Types of
Modulation
The bandwidth required for the transmission of commercial-quality speech
is
300 - 3400 Hz.Thus , as long as
a physical pair of wires, or two pairs of wires are
provided to connect between two
parties , a conversation is no longer a problem.
Telephone cable is , however very
expensive and together with the associated
duct work and main-holes, comprises
the major part of the cost linking two points.
It is desirable therefore to be
able to transmit more than one conversation over a
given link and thus economic in
telephone cable. If the number of telephone
conversations were merely transmitted
into one end of a line it would not be
possible to separate them at the
distant end of the line since each conversation
would be occupying
the same part of the frequency spectrum .
How then
can many different conversation
be transmitted over a single circuit and get be
separate at the distant end ?
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