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What kinds of interference can create noise in a telephone communication system?
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information theory
Shannon's communication model
Consider a simple telephone conversation: A person (message source) speaks into a telephone receiver (encoder), which converts the sound of the spoken word into an electrical signal. This electrical signal is then transmitted over telephone lines (channel) subject to interference (noise). When the signal reaches the telephone receiver (decoder) at the other end of the line it is converted back into vocal sounds. Finally, the recipient (message receiver) hears the original message.
In a telephone communication system, noise and interference arise from various physical and electrical phenomena that degrade signal quality. These can be categorized as follows:
- Natural and Man-Made Noise: Natural noise includes transient electrical discharges, such as lightning, which produce radio-frequency interference. Man-made noise stems from the switching of high-voltage power lines, the operation of nearby electrical machinery, and automobile ignition systems, which generate interference through spark plug discharges.1
- Electronic and Thermal Noise: Internal noise is caused by the random movement of electrons within metals, transistors, and electron tubes. This is often referred to as thermal noise (or Johnson noise), which manifests as a hiss in the receiver and ultimately limits the maximum useful signal amplification.12
- Crosstalk: This occurs when energy is transferred from one circuit to another through leakage or coupling, resulting in unwanted signals appearing in a communication channel.3
- Interference: This phenomenon happens when an undesired signal overlaps with the channel reserved for the desired transmission, potentially rendering the communication unintelligible.1
- Extraterrestrial Sources: Radio noise can also be picked up from outer space, appearing as a random hiss similar to electronic noise.1