Z3D153 - 2016 Edit Code 3, Volume 2 Part 2

When high-energy ultraviolet light waves from the sun enter the ionospheric region of the atmosphere and strike the gas atoms, it causes ionization. Ionization refers to the process of converting an atom or molecule into an ion by adding or removing charged particles. In this case, the high-energy UV light waves provide enough energy to remove electrons from the gas atoms, resulting in the formation of ions.

Multipathing refers to the phenomenon where a transmitted signal travels over multiple paths during transmission. This can occur due to reflections, refractions, or diffractions of the signal. As a result, the receiver may receive multiple copies of the signal at slightly different times, causing interference and signal degradation. This can lead to issues such as fading, ghosting, or signal loss. Therefore, multipathing is the correct answer to explain the given statement.

In sky-wave propagation, frequencies higher than the critical frequency are passed into space. Sky-wave propagation refers to the phenomenon where radio waves are reflected by the ionosphere back to Earth's surface. The critical frequency is the maximum frequency that can be reflected back to Earth. Frequencies higher than the critical frequency cannot be reflected and instead continue to travel into space. Therefore, they are passed into space rather than being returned to Earth.

Sunspots are disturbances that appear and disappear on the sun's surface. These dark spots are cooler areas compared to the surrounding surface, caused by intense magnetic activity. They can vary in size and shape, and their appearance and disappearance follow a cyclical pattern known as the solar cycle. The presence of sunspots is an indication of increased solar activity and can have effects on Earth's ionosphere and climate. Therefore, the correct answer is "on the sun's surface."

The Earth's atmosphere is made up of five layers. These layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer has its own unique characteristics and plays a crucial role in regulating the Earth's climate and protecting it from harmful radiation.

The atmospheric recombination process refers to the process by which charged particles in the atmosphere combine with other particles to form neutral molecules. This process is dependent on the time of day (TOD) because the concentration of charged particles in the atmosphere varies throughout the day. During the daytime, there is more ionization due to solar radiation, leading to a higher concentration of charged particles. At night, the ionization decreases, resulting in a lower concentration of charged particles. Therefore, the time of day plays a crucial role in determining the rate of atmospheric recombination.

During winter, the air is colder and denser, which leads to a wider range of critical frequencies. Additionally, the lower temperatures result in less absorption of sound frequencies, allowing sound waves to travel further and be heard more clearly.

The Earth's conductivity is determined by the type of soil and water in the propagation path. Soil and water can affect the conductivity of the Earth because they contain ions that can conduct electricity. Different types of soil and water have different levels of conductivity, which can impact the transmission of signals. Therefore, the conductivity of the Earth is influenced by the presence of soil and water in the propagation path.

High frequency (HF) signals have wavelengths that are relatively long compared to other frequency ranges. Precipitation, such as rain or snow, tends to scatter and attenuate electromagnetic waves. However, because HF signals have longer wavelengths, they are less affected by precipitation compared to higher frequency ranges like UHF, SHF, or EHF. Therefore, HF signals will show little effect from precipitation.

The F layer of the ionosphere is the most important for high-frequency (HF) communications. This layer is located approximately 200-400 km above the Earth's surface and is responsible for reflecting HF radio waves back to the Earth. It is further divided into two sub-layers, F1 and F2, with the F2 layer being the most significant for long-distance HF communications. The F layer's ability to reflect HF signals allows for long-range communication, making it crucial for HF communication systems.

Refraction is the correct answer because it refers to the bending of radio waves as they pass from one medium to another with different densities. This bending occurs due to the change in speed of the waves, causing them to change direction. Diffusion is the scattering of waves in different directions, diffraction is the bending of waves around obstacles, and reflection is the bouncing back of waves when they encounter a boundary.

Line-of-sight (LOS) radio waves that are guided through the air between two layers of the atmosphere are known as ducting. Ducting occurs when there is a temperature inversion in the atmosphere, causing the radio waves to be refracted and trapped within a layer of the atmosphere. This phenomenon allows the radio waves to travel much farther than they would under normal conditions, resulting in long-range communication. Channeling, guiding, and piping are not the correct terms for this specific phenomenon.

The angle at which a radio wave enters the ionosphere is known as the angle of incidence. This is because the angle of incidence refers to the angle at which a wave or ray approaches a surface. In the context of the ionosphere, the angle of incidence determines how the radio wave will interact with the ionized layers of the atmosphere. It influences factors such as refraction, reflection, and absorption of the wave, which ultimately affect its propagation and communication capabilities.

Sunspots occur on an 11-year cycle. Sunspots are dark areas on the sun's surface that are cooler than the surrounding areas. These sunspots are associated with strong magnetic activity and are more prevalent during periods of high solar activity, known as the solar maximum. The number of sunspots and the intensity of solar activity follow an 11-year cycle, with peaks and valleys occurring over this time period.

The refractive index of air is influenced by atmospheric pressure and temperature. Atmospheric pressure affects the density of air, which in turn affects the speed of light as it passes through the air. An increase in pressure leads to an increase in density and a decrease in the speed of light, causing the refractive index to change. Similarly, temperature affects the speed of light in air, with higher temperatures leading to faster speeds and a lower refractive index. Therefore, both atmospheric pressure and temperature play a role in determining the refractive index of air.

The skip zone refers to an area where no signals are received in sky- and ground-wave propagation. This occurs due to the phenomenon of radio waves being refracted or reflected by the Earth's atmosphere. The skip zone is the result of signals being refracted away from the receiving antenna, causing a gap in signal reception.

The radio horizon is farther away than the optical horizon by 15%. This means that the distance that can be covered by radio waves is 15% greater than the distance that can be covered by optical waves.

The term frequency of optimum transmission (FOT) refers to the frequency at which transmission is most efficient and effective. It is also known as the optimum traffic frequency because it represents the ideal frequency for transmitting data or information. This frequency ensures that the transmission is reliable and minimizes any potential interference or disruptions. Therefore, the correct answer is optimum traffic frequency.

Diffraction is the process that allows communication in shadow regions behind obstacles. It occurs when waves, such as sound or light waves, encounter an obstacle and bend around it, spreading out into the region behind the obstacle. This bending or spreading out of waves enables them to reach areas that would otherwise be in the shadow of the obstacle, allowing for communication to occur. Reflection, scattering, and refraction do not specifically address the ability to communicate in shadow regions behind obstacles.

When radio waves angle too low during sky-wave propagation, they are absorbed before refraction occurs. This means that the radio waves are absorbed by the ionosphere before they have a chance to be bent or refracted back towards the Earth's surface. This absorption prevents the radio waves from being reflected back to the Earth and instead they are lost or dissipated in the ionosphere.

Refraction is the correct answer because it is the condition that allows sky-wave propagation to communicate beyond the optical line-of-sight (LOS). Refraction occurs when radio waves encounter a change in the density of the atmosphere, causing them to bend and follow the curvature of the Earth. This bending effect allows the waves to reach areas that are beyond the direct line-of-sight, enabling long-distance communication. Reflection, Earth’s conductivity, and atmospheric charge do not play a significant role in sky-wave propagation's ability to communicate beyond the optical line-of-sight.