielding. It provides good cable flexibility but its alternating current resistance can increase with time because corrosion causes poor contact between wires. The space between wires allows interfering signals to penetrate the shield. A braided shield of tinned copper wires is not an economical type of construction because of the fabrication cost and the amount of material necessary to meet requirements of strength, conductivity and coverage of the cable insulation.
Both iron tape and steel tape have been suggested for outer coverings of cable, but these tapes have either been suggested in undesirable or impractical thicknesses or for purposes other than magnetic shielding of communication cables from external interference.
It is, therefore, an object of my invention to provide a communications cable with improved shielding from external electromagnetic interference.
Another object is to provide such a cable with improved transmission characteristics.
Still another object is to provide such a cable with more efficient use of shielding metal and fabricated by improved manufacturing methods.
These and other objects will become more apparent after referring to the following specification and attached drawings, in which:
FIG. 1 is a sectional perspective view of a coaxial cable of the invention; and
FIG. 2 is a sectional perspective view of a twin shielded cable of the invention.
Referring now to FIG. 1, reference numeral 2 indicates a central conductor, preferably copper, surrounded by a layer of insulating material 4. Insulating material 4 may be polyethylene or polypropylene commonly used in communication cables where high insulation resistance and low specific inductive capacity are desire. An outer conductor 6 is wrapped longitudinally over insulation 4. In conventional coaxial cables, conductor 6 is usually a copper braid or a copper or aluminum tape, thick enough to meet conductivity requirements of the cable and with the ends overlapped in electrical contact. A tinned annealed steel tape 8, which is 0.001 inch thick, is helically wrapped and lapped around the outer conductor. The steel tape must be of high permeability and should be sufficiently lapped to maintain complete coverage during flexing of the cable. Both tapes may be applied simultaneously in a simple manufacturing operation.
The steel tape 8 is a better shield than a copper braid because its higher magnetic permeability provides a higher radial impedance, the insulation is completely covered, and there are no spaces such as between the wires of a braid. As a result, any interfering magnetic field will be more attenuated by tape 8. This will considerably reduce any voltage induced in the cable by an interfering magnetic field.
The composition of the steel tape 8 is preferably a mild steel such as AISI 1010 having a composition by weight of generally 0.80 to 0.13 percent carbon; 0.30 to 0.60 percent manganese; not over 0.04 percent phosphorous; not over 0.05 percent sulfur; and the balance iron. Iron-nickel alloys or steel compositions high in silicon are also suitable. The tape should also be annealed to improve its flexibility and permeability. A tin coating is desired for protection from corrosion.
The tape 8 should not be thinner than 1 mil because it would not have sufficient strength to be wrapped around the cable without breading and would not provide sufficient shielding.
In the embodiment shown in FIG. 2, reference numeral 10 represents conductors, preferably copper, which may be stranded as well as solid as shown, and which are covered with insulation 12 which may be the same as insulating material 4 previously described. The conductors may be twin parallel as shown or stranded to reduce interference. A shield 14 surrounds the pair of conductors.
The shield 14 is of the same material and thickness as the steel tape shield 6 shown in the coaxial cable, a tinned annealed steel tape 0.001 inch thick helically wrapped and lapped to hold the twin conductors together. When a cable has stranded conductors, the tape may be applied during the stranding operation, whereas application of a braid requires a separate manufacturing operation. If the tape is thicker than approximately one mil, the attenuation of the signal in the cable increases to undesirable levels and the cable flexibility is reduced.
The following examples are illustrative of the present invention but are not intended to limit the scope of the invention.
EXAMPLE 1
An insulating layer of polyethylene 0.040 inch thick is extruded over a stranded conductor of 19 tinned copper wires each 0.0071 inch in diameter. A 0.003 inch × 0.5 inch copper tape is applied longitudinally with a lap and covered by a 0.001 inch × 0.5 inch tinned annealed steel tape helically applied with a 1/8-inch lap. The tape is tinned annealed AISI 1010 steel. The cable has a resistance of 16.2 ohms per 1,000 foot loop, a diameter of 0.133 inch, an outer conductor weight of 6.40 pounds of copper per 1,000 feet and a steel shield weight of 2.65 pounds of steel per 1,000 feet.
Table I shows the performance characteristics of my coaxial communications cable. Magnetically induced voltage in the looped conductors in millivolts per 10-foot length was measured at various frequencies after closely coupling the coaxial cable to a flat pair 300-ohm television lead in cable carrying 1-ampere current. The cable attenuation in decibels per 1,000 feet was calculated from bridge measurements at various frequencies. ------------------------------------------------------------ --------------- TABLE I
Induced voltage in Attenuation in Frequency in Induced millivolts Decibels Kilohertz per 10 feet per 1000 feet ____________________________________________________________ ______________ 1 0.02 -- 4 0.06 0.71 10 0.14 0.94 25 0.22 -- 50 0.27 -- 100 0.31 1.44 200 0.33 1.83 300 0.32 -- 400 0.31 -- 500 0.31 2.61 2200 -- 5.30 4000 -- 8.10 ____________________________________________________________ ______________
An RG-58 A/U military type cable with the jacket removed was tested in the same manner. This cable had the same central conductor and insulation as example 1 but with a cable shield of 16 carrier, 5 ends, 0.005-inch tinned copper braid. The cable had a loop DC resistance of 19.1 ohms per 1,000 feet, a shield and outer conductor weight of 8.93 pounds per 1,000 feet and a diameter of 0.141 inch. The steel tape shielded cable had an induced voltage about 40 percent of the voltage induced in the copper braid shielded cable at 1 kilohertz which diminished to about 1 percent at 500 kilohertz. Attenuation of the steel tape shielded cable was 3 to 17 percent less than the cable with copper braided shield. While both cables had about the same total weight for the outer conductor and shield, the use of steel tape resulted in an improved cable with 28 percent less copper in the outer conductor and a 6 percent reduction in diameter.
EXAMPLE 2
An insulating layer of polyethylene 0.031 inch thick was extruded over a No. 14 AWG solid copper conductor. Two parallel conductors were then covered by a 0.001 inch × 0.5 inch tinned annealed steel tape helically applied with a 1/8-inch lap. The cable had a major diameter of 0.256 inches and a shield weight of 3.31 pounds per 1,000 feet. Table II shows the performance characteristics of my twin communication cable. Induced voltage and attenuation was measured in the same manner as with the coaxial cable. ------------------------------------------------------------ --------------- TABLE II
Frequency Induced millivolts Decibels attenuation Kilohertz per 10 feet per 1000 feet ____________________________________________________________ ______________ 1 1.3 -- 4 5.3 0.22 10 12.8 0.27 25 30.0 -- 50 58.0 -- 100 102.0 1.37 200 172.0 2.53 300 217.0 -- 400 235.0 5.86 500 242.0 -- ____________________________________________________________ ______________
A twin cable with the same insulated conductors but with a conventional 24 carrier, 5 ends, 0.0063-inch tinned copper braid shield was also tested in the same manner. The cable diameter was 0.277 inches and the shield weight was 18.5 pounds per one thousand feet. The test showed that the cable induced voltage with steel tape shielding is 30 percent less than the copper braid shielding at lowest frequencies to about the same at 200 kilohertz while the attenuation was about 10 percent less at the lowest frequency to about the same for just over 100 kilohertz. The steel tape shielded cable had an 8 percent major diameter reduction and a 72 percent reduction in shield weight.
Electrical cables used to transmit audio or radio frequency signals are often shielded to prevent electromagnetic fields from exterior sources from interfering with the transmitted signals and thus permit a high signal to noise ratio at the receiver. A copper braid is often used for the shielding. It provides good cable flexibility but its alternating current resistance can increase with time because corrosion causes poor contact between wires. The space between wires allows interfering signals to penetrate the shield. A braided shield of tinned copper wires is not an economical type of construction because of the fabrication cost and the amount of material necessary to meet requirements of strength, conductivity and coverage of the cable insulation.
Both iron tape and steel tape have been suggested for outer coverings of cable, but these tapes have either been suggested in undesirable or impractical thicknesses or for purposes other than magnetic shielding of communication cables from external interference.
It is, therefore, an object of my invention to provide a communications cable with improved shielding from external electromagnetic interference.
Another object is to provide such a cable with improved transmission characteristics.
Still another object is to provide such a cable with more efficient use of shielding metal and fabricated by improved manufacturing methods.
These and other objects will become more apparent after referring to the following specification and attached drawings, in which:
FIG. 1 is a sectional perspective view of a coaxial cable of the invention; and
FIG. 2 is a sectional perspective view of a twin shielded cable of the invention.
Referring now to FIG. 1, reference numeral 2 indicates a central conductor, preferably copper, surrounded by a layer of insulating material 4. Insulating material 4 may be polyethylene or polypropylene commonly used in communication cables where high insulation resistance and low specific inductive capacity are desire. An outer conductor 6 is wrapped longitudinally over insulation 4. In conventional coaxial cables, conductor 6 is usually a copper braid or a copper or aluminum tape, thick enough to meet conductivity requirements of the cable and with the ends overlapped in electrical contact. A tinned annealed steel tape 8, which is 0.001 inch thick, is helically wrapped and lapped around the outer conductor. The steel tape must be of high permeability and should be sufficiently lapped to maintain complete coverage during flexing of the cable. Both tapes may be applied simultaneously in a simple manufacturing operation.
The steel tape 8 is a better shield than a copper braid because its higher magnetic permeability provides a higher radial impedance, the insulation is completely covered, and there are no spaces such as between the wires of a braid. As a result, any interfering magnetic field will be more attenuated by tape 8. This will considerably reduce any voltage induced in the cable by an interfering magnetic field.
The composition of the steel tape 8 is preferably a mild steel such as AISI 1010 having a composition by weight of generally 0.80 to 0.13 percent carbon; 0.30 to 0.60 percent manganese; not over 0.04 percent phosphorous; not over 0.05 percent sulfur; and the balance iron. Iron-nickel alloys or steel compositions high in silicon are also suitable. The tape should also be annealed to improve its flexibility and permeability. A tin coating is desired for protection from corrosion.
The tape 8 should not be thinner than 1 mil because it would not have sufficient strength to be wrapped around the cable without breading and would not provide sufficient shielding.
In the embodiment shown in FIG. 2, reference numeral 10 represents conductors, preferably copper, which may be stranded as well as solid as shown, and which are covered with insulation 12 which may be the same as insulating material 4 previously described. The conductors may be twin parallel as shown or stranded to reduce interference. A shield 14 surrounds the pair of conductors.
The shield 14 is of the same material and thickness as the steel tape shield 6 shown in the coaxial cable, a tinned annealed steel tape 0.001 inch thick helically wrapped and lapped to hold the twin conductors together. When a cable has stranded conductors, the tape may be applied during the stranding operation, whereas application of a braid requires a separate manufacturing operation. If the tape is thicker than approximately one mil, the attenuation of the signal in the cable increases to undesirable levels and the cable flexibility is reduced.
The following examples are illustrative of the present invention but are not intended to limit the scope of the invention.
EXAMPLE 1
An insulating layer of polyethylene 0.040 inch thick is extruded over a stranded conductor of 19 tinned copper wires each 0.0071 inch in diameter. A 0.003 inch × 0.5 inch copper tape is applied longitudinally with a lap and covered by a 0.001 inch × 0.5 inch tinned annealed steel tape helically applied with a 1/8-inch lap. The tape is tinned annealed AISI 1010 steel. The cable has a resistance of 16.2 ohms per 1,000 foot loop, a diameter of 0.133 inch, an outer conductor weight of 6.40 pounds of copper per 1,000 feet and a steel shield weight of 2.65 pounds of steel per 1,000 feet.
Table I shows the performance characteristics of my coaxial communications cable. Magnetically induced voltage in the looped conductors in millivolts per 10-foot length was measured at various frequencies after closely coupling the coaxial cable to a flat pair 300-ohm television lead in cable carrying 1-ampere current. The cable attenuation in decibels per 1,000 feet was calculated from bridge measurements at various frequencies. ------------------------------------------------------------ --------------- TABLE I
Induced voltage in Attenuation in Frequency in Induced millivolts Decibels Kilohertz per 10 feet per 1000 feet ____________________________________________________________ ______________ 1 0.02 -- 4 0.06 0.71 10 0.14 0.94 25 0.22 -- 50 0.27 -- 100 0.31 1.44 200 0.33 1.83 300 0.32 -- 400 0.31 -- 500 0.31 2.61 2200 -- 5.30 4000 -- 8.10 ____________________________________________________________ ______________
An RG-58 A/U military type cable with the jacket removed was tested in the same manner. This cable had the same central conductor and insulation as example 1 but with a cable shield of 16 carrier, 5 ends, 0.005-inch tinned copper braid. The cable had a loop DC resistance of 19.1 ohms per 1,000 feet, a shield and outer conductor weight of 8.93 pounds per 1,000 feet and a diameter of 0.141 inch. The steel tape shielded cable had an induced voltage about 40 percent of the voltage induced in the copper braid shielded cable at 1 kilohertz which diminished to about 1 percent at 500 kilohertz. Attenuation of the steel tape shielded cable was 3 to 17 percent less than the cable with copper braided shield. While both cables had about the same total weight for the outer conductor and shield, the use of steel tape resulted in an improved cable with 28 percent less copper in the outer conductor and a 6 percent reduction in diameter.
EXAMPLE 2
An insulating layer of polyethylene 0.031 inch thick was extruded over a No. 14 AWG solid copper conductor. Two parallel conductors were then covered by a 0.001 inch × 0.5 inch tinned annealed steel tape helically applied with a 1/8-inch lap. The cable had a major diameter of 0.256 inches and a shield weight of 3.31 pounds per 1,000 feet. Table II shows the performance characteristics of my twin communication cable. Induced voltage and attenuation was measured in the same manner as with the coaxial cable. ------------------------------------------------------------ --------------- TABLE II
Frequency Induced millivolts Decibels attenuation Kilohertz per 10 feet per 1000 feet ____________________________________________________________ ______________ 1 1.3 -- 4 5.3 0.22 10 12.8 0.27 25 30.0 -- 50 58.0 -- 100 102.0 1.37 200 172.0 2.53 300 217.0 -- 400 235.0 5.86 500 242.0 -- ____________________________________________________________ ______________
A twin cable with the same insulated conductors but with a conventional 24 carrier, 5 ends, 0.0063-inch tinned copper braid shield was also tested in the same manner. The cable diameter was 0.277 inches and the shield weight was 18.5 pounds per one thousand feet. The test showed that the cable induced voltage with steel tape shielding is 30 percent less than the copper braid shielding at lowest frequencies to about the same at 200 kilohertz while the attenuation was about 10 percent less at the lowest frequency to about the same for just over 100 kilohertz. The steel tape shielded cable had an 8 percent major diameter reduction and a 72 percent reduction in shield weight.