What is modulation?
· Operation of
varying amplitude, frequency or phase of carrier signal accordingly with the
instantaneous amplitude of the message signal is called modulation.
· Modulation=
Adding information to a carrier signal
HDMI Encoder Modulator, 16in1 Digital Headend, HD
RF Modulator at Soukacatv.com
Need for Modulation:
Baseband signals are incompatible for direct
transmission. For such a signal, to travel longer distances, its strength has
to be increased by modulating with a high frequency carrier wave, which doesn’t
affect the parameters of the modulating signal.
Advantages
of Modulation
The antenna used for transmission, had to be
very large, if modulation was not introduced. The range of communication gets
limited as the wave cannot travel a distance without getting distorted.
Following are some of the advantages for
implementing modulation in the communication systems.
·
Reduction of antenna size
·
No signal mixing
·
Increased communication range
·
Multiplexing of signals
·
Possibility of bandwidth adjustments
·
Improved reception quality
Signals
in the Modulation Process
Following are the three types of signals in
the modulation process.
Message or Modulating Signal
The signal which contains a message to be transmitted
is called as a message signal. It is a baseband signal, which has
to undergo the process of modulation, to get transmitted. Hence, it is also
called as the modulating signal.
Carrier Signal
The high frequency signal, which has a
certain amplitude, frequency and phase but contains no information, is called
as a carrier signal. It is an empty signal and is used to carry the
signal to the receiver after modulation.
Modulated Signal
The resultant signal after the process of
modulation is called as a modulated signal. This signal is a
combination of modulating signal and carrier signal.
Types of Modulation
There are many types of modulations.
Depending upon the modulation techniques used, they are classified as shown in
the following figure.
Continuous-wave Modulation
In continuous-wave modulation, a high
frequency sine wave is used as a carrier wave. This is further divided into
amplitude and angle modulation.
· If
the amplitude of the high frequency carrier wave is varied in accordance with
the instantaneous amplitude of the modulating signal, then such a technique is
called as Amplitude Modulation.
· If
the angle of the carrier wave is varied, in accordance with the instantaneous
value of the modulating signal, then such a technique is called as Angle
Modulation. Angle modulation is further divided into frequency modulation
and phase modulation. If the frequency of the carrier wave is varied, in
accordance with the instantaneous value of the modulating signal, then such a
technique is called as Frequency Modulation.
If the phase of the high frequency carrier
wave is varied in accordance with the instantaneous value of the modulating
signal, then such a technique is called as Phase Modulation.
Pulse Modulation
In Pulse modulation, a periodic sequence of
rectangular pulses is used as a carrier wave. This is further divided into
analog and digital modulation.
In analog modulation technique, if the
amplitude or duration or position of a pulse is varied in accordance with the
instantaneous values of the baseband modulating signal, then such a technique
is called as Pulse Amplitude Modulation (PAM) or Pulse Duration/Width
Modulation (PDM/PWM), or Pulse Position Modulation (PPM).
In digital modulation, the modulation
technique used is Pulse Code Modulation (PCM) where the analog signal is
converted into digital form of 1s and 0s. As the resultant is a coded pulse
train, this is called as PCM. This is further developed as Delta Modulation
(DM). These digital modulation techniques are discussed in our Digital
Communications tutorial
Another way
If the variation in the parameter of the
carrier is continuous in accordance to the input analog signal the modulation
technique is termed as analog modulation scheme. It is classified as:
1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation
If the variation in the parameter of the
carrier is discrete then it is termed as digital modulation technique.it is
classified as:
1. Amplitude
Shift Keying
2. Frequency Shift
Keying
3. Phase shift keying
Established in 2000, the Soukacatv.com main
products are modulators both in analog and digital ones, amplifier and
combiner. We are the very first one in manufacturing the headend system in
China. Our 16 in 1 and 24 in 1 now are the most popular products all over the
world.
For more, please access to https://www.soukacatv.com.
CONTACT US
DingShengwei Electronics Co., Ltd
Company Address: Building A, the first industry park of Guan
long, Xili Town, Nan Shan, Shenzhen, Guangdong, China
Tel: +86 0755 26909863
Fax: +86 0755 26984949
Phone: +86 13410066011
Email:ken@soukacatv.com
Skype: soukaken
Website: https://www.soukacatv.com
Source: eceacademy
没有评论:
发表评论