Communication cables are essential components in modern telecommunications, designed to transmit a wide range of signals including voice, data, and video. The core of a communication cable consists of multiple insulated conductors, often arranged in groups to minimize interference. These conductors are enclosed in a protective sheath, which may include an additional outer jacket for enhanced durability. Cables can be installed using various methods such as overhead lines, direct burial, underground conduits, or even underwater placements, depending on the environment and application.
Cables are categorized based on their structure and function. Structurally, they are divided into symmetrical, coaxial, and integrated types. Functionally, they can be classified as field cables (such as underground or submarine cables) or permanent cables. Communication cables offer high bandwidth, large capacity, and reduced external interference, but they can be difficult to repair once installed. They support a variety of communications, including telephony, telegrams, data transfer, and image transmission.
**Symmetrical Cable**
Symmetrical cables consist of two wires arranged symmetrically within a communication loop. These cables are available in low-frequency and high-frequency versions. High-frequency models can transmit up to 800 kHz, supporting around 180 telephone lines per loop, while low-frequency versions typically operate below 252 kHz, supporting approximately 60 lines. Due to their open electromagnetic field, these cables suffer from higher attenuation and greater mutual and external interference, making it challenging to increase frequency and capacity.
Long-distance symmetrical cables are composed of multiple four-wire groups with different insulation structures. Common configurations include star-shaped groups and double twisted pairs. Insulation materials vary, with paper, polyethylene, polystyrene, and foam polyethylene being widely used. High-frequency cables require more advanced insulation techniques, such as rope-and-insulated star twists, to maintain signal integrity.
Local telephone cables, also known as urban or regional cables, are designed for shorter distances and smaller areas. They feature a large number of wire pairs—often hundreds or thousands—and are commonly used in cities, suburbs, and industrial zones. These cables typically have a thinner diameter (around 0.5 mm) due to lower frequency usage and shorter communication ranges. Their internal structure includes twisted pairs, star-type groups, or double-pair configurations, with color-coded wires for easy identification during installation.
To improve moisture resistance and long-term stability, integrated sheathing has become standard in city telephone cables since the 1970s. Three main types are widely used: Alpeth, Stalpeth, and Lepeth. Each uses a combination of polyethylene, aluminum, and lead layers to provide excellent protection against environmental factors.
**Coaxial Cable**
Coaxial cables consist of two concentric conductors—an inner and an outer—separated by insulation. This design minimizes electromagnetic interference and allows for high-frequency signal transmission, often reaching up to 10–100 MHz or more. Coaxial cables are ideal for trunk lines in long-distance communication systems and are also used for broadcasting TV programs and efficient data transfer.
The inner conductor is typically made of copper, sometimes reinforced with a steel core for added strength, especially in submarine applications. The outer conductor is usually a copper tape, available in corrugated, indented, or lock-type designs. The insulation between the conductors must have a low dielectric constant and loss to ensure signal quality. To prevent misalignment and reduce interference, the outer conductor is often shielded with a double-layer steel strip before being twisted into the final cable structure.
Overall, communication cables play a crucial role in maintaining reliable and efficient data and voice transmission across various environments and applications.
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