- 2072 Kartik · 5 marks
Types of propagation
Short answer
Ground-wave propagation follows Earth's curvature, used below 2 MHz for AM radio. Sky-wave propagation refracts signals (2-30 MHz) off the ionosphere for long-distance HF communication. Line-of-sight propagation (above 30 MHz) requires direct visibility between antennas, used for FM, TV, mobile, and microwave links; maximum distance depends on antenna height.
Explain about different types of propagation.
Radio waves travel from transmitter to receiver in three main ways, depending on frequency.
1. Ground-wave propagation
Tx ~~~~~~~~~~~~~~> Rx (follows Earth's curvature)
====================================
The wave follows the curvature of the Earth's surface. It is used for frequencies below about 2 MHz (VLF, LF, MF, such as AM radio and navigation). The range can be hundreds to thousands of km, depending on power; losses grow with frequency.
2. Sky-wave (ionospheric) propagation
ionosphere -------------
/ \
/ \
Tx ---/ \--- Rx
===================================
Waves of 2 to 30 MHz (HF, shortwave) go up and are reflected (refracted) back by the ionosphere, so they can travel around the globe in multiple hops. It is used for shortwave broadcasting and long-distance amateur radio, and it is affected by the time of day and solar activity.
3. Line-of-sight (LOS) propagation
Tx antenna Rx antenna
| -------------------> |
_|_ _|_
Above 30 MHz (VHF, UHF, microwave, satellite), waves travel in a straight line and are not bent back by the ionosphere. The transmitting and receiving antennas must see each other, so the range is limited by the Earth's curvature. The radio horizon of one antenna of height h (in metres) is d = 3.57√(K·h) km with K = 4/3, so two antennas of equal height can be at most about 7.14√(K·h) km apart. Towers or satellites are used to extend the range. LOS is used for FM, TV, mobile, microwave links and satellites.
✓ Answer checked by Claude Opus 5.5 (high effort)