Interview Questions On Waves

1Q: What are sky waves?
Ans: The radio waves which propagate throughout the world on account of repeated reflection of radio waves by the ionosphere and the earth are called sky waves. These waves are capable to establish radio communication between two stations situated any where on the earth in the frequency range of 3 to 30 MHz.

2Q: What are direct waves?
Ans: The radio waves which propagate in straight line(i.e. line of sight) are called direct waves. These waves are capable to establish radio communication upto very long but straight distances and usually upto 100kms. on the earth's surface in the frequency range of 30 to 3 X 10^6 MHz.

3Q: What are ground reflected waves?
Ans: The radio waves which reach at a receiving aerial after being reflected by a mountain etc. are called ground reflected waves. These waves are capable to establish radio communication upto 250 kms. in the frequency range of 30 X 10^6 MHz.

4Q: What is ionosphere?
Ans: The air belt around the earth ranging from 10 to 400 kms. height above earth's surface is called ionosphere. It contains ionised gases which are capable to reflect the radio waves back to the earth's surface.

5Q: Which of the ionised layers of the ionosphere are more useful for radio communication purposes?
Ans: Kennerly-Heaviside layer and Appleton layer are capable to reflect radio waves of 3 to 30 MHz frequencies. These layers extend from 144 to 400 kms. height above earth's surface.

6Q: Are vision-horizon and radio-horizon the same?
Ans: No; Radio-horizon is slightly large than vision-horizon because of refraction property of the radio waves.

7Q: What is meant by critical angle?
Ans: The maximum value of the angle of radiation at which total reflection can occur is called critical angle.

8Q: What is skip distance?
Ans: In short wave propagation, the distance between the transmitting antenna and the point where the very first wave touches the earth's surface after reflection from the ionosphere is called skip distance.

9Q: What is skip zone?
Ans: Skip zone or the 'zone of silence' is the area where neither ground nor sky waves are able to reach and there is no reception of radio waves.

10Q: What is meant by fading?
Ans: In short wave reception, the magnitude of r.f. voltage induced in a receiving aerial changes continuously due to instability of ionospheric density. This effect is referred as fading and it results in an instability in the output sound at the receiver.

11Q: How does fading eliminated?
Ans: Fading is eliminated by employing an AVC circuit.

12Q: What are the basic principles of radio reception?
Ans: They are reception, selection, detection and reproduction.

13Q: What is meant by selective fading?
Ans: When a direct wave and a ground reflected wave reach a receiving aerial simultaneously, they produce a fading due to difference between the phases of the two waves which is called selective fading.

14Q: What are the fundamental principles of radio transmission?
Ans: They are 'production' of radio waves, 'modulation' of radio waves with signal waves, 'transmission' of modulated radio waves into space by the antenna.

15Q: What is the velocity of radio waves?
Ans: The velocity of radio waves is 3 X 10^8 metres per second or 1,86,000 miles per second.

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