What is modulation?
Modulation is the
process of encoding information from a message source in a way that is suitable
for transmission. This is achieved by altering the characteristics of a wave.
By superimposing a message on to a high frequency signal known as a carrier wave
(or sinusoidal signal), video, voice and other data can be transmitted.
In the modulation
process, a parameter of the carrier wave (such as amplitude, frequency or
phase) is varied in accordance with the modulating signal. This variation acts
as a code for data transmission.
This modulated signal
is then transmitted by the transmitter.
The receiver
demodulates the received modulated signal and gets the original information
signal back.
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Different types of
modulation
There are two main
types of modulation that are used in telecommunications; analog and digital.
In analog modulation,
a continuously varying sine wave is used as a carrier wave that modulates the
message signal or data signal.
How analog modulation
works
A carrier wave has
three defining properties, which are amplitude, frequency and phase. These
three defining properties are used to create three types of modulation:
Amplitude:
A high energy wave is
characterized by a high amplitude; a low energy wave is characterized by a low
amplitude.
Amplitude modulation
Amplitude modulation
or AM is the method of varying the instantaneous amplitude of carrier signal
accordingly with instantaneous amplitude of message signal.
Frequency:
The frequency of a wave is the number of waves passing a point in a
certain time.
Frequency modulation
FM or Frequency
modulation is the process of varying the in instantaneous frequency of Carrier
signal accordingly with instantaneous amplitude of message signal.
Phase:
Phase is the position of a point in time (an instant) on a waveform
cycle.
Phase modulation
PM or Phase
modulation is the process of varying the instantaneous phase of Carrier signal
accordingly with instantaneous amplitude of message signal.
Digital modulation is
similar analog except base band signal is of discrete amplitude level. For
binary signal it has only two levels, either high or logic 1 or low or logic 0.
The modulation scheme
can be broken down in to three main types.
1.
ASK or Amplitude Shift Key
2.
FSK or Frequency Shift Key
3.
PSK or Phase Shift Key
ASK or Amplitude
Shift Key
This form of
modulation is when the carrier amplitude is varied in proportion to message
signal.
FSK or Frequency
Shift Key
This type of
modulation transmits data by varying the frequency of the carrier. In this
modulation, the carrier has two predefined frequencies.
PSK or Phase Shift
Key
With PSK, the phase
of the carrier is shifted to transmit data.
Why is modulation
used in telecommunication?
There are many key
problems in telecommunications that modulation helps to solve, including:
Problem: Certain types
of data such as voice, video, and bit streams from computers have lower
frequency bands and therefore they cannot travel very far wirelessly because
they cannot propagate through space.
Solution: When using modulation,
the carrier wave (which has a much higher frequency) is used to carry the
signal, meaning it can travel further and more quickly through space.
Problem: Antenna length
would be impractical for voice, video and bit streams without modulation.
Solution: By using the high
frequency carrier waves, the necessary antenna size is greatly reduced.
Problem: Without modulation,
transmission of video, voice or data bit streams being sent on the same
frequency range would cause overlapping of channels (resulting in
interference).
Solution: Carrier radio waves
have a wide range of frequencies which allow you to select individual
non-overlapping channels to carry the information.
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the Soukacatv.com main products are modulators both in analog and digital ones,
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For more, please
access to https://www.soukacatv.com.
CONTACT US
Dingshengwei
Electronics Co., Ltd
Company Address:
Buliding A,the first industry park of Guanlong,Xili
Town,Nanshan,Shenzhen,Guangdong,China
Tel : +86 0755
26909863
Fax : +86 0755
26984949
Phone: +86
13410066011
Email:ken@soukacatv.com
Skype: soukaken
Source: carritech
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