let us now study about transmission of electromagnetic
signals through space , we have studied that-
in a communication system from information
sender, the information is fed to a transducer
. which converts it – the information into
the electrical form , and then from the transducer
it is first supplied to the amplifier which
increases the intensity of signal , and then
it will supply to transmitter, through which
- using an antenna the information is , broadcasted
in space .
now when we talk about an antenna we will
discuss about the antenna here , that when
an antenna is connected to the transmitter
here for broadcasting of, signals - in form
of electromagnetic waves, here we can write
that, analysis of - antenna, shows, this analysis
is not in , our scope that is why we are not
analyzing why this is, coming out but here
we can write analysis of antenna shows.
that.
for optimum power.
transmission.
of signals.
the size of antinna. must be at least.
lambda by 4 , where lambda is the wavelength
of, electromagnetic waves which are being
broadcasted , so here we can write- for a
sound signal, we know that sound signal , even
if we talk about highest pitch.
of 3000 hertz, the wavelength corresponding
to the electromagnetic wave would be- c by
n- that is 3 into 10 to power 8 divided by
3000.
that will be 10 to power 5 meter or it is,
about hundred kilometers . so if the wavelength
is hundred kilometers for a sound wave when
converted into an electromagnetic wave . then
in this situation the size of antenna required
lambda by 4 will be – here we can write
– size of , antenna required is approximately
25 kilometers or more .
which is not practically possible – which
is not practical, so such kind of antennas
can never be constructed , so – directly
the sound signal can never be transmitted
over the space , but when we talk about – for
a high frequency wave .
of frequency approximately , 1000 mega hertz
- that is 10 to power 9 hertz if we talk about
its , wavelength it will be c by n- that is
3 into 10 to power 8 divided by, 10 to power
9 that is 0.3 meter which is- 30 centimeter-
so in this situation the size of antenna required
for- the transmission of such a high frequency
wave would be- more than or equal to lambda
by 4 that is 7.5 centimeter which is practically
possible.
so in case of space transmission of electromagnetic
waves we prefer high frequency waves only,
where the size of antenna used for broadcasting
of signals would be practical, directly for
low frequency wave the size of antenna will
be- impractical or not feasible in, practical
life that is why only high frequency waves
- are used – for electromagnetic signal
transmission through space.
in coming section we will study that , voice
signals are superimposed with high frequency
carrier signal, and then it can be transmitted-
the phenomenon is called modulation- we will
study it, in separate section – as a separate
topic, we will study modulation in detail.
