PROPAGATION OF ELECTROMAGNETIC WAVES _ PART 02

Summary

The video explores various modes of radio wave propagation, including ionospheric and space wave propagation. It discusses how ionization in the atmosphere changes with height, and how electromagnetic waves are reflected or penetrate depending on frequency. The phenomenon of total internal reflection is linked to the bending of waves towards Earth. The space wave mode, used in line-of-sight communication and satellite systems, is explained, highlighting the impact of antenna height on signal reception. The script also covers the concept of the radio horizon and its relevance to communication systems like TV broadcasts and microwave links.

Takeaways

• 😀 The degree of ionization in the atmosphere varies with height, with ionization being low near the Earth's surface but increasing at intermediate heights.
• 😀 Solar radiation at high altitudes is intense, but due to the low number of molecules, ionization remains low. Close to Earth, despite a high molecular concentration, radiation intensity is low, leading to low ionization.
• 😀 A peak in ionization density occurs at certain intermediate heights in the atmosphere.
• 😀 The ionospheric layer reflects electromagnetic waves within a specific frequency range of 3 to 30 MHz, while waves with frequencies higher than 30 MHz escape the atmosphere.
• 😀 The bending of electromagnetic waves towards the Earth, akin to total internal reflection in optics, is a significant propagation phenomenon.
• 😀 Space waves are another mode of radio wave propagation, traveling in a straight line from transmitting to receiving antennas.
• 😀 Space waves are used in line-of-sight communication and satellite communication, primarily at frequencies around 40 MHz.
• 😀 At higher frequencies, communication is limited to the line of sight (LOS) between antennas, as the waves are blocked by Earth's curvature.
• 😀 The radio horizon distance (DT) is determined by the height of the transmitting antenna, and the formula for the radio horizon is DT = sqrt(2 * R * HT), where R is the Earth's radius and HT is the height of the transmitting antenna.
• 😀 The maximum line-of-sight distance (DM) between two antennas with heights HT and HR is given by the formula: DM = sqrt(2 * R * HT) + sqrt(2 * R * HR).
• 😀 Examples of communication systems using space wave propagation include television broadcasts, microwave links, and satellite communications.

Q & A

What causes the variation in the degree of ionization with height in the atmosphere?

The degree of ionization varies with height due to changes in atmospheric density and solar radiation intensity. At higher altitudes, the atmosphere's density decreases, and although solar radiation is intense, there are fewer molecules to ionize. Conversely, closer to Earth, molecular concentration is high, but radiation intensity is low, leading to lower ionization.

What happens at intermediate heights regarding ionization density?

At intermediate heights, there is a peak in ionization density due to a balance between the decreasing atmospheric density and the increasing intensity of solar radiation.

How does the ionospheric layer affect electromagnetic waves?

The ionospheric layer acts as a reflector for electromagnetic waves within the frequency range of 3 to 30 MHz. Waves with frequencies higher than 30 MHz penetrate the ionosphere and escape into space.

What is the phenomenon of wave bending in the ionosphere?

The bending of electromagnetic waves towards the Earth, similar to total internal reflection in optics, occurs due to the ionospheric conditions. This phenomenon helps to direct waves back to Earth, enhancing communication over longer distances.

What are space waves in radio wave propagation?

Space waves are a mode of radio wave propagation that travel in a straight line from the transmitting antenna to the receiving antenna. They are used in line-of-sight (LOS) communication and satellite communication.

What is the primary limitation of space wave propagation?

The primary limitation of space wave propagation is the line-of-sight nature, meaning the waves are blocked by the curvature of the Earth. To receive signals beyond the horizon, the receiving antenna must be elevated enough to intercept the line-of-sight waves.

How is the distance to the horizon calculated for space waves?

The distance to the horizon (DT) is given by the formula DT = √(2RH), where R is the radius of the Earth, approximately 6,400 km, and H is the height of the transmitting antenna.

What is the maximum line-of-sight distance between two antennas?

The maximum line-of-sight distance (DM) between two antennas, given their respective heights (HT and HR), is calculated using the formula: DM = √(2RHT) + √(2RHR).

What are some examples of systems that use space wave propagation?

Examples of systems that use space wave propagation include television broadcasting, microwave links, and satellite communication.

How does the Earth's curvature affect the transmission of radio waves?

The Earth's curvature blocks the direct path of radio waves at certain distances. For successful communication beyond the horizon, antennas must be placed at sufficient heights to maintain the line-of-sight path for the waves.