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 f_o - f_s. 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.