4.1.7 Noise is an important concept in networks such as LANs. Noise usually refers to sounds. However, noise related to communications refers to undesirable signals. Noise can originate from natural or technological sources and is added to the data signals in communications systems.
All communications systems have some amount of noise. Even though noise cannot be eliminated, its effects can be minimized if the sources of the noise are understood. There are many possible sources of noise:
• Nearby cables that carry data signals
• RFI from other signals that are transmitted nearby
• EMI from nearby sources such as motors and lights
• Laser noise at the transmitter or receiver of an optical signal
Noise that affects all transmission frequencies equally is called white noise. Noise that only affects small ranges of frequencies is called narrowband interference. White noise on a radio receiver would interfere with all radio stations. Narrowband interference would affect only a few stations whose frequencies are close together. When detected on a LAN, white noise could affect all data transmissions, but narrowband interference might disrupt only certain signals.
The Interactive Media Activity will allow students to generate white noise and narrowband noise.
The next page will describe analog bandwidth and digital bandwidth.
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