The communication process The communication process utilizing the physical space utilizing the physical space

around the Earth is known as around the Earth is known as Space CommunicationSpace Communication

Let us take an example of two Let us take an example of two children playing with a ball in a children playing with a ball in a

closed roomclosed room..

The The child who throws the ballchild who throws the ball acts acts as a as a transmittertransmitter and the and the child child

receiving the ballreceiving the ball acts as a acts as a receiverreceiver..

Now, the Now, the ballball is the is the message or message or informationinformation that has to be that has to be

transmittedtransmitted..

The boy can throw the ball in THREE The boy can throw the ball in THREE ways:-ways:-

By rolling it along the ground.

By throwing it directly to the

receiving person.

By throwing first towards the roof from where it is then reflected towards the receiving person.

As we have seen the above example As we have seen the above example describing two children playing with a ball describing two children playing with a ball in a closed room, we are now in a position in a closed room, we are now in a position to describe the ways the electromagnetic to describe the ways the electromagnetic

waves are propagated in the space…waves are propagated in the space…

The field component of a wave The field component of a wave launched from an antenna close to launched from an antenna close to

the surface of the earth soon the surface of the earth soon becomes becomes vertically polarizedvertically polarized as it as it

glides over the surface of the earth. glides over the surface of the earth. The electrical fields due to the wave The electrical fields due to the wave

induce chargesinduce charges in the earth’s in the earth’s surface, As the wave travels, the surface, As the wave travels, the induced charges in the earth or induced charges in the earth or ground also travel along with it. ground also travel along with it. This constitutes a This constitutes a current in the current in the

earth’s surface.earth’s surface.Reference Diagram

on the Next Slide

Direction of travel

EARTEARTHH

2

Vertically polarized wave traveling over the surface of the earth. The solid lines represent

the electric field (E) of the electromagnetic wave.

The transmitted waves, traveling in a straight line, directly reach the receiver end and are then picked up by the receiving antenna.

The effective reception of the broadcast of such waves is the region of the line of sight in

the conventional sense.

Hence, this mode of communication is sometimes termed as line of sight

communication.Reference Diagram on the Next Slide

P R2

R1

O

r

d

h

Radiated Wave

Q Antenna

A transmitted wave going up in the sky is A transmitted wave going up in the sky is reflected back from the ionized region of the reflected back from the ionized region of the

earth’s atmosphere, the earth’s atmosphere, the ionosphereionosphere..

The UV and other high energy radiations The UV and other high energy radiations coming from Sun are absorbed by air coming from Sun are absorbed by air

molecules which get ionized and form an molecules which get ionized and form an ionized layer of electrons and ions around the ionized layer of electrons and ions around the

earth. The ionosphere extends from a height of earth. The ionosphere extends from a height of ~ 80 to 300 km above the earth’s surface.~ 80 to 300 km above the earth’s surface.

Reference Diagram on the Next Slide

R`R

R``TransmittTransmitt

erer

Sky Sky WavesWaves

IonosphereIonosphere

Immense help has been taken in the form of Immense help has been taken in the form of text from the NCERT book for class XII text from the NCERT book for class XII

prescribed by the CBSE.prescribed by the CBSE.

Thanks to my uncle Mr. Mohit Sachdeva who Thanks to my uncle Mr. Mohit Sachdeva who provided me with the clipart CD “Click Art provided me with the clipart CD “Click Art

Premium Collection”.Premium Collection”.

Extensive images have been collected from Extensive images have been collected from the website:- the website:- www.digitalblasphemy.com and and

www.nationalgeographic.com

Most of all I would like to thank my parents Most of all I would like to thank my parents and my teacher Ms. Yashu Kumar for their and my teacher Ms. Yashu Kumar for their unrelenting motivation and impetus which unrelenting motivation and impetus which

gave the proper path to this marvelous gave the proper path to this marvelous project.project.