Umair Gaines
Coaxial cable, also known as coax, is a type of electrical cable that transmits high-frequency electrical signals with minimal loss. It is commonly used for applications such as broadband internet, cable television, and computer data connections. Coaxial cables are designed with an inner conductor, typically made of copper or copper-plated wire, surrounded by an insulating layer, and enclosed by a shield. The insulating material, known as a dielectric, plays a crucial role in determining the electrical properties of the cable. However, coaxial cables can sometimes sustain damage, resulting in exposed copper wiring. In such cases, it is important to repair or replace the cable to ensure optimal performance and prevent further issues.
Characteristics and Values of Coaxial Cable Insulation
| Characteristics | Values |
|---|---|
| Inner Conductor | Usually solid copper, stranded copper, or copper-plated steel wire |
| Insulating Layer | Plastic, foam plastic, air with spacers, solid polyethylene (PE), or Teflon (PTFE) |
| Shield | One to four layers of woven metallic braid and metallic tape, or braided copper |
| Outer Jacket | May be omitted for internal chassis connections; may need protection from UV light, oxidation, rodents, and burial for outdoor use |
| Electrical Signal | Carries high-frequency electrical signals with low losses |
| Applications | Telephone trunk lines, broadband internet, cable television, RF and microwave transmission, computer data connections |
| Repair | Electricians can repair damage with an F-female to F-female connector or liquid electrical tape |
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What You'll Learn
Coaxial cable design choices
The inner conductor of a coaxial cable might be solid or stranded, with stranded being the more flexible option. The inner conductor may also be silver-plated to improve high-frequency performance and smooth the surface, reducing losses due to skin effect. Copper-plated steel wire is often used as the inner conductor for cable in the cable TV industry.
The insulator surrounding the inner conductor can be solid plastic, foam plastic, or air with spacers supporting the inner wire. The dielectric insulator's properties determine some of the electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE) is also used as an insulator, exclusively in plenum-rated cables.
The cable is then protected by an outer insulating jacket, which can be made from various materials, commonly PVC, but fire-resistant materials may be required for certain applications. For outdoor use, the jacket may need to resist ultraviolet light, oxidation, rodent damage, or direct burial. Flooded coaxial cables use a water-blocking gel to protect against water infiltration through minor cuts in the jacket.
The shield surrounding the insulating layer can be made of braided copper wire, allowing for flexibility, but this also means there are gaps in the shield layer, and the inner dimension of the shield varies. Silver-plating may be used on the braid for improved performance. Some cables have a double-layer shield, with two braids or a combination of a thin foil shield and a wire braid. Quad-shield cables use four alternating layers of foil and braid. Other designs sacrifice flexibility for better performance, with a solid metal tube shield that cannot be bent sharply.
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Insulating jacket
Coaxial cables, or coax, are a type of electrical cable that transmits high-frequency electrical signals with minimal loss. They are commonly used for applications such as broadband internet networking cables, cable television signals, and connecting radio transmitters and receivers.
The design of coaxial cables includes an inner conductor, typically made of solid or stranded copper, copper-plated steel wire, or, occasionally, silver-plated wire, which is surrounded by an insulating layer. This insulating layer, also known as the dielectric, plays a crucial role in determining the electrical properties of the cable. It can be composed of solid plastic, foam plastic, or air with spacers to support the inner wire.
The insulating layer is enclosed by a shield, typically consisting of one to four layers of woven metallic braid and metallic tape, or, in some cases, woven braided aluminium or copper wire and aluminium foil. This shield helps to contain the signal's electric and magnetic fields within the dielectric and shields the inner conductor from external interference.
Finally, the coaxial cable is often protected by an outer insulating jacket, which serves as a protective outer sheath. This jacket can be designed to resist various elements, such as ultraviolet light, oxidation, and rodent damage, depending on the intended outdoor or indoor use.
In terms of repair and maintenance, it is important to note that coaxial cables cannot be reliably spliced without careful consideration of the joint geometry due to the high frequencies involved. Minor damage to the insulation, such as small breaks or exposed copper, may be addressed with liquid electrical tape or by installing an F-female to F-female connector "bridge." For more significant damage, it may be necessary to consult an electrician or consider replacing the cable, especially if the centre conductor or dielectric is compromised.
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Cable damage
Coaxial cables are fragile, and there are several ways they can become damaged. Firstly, coaxial cables are not waterproof, so they should be kept away from water and rain to prevent waterlogging, which can alter their electrical characteristics and render them useless. Small nicks in the outer sheath can cause water to enter, so coaxial cables should not be submerged. Additionally, the insulation within coaxial cables has a low melting point and can start to soften at temperatures as low as 150 degrees Fahrenheit. Prolonged exposure to heat can cause the insulation to shift, leading to a potential short circuit if the centre conductor and shielding touch. Therefore, coaxial cables should be kept away from heat sources such as heat sinks and stage lights.
Another way coaxial cables can be damaged is by improper handling. Coaxial cables need to be handled with care and should not be pulled too tightly, as this can harm the signal quality by tightening the braided wire shielding and compressing the foam insulation. Instead of a long, hard pull, it is better to make several short pulls through walls and ceilings. It is also important to use the correct tools when preparing the ends of the cable for connectors, as a tiny nick in the wire can cause significant signal issues. A special coaxial cable stripper is recommended for this purpose.
Furthermore, coaxial cables should be kept away from electrical cables to prevent interference. Electrical lines can cause interference and affect the signal quality of coaxial cables. It is recommended to maintain a distance of at least 6 inches between coaxial and electrical cables. If the coaxial cable must cross an electrical line, it should do so at a 90-degree intersection. To further minimise interference, it is recommended to use shielded wiring or install 'twisted pair' phone wiring.
To protect coaxial cable junctions located outdoors from weather damage, it is advisable to use waterproof coax connectors, which have a rubber gasket that seals the connection. Alternatively, standard compression coax connectors can be used with heat shrink tubing to seal them. Enclosing the connections in a waterproof electrical box with a weatherproof cover is also an effective way to protect them from the elements.
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Splicing coaxial cable
To splice a coaxial cable, you will need the following tools:
- Coaxial cable stripper (or a utility knife)
- Compression or F-connectors compatible with your coaxial cable type
- BNC female-to-female coaxial adapter
- Small, sharp wire cutters
- Cut off the ends of the coax cables to be spliced using small, sharp wire cutters. Create squared-off surfaces, rather than bevelled surfaces.
- Mould the ends of the coax cables back into cylinders using your fingers. They will likely have been distorted by the pressure of the cutting.
- Insert each cable into a coax stripper tool, ensuring that the end of the cable is seated flush against the wall or guide on the stripping tool.
- Connect the two cables to either end of a BNC female-to-female coaxial adapter.
It is important to note that splicing coaxial cable can degrade the signal. This is because the space around the cable is electronically active, not just the metal part itself. Therefore, careful consideration of the joint geometry is required to avoid signal interference.
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Electric signals
Coaxial cable, or coax, is a type of electrical cable that carries high-frequency electrical signals with low losses. It is used in applications such as telephone trunk lines, broadband internet networking, and cable television signals. The cable consists of an inner conductor, usually made of solid copper, stranded copper, or copper-plated steel wire, surrounded by an insulating layer, and enclosed by a shield. The insulating material, also known as a dielectric, can be solid plastic, foam plastic, or air with spacers supporting the inner wire.
The choice of insulating material is important as it determines some of the electrical properties of the cable. For example, a solid polyethylene (PE) insulator is commonly used in lower-loss cables, while solid Teflon (PTFE) is used exclusively in plenum-rated cables. The shield surrounding the insulating layer is typically made of one to four layers of woven metallic braid and metallic tape, providing protection and ensuring the cable's functionality as a transmission line.
To splice a coaxial cable, one must carefully consider the joint geometry due to the physical effects at high frequencies. The process involves using a coax stripper tool to expose the bare centre conductor of each cable. After stripping the insulation, the cables are pressed into F connectors, ensuring the white inner insulation is visible against the front flange. It is important not to twist the coax during this step. Next, a coax crimping tool is used to crimp the connections, fully squeezing and then releasing the handle. Finally, the two cables are connected using a BNC female-to-female coaxial adapter.
In some cases, a coaxial cable may be damaged, affecting the insulation. If the dielectric is mostly intact and the centre conductor is not exposed, the cable may continue to function. However, if the centre conductor is broken or the dielectric is severely damaged, the cable's performance may be compromised. In such cases, it is recommended to consult an electrician or consider repairing or replacing the cable.
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Frequently asked questions
Coaxial cable, or coax, is a type of electrical cable that consists of an inner conductor surrounded by a concentric conducting shield, separated by a dielectric (insulating material).
Coaxial cable is used to carry high-frequency electrical signals with low losses. Applications include telephone trunk lines, broadband internet networking cables, cable television signals, and connecting radio transmitters and receivers to their antennas.
The inner conductor is typically made of solid copper, stranded copper, or copper-plated steel wire.
The insulating material, or dielectric, can be solid plastic, foam plastic, or air with spacers supporting the inner wire. Common choices include solid polyethylene (PE) and solid Teflon (PTFE).
If the dielectric is mostly intact and the centre conductor is not exposed, the cable will likely work fine. If the centre conductor is exposed, the cable should be replaced. In some cases, a coax stripper tool can be used to splice the cable, but this requires careful consideration of the joint geometry.
