Carrier wave; Modulation types (Part - 12) - Physics Communication Systems, Physics, Class 12 Video Lecture

hello friends this video on
communication systems pac-12
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more fear from exam okay so now we are
clear with the idea of what is the need
of modulation you all know why this
modulation needed now let us try to
understand the courier wave in detail
because whenever we talk of modulation
we will be talking about a high
frequency wave that means that in our
message signal is a low frequency wave
but how are we going to translate it
into a high frequency wave with the help
of another high frequency wave which is
known as a courier wave for example if
we take the previous example of that
letter so the letter is our low
frequency message signal and the Train
is a high frequency wave so a high
frequency signal to which the
information of the original message
signal is attached so what do we do in
the process of modulation we pick a high
frequency wave right now we change
something in that high frequency wave
such that we can attach the information
of the message signal into that high
frequency wave right so that is what we
do we do not make any changes to the
message signal so here
when whenever we talked about modulation
there will be two things which are
involved so what are the two things
involved one is the message signal now
the message signals the signal which is
sent by the sender at the transmitter so
that is a low frequency signal and the
second one is the courier wave so
courier wave is a high frequency wave
now we will not make any changes to the
message signal during the process of
modulation why because message signal
contains the information and we do not
want any change to the information the
information
to be reading it is something like if I
am talking to my mom over the phone if I
say hello mom how are you I do not want
this information to get changed now if I
am saying hello mom how are you and if
my mom hears hello mom what are you
doing so the information is getting
changed so there is no process no use of
such a communication system because I
want to communicate the information
which I have so there should be no
change in the message signal so the
message signal remains unchanged so
where will the modification happen
processes modulation that means
modifying what will get modified this
high frequency carrier wave is the one
which will get modified now how will it
get modified that is what we are going
to study in this topic of modulation
that how the carrier wave is modified so
that it carries the message signal
intact without causing any change to the
information so that is our agent again
so this carrier wave can be a sinusoidal
wave that is a sine wave or it can be in
the form of pulses so this is the sine
wave we are all familiar with these are
pulses so water pulses pulses are
nothing but they are similar to square
waves so they basically represent the
digital signals right so carrier wave
can be either of them it can be a sine
wave it can be a pulse so let us now
talk about the types of modulation in
case of sinusoidal waves because as I
said carrier waves can be of two types
it can either be a sinusoidal wave or it
can be a pulse so in case of sinusoidal
wave your waves let us see what are the
different types of modulation possible
so what are the different types of
modulation which we will talk about we
are going to talk about amplitude
modulation frequency modulation and
phase modulation so these are the three
types of modulation which we will be
discussing for a sine B now before that
there are certain features of sinusoidal
beams which we should
aware of because we will be using that
them quite often and and I have also
covered them in the previous lessons
when we talked about the lesson on
oscillations the lesson on waves the
lesson on electromagnetic wave so in all
those lessons I have already discussed
about each of these characteristics of a
sinusoidal wave in detail right so when
I say different types of modulation how
do you think that modulation can happen
in many different ways
well when I say modulation what is it it
is nothing but a modification which
happens in the Korean Wave as per the
message signal right now this
modification in the Korean Wave can
happen in many different ways the
modification can happen in the amplitude
of the carrier wave then we call it as
amplitude modulation
if the modulation happens in the
frequency we call it frequency
modulation if it happens in phase we
call it phase modulation so I am sure
that you may of you already remember
what is amplitude what is frequency and
what is phase but still for those who do
not remember them let us have a quick
review of these parameters of a width
because in case any of you do not
remember them then it will really be
difficult for you for the next half of
the lesson because I will often be using
these terms so let us have a quick recap
of the parameters of a wave so what are
the different parameters which describe
or which characterize a wave amplitude
phase wave number wave length time
period and hillard frequency so these
are some of the parameters or some of
the things which actually describe away
they can describe a wheel now I not talk
about all of them in detail but most of
them are being used when I talk about
modulation so let us have a quick review
of each of them what does amplitude of a
wave it is the maximum displacement of
the elements of the medium from their
equilibrium position
as the wave passes through them so the
key point here is maximum displacement
from equilibrium position so that
defines the amplitude so it is generally
denoted by a capital A so if you think
of a wave a sinusoidal wave in this form
so this is the maximum displacement
right because here the displacement is
this might share the displacement is
this much here the displacement is this
much so gradually the displacement is
increasing so the maximum displacement
is this distance so this is defined as
the amplitude of this wave and
equilibrium position as this position
this red line denotes the equilibrium
position or the mean position next is
phase of a wave what is phase it
describes the state of motion as the
wave sweeps through an element at a
particular position so it talks about
the state of motion of each point on a
wave so let us look at the way so that
we get a better understanding now if you
look at this wave if you look at the
behavior of this point and the behavior
of this point so both of them have the
same behavior both of them are trying to
move upward right so these two points
are in phase with each other that means
they the both the points are in the same
state of motion but if you compare at
this point with this point are they in
the same state of motion
no this point is trying to move up
whereas this point is trying to move
down so they are not in the same state
of motion so we say they are out of
phase similarly if you compare at this
point with this point do you think they
are in the same stage no even though
both of them are trying to move up but
the way this point is trying to move and
the way this point is trying to move and
the way at this point is far away from
the proposed position is different from
the way this point is far away from the
destination right so these two points
are also not in phase so this point this
point this point they
are all infants similarly at this point
this point this point they are all in
phase again this point this point this
point they are all in phase right so you
remember the concept of phase so it
talks about the state of motion of a
particular point right okay next is
wavelength of a wave what is wavelength
it is the minimum distance between two
consecutive points in the same phase of
wave motion it is generally denoted by
lambda so if you take this wave just
consider any two points which are in the
same phase so this point at this point
these are the two points which are in
same phase so the distance between these
two points is lambda similarly if you
consider this point this point at this
point they are in same phase so the
distance between these two points is
lambda so this distance and this
distance they are equal right so the
distance between any two points which
are in the same phase is known as
wavelength of a wave so here I have
shown the wavelengths both in case of a
transverse wave as well as along you two
general ways I hope you remember these
terms anyways I'm not going to discuss
them in detail right now in transverse
waves the movements are perpendicular to
the direction of wave propagation but in
longitudinal way they are in the same
direction M is even if you don't
remember you can refer the videos on
waves okay let us look at the next
parameter that is the angular frequency
before that let us try to understand
what is period of a wave what do we mean
by period or time period it is the time
taken to move through one complete
oscillation that means then suppose if
the oscillation starts so how much time
it
takes to complete one oscillation that
is known as time theorem so in simple
terms if you have a wave like this right
so how much time it takes for this wave
to complete one oscillation that is one
cycle so this is one cycle right from
air the same reputation starts so this
is the second cycle this is the third
cycle so the time it takes to complete
one cycle or one oscillation is known as
time period or it is also known as
period of a wave it is denoted by
capital T now we will talk about
frequency of a wave
what is frequency the number of
oscillations per unit time that means
how many waves occur in a time period
now let us understand it in this way let
us suppose I have a wave like this and I
have another wave like this right and
then suppose I have yet another wave
like this so I have three different
waves so what is the time period of this
wave the time taken to complete one
oscillation and this is one oscillation
T now for the same time period t if you
see for the first wave in time period t
how many oscillations happened one now
for the same amount of time how many
oscillations happened for the second
wave one two and three so for the second
value three what about the third week
for the same time period one two three
four five six seven like so the number
of oscillations per unit time so if you
keep the time constant and all of them
then in which wave more number of
oscillations happen the third one right
so we say the frequency of the third
wave is sev
so the frequency is maximum for the
third way that it is least or minimum
for the first way okay so now you
understand what is frequency of a wave
so if I am talking about a high
frequency wave it would look somewhat
like this if I am talking about a low
frequency wave it will look somewhat
like this clear okay stays generally
denoted by nu let us now talk about
angular frequency so now once the term
frequency is cleared it will be easier
to understand annular frequency it is
very much related to frequency it is
just that when I talk of frequency and
talking in linear terms but when I am
talking taking into consideration that
angle when I am taking into
consideration the circular aspect of it
we involve angle into it and then we
call it as angular frequency so like how
we have linear velocity and angular
velocity how we have linear acceleration
and angular acceleration similarly we
have linear frequency and angular
frequency so how do we define angular
frequency so angular frequency is
defined as 2 pi nu so this is angular
frequency and this is linear frequency
so with this linear frequency you added
2 pi right that is the angle is
incorporated into it now frequency is
calculated as inverse of time period
that is the relationship between
frequency and time period of a wave so
we can say that angular frequency is
equal to 2 pi by T
so that is all about the angular
frequency above it so now if I say that
I have any sinusoidal wave in general so
how do i denote or how do I describe a
sinusoidal wave because just before
sometime I told that if they are aware
of all these parameters if we know the
frequency of a wave the period of a wave
amplitude of a wave phase of a wave if
we know all these things we can describe
the wheel start let us suppose that we
know that we have a wave whose amplitude
is a let us suppose that I'm talking
about this wave itself so if I know that
its amplitude is a its time period is T
its angular frequency is Omega so how do
you think will we denote or describe
this wave so that signal strength on
this wave can be described as a sine
Omega T plus Phi where Y is again a
function of time because the signal
strength is also varying with time now
what is this Y T it is either voltage or
current because whenever we are talking
about signals we are talking either in
terms of voltage or current so this is
equal to amplitude sine of Omega T where
Omega is the angular frequency plus Phi
where Phi denotes the phase constant
right so this is how we denote a
sinusoidal wave now that we had a recap
of these parameters of the wave let us
try to see the different modulation
types of sinusoidal waves now depending
upon the parameter of the courrier wave
the parameters which we discussed now
one of these parameters can be modified
in the career wave now depending upon
which parameter is getting modified we
classify that modified ulation into a
specific type of modulation now how the
modification will happen that is
determined by the message signal so
there are three types of modulation
amplitude modulation frequency
modulation and
is moderation so amplitude modulation
when the amplitude of the courier wave
gets modified frequency modulation when
the frequency of the Korean Wave gets
modified phase modulation when the phase
of the courier wave gets modified please
understand this that during modulation
no change happens to the message signal
the modification or the modulation
happens to the courier wave now one of
any one of the parameter of the courier
wave will get modified either the
amplitude or the frequency order fees
right so we will now talk about
amplitude modulation phase modulation
and frequency modulation in detail one
by one just to see that how exactly this
modulation take case thank you please
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