5.1 “Digital transmission is essential in today’s telecommunication as it is the most efficient way
of reproducing the transmitted signal at the receiving end.”
Explain the above statement with reference to different stages in digital transmission.

In digital transmission, first a band-limited analog signal is sampled using the Nyquist
theorem. This makes it possible to reproduce the original signal with a minimum noise at the
receiver. These discrete samples are then quantized using non-liner quantization. As most of
the signals lie Within +Vm/2 and –Vm/2, non-linear quantizing is used to have a S/N ratio all
the sampled values.

Quantized values are then encoded so that every sampled and quantized values are
represented as 8-bits. Finally, a PCM frame is built with such encoded patterns and
transmitted through the medium. In such a way, in all stages, attention is paid to reduce the
noise introduced to the original signal while undergoing this process.

Therefore, digital transmission is essential in today’s networks as it ensures reproduction of
original signal at the receiving end.

5.2 What are the different types of repeaters?

i. Active repeaters – feeds power, repeats the signal

ii. Passive repeaters – functions as a reflector

5.3 Repeaters are extensively used in Pulse Code Modulated (PCM) transmission links in
Cable PCM transmission systems.
Explain different sections of a repeater with reference to the functions of each unit.

Repeaters carryout 3 different functions in cable PCM networks.
i. Reshaping
ii. Retiming
iii. Power feeding

Different functional units in a repeater:

i. Line equalize – Amplifies low frequency signals with a high gain and high
frequency signals with a low gain, to equalize different frequency signals
received
ii. Rectifier – O/p values is rectified
iii. Tuned amplifier – Driven by the rectifier o/p and regenerates the clock pulse
iv. + Threshold detector – Gives an o/p when the signal value is higher than the
threshold
v. – Threshold detector - Gives an o/p when the signal value is lower than the
negative threshold
vi. Differentiator – Provides a short spark when there is an output from the Tuned
amplifier
vii. + Reshaper – O/p a signal if there is a value when +Threshold detector gives a
spark
viii. – Reshaper - O/p a signal if there is a value when -Threshold detector gives a
spark
ix. Power feeding equipment