Question

Which of the following mode of propagation can be used to transmit radio waves?
1. Space wave propagation
2. Sky wave propagation
3. Ground wave propagation
4. All of the above

Answer 1

Correct Answer - Option 4 : All of the above

The correct answer is option 4) i.e. All of the above

CONCEPT:

• Propagation of electromagnetic waves: An electromagnetic wave is transmitted between two points by using an antenna in the transmitter which radiates these waves through a medium, and is made available at another antenna at the receiving end. This is the basic principle of communication systems.
• The propagation is dependent on different layers of Earth and can be classified as follows.

Ground wave propagation	​This method is used in transmitting waves of frequency less than 1 MHz through the ground.  It transmits the waves through the ground by using antennas of sizes comparable to the wavelength of the EM waves.
Sky wave propagation	This method is used in transmitting waves of frequency between 3 MHz and 30 MHz through the ionosphere in the atmosphere. The ions in the ionosphere provide a reflection medium for long-distance transmission of the waves without much attenuation.
Space wave propagation	This method is used in transmitting waves of frequency between 30 MHz and 300 MHz. It involves sending the required waves in a straight line from the transmitter to the receiver and hence called line-of-sight communication. The height of the towers containing transmitter and receiver should be such that the signal does not interfere with the curvature of Earth.

EXPLANATION:

• From the electromagnetic spectrum, it is inferred that the frequency range of radio waves is 3 kHz to 300 GHz.
• Hence, depending on the frequency of the given radio wave any three modes of propagation - ground, sky, and space can be used.