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A telephone company transmits 15 speech channels across a single transmission link - AQA - A-Level Physics - Question 5 - 2019 - Paper 8
Question 5
A telephone company transmits 15 speech channels across a single transmission link. The analogue information is first subjected to pulse code modulation (PCM) before... show full transcript
Worked Solution & Example Answer:A telephone company transmits 15 speech channels across a single transmission link - AQA - A-Level Physics - Question 5 - 2019 - Paper 8
Step 1
pulse code modulation (PCM)
Answer
Pulse code modulation (PCM) is a method used to digitally represent analog signals. The process begins by sampling the analog signal at regular intervals. Each sample is then quantized to a discrete value. In PCM, the quantized samples are converted into a binary format, resulting in a serial signal suitable for digital transmission. The sampling frequency should be at least twice the maximum frequency of the signal being transmitted, adhering to the Nyquist theorem, to avoid aliasing and ensure accurate signal reproduction.
Step 2
time division multiplexing (TDM)
Answer
Time division multiplexing (TDM) is a technique allowing multiple signal streams to share the same communication medium by allocating time slots for each channel. In the case of transmitting 15 speech channels, each channel is assigned a time slot, allowing it to transmit data in its designated interval. TDM ensures that the signals do not overlap, preserving the integrity of each channel while maximizing the usage of the available bandwidth of the transmission link.
Step 3
a regenerator
Answer
A regenerator is a device used in digital transmission systems to restore and enhance the quality of the signal. It functions by receiving a degraded signal and cleaning it of noise, thereby regenerating a new signal that matches the original. This process typically involves using a switching element to improve the signal quality while removing any distortion or noise that may have accumulated during transmission. Regenerators are crucial in maintaining the strength and clarity of the transmitted information over long distances.