3D153 CDC, Volume 1. General Subjects

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3D153-01-1009, Edit Code 01

This quiz is to help new Airmen study for their CDCs and for Senior Airmen to study for Staff. This quiz is made up by all the UREs from the first 3D153 CDC volume.

Edited and updated as of December 16, 2012

If you have find an error on a question you can email me at cfloyd8890@gmail. Com
and I will fix it!

• 1.

001 - What reason for modulation involves modulating low frequency signals for transmission over long distances?

• A.

Spectrum conservation

• B.

Channel allocation

• C.

• D.

Companding

C. Ease of radiation
Explanation
Modulating low frequency signals for transmission over long distances is done to ensure ease of radiation. This means that by modulating the signals, they can be efficiently transmitted and propagated through the air or any other medium. This modulation process allows for better reception and reduces the chances of signal loss or degradation during long-distance transmission.

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• 2.

001 - What are the three genereal categories used to produce modulation in radio frequency (RF) transmission today?

• A.

Binary amplitude shift keying, frequency shift keying, and phase shift keying.

• B.

Pulse amplitude, pulse width, and pulse position.

• C.

Amplitude, frequency, and phase.

• D.

Analog, digital and shift keying

C. Amplitude, frequency, and phase.
Explanation
The three general categories used to produce modulation in radio frequency (RF) transmission today are amplitude, frequency, and phase. Amplitude modulation (AM) involves varying the strength of the RF signal. Frequency modulation (FM) involves varying the frequency of the RF signal. Phase modulation (PM) involves varying the phase of the RF signal. These three categories are commonly used in RF transmission to encode and transmit information.

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• 3.

002 - When the modulating signal and carrier signal are combined within a modulator, the output signal contains a/an

• A.

Modulating signal, upper sideband (USB), lower sideband (LSB)

• B.

Carrier, USB, and LSB

• C.

USB and modulating signal

• D.

Carrier and modulating signal

A. Modulating signal, upper sideband (USB), lower sideband (LSB)
Explanation
When the modulating signal and carrier signal are combined within a modulator, the output signal contains a modulating signal, upper sideband (USB), and lower sideband (LSB). The modulating signal is the original signal that carries the information to be transmitted. The carrier signal is a high-frequency signal that is modulated by the modulating signal. The upper sideband (USB) is the portion of the modulated signal above the carrier frequency, while the lower sideband (LSB) is the portion below the carrier frequency. Therefore, the correct answer is modulating signal, upper sideband (USB), lower sideband (LSB).

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• 4.

002 - If a carrier frequency of 1 MHz and a modulating tone of 10 kHz goes to the modulator the output signal includes

• A.

1.01 MHz, 1 MHz, and 0.99 MHz.

• B.

1.1 MHz, 1 MHz, and 0.9 MHz.

• C.

1.11 MHz, 1 MHz, 0.99 MHz

• D.

1.111 MHz, 1 MHz, .0999 MHz

A. 1.01 MHz, 1 MHz, and 0.99 MHz.
Explanation
When a carrier frequency of 1 MHz and a modulating tone of 10 kHz go to the modulator, the output signal includes the sum and difference frequencies of the carrier and modulating tone. The sum frequency is obtained by adding the carrier frequency and the modulating tone frequency, resulting in 1.01 MHz. The carrier frequency itself remains unchanged at 1 MHz. The difference frequency is obtained by subtracting the modulating tone frequency from the carrier frequency, resulting in 0.99 MHz. Therefore, the correct answer is 1.01 MHz, 1 MHz, and 0.99 MHz.

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• 5.

002 - If the modulating audio signal is 10 kHz wide, what is the bandwidth of the transmitted amplitude modulated signal?

• A.

5 kHz

• B.

10 kHz

• C.

15 kHz

• D.

20 kHz

D. 20 kHz
Explanation
The bandwidth of an amplitude modulated signal is determined by the sum of the highest frequency component of the modulating signal and the carrier frequency. In this case, the modulating audio signal is 10 kHz wide, so the highest frequency component is 10 kHz. If the carrier frequency is also 10 kHz, then the bandwidth would be 20 kHz.

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• 6.

002 - The bandwidth of an amplitude modulated signal is

• A.

Two times the modulating signal

• B.

The same as the modulating signal

• C.

Determined by the modulation index

• D.

Defined in terms of maximum amount of modulation

A. Two times the modulating signal
Explanation
The correct answer is "two times the modulating signal." In amplitude modulation, the bandwidth refers to the range of frequencies required to transmit the modulated signal. Since the modulating signal is responsible for creating the variations in the carrier signal, the bandwidth needs to be wide enough to accommodate these variations. In amplitude modulation, the bandwidth is directly proportional to the frequency of the modulating signal. Therefore, the bandwidth is two times the modulating signal frequency.

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• 7.

002 - The amount of effect or change that the intelligence has on the carrier in an amplitude modulated signal is expressed as the

• A.

Percent of modulation

• B.

Modulation index

• C.

Bandwidth

• D.

Deviation

A. Percent of modulation
Explanation
The correct answer is "percent of modulation." In amplitude modulation, the amount of effect or change that the intelligence has on the carrier signal is expressed as the percentage of modulation. This indicates the extent to which the carrier signal is varied by the intelligence signal. The higher the percentage of modulation, the greater the variation in the carrier signal, resulting in a stronger representation of the intelligence signal.

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• 8.

002 - Which statement concerning bandwidth is true?

• A.

Overmodulating increases bandwidth due to the production of harmonics.

• B.

Undermodulating increases bandwidth due to the production of harmonics.

• C.

Overmodulating increases bandwidth due to the output's increased amplitude.

• D.

Undermodulating increases bandwidth due to the output's decreased amplitude.

A. Overmodulating increases bandwidth due to the production of harmonics.
Explanation
Overmodulating refers to the process of increasing the amplitude of a signal beyond its normal range. This causes the signal to become distorted and produce harmonics, which are additional frequencies that are multiples of the original signal frequency. These harmonics contribute to an increase in bandwidth because they occupy additional frequency space. Therefore, the statement that overmodulating increases bandwidth due to the production of harmonics is true.

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• 9.

002 - Reducing modulation to less than 100% gives

• A.

More total power

• B.

A reduction in carrier power

• C.

No reduction in carrier power

• D.

A reduction in carrier and sideband power

C. No reduction in carrier power
Explanation
When modulation is reduced to less than 100%, it means that the amplitude of the carrier signal is not fully modulated by the information signal. In this case, the carrier power remains unchanged because it is not being affected by the modulation. The reduction in modulation only affects the sideband power, which carries the information signal. Therefore, there is no reduction in carrier power.

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• 10.

003 - In frequency modulation (FM), the amount of oscillator frequency change is

• A.

Inversely proportional to the amplitude of the modulating signal

• B.

Directly proportional to the amplitude of the modulating signal

• C.

Inversely proportional to the phase of the modultaing signal

• D.

Directly proportional to the phase of the modulating signal

B. Directly proportional to the amplitude of the modulating signal
Explanation
In frequency modulation (FM), the amount of oscillator frequency change is directly proportional to the amplitude of the modulating signal. This means that as the amplitude of the modulating signal increases, the frequency of the carrier signal will also increase, and vice versa. This relationship allows for the encoding of information in the frequency variations of the carrier signal in FM communication systems.

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• 11.

003 - In FM, what is considered a significant sideband?

• A.

Sibebands (SB) containing at least 1% of the total transmitted power

• B.

SB containing at least 3% of the total transmitted power

• C.

SB containing at least 10 percent of the total transmitted power

• D.

SB containing at least 0.1% of the total transmitted power

A. Sibebands (SB) containing at least 1% of the total transmitted power
Explanation
A significant sideband in FM is considered to be one that contains at least 1% of the total transmitted power. This means that the sideband carries a substantial amount of the signal and is not negligible in terms of power.

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• 12.

003 - What is the formula to find the modulating index?

• A.

Deviation divided by frequency of modulation.

• B.

Deviation time frequency of modulation.

• C.

Sideband divided by carrier frequency.

• D.

Sideband times carrier frequency.

A. Deviation divided by frequency of modulation.
Explanation
The modulating index is a measure of how much the carrier wave is modulated by the input signal. It is calculated by dividing the deviation (the maximum change in frequency or amplitude from the carrier wave) by the frequency of modulation (the frequency of the input signal). This formula allows us to determine the extent of modulation in a given system.

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• 13.

004 - In Phase Modulation (PM), the carrier's

• A.

Phase is shifted at the rate of the modulating signal.

• B.

Phase shifted with the phase of the modulating signal.

• C.

Amplitude is shifted at the rate of the modulating signal.

• D.

Amplitude is shifted with the phase of the modulating signal.

B. Phase shifted with the phase of the modulating signal.
Explanation
In Phase Modulation (PM), the phase of the carrier signal is shifted in accordance with the phase of the modulating signal. This means that the instantaneous phase of the carrier signal is modified based on the phase of the modulating signal. The amplitude of the carrier signal remains constant, as PM is primarily concerned with changing the phase. Therefore, the correct answer is "phase shifted with the phase of the modulating signal."

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• 14.

004 - What is the advantage of adding more phase shifts?

• A.

Easier detection.

• B.

Smaller bit error rate.

• C.

Better signal-to-noise ratio.

• D.

Higher data rates within a given bandwidth.

D. Higher data rates within a given bandwidth.
Explanation
Adding more phase shifts allows for a higher number of distinct symbols to be represented, which increases the data rate that can be transmitted within a given bandwidth. This means that more information can be transmitted in a shorter amount of time, leading to higher data rates.

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• 15.

005 - What is the first step in pulse code modulation (PCM) process?

• A.

Discrete amplitudes are assigned to the sampling pulses.

• B.

A binary code number is assigned to the sample.

• C.

The quantizer limits the amplitude of the pulses.

• D.

The analog signal is band-limited.

D. The analog signal is band-limited.
Explanation
In pulse code modulation (PCM), the first step is to band-limit the analog signal. Band-limiting ensures that the analog signal does not contain any frequencies beyond a certain range, which helps in reducing noise and distortion during the sampling process. By band-limiting the analog signal, it becomes easier to accurately sample and encode the signal into discrete amplitudes or binary code numbers. This step is crucial in ensuring the fidelity and accuracy of the digital representation of the analog signal in PCM.

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• 16.

005 - What part of the pulse code modulation (PCM) process converts a continuous time signal into a discrete time signal?

• A.

Sampling.

• B.

Rectifying.

• C.

Oscillating.

• D.

Band Limiting.

A. Sampling.
Explanation
Sampling is the part of the pulse code modulation (PCM) process that converts a continuous time signal into a discrete time signal. In sampling, the continuous signal is measured at regular intervals, and these samples are used to represent the original signal. This allows for the conversion of the continuous signal into a series of discrete values that can be easily processed and transmitted. Sampling is a fundamental step in PCM and is essential for accurately representing analog signals in digital form.

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• 17.

005 - A type of pulse modulation (PM) that causes the amplitude of the pulse train to vary according to the amplitude of the input signal is called

• A.

Pulse width modulation (PWM)

• B.

Pulse position modulation (PPM)

• C.

Pulse duration modulation (PDM)

• D.

Pulse amplitude modulation (PAM)

D. Pulse amplitude modulation (PAM)
Explanation
Pulse amplitude modulation (PAM) is a type of pulse modulation where the amplitude of the pulse train varies according to the amplitude of the input signal. In PAM, the amplitude of the pulses represents the information being transmitted. This modulation technique is commonly used in analog communication systems to transmit analog signals over a digital medium. PAM is different from other types of pulse modulation such as pulse width modulation (PWM), pulse position modulation (PPM), and pulse duration modulation (PDM) which modulate the width, position, or duration of the pulses respectively.

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• 18.

006 - If an error should occur, what data transmission is lost in a synchronous transmission?

• A.

One character.

• B.

Block of data.

• C.

A parity bit.

• D.

Synchronization (SYNC) bit.

B. Block of data.
Explanation
In synchronous transmission, data is transmitted in blocks rather than individual characters. Therefore, if an error occurs, it is likely that an entire block of data will be lost, rather than just one character. This is because synchronous transmission relies on the synchronization of data between the sender and receiver, and if there is an error in one block, it can disrupt the synchronization and cause the loss of the entire block of data.

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• 19.

007 - When using vertical redundancy check (VRC), what significance does the amount of ones have in a data bit pattern?

• A.

Determines parity

• B.

Determines transmission rate

• C.

Determines whether transmission is in American Standard code for Information Interchange (ASCII) format

• D.

Determines whether transmission is synchronous or asynchronous

A. Determines parity
Explanation
The amount of ones in a data bit pattern when using vertical redundancy check (VRC) determines parity. Parity is a form of error checking where an extra bit is added to a data transmission to ensure that the number of ones in the transmission is always either even or odd. By checking the parity bit at the receiving end, errors in transmission can be detected. If the number of ones in the data bit pattern is not consistent with the expected parity, it indicates that an error has occurred during transmission.

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• 20.

007 - What two error detection methods, when used together, are 98 percent effective in detecting errors?

• A.

Checksum and cyclic redundancy check

• B.

Longitudinal redundancy check and checksum

• C.

Cyclic redundancy check and vertical redundancy check

• D.

Vertical redundancy check and longitudinal redundancy check

D. Vertical redundancy check and longitudinal redundancy check
Explanation
The vertical redundancy check and longitudinal redundancy check are the two error detection methods that, when used together, are 98 percent effective in detecting errors. These methods work by adding extra bits to the data to detect and correct errors during transmission. The vertical redundancy check checks for errors in each column of data, while the longitudinal redundancy check checks for errors in each row of data. By combining these two methods, a high level of error detection can be achieved.

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• 21.

007 - What error detection method adds stacked characters, divides it by 255, and disregards the answer except for the remainder?

• A.

Checksum

• B.

Block check character

• C.

Cyclic redundancy check

• D.

Vertical redundancy check

A. Checksum
Explanation
Checksum is an error detection method that involves adding the ASCII values of each character in a message, dividing the sum by 255, and keeping only the remainder. This remainder is then appended to the message as a checksum. When the message is received, the same process is applied, and if the calculated checksum matches the received checksum, it is assumed that the message was transmitted without errors. This method is simple and efficient for detecting errors in transmitted data.

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• 22.

007 - What error-correction technique sends a retransmittal request by the receiver to the sender if it finds an error in a received frame?

• A.

Error-correcting code (ECC)

• B.

Forward error control (FEC)

• C.

Redundant data transfer (RDT)

• D.

Automatic retransmit on request (ARQ)

D. Automatic retransmit on request (ARQ)
Explanation
ARQ is an error-correction technique that sends a retransmittal request by the receiver to the sender if it finds an error in a received frame. This technique allows for the detection and correction of errors in data transmission by requesting the sender to resend the frame that contains errors. By using ARQ, the receiver can ensure that the data is received correctly without errors.

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• 23.

007 - When using forward error control as a method of error correction, where does error correction take place?

• A.

Receiving end.

• B.

In the oscillator.

• C.

Transmitting end.

• D.

In the primary buffers.

A. Receiving end.
Explanation
When using forward error control as a method of error correction, error correction takes place at the receiving end. Forward error control involves adding redundant information to the transmitted data, which allows the receiver to detect and correct errors. This method is commonly used in communication systems to ensure that the received data is accurate and reliable. By performing error correction at the receiving end, any errors that occurred during transmission can be identified and corrected, ensuring the integrity of the data.

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• 24.

008 - What does an optical source do?

• A.

Terminates fiber optics cable

• B.

Converts electrical energy into optical energy

• C.

Extends the distance and to preserve signal integrity

• D.

Accepts optical signals and converts them into electrical signals

B. Converts electrical energy into optical energy
Explanation
An optical source is responsible for converting electrical energy into optical energy. This means that it takes electrical signals and transforms them into light signals that can be transmitted through fiber optic cables. This conversion is essential for the transmission of data over long distances, as optical signals can travel much farther without losing signal integrity compared to electrical signals. Therefore, an optical source plays a crucial role in enabling the efficient and reliable transmission of information through fiber optic networks.

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• 25.

008 - Light sources that are applicable to fiber optic waveguide are light-emitting diodes (LED) and

• A.

Photo transistors.

• B.

Hybrid photodiodes.

• C.

Emiconductor laser diodes (LD).

• D.

Integrated photodiode preamplifiers.

C. Emiconductor laser diodes (LD).
Explanation
Semiconductor laser diodes (LD) are applicable to fiber optic waveguides because they can generate coherent light with high intensity. This makes them suitable for long-distance communication through optical fibers. Light-emitting diodes (LED) can also be used, but they produce incoherent light with lower intensity. Hybrid photodiodes and integrated photodiode preamplifiers are not light sources, but rather detectors used to convert light signals into electrical signals. Therefore, the correct answer is semiconductor laser diodes (LD).

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• 26.

008 - What type of light is emitted from a laser?

• A.

Incoherent

• B.

Coherent

• C.

Ordinary

• D.

Invisible

B. Coherent
Explanation
A laser emits coherent light. Coherent light is characterized by its single wavelength and phase, meaning that all the light waves are in sync with each other. This is achieved through a process called stimulated emission, where photons are emitted in the same direction and with the same frequency and phase. This coherence allows laser light to be focused into a tight beam and to maintain its intensity over long distances.

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• 27.

008 - Laser diode power coupling is measured in which range

• A.

Megawatt

• B.

Microwatt

• C.

Milliwatt

• D.

Kilowatt

C. Milliwatt
Explanation
Laser diode power coupling is measured in the milliwatt range. This is because laser diodes are compact and efficient devices that typically operate at low power levels. Milliwatt power levels are sufficient for many applications such as telecommunications, barcode scanning, laser pointers, and optical data storage. Higher power levels, such as kilowatts or megawatts, are typically used in industrial applications like laser cutting or welding, where a greater amount of energy is required. Therefore, milliwatt is the appropriate range for measuring laser diode power coupling.

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• 28.

009 - A device that accepts optical signals from an optical fiber and converts them into electical signals is called an optical

• A.

Regenerator

• B.

Transmitter

• C.

Amplifier

• D.

Explanation
A device that accepts optical signals from an optical fiber and converts them into electrical signals is called a receiver. Receivers are an essential component in optical communication systems as they receive the optical signals and convert them into electrical signals that can be further processed and utilized.

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• 29.

009 - Small current that flows from a photodiode even with no light is called

• A.

Dark current

• B.

Dispersion

• C.

Distortion

• D.

Ionization

A. Dark current
Explanation
Dark current refers to the small current that flows through a photodiode even when there is no light present. This current is caused by the random generation of electron-hole pairs within the photodiode due to thermal energy. As a result, the dark current can affect the accuracy and sensitivity of the photodiode in low-light conditions, and it needs to be minimized for optimal performance.

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• 30.

009 - The responsivity of a photo detector is dependent on the

• A.

Emitter rise time.

• B.

Wavelength of light.

• C.

Signal-to-noise ratio (SNR).

• D.

Emitter modulation speed.

B. Wavelength of light.
Explanation
The responsivity of a photo detector refers to its ability to convert light into an electrical signal. The wavelength of light plays a crucial role in determining the responsivity of a photo detector. Different materials and designs of detectors have different responsivity curves, which indicate the efficiency of converting light of different wavelengths into electrical signals. Therefore, the responsivity of a photo detector is dependent on the wavelength of light it is designed to detect.

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• 31.

009 - What are two main types of photo detectors?

• A.

Positive intrinsic negative (PIN) and avalanche photodiode (ADP).

• B.

Light-emitting diode (LED) and avalanche photodiode (ADP).

• C.

LED and semiconductor diodes.

• D.

Tunnel and zener diodes.

A. Positive intrinsic negative (PIN) and avalanche photodiode (ADP).
Explanation
The correct answer is Positive intrinsic negative (PIN) and avalanche photodiode (ADP). PIN photodiodes are widely used in optical communication systems and have a high sensitivity to light. They have a large depletion region, which allows for efficient collection of photons. Avalanche photodiodes, on the other hand, are used in applications that require high gain and low noise. They operate in the avalanche breakdown region, where a single photon can generate a large number of electron-hole pairs.

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• 32.

009 - What photo detector converts one photon to one electron?

• A.

Light emitting diode (LED).

• B.

Avalanche photodiode.

• C.

Positive intrinsic negative (PIN) diode.

• D.

Integrated photodiode/preamplifier (IDP).

C. Positive intrinsic negative (PIN) diode.
Explanation
The correct answer is Positive intrinsic negative (PIN) diode. A PIN diode is a type of photo detector that converts one photon to one electron. It consists of three layers - P, I, and N, where the intrinsic (I) layer is lightly doped. When a photon is absorbed by the intrinsic layer, it creates an electron-hole pair, and due to the electric field between the P and N layers, the electron is swept towards the N layer, generating a current. Hence, the PIN diode is capable of converting one photon to one electron.

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• 33.

010 -  What is used to extend the distance of a fiber optic communication systems link?

• A.

• B.

Transmitter.

• C.

Repeater.

• D.

Patch cords.

C. Repeater.
Explanation
A repeater is used to extend the distance of a fiber optic communication system's link. A repeater receives the signal from the transmitter, amplifies it, and then retransmits it, allowing the signal to travel further without degradation. This is necessary because fiber optic signals can weaken over long distances, and a repeater helps to maintain the signal strength and quality. Patch cords are used to connect devices, but they do not extend the distance of the communication link.

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• 34.

010 - Which repeater amplifies optical signals without converting to and from the electrical domain?

• A.

Repeaters.

• B.

Regenerators.

• C.

Optical amplifiers.

• D.

C. Optical amplifiers.
Explanation
Optical amplifiers are devices that boost the strength of optical signals without the need for converting them to electrical signals. Unlike regenerators and repeaters, which convert the optical signals to electrical signals before amplifying them, optical amplifiers directly amplify the optical signals in their original form. Receivers, on the other hand, are responsible for converting the optical signals back into electrical signals for further processing. Therefore, optical amplifiers are the correct answer as they amplify optical signals without converting to and from the electrical domain.

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• 35.

011 - Short sections of a single fiber cables that has a connector at each end is called a

• A.

Pigtail.

• B.

Patch cord.

• C.

Jumper.

• D.

Breakout cables.

B. Patch cord.
Explanation
A short section of a single fiber cable that has a connector at each end is called a patch cord. Patch cords are used to connect devices or equipment within a network, providing a temporary or permanent connection. They are commonly used in data centers, telecommunications systems, and computer networks to establish reliable and efficient connections between devices.

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• 36.

011 - Which fiber-optic connector uses a quick-release, keyed bayonet couplings that are preferred in situations where severe vibrations are not expected?

• A.

Biconic.

• B.

Field Connector (FC).

• C.

Straight Tip (ST).

• D.

Sub-Miniature, Type A (SMA).

C. Straight Tip (ST).
Explanation
The Straight Tip (ST) fiber-optic connector uses quick-release, keyed bayonet couplings that are preferred in situations where severe vibrations are not expected. This connector provides a secure and reliable connection, while still allowing for easy installation and removal. The design of the ST connector ensures that it remains firmly connected even in environments with minimal vibrations, making it a suitable choice for applications where stability is important.

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• 37.

011 - Which fiber optic connector uses a push-pull engagement for mating?

• A.

Biconic.

• B.

Field (FC).

• C.

Subscriber (SC).

• D.

Sub-Miniature, Type A (SMA).

C. Subscriber (SC).
Explanation
The Subscriber (SC) fiber optic connector uses a push-pull engagement for mating. This means that the connector can be easily inserted and removed by pushing and pulling it, making it convenient and user-friendly. The other options, such as Biconic, Field (FC), and Sub-Miniature, Type A (SMA), do not use a push-pull engagement for mating.

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• 38.

012 - What initial nuclear radiation elements generate electromagnetic pulses?

• A.

Gamma rays and neutrons.

• B.

Thermally generated x-rays.

• C.

Transient radiation effects on electronics.

• D.

Neutrons and thermally generated x-rays.

A. Gamma rays and neutrons.
Explanation
Gamma rays and neutrons are the initial nuclear radiation elements that generate electromagnetic pulses. Gamma rays are high-energy photons that are emitted during nuclear reactions, while neutrons are subatomic particles that are also released in nuclear reactions. Both gamma rays and neutrons can cause ionization and excitation of atoms and molecules, leading to the generation of electromagnetic pulses. Thermally generated x-rays and transient radiation effects on electronics are not initial nuclear radiation elements, and they do not directly generate electromagnetic pulses.

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• 39.

012 - High-altitude electromagnetic pulse is what type of frequency phenomenon, and involves which frequency range?

• A.

Secondary; 1 hertz to 1 gigahertz

• B.

Wideband; 1 hertz to 1 gigahertz

• C.

Secondary; 10 hertz to 10 gigahertz

• D.

Wideband; 10 hertz to 10 gigahertz

B. Wideband; 1 hertz to 1 gigahertz
Explanation
High-altitude electromagnetic pulse (HEMP) is a wideband frequency phenomenon that involves a frequency range of 1 hertz to 1 gigahertz. HEMP refers to the burst of electromagnetic radiation that occurs as a result of a high-altitude nuclear explosion. This burst covers a wide range of frequencies, from very low frequencies (1 hertz) to radio frequencies (1 gigahertz). The wideband nature of HEMP allows it to affect a wide range of electronic systems and devices, making it a significant concern for military and civilian infrastructure.

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• 40.

012 - A system-generated pulse is a problem for satellites and reentry vehicles that are

• A.

Susceptible to the wideband frequency phenomenon.

• B.

Directly exposed to nuclear radiations from a high-altitude burst.

• C.

Affected by the azimuth magnetic fields and time-varying air conductivity.

• D.

Influenced by the signal fading or waveform distortion caused by the structured plasma field.

B. Directly exposed to nuclear radiations from a high-altitude burst.
• 41.

012 - Which distinct region of the source region electromagnetic pulse is produced by the interactions between the weapon products and the earth's atmosphere?

• A.

Secondary

• B.

• C.

Plasma

• D.

Source

Explanation
The correct answer is "Radiated." When a weapon detonates, the interactions between the weapon products and the Earth's atmosphere produce an electromagnetic pulse (EMP) that is radiated outward. This radiated EMP is a distinct region of the source region, indicating that it is separate from the secondary, plasma, and source regions.

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• 42.

012 - What electromagnetic pulse region is the principal threat to electronics systems by cable?

• A.

Local

• B.

• C.

Long-line

• D.

Source

A. Local
Explanation
The principal threat to electronics systems by cable is the local electromagnetic pulse (EMP) region. This region refers to the area in close proximity to the source of the EMP, where the electromagnetic energy is strong enough to induce damaging currents and voltages in cables and other conductive materials. The local EMP region poses a significant risk to electronics systems as it can cause disruptions, malfunctions, or even permanent damage to the components connected by cables.

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• 43.

012 - How does scintillation effect communications?

• A.

Large attenuation of the transmitted signal causing the received signal-to-noise ratio (SNR) to fall below unity.

• B.

Transmitted signal fading caused by multiple path propagation through the structured plasma field.

• C.

Layers of charged electrons are trapped and prevent transmissions through the layer.

• D.

Absorption of the transmitted signal through the contaminated area.

A. Large attenuation of the transmitted signal causing the received signal-to-noise ratio (SNR) to fall below unity.
Explanation
The scintillation effect in communications refers to the large attenuation of the transmitted signal, which results in a decrease in the received signal-to-noise ratio (SNR) to a level below unity. This attenuation is caused by various factors, such as multiple path propagation through the structured plasma field. As a result, the signal experiences fading and becomes weaker, leading to a reduced SNR and potentially causing communication disruptions.

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• 44.

012 - Atmospheric disturbances from initial nuclear radiation on higher frequencies affect communications by which types of effects?

• A.

Blackout.

• B.

Scintillation.

• C.

Attenuation.

• D.

Absorption.

B. Scintillation.
Explanation
Scintillation refers to the rapid fluctuations in the amplitude and phase of a radio signal caused by atmospheric disturbances. These disturbances, which are a result of initial nuclear radiation, affect communications by causing the signal to fluctuate and become unstable. This can lead to difficulties in receiving or transmitting messages accurately, resulting in a disruption or blackout of communication. Attenuation and absorption, on the other hand, refer to the weakening or loss of signal strength, but they are not specifically related to atmospheric disturbances from nuclear radiation.

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• 45.

013 - Which one of the following statements is true concerning shielding?

• A.

All power lines supplying the shielded areas does not require filters.

• B.

Cables should be of unshielded construction.

• C.

Only ventilation ports are shielded along the walls.

• D.

Sensitive equipment will be located within the shielded barrier.

D. Sensitive equipment will be located within the shielded barrier.
Explanation
Sensitive equipment will be located within the shielded barrier because shielding is used to protect sensitive equipment from electromagnetic interference (EMI) and radio frequency interference (RFI). By locating the sensitive equipment within the shielded barrier, it is effectively protected from external sources of interference.

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• 46.

013 - What is the purpose of bonding?

• A.

To ensure a mechanically strong, low impedance interconnection between metal objects.

• B.

To eliminate harmful differences of potential between the various telephone cables entering facility.

• C.

To reduce interference coupling around circuits and around interconnecting lines.

• D.

To isolate facility from any external electrical electromagnetic propagation.

A. To ensure a mechanically strong, low impedance interconnection between metal objects.
Explanation
Bonding is the process of creating a connection between metal objects to ensure a mechanically strong, low impedance interconnection. This helps to prevent any potential differences between the objects and reduces interference coupling around circuits and interconnecting lines. Bonding also helps to isolate the facility from any external electrical electromagnetic propagation.

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• 47.

014 - What types of filters are always used in combination with surge arresters?

• A.

Linear.

• B.

Alternating current (AC) line.

• C.

Power line.

• D.

Direct current (DC) line.

A. Linear.
Explanation
Surge arresters are used to protect electrical systems from voltage surges. They work by diverting the excess voltage to the ground. In order to ensure their proper functioning, surge arresters are always used in combination with linear filters. Linear filters are designed to remove noise and harmonics from the electrical signal, ensuring a clean and stable power supply. By using linear filters in conjunction with surge arresters, the electrical system is protected from both voltage surges and unwanted electrical disturbances.

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• 48.

014 - If the interference can be eliminated by disconnecting the receiving antenna, the source of the disturbance is most likely

• A.

Line noise.

• B.

Internal to the radio.

• C.

• D.

External to the radio.

D. External to the radio.
Explanation
If disconnecting the receiving antenna eliminates the interference, it suggests that the disturbance is coming from an external source rather than being internal to the radio or caused by radio receiver trouble. This could be due to line noise, which refers to interference caused by electrical noise on the power lines or other nearby electronic devices. Therefore, the most likely source of the disturbance is external to the radio.

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• 49.

014 - What is an example of intentionally induced electromagnetic interference (EMI)?

• A.

Spurious responses.

• B.

Jamming.

• C.

Power line noise.

• D.

Intermodulation.

B. Jamming.
Explanation
Jamming is an example of intentionally induced electromagnetic interference (EMI). Jamming refers to the deliberate transmission of signals or noise on specific frequencies to disrupt or interfere with the normal functioning of electronic devices or communication systems. It is often used in military operations to disrupt enemy communications or radar systems.

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• 50.

014 - What type of electromagnetic interference (EMI) occurs when a receiver responds to off-frequency signals?

• A.

Brute force.

• B.

Co-channel.

• C.

Spurious responses.

• D.

Rusty bolt.