Data Transmission Media: Cables, Fiber Optics and Satellite

Transmission Media Types

Transmission media include twisted pair, coaxial cable, fiber optics, optical paths, and satellite communication.

Twisted Pair

As one of the most established media, twisted pair is frequently used in telephone systems. It supports both analog and digital transmission, with variable bandwidth depending on the cable type.

Types of Twisted Pair

• Unshielded: Standard, cost-effective, and easy to handle, though it has a higher error rate.
• Shielded: Features a metal mesh for EMI protection, resulting in a lower error rate but increased cost.
• Uniform: Includes a metal shield for each pair; offers a more sophisticated construction.

Coaxial Cable

Widely used since the 1940s, coaxial cable consists of a solid copper core covered by insulating material, surrounded by a woven copper mesh, and protected by a plastic layer. It was historically used for long-distance lines before becoming common in local area networks (LANs).

Advantages and Disadvantages

• Advantages: High transmission capacity.
• Disadvantages: Large physical size and sensitivity to acute angles.

Coaxial Types

• Baseband: 50 Ohms, used for digital transmission.
• Broadband: 75 Ohms, used for analog transmission.

Fiber Optics

Fiber optics transmit light (analog or digital) through strands as thin as a human hair. They are lightweight, offer low signal loss, high capacity, and high reliability.

Components of Optical Transmission

• Transmission Medium: Fiberglass.
• Light Source: Light-emitting diode (LED) or laser diode.
• Detector: Photodiode that generates electrical pulses upon receiving light beams.

Fiber Optic Modes

• Multimode: Uses multiple strands, is cost-effective, and is ideal for short distances.
• Single-mode: Provides a single path for light; while more expensive, it supports great distances and high speeds.

Pros and Cons

• Advantages: Massive bandwidth and immunity to voltage changes.
• Disadvantages: Complex implementation and expensive unidirectional interfaces.

Optical Path

Transmission occurs through the air using infrared, laser, microwave, or radio techniques. Performance can be negatively impacted by rain and fog.

Satellite Communication

Satellites utilize multiple antennas, transmitters, and receivers. They function by listening to a specific spectrum portion, amplifying the input signal, and relaying it to a different frequency to avoid interference. They support high speeds (up to 1544 Mbps).

Transmission Parameters

• Primary Parameters: Depend on the physical characteristics of the medium and the frequency of use.
• Secondary Parameters: Calculated based on primary parameters.

Coaxial Cable Specifications

Coaxial cables feature an outer conductor mesh and a solid inner conductor, both insulated and encased in flexible material.

Applications and Characteristics

Coaxial cable is used for TV distribution and long-distance telephony, capable of transporting 10,000 simultaneous voice calls. While fiber optics are replacing it in many areas, it remains relevant in local networks.

• Analog Transmission: Requires amplifiers every few kilometers; supports frequencies up to 500 MHz.
• Digital Transmission: Requires repeaters every 1 km to maintain high-speed data integrity.