Signal modulation

Modulation
and demodulation

·       About: Modulation
is defined as the process of superimposing a low-frequency signal on a
high-frequency carrier signal. Or the process of varying the RF carrier wave in
accordance with the information in a low-frequency signal.

·       Types of modulation: Amplitude modulation- It is a kind of
modulation where the amplitude of the carrier signal is changed in proportion
to the message signal while the phase and frequency are kept constant.

Phase modulation- In this type of modulation,
the phase of the carrier signal is altered according to the low frequency of
the message signal and hence it is called phase modulation.

Frequency modulation- In this
modulation the frequency of the carrier signal is altered in proportion to the
message signal while the phase and amplitude are kept constant is called
frequency modulation.

·       Demodulation: Demodulation
is defined as extracting the original information-carrying signal from a modulated
carrier wave. A demodulator is an electronic circuit that is mainly used to
recover the information content from the modulated carrier wave. There are
different types of modulation, and so are demodulators.

·       Difference between modulation &
demodulation: Modulation is the process of influencing data
information on the carrier, while demodulation is the recovery of original
information at the distant end of the carrier.

A modem is
equipment that performs both modulation and demodulation.

Both
processes aim to achieve transfer information with the minimum distortion,
minimum loss, and efficient utilisation of the spectrum.

Key
points

·       Measuring of waves: If you
dropped small gravel, the resulting wave would have had a short height. If the
stone had been heavier, the impact would have been more energetic and the wave
would have been taller. This height is called the wave’s amplitude. A high
amplitude sound wave will be louder; a high amplitude light wave will be
brighter. Dropping a stone every second will create a series of waves,
traversing the surface one after another in concentric circles. The number of
successive crests arriving at a spot per second is the wave’s frequency,
measured in hertz (Hz). One Hz equals one cycle per second.

·       Digital & analog: PM is
unsuitable for analog radio or TV broadcasts because it’s digital. When we use
AM or FM to propagate composite waves, it is analog transmission.

·       Usage of signal modulation: An
important advantage of modulation is that multiple signals modulated differently
can travel in the same channel — like the airwaves in a city or a fibre-optic
cable — without interrupting each other.

AM’s
frequency range, from 535 to 1,705 kHz, makes room for high wavelength signals
that can pass over mountains and buildings, providing more coverage.

FM’s frequency
range is 88-108 MHz, the waves have lower wavelengths and the transmission
distance is limited to line of sight.