Q.Mention the four types of radio wave propagation.

Propagation is the forward travel of radio waves from the transmitter to the receiver. Once a signal leaves the transmitting antenna, it does not have just one way to reach the far end — it can follow one of three basic paths through the atmosphere, and which path dominates depends mainly on the signal's frequency band.

The three modes are:

1. Ground wave — the wave is guided along the earth's surface, using the ground itself as part of the path. This works best at low and medium frequencies (LF and MF).
2. Space wave — the wave travels in a straight, line-of-sight path directly between the transmitting and receiving antennas, staying in the lower atmosphere. This is the main mode at VHF and higher frequencies.
3. Sky wave — the wave is beamed upward and bent back to earth by the ionosphere, allowing very long-distance communication. This is the HF mode. …