“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
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
represented as 8-bits. Finally, a PCM frame is built with such encoded
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.
What are the different types of repeaters?
repeaters – feeds power, repeats the
ii. Passive repeaters
– functions as a reflector
Repeaters are extensively used in Pulse Code Modulated (PCM) transmission
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.
iii. Power feeding
Different functional units in
i. Line equalize – Amplifies low frequency
signals with a high gain and high
frequency signals with a low gain, to equalize different frequency
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
v. – Threshold detector - Gives an o/p when the signal value
is lower than the
vi. Differentiator – Provides a short spark when there is
an output from the Tuned
vii. + Reshaper – O/p a signal if there is a value when +Threshold
detector gives a
viii. – Reshaper - O/p a signal if there is a value when -Threshold
detector gives a
ix. Power feeding equipment