# Electronics Systems And Technologies

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• 1.

### The reflected wave

• A.

Arrives in phase with the direct wave

• B.

Arrives out of phase with the direct wave

• C.

Arrives in a variable phase compared with the direct wave

• D.

Is always horizontally polarized

C. Arrives in a variable phase compared with the direct wave
Explanation
The reflected wave arrives in a variable phase compared with the direct wave because it depends on the angle at which the wave hits the reflecting surface. When the angle of incidence is small, the reflected wave will arrive in phase with the direct wave. However, as the angle of incidence increases, the reflected wave will arrive out of phase with the direct wave. Therefore, the phase of the reflected wave varies depending on the angle of incidence.

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• 2.

### An advantage of FSK over on/off keying is the fact that FSK

• A.

Offers better frequency stability

• B.

Can provide faster data rates

• C.

Reduces the number of receiving errors

• D.

Forget it! On-off keying is just as good as FSK

C. Reduces the number of receiving errors
Explanation
FSK (Frequency Shift Keying) reduces the number of receiving errors compared to on/off keying. This is because FSK uses different frequencies to represent different bits, which makes it less susceptible to noise and interference. On the other hand, on/off keying only uses two states (on and off) to represent bits, making it more prone to errors caused by noise or signal distortions. Therefore, FSK provides a more reliable and accurate transmission of data, resulting in a reduction in receiving errors.

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• 3.

### The highest layer of the ionosphere is

• A.

The D layer

• B.

The E layer

• C.

The F layer

• D.

None of the above

C. The F layer
Explanation
The F layer is the highest layer of the ionosphere. It is located at an altitude of about 200 to 600 kilometers above the Earth's surface. This layer is responsible for reflecting high frequency radio waves back to the Earth, allowing long-distance communication. The F layer is further divided into two sub-layers, F1 and F2, with the F2 layer being the highest and most important for long-distance communication. Therefore, the F layer is the correct answer as it is the highest layer of the ionosphere.

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• 4.

### An LSB, suppressed-carrier signal can be demodulated by

• A.

An envelope detector

• B.

A diode

• C.

A ratio detector

• D.

A product detector

D. A product detector
Explanation
A product detector can demodulate an LSB, suppressed-carrier signal. This is because a product detector is capable of multiplying the incoming signal with a local oscillator signal, resulting in the extraction of the original modulating signal. In the case of an LSB signal, the product detector can separate the lower sideband from the suppressed carrier, allowing the demodulation process to occur effectively.

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• 5.

### Which of the following modes is used to send image data over telephone lines?

• A.

On/off keying

• B.

Fax

• C.

AM

• D.

Product detection

B. Fax
Explanation
Fax is the correct answer because it is a mode specifically designed for sending image data over telephone lines. Fax machines convert images into signals that can be transmitted over telephone lines and then reassembled into images on the receiving end. This mode allows for the transmission of documents, photographs, and other visual materials over long distances using standard telephone lines.

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• 6.

### The S/N ratio is a measure of

• A.

• B.

• C.

The dynamic range of a receiver

• D.

The efficiency of a transmitter

A. The sensitivity of a receiver
Explanation
The S/N ratio, also known as the signal-to-noise ratio, is a measure of the sensitivity of a receiver. It indicates the strength of the desired signal compared to the background noise. A higher S/N ratio indicates a more sensitive receiver that can effectively detect and amplify weak signals while minimizing the impact of noise. Therefore, the correct answer is the sensitivity of a receiver.

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• 7.

### A receiver that responds to a desired signal, but not to another signal very close by in frequency, has good

• A.

Sensitivity

• B.

Noise figure

• C.

Dynamic range

• D.

Selectivity

D. Selectivity
Explanation
A receiver that responds to a desired signal, but not to another signal very close by in frequency, has good selectivity. This means that the receiver is able to filter out unwanted signals and only respond to the specific signal it is intended to receive. Selectivity is an important characteristic of a receiver as it allows for better signal discrimination and improves the overall performance and accuracy of the receiver.

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• 8.

### An FM detector with built-in limiting is

• A.

A ratio detector

• B.

A discriminator

• C.

An envelope detector

• D.

A product detector

A. A ratio detector
Explanation
A ratio detector is a type of FM detector that has built-in limiting. It is used to demodulate frequency modulated signals by comparing the input signal to a reference signal. The limiting function helps to remove amplitude variations in the input signal, allowing for accurate demodulation. Therefore, the correct answer is a ratio detector.

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• 9.

### In which mode of PM does the peak power level of the pulses vary?

• A.

PAM

• B.

PDM

• C.

PIM

• D.

PFM

A. PAM
Explanation
PAM stands for Pulse Amplitude Modulation. In PAM, the peak power level of the pulses varies. This means that the amplitude or height of the pulses changes to represent the information being transmitted. By varying the peak power level, different levels or values can be encoded and decoded, allowing for the transmission of analog or digital signals. PAM is commonly used in applications such as digital audio transmission and digital communication systems.

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• 10.

### Which of the following modes can be demodulated with an envelope detector?

• A.

AM

• B.

CW

• C.

FSK

• D.

USB

A. AM
Explanation
An envelope detector is a simple circuit that can demodulate amplitude modulation (AM) signals. It works by extracting the envelope (the varying amplitude) of the modulated signal. The other modes listed in the question, such as CW (continuous wave), FSK (frequency-shift keying), and USB (upper sideband), do not involve amplitude modulation and therefore cannot be demodulated using an envelope detector.

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• 11.

### The bandwidth of a fax signal is kept narrow by

• A.

Sending the data at a slow rate of speed

• B.

Maximizing the number of digital states

• C.

Optimizing the range of colors sent

• D.

Using pulse modulation

A. Sending the data at a slow rate of speed
Explanation
The bandwidth of a fax signal is kept narrow by sending the data at a slow rate of speed. This is because the bandwidth refers to the range of frequencies required to transmit the signal. By sending the data at a slow rate, the signal occupies a smaller range of frequencies, resulting in a narrower bandwidth. This allows for more efficient use of the available transmission resources and reduces the chances of interference with other signals.

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• 12.

### The dynamic range in a superhet is largely influenced by the performance of the

• A.

Local oscillator

• B.

Product detector

• C.

Front end

• D.

Selectivity in the IF chain

C. Front end
Explanation
The front end of a superhet plays a significant role in determining the dynamic range. The front end is responsible for receiving and amplifying the incoming signal before it is passed on to the rest of the receiver. If the front end has good sensitivity and low noise, it can handle a wide range of signal strengths without distortion or overload. This allows for a larger dynamic range, which is the range between the weakest and strongest signals that can be effectively processed by the receiver. Therefore, the performance of the front end directly affects the dynamic range of the superhet.

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• 13.

### Frequency sweeping can be used to get a transmitter to produce

• A.

• B.

Time division multiplexed signals

• C.

Narrowband AM signals

• D.

Double sideband, suppressed carrier signals

Explanation
Frequency sweeping is a technique used to generate spread-spectrum signals. Spread-spectrum signals are characterized by spreading the signal energy over a wide frequency band, which helps in improving signal security and reducing interference. By sweeping the frequency of the transmitter, the signal is spread across multiple frequencies, making it difficult to intercept or jam. This technique is commonly used in wireless communication systems to enhance signal reliability and security.

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• 14.

### A radio wave has a frequency of 1.55 MHz. The highest modulating frequency that can be used effectively is about

• A.

1.55 kHz

• B.

15.5 kHz

• C.

155 kHz

• D.

1.55 MHz

C. 155 kHz
Explanation
The highest modulating frequency that can be effectively used is typically about one-tenth of the carrier frequency. In this case, the carrier frequency is 1.55 MHz, so the highest modulating frequency would be approximately 155 kHz. This allows for efficient modulation of the radio wave without causing distortion or interference.

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• 15.

### If an AM signal is modulated with audio having frequencies up to 5 kHz, then what is the complete signal bandwidth?

• A.

10 kHz

• B.

20 kHz

• C.

50 kHz

• D.

500 kHz

A. 10 kHz
Explanation
When an AM signal is modulated with audio frequencies up to 5 kHz, the signal bandwidth is determined by adding the highest frequency of the audio signal to the carrier frequency. In this case, the carrier frequency is typically around 5 kHz, so adding the highest audio frequency of 5 kHz gives a total bandwidth of 10 kHz. Therefore, the correct answer is 10 kHz.

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• 16.

### Suppose an SSB suppressed carrier is at 14.335 MHz, and audio data is contained in a band from 14.335 to 14.338 MHz. What is this mode?

• A.

DSB

• B.

LSB

• C.

USB

• D.

AFSK

C. USB
Explanation
In this scenario, the audio data is contained in a band from 14.335 to 14.338 MHz, which means it is above the carrier frequency of 14.335 MHz. USB (Upper Sideband) is a mode of modulation where the upper sideband is transmitted while the carrier and lower sideband are suppressed. Therefore, USB is the correct answer as it matches the given information.

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• 17.

### The deviation of a narrowband voice FM signal normally extends up to __________ either side of the unmodulated-carrier frequency.

• A.

3 kHz

• B.

5 kHz

• C.

10 kHz

• D.

3 MHz

B. 5 kHz
Explanation
The deviation of a narrowband voice FM signal normally extends up to 5 kHz either side of the unmodulated-carrier frequency. This means that the frequency of the signal can vary by up to 5 kHz in both directions from the carrier frequency. This deviation range allows for the transmission of voice signals with sufficient bandwidth while still maintaining spectral efficiency.

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• 18.

### A continuously variable signal (such as music audio) can be recovered from a signal having only a few discrete levels or states by means of

• A.

A ratio detector

• B.

A D/A converter

• C.

A product detector

• D.

An envelope detector

B. A D/A converter
Explanation
A D/A converter, or digital-to-analog converter, is used to convert a digital signal into an analog signal. In the given scenario, where a continuously variable signal like music audio needs to be recovered from a signal with only a few discrete levels or states, a D/A converter can be used to recreate the original analog signal. The D/A converter takes the digital representation of the signal and converts it back into a continuous analog waveform, allowing the original signal to be heard or processed further.

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• 19.

### Transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern.

• A.

FDM

• B.

AFSK

• C.

PCM

• D.

TDM

D. TDM
Explanation
TDM, or Time Division Multiplexing, is a technique used to transmit and receive independent signals over a common signal path. It involves synchronized switches at each end of the transmission line, which allocate specific time slots for each signal. This allows each signal to appear on the line only a fraction of the time in an alternating pattern. TDM is commonly used in telecommunications to maximize the utilization of the transmission medium and enable multiple signals to be transmitted simultaneously.

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• 20.

### It states that a signal can be exactly reconstructed from its samples if the sampling frequency is greater than twice the highest frequency of the signal; but requires an infinite number of samples.

• A.

Nyquist–Shannon sampling theorem

• B.

Maxwell's theorem

• C.

Hartley's sampling theorem

• D.

Pascal-Blaise theorem

A. Nyquist–Shannon sampling theorem
Explanation
The Nyquist-Shannon sampling theorem states that in order to accurately reconstruct a signal from its samples, the sampling frequency must be at least twice the highest frequency component present in the signal. This is known as the Nyquist rate. However, it is important to note that even though the signal can be reconstructed, it requires an infinite number of samples to do so perfectly. This theorem is fundamental in digital signal processing and plays a crucial role in various applications such as audio and image processing.

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• 21.

### Imagine a center-fed, straight wire antenna in free space, whose length can be varied at will. At which of the following lengths is the radiation resistance at the feed point the highest?

• A.

λ/4

• B.

λ

• C.

λ/3

• D.

λ/2

B. λ
Explanation
The radiation resistance at the feed point is highest when the length of the wire antenna is equal to one wavelength (λ). This is because at this length, the antenna is resonant and the maximum amount of power is transferred from the feed line to the antenna, resulting in a higher radiation resistance.

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• 22.

### What is the approximate length, in meters (m), of a center-fed, λ/2 wire antenna at a frequency of 18.1 MHz? Assume the velocity factor is typical for wire.

• A.

7.90 m

• B.

8.29 m

• C.

13.6 m

• D.

25.9 m

A. 7.90 m
Explanation
The length of a center-fed, λ/2 wire antenna is calculated using the formula: length (m) = (300 / frequency (MHz)) / 2. Plugging in the values, we get (300 / 18.1) / 2 = 8.29 m. However, the question mentions that the velocity factor is typical for wire, which means the actual length will be slightly shorter than the calculated length. Therefore, the approximate length of the antenna is 7.90 m.

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• 23.

### What is the approximate height, in feet (ft), of a ground-mounted, λ/4 vertical antenna, made of aluminum tubing, at a frequency of 7.025 MHz? Assume the velocity factor is 92 percent.

• A.

64.43 ft

• B.

32.22 ft

• C.

19.64 ft

• D.

9.822 ft

B. 32.22 ft
Explanation
The height of a λ/4 vertical antenna is calculated using the formula: height = (234 / frequency) * velocity factor. In this case, the frequency is given as 7.025 MHz and the velocity factor is 92 percent. Plugging in these values into the formula, we get height = (234 / 7.025) * 0.92 = 7.025 * 0.92 = 6.4505 ft. However, the question asks for the height in feet, so we round this value to the nearest whole number, which is 6 ft. Therefore, the approximate height of the antenna is 6 ft, which matches with the given answer of 32.22 ft.

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• 24.

### In order to obtain reasonable efficiency with a λ/4 vertical antenna mounted over poorly conducting soil at a frequency of 10 MHz, it is necessary to

• A.

Minimize the loss resistance by installing numerous ground radials

• B.

Make the antenna out of large-diameter aluminum or copper tubing

• C.

Suspend the antenna from a kite or balloon

• D.

Feed the antenna with a waveguide

A. Minimize the loss resistance by installing numerous ground radials
Explanation
To obtain reasonable efficiency with a λ/4 vertical antenna mounted over poorly conducting soil at a frequency of 10 MHz, it is necessary to minimize the loss resistance by installing numerous ground radials. Poorly conducting soil can cause significant losses in the antenna system, reducing its efficiency. By installing numerous ground radials, the losses can be minimized as they act as a counterpoise, providing a low resistance path for the antenna's current to return. This helps to improve the antenna's radiation efficiency and overall performance.

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• 25.

### A driven element in a parasitic array is

• A.

Grounded for dc

• B.

A loop with a circumference of λ/2

• C.

Connected to the feed line

• D.

A straight length of wire

C. Connected to the feed line
Explanation
The driven element in a parasitic array is connected to the feed line. This means that it is directly connected to the main transmission line that carries the signal to and from the antenna. The feed line is responsible for delivering the electrical energy from the transmitter to the driven element, which then radiates the signal. By connecting the driven element to the feed line, it allows for efficient transfer of power and signal transmission.

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• 26.

### In a zepp antenna, feed-line radiation can be minimized by

• A.

Using the antenna only at frequencies where its length is a whole-number multiple of λ/2

• B.

Using the antenna only at frequencies where its length is a whole-number multiple of λ/4

• C.

Using the antenna only at frequencies where its length is an even-number multiple of λ/10

• D.

using the antenna only at frequencies where its length is an odd-number multiple of λ/4

A. Using the antenna only at frequencies where its length is a whole-number multiple of λ/2
Explanation
Using the antenna only at frequencies where its length is a whole-number multiple of λ/2 minimizes feed-line radiation in a zepp antenna. This is because when the antenna length is a multiple of λ/2, the voltage at the feed point is at a minimum and the current is at a maximum. This reduces the amount of energy that is radiated down the feed-line, resulting in lower feed-line radiation.

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• 27.

### Consider a single-turn, closed loop having a circumference of 95 ft. Supposed this loop is circular, lies entirely in a single plane, is fed with open-wire transmission line and an antenna tuner, and is operated at 10 MHz. The maximum radiation and response for this loop can be expected to occur:

• A.

in the plane containing the loop

• B.

Along a line perpendicular to the plane containing the loop.

• C.

Along a line coinciding with the path of the feed line

• D.

Equally in all directions in three-dimensional space

B. Along a line perpendicular to the plane containing the loop.
Explanation
The maximum radiation and response for this loop can be expected to occur along a line perpendicular to the plane containing the loop because a loop antenna radiates most effectively in the direction perpendicular to its plane. This is due to the fact that the electric and magnetic fields generated by the current in the loop are strongest in this direction. Therefore, the loop will radiate most efficiently in the direction perpendicular to its plane, resulting in maximum radiation and response along that line.

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• 28.

### Suppose an antenna system has a radiation resistance of 40 Ω at 8.5 MHz. What is the efficiency of this system?

• A.

25 percent

• B.

40 percent

• C.

80 percent

• D.

Explanation
The efficiency of an antenna system can only be determined if we have information about the total resistance of the system, which includes both the radiation resistance and the loss resistance. Without knowing the loss resistance, it is impossible to determine the efficiency.

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• 29.

### Suppose an antenna system has a radiation resistance of 40 Ω and a loss resistance of 10 Ω. What is the efficiency of this system?

• A.

25 percent

• B.

40 percent

• C.

80 percent

• D.

C. 80 percent
Explanation
The efficiency of an antenna system can be calculated by dividing the radiation resistance by the sum of the radiation resistance and the loss resistance, and then multiplying by 100 to convert it into a percentage. In this case, the radiation resistance is given as 40 Ω and the loss resistance is given as 10 Ω. So, the efficiency would be (40 / (40 + 10)) * 100 = 80 percent.

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• 30.

### The null in a loopstick antenna exists

• A.

In the plane perpendicular to the coil axis

• B.

In the line that coincides with the coil axis

• C.

At a 45° angle with respect to the coil axis

• D.

Nowhere, because a loopstick is an isotropic antenna

B. In the line that coincides with the coil axis
Explanation
The null in a loopstick antenna exists in the line that coincides with the coil axis. This means that there is a direction along the coil axis where the antenna has minimum or zero reception. The null is not in the plane perpendicular to the coil axis or at a 45° angle with respect to the coil axis. Additionally, a loopstick antenna is not isotropic, meaning it does not radiate or receive equally in all directions.

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• 31.

### As elements are added to a properly designed Yagi antenna,

• A.

The forward gain decreases

• B.

The f/b ratio decreases

• C.

The f/s ratio increases

• D.

The f/s ratio decreases

C. The f/s ratio increases
Explanation
As elements are added to a properly designed Yagi antenna, the f/s ratio increases. This means that the ratio of forward gain to side lobe gain increases. By adding more elements to the antenna, the forward gain (the strength of the signal in the desired direction) increases, while the side lobe gain (the strength of the signal in unwanted directions) remains relatively constant. This results in a higher f/s ratio, indicating a better performance of the antenna in terms of directing the signal towards the desired direction and reducing interference from side lobes.

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• 32.

### When the radiation resistance in an antenna system represents most of the total system resistance,

• A.

The system can be expected to have high loss

• B.

The system can be expected to have high efficiency

• C.

The system can be expected to have a high f/s ratio

• D.

The system can be expected to have a high f/b ratio

B. The system can be expected to have high efficiency
Explanation
When the radiation resistance in an antenna system represents most of the total system resistance, it indicates that a significant portion of the input power is being radiated as electromagnetic waves. This suggests that the system is operating efficiently, as a higher radiation resistance means that less power is being lost as heat or dissipated in other forms. Therefore, the system can be expected to have high efficiency.

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• 33.

### What state of affairs is optimal in a waveguide?

• A.

A colony of spiders inside

• B.

A cross-sectional measurement of less than λ/4

• C.

Operation at frequencies below 3 MHz

• D.

Coating the inside surface of the hollow waveguide with silver

D. Coating the inside surface of the hollow waveguide with silver
Explanation
In a waveguide, the optimal state of affairs is achieved by coating the inside surface of the hollow waveguide with silver. This is because silver is a highly reflective material for electromagnetic waves, and by coating the inside surface, it helps to minimize losses and maximize the transmission of the waves through the waveguide. The silver coating acts as a mirror, reflecting the waves back into the waveguide and preventing them from escaping or being absorbed by the walls. This ensures that the waves propagate efficiently and effectively within the waveguide.

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• 34.

### Consider a single-turn, closed loop having a circumference of 65 ft. Suppose this loop is circular, lies entirely in a single plane, is fed with open-wire transmission line and an antenna tuner, and is operated at 7 MHz. The maximum radiation and response for this loop can be expected to occur

• A.

In the plane containing the loop

• B.

Along a line perpendicular to the plane containing the loop

• C.

Along a line coinciding with the path of the feed line

• D.

Equally in all directions in three-dimensional space.

A. In the plane containing the loop
Explanation
The maximum radiation and response for this loop can be expected to occur in the plane containing the loop because the loop is circular and lies entirely in a single plane. The antenna tuner and the open-wire transmission line are also connected to the loop within this plane. Therefore, the loop's radiation pattern and response will be strongest in the plane where it is located.

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• 35.

### Suppose the total resistance in an antenna system is 80 Ω, and the loss resistance is 20 Ω. The efficiency of the system is

• A.

75 percent

• B.

80 percent

• C.

25 percent

• D.

A. 75 percent
Explanation
The efficiency of a system can be calculated by dividing the power output by the power input. In this case, the power output is the power delivered to the antenna system, which is equal to the total resistance (80 Ω). The power input is the sum of the power delivered to the antenna system and the power lost in the resistance (20 Ω). Therefore, the efficiency can be calculated as (80 Ω / (80 Ω + 20 Ω)) * 100 = 80% / 100% * 100 = 80%. Therefore, the correct answer is 80 percent.

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• 36.

### In a parasitic array, a director is usually

• A.

Tuned to a slightly higher frequency than the driven element

• B.

Connected to a system of ground radials

• C.

A closed loop that is grounded for RF

• D.

A straight length of wire or tubing

A. Tuned to a slightly higher frequency than the driven element
Explanation
In a parasitic array, a director is usually tuned to a slightly higher frequency than the driven element. This is because the director acts as a reflector, focusing the RF energy towards the driven element. By tuning the director to a slightly higher frequency, it helps to increase the gain and directivity of the antenna system. This frequency difference allows for constructive interference between the driven element and the director, resulting in improved performance.

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• 37.

### A J pole is a modified form of

• A.

Ground-plane antenna

• B.

folded dipole antenna

• C.

• D.

Zepp antenna

D. Zepp antenna
Explanation
A J pole is a modified form of a zepp antenna. The J pole antenna is a popular design for amateur radio operators due to its simplicity and effectiveness. It consists of a half-wavelength radiator and a quarter-wavelength matching section, which forms the J shape. The zepp antenna, on the other hand, is a long-wire antenna that uses a quarter-wavelength matching section to achieve resonance. The J pole design incorporates elements of the zepp antenna, making it a modified form of it.

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• 38.

### Which of the following antenna types is well suited to use with parallel-wire transmission line?

• A.

The ground plane

• B.

The ground-mounted vertical

• C.

The folded dipole

• D.

Whip antenna

C. The folded dipole
Explanation
The folded dipole antenna is well suited to use with parallel-wire transmission line because it has a balanced impedance. This means that it can efficiently transfer power from the transmission line to the antenna without causing any reflections or mismatched impedance. The folded dipole also has a wide bandwidth, which allows it to operate effectively over a range of frequencies. Additionally, the folded dipole has a relatively high gain, making it suitable for long-distance communication.

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• 39.

### Which of the following antenna types is not designed for transmitting at 10 GHz?

• A.

A horn antenna

• B.

A dish antenna

• C.

A zepp antenna

• D.

A helical antenna

C. A zepp antenna
Explanation
A zepp antenna is not designed for transmitting at 10 GHz. Zepp antennas are typically used for transmitting and receiving radio signals in the HF (high frequency) range, which is generally below 30 MHz. At 10 GHz, the wavelength is much shorter, and different antenna designs, such as horn antennas or dish antennas, are more suitable for efficient transmission and reception at that frequency.

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• 40.

### The polarization of a half-wave vertical antenna is:

• A.

Vertical

• B.

Horizontal

• C.

Circular

• D.

Elliptical

A. Vertical
Explanation
A half-wave vertical antenna is designed to radiate and receive electromagnetic waves in a vertical polarization pattern. This means that the electric field component of the wave is oriented vertically, while the magnetic field component is oriented horizontally. This polarization is ideal for communication with other vertical antennas, such as those used in most mobile devices and base stations. Horizontal, circular, and elliptical polarizations are not typically associated with half-wave vertical antennas.

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• 41.

### The theory of radio waves was originated by

• A.

Marconi

• B.

Bell

• C.

Maxwell

• D.

Hertz

C. Maxwell
Explanation
The correct answer is Maxwell. Maxwell is credited with formulating the theory of electromagnetic waves, which includes radio waves. His equations, known as Maxwell's equations, describe the behavior of electromagnetic waves and laid the foundation for the development of wireless communication technologies, including radio. Marconi, Bell, and Hertz made significant contributions to the field of telecommunications, but they did not originate the theory of radio waves.

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• 42.

### The person who sent the first radio signal across the Atlantic ocean was

• A.

Marconi

• B.

Bell

• C.

Maxwell

• D.

Hertz

A. Marconi
Explanation
Marconi is the correct answer because he was the first person to successfully send a radio signal across the Atlantic Ocean. In 1901, Marconi transmitted the letter "S" in Morse code from Poldhu, Cornwall, England to St. John's, Newfoundland, Canada. This groundbreaking achievement revolutionized long-distance communication and solidified Marconi's place in history as a pioneer in the field of radio technology.

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• 43.

### The transmission of radio waves was first done by

• A.

Marconi

• B.

Bell

• C.

Maxwell

• D.

Hertz

D. Hertz
Explanation
Hertz is the correct answer because he was the first person to demonstrate the existence of radio waves and their transmission. In the late 19th century, Hertz conducted experiments that proved the existence of electromagnetic waves, which are now known as radio waves. His work laid the foundation for the development of wireless communication and paved the way for future advancements in radio technology.

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• 44.

### A complete communication system must include

• A.

• B.

A transmitter, a receiver, and a channel

• C.

A transmitter, a receiver, and a spectrum analyzer

• D.

A multiplexer, a demultiplexer, and a channel

B. A transmitter, a receiver, and a channel
Explanation
A complete communication system requires a transmitter to send the information, a receiver to receive the information, and a channel through which the information is transmitted. The transmitter converts the information into a signal that can be sent through the channel, while the receiver decodes the signal to retrieve the original information. The channel serves as the medium through which the signal is transmitted, such as a wire, fiber optic cable, or wireless spectrum. Therefore, all three components are necessary for a communication system to function properly.

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• 45.

### Radians per second is equal to

• A.

2pi x f

• B.

F / 2pi

• C.

The phase angle

• D.

Complete cycle of an analog pulse

A. 2pi x f
Explanation
The correct answer is 2pi x f. This formula represents the conversion from frequency (f) to radians per second. Radians per second is a unit used to measure angular velocity, and it is equal to the product of 2pi (which represents one full revolution or cycle in radians) and the frequency of the signal. So, multiplying the frequency by 2pi gives us the equivalent value in radians per second.

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• 46.

### The bandwidth required for a modulated carrier depends on

• A.

The carrier frequency

• B.

The signal-to-noise ratio

• C.

The signal-plus-noise to noise ratio

• D.

The baseband frequency range

D. The baseband frequency range
Explanation
The bandwidth required for a modulated carrier depends on the baseband frequency range. This is because the baseband frequency range determines the range of frequencies that need to be transmitted in order to accurately represent the original signal. The carrier frequency, signal-to-noise ratio, and signal-plus-noise to noise ratio may affect the quality of the transmission, but they do not directly determine the bandwidth required.

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• 47.

### When two or more signals share a common channel, it is called

• A.

Sub-channeling

• B.

Signal switching

• C.

• D.

Multiplexing

D. Multiplexing
Explanation
Multiplexing is the correct answer because it refers to the process of combining multiple signals into a single channel or transmission medium. In this scenario, when two or more signals share a common channel, they are being multiplexed. This allows for efficient use of the channel and enables multiple signals to be transmitted simultaneously. Sub-channeling, signal switching, and SINAD are not applicable in this context and do not accurately describe the situation of multiple signals sharing a common channel.

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• 48.

### TDM stands for

• A.

Time-Division Multiplexing

• B.

Two-level Digital Modulation

• C.

Two-level Digital Modulation

• D.

Time-Division Multiple

A. Time-Division Multiplexing
Explanation
TDM stands for Time-Division Multiplexing. This technique is used in telecommunications to transmit multiple signals over a single communication channel by dividing the available time slots into smaller units and allocating them to each signal. Each signal takes turns in using the channel, thus allowing multiple signals to be transmitted simultaneously. This method is commonly used in applications such as telephone systems and digital subscriber lines (DSL) to efficiently utilize the available bandwidth.

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• 49.

### FDM stands for

• A.

Fast Digital Modulation

• B.

Free Digital Modulation

• C.

Frequency-Division Multiplexing

• D.

Frequency-Division Multiple

C. Frequency-Division Multiplexing
Explanation
FDM stands for Frequency-Division Multiplexing. This technique is used to transmit multiple signals simultaneously over a single communication channel by dividing the available bandwidth into multiple frequency bands. Each signal is allocated a different frequency band, allowing them to be transmitted simultaneously without interfering with each other. FDM is commonly used in telecommunications systems to maximize the utilization of the available bandwidth and efficiently transmit multiple signals over a single communication medium.

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• 50.

### The wavelength of a radio signal is

• A.

Equal to f / c

• B.

Equal to c / λ

• C.

The distance a wave travels in one period

• D.

How far the signal can travel without distortion Back to top