# Z3D153 - 2016 Edit Code 3, Volume 2 Part 2

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• 1.

### The Earth’s conductivity is determined by the type of

• A.

Atmospheric conditions at the time of transmission.

• B.

Air and moisture content in the propagation path.

• C.

Soil and water in the propagation path.

• D.

Soil and air in the propagation path.

C. Soil and water in the propagation path.
Explanation
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.

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• 2.

### This term is used to describe radio waves that bend as they travel from one medium toanother that has different density.

• A.

Diffusion.

• B.

Diffraction.

• C.

Refraction.

• D.

Reflection.

C. Refraction.
Explanation
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.

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• 3.

### The refractive index of air depends on moisture,

• A.

Atmospheric pressure, and temperature.

• B.

Atmospheric pressure, and frequency.

• C.

• D.

A. Atmospheric pressure, and temperature.
Explanation
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.

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• 4.

### When comparing the radio and optical horizons, which one is farther away and by what percentage?

• A.

Optical; 15.

• B.

• C.

Optical; 33.

• D.

Explanation
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.

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• 5.

### Which process permits communication in shadow regions behind obstacles?

• A.

Reflection.

• B.

Scattering.

• C.

Refraction.

• D.

Diffraction.

D. Diffraction.
Explanation
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.

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• 6.

### Which frequency range will show little effect from precipitation?

• A.

High frequency (HF).

• B.

Ultra-high frequency (UHF).

• C.

Super-high frequency (SHF).

• D.

Extremely-high frequency (EHF).

A. High frequency (HF).
Explanation
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.

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• 7.

### Line-of-sight (LOS) radio waves that are guided through the air between two layers of the atmosphere are known as

• A.

Channeling.

• B.

Guiding.

• C.

Ducting.

• D.

Piping.

C. Ducting.
Explanation
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.

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• 8.

### Which condition gives sky-wave propagation its ability to communicate beyond the optical line-of-sight (LOS)?

• A.

Refraction.

• B.

Reflection.

• C.

Earth’s conductivity.

• D.

Atmospheric charge.

A. Refraction.
Explanation
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.

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• 9.

### The angle at which a radio wave enters the ionosphere is known as the

• A.

Skip angle.

• B.

Critical angle.

• C.

Angle of entrance.

• D.

Angle of incidence.

D. Angle of incidence.
Explanation
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.

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• 10.

### There are several critical sky-wave propagation angles and frequencies. Radio waves that angle too low are

• A.

Refracted.

• B.

Returned to Earth.

• C.

Absorbed before refraction occurs.

• D.

Passed through the ionosphere into space.

C. Absorbed before refraction occurs.
Explanation
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.

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• 11.

### In sky-wave propagation, frequencies higher than the critical frequency are

• A.

Returned to Earth.

• B.

Passed into space.

• C.

The most desirable.

• D.

Refracted by the F2 layer.

B. Passed into space.
Explanation
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.

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• 12.

### The term frequency of optimum transmission (FOT) is also referred to as the

• A.

Outbound traffic frequency.

• B.

Optimum tropospheric frequency.

• C.

Optimum traffic frequency.

• D.

Frequency of outbound transmission.

C. Optimum traffic frequency.
Explanation
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.

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• 13.

### In sky- and ground-wave propagation, the area of silence where no signals are received is known as the

• A.

Propagation distance.

• B.

Skip distance.

• C.

• D.

Skip zone.

D. Skip zone.
Explanation
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.

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• 14.

### This occurs when a transmitted signal travels over two or more separate paths during transmission.

• A.

Skip effects.

• B.

Modulation.

• C.

Multipathing.

• D.

Magneton splitting.

C. Multipathing.
Explanation
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.

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• 15.

### How many layers make up the Earth’s atmosphere?

• A.

2.

• B.

3.

• C.

4.

• D.

5.

D. 5.
Explanation
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.

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• 16.

### This occurs when high-energy ultraviolet light waves from the sun enter the ionospheric region of the atmosphere and strike the gas atoms.

• A.

Ionization.

• B.

Modulation.

• C.

Conductivity.

• D.

Recombination.

A. Ionization.
Explanation
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.

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• 17.

### The atmospheric recombination process is dependent on the

• A.

Season.

• B.

Time of day (TOD).

• C.

Regular variation.

• D.

Irregular variations.

B. Time of day (TOD).
Explanation
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.

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• 18.

### Which layer of the ionosphere is most important for high-frequency (HF) communications?

• A.

D.

• B.

E.

• C.

F.

• D.

Topside.

C. F.
Explanation
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.

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• 19.

### During which season do we have the wider range of critical frequencies and less absorption of all frequencies?

• A.

Fall.

• B.

Winter.

• C.

Spring.

• D.

Summer.

B. Winter.
Explanation
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.

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• 20.

### As ionospheric solar variations, sunspots are disturbances that appear and disappear

• A.

In the sun’s atmosphere.

• B.

On the sun’s surface.

• C.

In the ionosphere

• D.

Beneath the sun’s surface.

B. On the sun’s surface.
Explanation
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."

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• 21.

### On which regular ionospheric variation do sunspots occur?

• A.

11-day cycle.

• B.

11-week cycle.

• C.

11-month cycle.

• D.

11-year cycle.

D. 11-year cycle.
Explanation
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.

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• Current Version
• Mar 19, 2023
Quiz Edited by
ProProfs Editorial Team
• Nov 30, 2017
Quiz Created by
Scott

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