Resume of The 3rd Video, MODULATION TECHNIQUE
MODULATION TECHNIQUES
The video will mainly display and explain about :
a. Block
Diagram of Modulation
b. Types
of Modulation
i)
Analog Modulation
ii)
Digital Modulation
c. Analog
Modulation
i)
Amplitude Modulation
ii)
Frequency Modulation
iii)
Phase Modulation
I.
INTRODUCTION
A
message or information that needs to be sent to another user can relate to baseband
signals. There will also be a transmitter that generates carrier also the receiver as the destination.
The
information signals are first converted onto electrical form known as a baseband
signal. The characteristic of the signals needs to be changed to make it suitable
for transmitting. The process of varying the characteristics of a carrier signal
is called as Modulation.
II.
NEED OF MODULATION
Ø Reduction
in the higher of an antenna
Ø Avoid
the mixing of the signals
Ø Makes
multiplexing possible
Ø Increases
the range of communication
III.
BLOCK DIAGRAM OF MODULATION
There
are inputs such as modulating signals and carrier signals and a modulated
signal is the output. Modulating signal has two form, analog signal (music,
image, etc) and Digital Signal (computer data)
IV.
TYPES OF MODULATION
a. Analog
Modulation
i)
Amplitude Modulation
Changing
the amplitude of the high frequency signal (carrier signal) depending on the
value of the modulating signal while the frequency and the phase remain constant.
Information is contained in the amplitude of the carrier signal
ii)
Frequency Modulation
In
this modulation, the frequency if the carrier signal varies whereas the
amplitude and the phase remains constant. Frequency and time period are reciprocals
to each other, when the time period is minimum we get the maximum frequency and
vice versa. As the time period decrease and the frequency increases, the signal
gets compressed.
Frequency
Deviation,
Advantages
of FM Transmitter
o
Improved Noise Immunity
o
Entire Transmitted Signal is Useful
o
Covers Larger Area with the Same Amount of
Transmitted Power
o
Transmitted Power Remains Constant
Disadvantages of FM
·
Very large Bandwidth is required
·
Complex
Application: radio
broadcasting, sound broadcasting, satellite communication.
SUPERHETERODYNE RECEIVER
Heterodyning is the process of combining two signals with different frequencies to produce a new frequency. The receiver converts every selected RF Signal to a certain lower frequency called as Intermediate Frequently.
In superheterodyne AM receiver
In detail, the signals is
transmitted in the form of electromagnetic waves. The receiever is safe and the
receiver antenna induces a small voltage. And then, in RF Stage or an amplifier
with selects required signal and rehect other signals. This function help to
reduce effect of noise. After that the mixer get two inputs, from RF amplifier
and one from the local oscillater. Intermediate frequency is produced by a mixer with the difference component of fo
- fs. This signal is amplified and provides gain to the
receiver while the sensitivity and selectivity of a receiver do not change.
After that, the amplified
IF Signal is detected by the detector to recover the original modulating signal.
Finally, this signal sent to the loudspeaker to automatically gain control.
Advantages of Superheterodyning
:
· No
variation in the bandwidth
· High
sensitivity and selectivity
· High
adjacent channel rejection
DIAGRAMS OF SUPERHETERODYNE
FM RECEIVER
a. RF
Amplifier used to improve signal to noise ratio and matches the receiver input
impedance.
b. Mixer, converts the received signal to the intermediate frequency IF
c. IF Amplifier, perform intermediate frequency to the desired level with more bandwidth than AM.
d. Limiter,
removes all unwanted signal
The
amplitude of a modulated were remains constant but practically when the wave is
transmitted, random noise and other signals might get added
e. FM
Detector, used to demodulated the WM w ave, passing the wire, it is then
amplified to the loudspeaker.
iii)
Phase Modulation
Has
more or less the same neighborhood. With the change of phase, amplitude and
frequency remains the same.
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