Question :
a) Describe the following modes of wave propagation:
- Line of sight
- Ground waves
- Skywaves
b) Why can waves with a very low frequency be used for submarine communication? Give one reason why are they not used for data transmission in mobile phones and computer networks.
c) A Line-of-sight (LOS) is usually required between a sender and receiver for radio waves with frequency > 30 MHz, nevertheless, mobile phones can work in big cities without such LOS. Explain.
d) Spread spectrum is a technique which generates signals which are strong and loud, that is resistant to interference. Explain how this is achieved.
e) Briefly explain how directional and omni-direction antennas work. Is a directional antenna suitable for mobile phone communication?