Comm Stuff Volume 2 UREs
Questions and Answers
- 1.
Which US government agency divides the radio frequency spectrum into different bands?
- A.
Federal Aviation Agency.
- B.
American National Standard Institute.
- C.
Federal Communications Commission (FCC).
- D.
Institute of Electrical & Electronics Engineers, Inc.
Correct Answer
C. Federal Communications Commission (FCC).Explanation
The Federal Communications Commission (FCC) is the US government agency responsible for dividing the radio frequency spectrum into different bands. This division is necessary to allocate specific frequencies for various uses such as broadcasting, telecommunications, and wireless communication. The FCC ensures that different users, including government agencies, private companies, and individuals, can access the spectrum without interference. By regulating and managing the allocation of radio frequencies, the FCC promotes efficient and effective use of the spectrum for communication purposes.Rate this question:
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- 2.
High-frequency (HF) transmissions are normally conducted in which two operating modes?
- A.
Frequency modulation (FM) and independent sidebands (ISB).
- B.
Continuous wave (CW) and amplitude modulation (AM).
- C.
Single side band (SSB) and FM.
- D.
SSB and ISB.
Correct Answer
D. SSB and ISB.Explanation
High-frequency (HF) transmissions are normally conducted in Single Side Band (SSB) and Independent Side Bands (ISB) operating modes. SSB is a modulation technique where only one sideband is transmitted, resulting in more efficient use of bandwidth. ISB is a technique where multiple sidebands are transmitted independently, allowing for simultaneous transmission of different signals. These operating modes are commonly used in HF communications to maximize efficiency and optimize signal transmission.Rate this question:
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- 3.
Which frequency band is most susceptible to jamming?
- A.
Low frequency (LF).
- B.
Medium frequency (MF).
- C.
High frequency (HF).
- D.
Very high frequency (VHF).
Correct Answer
C. High frequency (HF).Explanation
High frequency (HF) is the correct answer because it is the frequency band that is most susceptible to jamming. HF signals can travel long distances and are used for long-range communication, making them more vulnerable to interference and intentional jamming. Additionally, HF signals can be easily disrupted by atmospheric conditions and natural phenomena such as solar flares, further increasing their susceptibility to jamming.Rate this question:
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- 4.
The ability of a receiver to reproduce the signal of a very weak station is characteristic of a receiver’s
- A.
Fidelity.
- B.
Capacity.
- C.
Sensitivity.
- D.
Selectivity.
Correct Answer
C. Sensitivity.Explanation
The ability of a receiver to reproduce the signal of a very weak station is determined by its sensitivity. A receiver with high sensitivity can detect and amplify weak signals, allowing it to pick up and reproduce the signal of a weak station. Fidelity refers to the accuracy and faithfulness with which a receiver reproduces the original signal, capacity refers to the maximum amount of information a receiver can handle, and selectivity refers to the ability to separate and filter out unwanted signals. However, in this context, the most relevant characteristic is sensitivity.Rate this question:
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- 5.
The ability of a receiver to reproduce the input signal accurately is characteristic of its
- A.
Fidelity.
- B.
Capacity.
- C.
Sensitivity.
- D.
Selectivity.
Correct Answer
A. Fidelity.Explanation
Fidelity refers to the ability of a receiver to reproduce the input signal accurately. It measures how faithfully the receiver can reproduce the original signal without distortion or loss of information. Capacity refers to the amount of information that can be transmitted or stored. Sensitivity refers to the ability of a receiver to detect weak signals. Selectivity refers to the ability of a receiver to separate desired signals from unwanted interference.Rate this question:
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- 6.
A combination transmitter and receiver, built as a single unit and shares common tuned circuits, is called a
- A.
Transmitter.
- B.
Transceiver.
- C.
Receiver.
- D.
Coupler.
Correct Answer
B. Transceiver.Explanation
A combination transmitter and receiver, built as a single unit and sharing common tuned circuits, is called a transceiver. This device allows for both the transmission and reception of signals, making it more efficient and compact compared to separate transmitter and receiver units. Transceivers are commonly used in various communication systems, such as radios, cell phones, and wireless networks.Rate this question:
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- 7.
Conductor material resistance in a transmission line leads to this type of loss.
- A.
Copper.
- B.
Radiation.
- C.
Inductive.
- D.
Skin-effect.
Correct Answer
A. Copper.Explanation
The correct answer is Copper. Copper is a conductor material commonly used in transmission lines. When current flows through the copper conductor, it encounters resistance, which leads to energy loss in the form of heat. This resistance is known as copper resistance or conductor resistance. Therefore, the presence of copper in a transmission line contributes to this type of loss.Rate this question:
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- 8.
The amount of skin-effect loss is directly proportional to the
- A.
Line length.
- B.
Frequency.
- C.
Voltage level.
- D.
Resistive loss.
Correct Answer
B. Frequency.Explanation
The skin-effect loss refers to the phenomenon where high-frequency currents tend to flow near the surface of a conductor, resulting in increased resistance and power loss. This effect becomes more significant as the frequency increases. Therefore, the amount of skin-effect loss is directly proportional to the frequency.Rate this question:
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- 9.
Leakage loss in a transmission line is minimized by using a
- A.
Thinner conductor.
- B.
Thicker conductor.
- C.
Very low-resistance dielectric.
- D.
Very high-resistance dielectric.
Correct Answer
D. Very high-resistance dielectric.Explanation
Using a very high-resistance dielectric minimizes leakage loss in a transmission line. Leakage loss refers to the loss of energy that occurs when the electric current leaks from the conductor to the surrounding environment. By using a high-resistance dielectric, the leakage current is minimized, resulting in reduced energy loss. Thicker conductors would increase the surface area for leakage, leading to higher leakage loss. Using a thinner conductor would also increase resistance and result in higher power loss. A very low-resistance dielectric would not effectively prevent leakage.Rate this question:
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- 10.
A transmission line that consists of a center conductor, placed inside a rigid metal tube that functions as the outer shield, is called
- A.
Flexible coaxial cable.
- B.
Rigid coaxial cable.
- C.
Waveguide.
- D.
Twin lead.
Correct Answer
B. Rigid coaxial cable.Explanation
A transmission line that consists of a center conductor, placed inside a rigid metal tube that functions as the outer shield, is called a rigid coaxial cable. The rigid structure of the metal tube provides stability and protection to the center conductor, making it suitable for applications that require durability and resistance to external interference. Unlike flexible coaxial cables, which have a flexible outer jacket, rigid coaxial cables are less prone to bending or deformation, making them ideal for installations where the cable needs to maintain its shape and position. Waveguides and twin leads are different types of transmission lines that have distinct structures and characteristics.Rate this question:
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- 11.
A waveguide is a type of transmission line that you would use
- A.
When the frequencies are so high that their wavelength is miniscule.
- B.
To transmit on frequencies too low for ground propagation.
- C.
For high power at frequencies up to 30 megahertz (MHz) primarily.
- D.
To receive television frequencies over the air.
Correct Answer
A. When the frequencies are so high that their wavelength is miniscule.Explanation
A waveguide is a type of transmission line that is used when the frequencies are so high that their wavelength is minuscule. This is because at high frequencies, traditional transmission lines like coaxial cables become inefficient and cause significant signal loss. Waveguides, on the other hand, can effectively transmit these high-frequency signals with minimal loss. The design of waveguides allows them to confine and guide the electromagnetic waves within a narrow channel, ensuring efficient transmission at high frequencies. Therefore, using a waveguide becomes necessary when dealing with high-frequency signals where the wavelength is very small.Rate this question:
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- 12.
All statements concerning waveguides are true except
- A.
Their outer surface will arc from being very slightly damaged.
- B.
Their conductive material construction is easily dented.
- C.
Their effectiveness is hindered by moisture.
- D.
They can be destroyed by corrosion.
Correct Answer
A. Their outer surface will arc from being very slightly damaged.Explanation
This statement is false because the outer surface of waveguides will not arc from being very slightly damaged. Arcing occurs when there is a high voltage breakdown across a gap, but waveguides are designed to prevent such breakdowns. The other statements are true: waveguides can be easily dented due to their conductive material construction, their effectiveness can be hindered by moisture, and they can be destroyed by corrosion.Rate this question:
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- 13.
Which two transmission line properties determine its characteristic impedance (ZO)?
- A.
Inductance and resistance.
- B.
Inductance and capacitance.
- C.
Resistance and capacitance.
- D.
Length and type of shielding.
Correct Answer
B. Inductance and capacitance.Explanation
The characteristic impedance (ZO) of a transmission line is determined by its inductance and capacitance. Inductance is the property of a transmission line that resists changes in current, while capacitance is the property that resists changes in voltage. The combination of these two properties determines the characteristic impedance, which is important for matching the impedance of the transmission line with the source and load to minimize signal reflection and maximize power transfer. Resistance and capacitance do not solely determine the characteristic impedance, and the length and type of shielding are not directly related to the characteristic impedance.Rate this question:
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- 14.
This is the correct statement concerning a wavelength.
- A.
Wavelength is inversely related to frequency.
- B.
Wavelength is directly related to frequency.
- C.
Wavelength is determined by the line length.
- D.
Wavelength is expressed in lambdas (λ).
Correct Answer
A. Wavelength is inversely related to frequency.Explanation
The correct answer is "Wavelength is inversely related to frequency." This means that as the wavelength increases, the frequency decreases, and vice versa. This relationship is based on the wave equation, where wavelength (λ) is equal to the speed of light (c) divided by the frequency (f). Since the speed of light is constant, if the wavelength increases, the frequency must decrease to maintain this equation. Therefore, wavelength and frequency have an inverse relationship.Rate this question:
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- 15.
Determine the wavelength of a 250 megahertz (MHz) signal.
- A.
12.0 meters.
- B.
3.0 meters.
- C.
1.5 meters.
- D.
1.2 meters.
Correct Answer
D. 1.2 meters.Explanation
The wavelength of a signal can be determined by dividing the speed of light by the frequency of the signal. In this case, the frequency is given as 250 megahertz (MHz), which is equivalent to 250 million hertz (Hz). The speed of light is approximately 3 x 10^8 meters per second. Dividing the speed of light by the frequency, we get a wavelength of 1.2 meters.Rate this question:
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- 16.
A nonresonant transmission line is one with
- A.
Reflected waves.
- B.
No reflected waves.
- C.
Maximum voltage across its open termination.
- D.
Maximum voltage across its shorted termination.
Correct Answer
B. No reflected waves.Explanation
A nonresonant transmission line is designed in such a way that there are no reflected waves. This means that all the energy that is sent down the line is completely absorbed by the load at the end of the line, with no energy bouncing back towards the source. This is achieved by matching the impedance of the transmission line with the impedance of the load. As a result, there is no voltage or current wave that travels back along the line, indicating the absence of reflected waves.Rate this question:
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- 17.
When discussing resonant and nonresonant transmission lines,
- A.
Resonant lines are often referred to as flat lines.
- B.
Maximum power transfer results from a resonant line.
- C.
Maximum power transfer results from a nonresonant line.
- D.
Significant loss and damage to equipment results from using a nonresonant line.
Correct Answer
C. Maximum power transfer results from a nonresonant line. -
- 18.
This will likely result if a transmission line is terminated in an open.
- A.
Signal loss would be negligible.
- B.
Signal loss would be significant.
- C.
Current would be maximum at the termination.
- D.
Voltage would be minimum at the termination.
Correct Answer
B. Signal loss would be significant.Explanation
If a transmission line is terminated in an open, it means that there is no load connected to the line. In this case, the signal will reflect back towards the source, causing interference and signal loss. This is because the open termination does not provide impedance matching, leading to a mismatch between the transmission line and the load. As a result, a significant amount of the signal will be lost, leading to significant signal loss.Rate this question:
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- 19.
Direct waves are radio waves that travel
- A.
Long distances with few interruptions.
- B.
From point to point along the Earth’s surface.
- C.
No more than 20 miles to the receive antenna.
- D.
Through the air in a straight line from transmitter to receiver.
Correct Answer
D. Through the air in a straight line from transmitter to receiver.Explanation
Direct waves are radio waves that travel through the air in a straight line from transmitter to receiver. This means that there are no obstacles or interruptions in the path of the waves. They do not bounce off the Earth's surface or any other objects, and they do not follow the curvature of the Earth. This allows direct waves to travel long distances without significant loss of signal strength. The statement "through the air in a straight line from transmitter to receiver" accurately describes the nature of direct waves.Rate this question:
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- 20.
Radio waves that travel near the Earth’s surface are called
- A.
Earth waves.
- B.
Global waves.
- C.
Ground waves.
- D.
Terrestrial waves.
Correct Answer
C. Ground waves.Explanation
Radio waves that travel near the Earth's surface are called ground waves. This is because these waves propagate by hugging the surface of the Earth and following its curvature. Ground waves are able to travel long distances and are commonly used for broadcasting purposes. They are also able to penetrate buildings and other obstacles, making them suitable for communication in urban areas.Rate this question:
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- 21.
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.
Correct Answer
C. Soil and water in the propagation path.Explanation
The Earth's conductivity, which affects the propagation of signals, is determined by the type of soil and water in the propagation path. Soil and water have different electrical properties that can impact the transmission of signals. The composition and moisture content of the soil and water can influence how well they conduct electricity, which in turn affects the propagation of signals through them.Rate this question:
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- 22.
This term is used to describe radio waves that bend as they travel from one medium to another that has different density.
- A.
Diffusion.
- B.
Diffraction.
- C.
Refraction.
- D.
Reflection.
Correct Answer
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 phenomenon occurs due to the change in speed of the waves, causing them to change direction. Diffusion refers to the spreading out of waves in different directions, while diffraction refers to the bending of waves around obstacles. Reflection occurs when waves bounce off a surface.Rate this question:
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- 23.
The refractive index of air depends on moisture,
- A.
Atmospheric pressure, and temperature.
- B.
Atmospheric pressure, and frequency.
- C.
Receive signal level, and temperature.
- D.
Receive signal level, and frequency.
Correct Answer
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 at which light travels through it. As pressure increases, the refractive index of air increases. Temperature also affects the density of air, causing it to expand or contract. As temperature increases, the refractive index of air decreases. Therefore, both atmospheric pressure and temperature play a role in determining the refractive index of air.Rate this question:
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- 24.
When comparing the radio and optical horizons, which one is farther away and by what percentage?
- A.
Optical; 15.
- B.
Radio; 15.
- C.
Optical; 33.
- D.
Radio; 33.
Correct Answer
B. Radio; 15.Explanation
The correct answer is "Radio; 15." This means that the radio horizon is farther away by 15% compared to the optical horizon. This suggests that when comparing the distance at which radio waves can be detected versus the distance at which optical waves can be detected, the radio waves can be detected at a greater distance, specifically 15% farther than the optical waves.Rate this question:
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- 25.
Which process permits communication in shadow regions behind obstacles?
- A.
Reflection.
- B.
Scattering.
- C.
Refraction.
- D.
Diffraction.
Correct Answer
D. Diffraction.Explanation
Diffraction is the process that allows communication in shadow regions behind obstacles. When a wave encounters an obstacle or a slit that is comparable in size to its wavelength, it bends around the edges and spreads out into the region behind the obstacle. This bending and spreading out of the wave is known as diffraction. It enables the wave to reach areas that are not directly in its path, including shadow regions, allowing for communication even when obstacles are present. Reflection, scattering, and refraction do not specifically address communication in shadow regions behind obstacles.Rate this question:
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- 26.
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).
Correct Answer
A. High frequency (HF).Explanation
High frequency (HF) signals have shorter wavelengths and are less affected by precipitation compared to signals in other frequency ranges. Precipitation, such as rain or snow, can cause signal attenuation and scattering, leading to signal degradation. However, HF signals have better penetration capabilities and can travel longer distances through the atmosphere, making them less susceptible to the effects of precipitation. Therefore, HF frequency range will show little effect from precipitation.Rate this question:
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- 27.
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.
Correct Answer
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 atmospheric conditions cause radio waves to be trapped and guided along a specific path, allowing them to travel much farther than they would in normal conditions. This phenomenon is commonly observed in certain weather conditions, such as temperature inversions, where the air near the ground is cooler than the air above it, creating a duct or channel for the radio waves to follow.Rate this question:
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- 28.
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.
Correct Answer
A. Refraction.Explanation
Refraction is the condition that gives sky-wave propagation its ability to communicate beyond the optical line-of-sight (LOS). When radio waves encounter a change in the density of the atmosphere, they bend or refract towards the Earth's surface. This bending allows the waves to follow the curvature of the Earth and reach areas that are beyond the direct line-of-sight. This phenomenon is essential for long-distance communication, as it enables radio signals to be received over the horizon, making refraction the correct answer.Rate this question:
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- 29.
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.
Correct Answer
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 approaches a boundary between two mediums, in this case, the ionosphere. It is important to understand the angle of incidence as it determines how the wave will be refracted or reflected upon entering the ionosphere.Rate this question:
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- 30.
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.
Correct Answer
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 refracted back towards Earth. This absorption prevents the radio waves from being returned to Earth or passing through the ionosphere into space.Rate this question:
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- 31.
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.
Correct Answer
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 transmission of radio waves from a ground-based transmitter to a receiver by reflecting them off the ionosphere. The critical frequency is the maximum frequency that can be reflected back to Earth by the ionosphere. Frequencies higher than the critical frequency are not reflected back and instead continue to travel into space. Therefore, they are passed into space rather than being returned to Earth or refracted by the F2 layer.Rate this question:
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- 32.
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.
Correct Answer
A. Outbound traffic frequency.Explanation
The term frequency of optimum transmission (FOT) refers to the frequency at which outbound traffic is transmitted. It is commonly known as the outbound traffic frequency.Rate this question:
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- 33.
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.
Dead zone.
- D.
Skip zone.
Correct Answer
D. Skip zone.Explanation
In sky- and ground-wave propagation, signals can travel in multiple paths. The skip zone refers to an area where the signal does not reach directly from the transmitter to the receiver due to the signal being refracted or reflected away. This results in a silence zone where no signals are received. Therefore, the correct answer is skip zone.Rate this question:
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- 34.
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.
Correct Answer
C. Multipathing.Explanation
Multipathing occurs when a transmitted signal travels over two or more separate paths during transmission. This can happen due to reflections, refractions, or diffractions of the signal. As a result, multiple copies of the signal reach the receiver at slightly different times, causing interference and signal degradation. Multipathing is a common phenomenon in wireless communication systems and can be mitigated using techniques like equalization and diversity reception.Rate this question:
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- 35.
How many layers make up the Earth’s atmosphere?
- A.
2.
- B.
3.
- C.
4.
- D.
5.
Correct Answer
D. 5.Explanation
The correct answer is 5 because the Earth's atmosphere is composed of five distinct layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer has its own unique characteristics and plays a vital role in the Earth's climate and weather patterns.Rate this question:
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- 36.
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.
Correct Answer
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 the atoms to lose or gain electrons, resulting in the formation of ions. This process is known as ionization.Rate this question:
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- 37.
The atmospheric recombination process is dependent on the
- A.
Season.
- B.
Time of day (TOD).
- C.
Regular variation.
- D.
Irregular variations.
Correct Answer
B. Time of day (TOD).Explanation
The atmospheric recombination process refers to the process in which ions and electrons in the atmosphere combine to form neutral molecules. This process is influenced by various factors, including the time of day. During the daytime, the presence of sunlight and increased temperature enhances the recombination process. In contrast, during the nighttime, the absence of sunlight and lower temperatures hinder the recombination process. Therefore, the time of day (TOD) plays a crucial role in determining the rate and efficiency of atmospheric recombination.Rate this question:
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- 38.
Which layer of the ionosphere is most important for high-frequency (HF) communications?
- A.
D.
- B.
E.
- C.
F.
- D.
Topside.
Correct Answer
C. F.Explanation
The F layer of the ionosphere is the most important for high-frequency (HF) communications. This layer is located at an altitude of around 200-400 km above the Earth's surface and is responsible for reflecting and refracting HF radio waves back to the Earth. It is the highest layer of the ionosphere and is further divided into two sub-layers, F1 and F2. The F layer is particularly crucial for long-distance HF communications as it allows for long-range propagation of radio waves by reflecting them back to the Earth's surface.Rate this question:
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- 39.
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.
Correct Answer
B. Winter.Explanation
During winter, the air is colder and denser, which leads to a wider range of critical frequencies and less absorption of all frequencies. This is because sound waves travel faster in colder air, allowing for a wider range of frequencies to be transmitted. Additionally, the colder air also reduces the amount of moisture and humidity, which can absorb sound waves. Therefore, winter is the season with the wider range of critical frequencies and less absorption of all frequencies.Rate this question:
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- 40.
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.
Correct Answer
B. On the sun’s surface.Explanation
Sunspots are disturbances that appear and disappear on the sun's surface. Sunspots are dark, cooler areas on the sun's photosphere caused by intense magnetic activity. They are temporary phenomena that can last from a few hours to several weeks before fading away. These sunspots are visible as dark spots on the sun's surface and can be observed using telescopes equipped with solar filters. The presence and movement of sunspots provide valuable information about the sun's magnetic field and can also affect space weather conditions on Earth.Rate this question:
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- 41.
On which regular ionospheric variation do sunspots occur?
- A.
11-day cycle.
- B.
11-week cycle.
- C.
11-month cycle.
- D.
11-year cycle.
Correct Answer
D. 11-year cycle.Explanation
Sunspots occur on an 11-year cycle. Sunspots are dark spots on the surface of the Sun that are caused by strong magnetic activity. These spots appear and disappear over time, following a pattern known as the solar cycle. The solar cycle has an average duration of 11 years, during which the number of sunspots reaches a maximum (solar maximum) and then decreases to a minimum (solar minimum) before starting the cycle again. This 11-year cycle is a regular variation in the ionosphere, the upper part of the Earth's atmosphere, where sunspots can have an impact on radio communications and other ionospheric phenomena.Rate this question:
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- 42.
In a basic communication system, this is used to convert radio frequency (RF) current oscillation into electric and magnetic fields of force.
- A.
Antenna.
- B.
Transmitter.
- C.
Coupler.
- D.
Transmission lines.
Correct Answer
A. Antenna.Explanation
In a basic communication system, the antenna is used to convert radio frequency (RF) current oscillation into electric and magnetic fields of force. The antenna acts as a transducer, transforming the electrical signals into electromagnetic waves that can be transmitted through space. It plays a crucial role in transmitting and receiving signals, allowing communication to occur wirelessly.Rate this question:
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- 43.
The concept where alternating current (AC) changes in magnitude, and reverses its direction during each cycle, is
- A.
An unproven hypothesis.
- B.
The definition of propagation.
- C.
What makes radio transmission possible.
- D.
What led to the discovery of direct current (DC).
Correct Answer
C. What makes radio transmission possible.Explanation
The concept where alternating current (AC) changes in magnitude, and reverses its direction during each cycle, is what makes radio transmission possible. This is because radio waves are a form of electromagnetic radiation that can be generated and transmitted using AC. The changing magnitude and direction of AC allows for the creation and propagation of electromagnetic waves, which can then be received and decoded by radio receivers.Rate this question:
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- 44.
At which point do magnetic fields around a wire no longer have time to collapse completely between alternations?
- A.
60 cycles per second (cps).
- B.
120 cps.
- C.
10,000 cps.
- D.
15,000 cps.
Correct Answer
C. 10,000 cps.Explanation
At 10,000 cycles per second (cps), the magnetic fields around a wire do not have enough time to collapse completely between alternations. This means that the magnetic fields are constantly changing direction at such a high frequency that they cannot fully collapse before the next alternation begins. This is known as the frequency limit or the point at which the wire's magnetic fields no longer have time to collapse completely.Rate this question:
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- 45.
In radio-wave creation, which type of field detaches from the antenna and travels through space at great distances?
- A.
Radiation.
- B.
Induction.
- C.
Gravitational.
- D.
Electromotive.
Correct Answer
A. Radiation.Explanation
In radio-wave creation, the type of field that detaches from the antenna and travels through space at great distances is radiation. Radiation refers to the emission of energy as electromagnetic waves or as moving subatomic particles, such as electrons. In the context of radio waves, radiation is the process by which the energy from the antenna is propagated outward in the form of electromagnetic waves, which can travel through space and be received by other devices.Rate this question:
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- 46.
Which types of polarization do most satellite communication terminals transmit and receive?
- A.
Transmit horizontal and receive vertical polarizations.
- B.
Transmit vertical and receive horizontal polarizations.
- C.
Transmit right-hand circular and receive left-hand circular polarizations.
- D.
Transmit left-hand circular and receive right-hand circular polarizations.
Correct Answer
C. Transmit right-hand circular and receive left-hand circular polarizations.Explanation
Most satellite communication terminals transmit right-hand circular polarizations and receive left-hand circular polarizations. Circular polarization allows for better signal reception and reduces the effects of signal fading caused by obstacles and atmospheric conditions. Transmitting and receiving circular polarizations also helps to mitigate interference from other signals and minimize cross-polarization losses.Rate this question:
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- 47.
A resonant antenna effectively radiates a radio signal for frequencies close to its designed frequency. Which percentage range, plus or minus, is it usually within?
- A.
1
- B.
2
- C.
3
- D.
4
Correct Answer
B. 2Explanation
A resonant antenna is designed to efficiently radiate radio signals at a specific frequency. It is usually within a range of plus or minus 2% of its designed frequency. This means that the antenna will effectively radiate signals for frequencies that are very close to its intended frequency, providing optimal performance and signal transmission.Rate this question:
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- 48.
The design frequency of a resonant antenna is 10 megahertz (MHz). What will be its frequency range?
- A.
8–10 MHz.
- B.
9–11 MHz.
- C.
9.5–10.5 MHz.
- D.
9.8–10.2 MHz.
Correct Answer
D. 9.8–10.2 MHz.Explanation
The design frequency of a resonant antenna is 10 megahertz (MHz), which means that it is specifically designed to operate at this frequency. However, due to various factors such as manufacturing tolerances and environmental conditions, the actual operating frequency of the antenna may vary slightly. Therefore, the frequency range of the resonant antenna is expected to be within a small range around the design frequency. In this case, the correct answer is 9.8–10.2 MHz, which represents a narrow range of frequencies close to the design frequency of 10 MHz.Rate this question:
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- 49.
The lowest frequency at which an antenna resonates is known as its
- A.
Standing wave.
- B.
Fundamental.
- C.
Resonation.
- D.
Primary.
Correct Answer
B. Fundamental.Explanation
The lowest frequency at which an antenna resonates is known as its fundamental frequency. Resonance occurs when the antenna vibrates at its natural frequency, resulting in maximum energy transfer and efficient signal transmission. The fundamental frequency is the base frequency at which the antenna can resonate and is crucial for its proper functioning. Standing wave refers to the pattern formed when waves reflect back and forth between two points, resonation is not a term commonly used in the context of antennas, and primary does not accurately describe the lowest resonating frequency.Rate this question:
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- 50.
The ability of an antenna to both receive and transmit equally well is known as the antenna’s
- A.
Bandwidth.
- B.
Resonance.
- C.
Reciprocity.
- D.
Effectiveness.
Correct Answer
C. Reciprocity.Explanation
Reciprocity refers to the ability of an antenna to both receive and transmit signals equally well. It means that the characteristics of an antenna remain the same regardless of whether it is used for receiving or transmitting. This property is important in various communication systems as it allows for efficient and reliable signal transmission and reception. Bandwidth refers to the range of frequencies over which an antenna can operate effectively. Resonance refers to the frequency at which an antenna operates most efficiently. Effectiveness is a general term that does not specifically describe the ability of an antenna to receive and transmit signals equally well.Rate this question:
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