Signal Integrity in Guided Transmission Media

Electronic Communication Processes

In electronic communication, information in a signal moves from one device to another. Along the way, signals undergo a series of processes, including:

• Noise: The information signal gets mixed with other unwanted signals produced by highly diverse sources.
• Attenuation: This is the loss of energy a signal suffers as it propagates through a medium. This is resolved using amplifiers, repeaters, or signal regenerators at the transmitter and receiver.
• Signal Collision: A medium can be shared by several signals, but if they coincide, they collide and interfere with each other.

Denoising with Balanced Cables

This method consists of two conductors, where each carries the same signal but with opposite polarity to the other. The receiving device calculates the difference between the two signals.

For example: Input = Conductor 1 - Conductor 2 = (V + N) - (-V + N) = 2V. As a result, the noise (N) is canceled, and the original signal voltage (V) is doubled.

Transmission Media

Transmission media can be of two main types:

• Guided or Cabled: The signals are transmitted through a confined physical path, like a wire or fiber optic cable.
• Unguided or Wireless: The signals travel through the air or space without being confined to a physical path.

Guided Media: An In-Depth Look

Electrical cables were the primary means of guided transmission. Their electrical characteristics and resistance cause the signal to attenuate quickly, and cable harnesses can be bulky and heavy.

Techniques to Improve Cable Performance

To avoid the problems inherent in basic electrical cables, several techniques were devised:

• Twisting: Each pair of wires that transmits information is braided together. This technique helps to cancel out electromagnetic interference from external sources.
• Shielding: The cable is coated in a conductive material (a shield) that absorbs and eliminates external interference.

Twisted Pair Cables

These cables are grouped into categories according to their transmission characteristics.

Common Twisted Pair Categories

• Category 1: Designed primarily for telephone networks.
• Category 2: Similar to Category 1, with the added ability to transmit data.
• Category 3: Used in computer networks with speeds up to 16 Mbps.
• Category 4: Defined for token ring-type computer networks.
• Category 5: Widely used in Local Area Networks (LAN).
• Category 5e (or 5+ / 5a): An enhanced Category 5 cable that minimizes attenuation and interference.
• Category 6: A standardized cable that offers better performance and higher speeds than Cat5e.
• Category 7: A standardized, fully shielded cable offering even higher performance and bandwidth.

Advantages of Twisted Pair Cables

• Depending on the category, they can transmit analog and digital signals, including audio, video, and data.
• They are easy to install and handle.
• They are well-established and widely available in the market.

Disadvantages of Twisted Pair Cables

• They have limitations on transmission speed and distance.
• They can be heavy, especially in large bundles.

Coaxial Cable

In a coaxial cable, the signal is confined within concentric layers that act as an insulator and shield, effectively preventing electromagnetic interference.

Advantages of Coaxial Cable

• They are more immune to interference than unshielded twisted-pair cables.
• They are more resistant to crosstalk (signal leakage between adjacent cables).
• They are highly standardized and familiar to installers.

Disadvantages of Coaxial Cable

• Signal loss can occur at seams, connectors, and joints.