Previous Year Question
Television viewers using dish antenna to receive satellite signals do not receive signals during rain because:
Of the small size of the antenna.
Rain droplets absorb the energy of radio waves.
Rain droplets disperse the energy of radio waves from their original direction.
Which of the above statements are correct?
Only 1
Only 1 and 2
Only 2 and 3
1, 2 and 3
Correct Answer: D
Detailed Solution
In Satellite Television Communication, microwave signals are received through a dish antenna. During heavy rainfall, the intensity of these signals may decrease, causing the television picture to freeze, break up, or lose signal completely. This phenomenon is called Rain Attenuation or Rain Fade.
Statement 1 is correct in context. Small dish antennas used for domestic television reception generally have lower Antenna Gain than larger antennas. Larger antennas may be capable of receiving weaker signals. Therefore, it may become difficult for small dish antennas to receive satellite signals already weakened by heavy rainfall. However, the small size of an antenna does not itself produce rain attenuation; it affects the ability to receive signals.
Statement 2 is correct. Raindrops absorb (Absorption) part of the energy of microwave signals arriving from satellites. Due to interactions between water molecules and the electromagnetic field, part of the electromagnetic energy is converted into thermal energy. This reduces the signal power reaching the receiver.
Statement 3 is correct. Microwave waves undergo Scattering when they encounter raindrops. During this process, part of the wave energy is dispersed from its original direction of propagation into other directions. This causes an additional reduction in the signal power reaching the dish antenna.
Rain Fade mainly results from the combined effects of absorption and scattering. Its severity depends on the frequency of the waves, rainfall intensity, raindrop size, and the length of the rain-affected path travelled by the signal.
Domestic Direct-to-Home (DTH) television systems commonly use microwave frequencies in the Ku-Band. Higher-frequency signals may be more strongly affected by rainfall. Sufficient Antenna Gain and Link Margin can reduce the possibility of signal interruption during rain.