Topic 5 –Modulation
and
Communication Concepts
5.1 – General Consideration of Modulation
5.1.1-Why we need modulation ?
Modulation
• In general telecommunications, modulation is a process of conveying message
signal, for example, a digital bit stream or an analog audio signal, inside another
signal that can be physically transmitted.
• The primary purpose of modulation in a communication system is to generate a
modulated signal suited to the characteristics of a transmission channel.
• In radio communications, modulation is needed in the transmission systems to
transfer the message into the available high frequency radio channel.
Why we bother to use modulation at all?
𝑓𝑟𝑒𝑞
Why we bother to use modulation at all?
𝑓𝑟𝑒𝑞
Why we bother to use modulation at all?
𝑓𝑟𝑒𝑞
 There are more than a dozen channels on the radio at any time,
each with a given frequency: 100.1 MHz, 102.5 MHz etc...
 Each channel gets a certain range (usually about 0.22 MHz), and the
entire station gets transmitted over that range.
 Modulation makes it all possible, because it allows us to send voice and
music (which are essential baseband signals) over a bandpass (or
"Broadband") channel.
Propose of Modulation
• Transfer the message into the available high frequency radio channel.
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Efficiency in propagation. (Higher frequency waves transmitter better.)
Immunity to some forms of noise.
The size of the antenna required. (Higher frequency -> smaller size)
Allow multiple signals transmit at the same time without interference.
Exchange of power and bandwidth.