Ground wave propagation: frequency less than 2 MHz
Sky wave propagation: 3 to 30 MHz
Space wave propagation: Above 30 MHz to 400 GHz
Satellite communication: uplink communication 6 GHz band downlink communication 4 GHz band

i) LOS: Line Of Sight communication.
ii) In this communication the space waves travel directly from transmitting antenna to receiving antenna.
iii) Frequency for LOS must be more than 40 MHz.

i) The TV signals are frequency modulated. The transmission of TV signals cannot be obtained the ground wave propagation, as such signals get absorbed by ground due to their high frequency.
ii) TV signals cannot be transmitted via skywave propagation as the ionosphere is unable to reflect radio waves of frequencies greater than 40 MHz.
iii) Therefore, the only way out for the transmission of TV signals is that receiving antenna should directly intercept the signal from the transmitting antenna.

It is the maximum distance between the source and the destination up to which the signal is received with sufficient strength.

It is a combination of receiver and transistor placed along the path of signal so as to extend the range of the communication system.

Mobile communication is used to communicate with others in different locations without the use of any physical connection like wires or cables.

RADAR stands for RAdio Detection And Ranging.

When the frequency of the baseband signal is zero (no input signal), there is no change in the frequency of the carrier wave. It is at its normal frequency. This is called centre frequency or resting frequency.

(i) The satellite communication is a mode of transmission of signal between transmitter and receiver via satellite.
(ii) The message signal from the Earth station is transmitted to the satellite on board via an uplink (frequency band 6 GHz), amplified by a transponder and then retransmitted to another earth station via a downlink (frequency band 4 GHz).
Applications:
Satellites are classified into different types based on their applications.
(i) Weather Satellites:
They are used to monitor the weather and climate of Earth. By measuring cloud mass, these satellites enable us to predict rain and dangerous storms like hurricanes, cyclones etc.
(ii) Communication satellites:
They are used to transmit television, radio, internet signals etc. Multiple satellites are used for long distance communication
(iii) Navigation satellites:
These are employed to determine the geographic location of ships, aircraft or any other object.

(i) It is used for personal communication and cellular phones offer voice and data connectivity with high speed.
(ii) Transmission of news across the globe is done within a few seconds.
(iii) Using Internet of Things (UIT), it is made possible to control various devices from a single device. Example: home automation using a mobile phone.
(iv) It enables smart classrooms, online availability of notes, monitoring student activities etc. in the field of education.

Fiber optic communication:
(i) The method of transmitting information from one place to another in terms of light pulses through an optical fiber is called fiber optic communication. It works on the principle of total internal reflection.
Applications:
(ii) Optical fiber system has a number of applications namely, international communication, inter-city communication, data links, plant and traffic control and defense applications.
(iii) Fiber cables are very thin and weigh lesser than copper cables.
(iv) This system has much larger band width. This means that its information carrying capacity is larger.
(v) Fiber optic system is immune to electrical interferences.
(vi) Fiber optic cables are cheaper than copper cables.

a) Agriculture:
The implementation of information and communication technology (lCT) in agriculture sector enhances productivity, improves the living standards of farmers and overcomes the challenges and risk factors.
i) Increasing food productivity and farm management.
ii) To optimize the use of water; seeds and fertilizers etc.
iii) Sophisticated technologies that include robots, temperature and moisture sensors, aerial images, and GPS technology can be used.
iv) Geographic information systems are extensively used in farming to decide the suitable place for the species to be planted.
b) Fisheries:
i) Satellite vessel monitoring system helps to identify fishing zones
ii) Use of barcodes helps to identify time and date of catch, species name, quality of fish
c) Mining:
i) ICT in mining improves operational efficiency, remote monitoring, and disaster locating system.
ii) Information and communication technology provide audio-visual warnings to the trapped underground miners.
iii) It helps 10 connect remote sites.

a) Ground wave propagation:
i) If the electromagnetic waves transmitted by the transmitter glide over the surface of the Earth to reach the receiver, then the propagation is called ground wave propagation.
ii) The corresponding waves are called ground waves or surface waves.
iii) Both transmitting and receiving antennas must be close to the Earth's surface.
iv) It is used in local broadcasting, radio navigation, for ship-to-ship, ship-to-shore communication and mobile communication.

b) Space wave propagation:
i) The process of sending and receiving information signal through space is called space wave communication.
ii) The frequency range for this mode of propagation is above 30 MHz to 400 GHz.
iii) These waves travel in a straight line from the transmitter to the receiver. Hence, it is used for a line of sight (LOS) communication.
iv) Television telecast, satellite communication and RADAR type of communication are based on space wave propagation
v) Range or distance (d) of coverage of propagation depends on height (h) of the antenna given by the equation d = \(\sqrt{2hR}\) where R is radius of the earth, which is R = 6400 km.