# 3D153 CDC Volume 1

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Questions: 37 | Attempts: 463  Settings  Radio Frequency Transmission Systems Journeyman Volume 1

• 1.

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

• A.

Spectrum conservation

• B.

Channel Allocation

• C.

• D.

Companding

Explanation
Modulating low frequency signals for transmission over long distances allows for ease of radiation. This means that the modulated signal can be efficiently transmitted and propagated through the transmission medium without significant loss or distortion. By modulating the low frequency signals, they can be converted into higher frequency signals that are better suited for long-distance transmission. This allows for better signal quality and reduces the chances of interference or degradation during transmission.

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• 2.

### What are the three general 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 correct answer is "Amplitude, frequency, and phase." In radio frequency transmission, modulation is used to encode information onto a carrier wave. Amplitude modulation (AM) varies the amplitude of the carrier wave, frequency modulation (FM) varies the frequency, and phase modulation (PM) varies the phase. These three categories are commonly used in RF transmission today to transmit and decode signals.

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• 3.

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

• A.

Modulating signal, upper sideband, lower sideband

• B.

Carrier, upper sideband, and lower sideband

• C.

Upper sideband and modulating signal

• D.

Carrier and modulating signal

B. Carrier, upper sideband, and lower sideband
Explanation
When the modulating signal and carrier signal are combined within a modulator, the resulting output signal will contain the carrier signal itself, as well as the upper sideband and lower sideband. The carrier signal represents the original frequency of the carrier wave, while the upper and lower sidebands represent the frequency components that are shifted above and below the carrier frequency due to modulation. Therefore, the correct answer is carrier, upper sideband, and lower sideband.

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• 4.

### If a carrier frequency of 1 MHz and a modulating tone of 10 kHz goes to the modulator, the output signal include

• A.

1.01 MHz, 1 MHz, and .99 MHz

• B.

1.1 MHz, 1 MHz, and .9 MHz

• C.

1.11 MHz, 1 MHz, .99 MHz

• D.

1.111 MHz, 1 MHz, .999 MHz

A. 1.01 MHz, 1 MHz, and .99 MHz
Explanation
When a carrier frequency of 1 MHz and a modulating tone of 10 kHz are combined in a modulator, the resulting output signal will consist of the original carrier frequency (1 MHz), the sum of the carrier frequency and the modulating tone (1.01 MHz), and the difference between the carrier frequency and the modulating tone (.99 MHz). Therefore, the correct answer is 1.01 MHz, 1 MHz, and .99 MHz.

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• 5.

### 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 equal to the sum of the highest frequency component of the modulating signal and the highest frequency component of the carrier signal. In this case, the modulating audio signal is 10 kHz wide, so the highest frequency component is 10 kHz. Assuming the carrier signal has a frequency higher than 10 kHz, the bandwidth of the transmitted signal would be 10 kHz (modulating signal) + carrier signal frequency. Therefore, the correct answer is 20 kHz.

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• 6.

### 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 modulating index.

• D.

Defined in terms of maximum amount of modulation.

A. Two times the modulating signal.
Explanation
The bandwidth of an amplitude modulated signal is two times the modulating signal because amplitude modulation creates two sidebands on either side of the carrier frequency. These sidebands contain the modulating signal and are mirrored copies of each other. Therefore, the bandwidth required to transmit the entire modulated signal is equal to twice the bandwidth of the modulating signal.

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• 7.

### 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 percent of modulation. This refers to the percentage of variation in the amplitude of the carrier signal caused by the modulating signal. It indicates the strength or intensity of the modulating signal in relation to the carrier signal. The higher the percent of modulation, the greater the variation in the carrier signal's amplitude, resulting in a more pronounced modulation effect.

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• 8.

### 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 increases bandwidth due to the production of harmonics. When a signal is overmodulated, it means that the amplitude of the signal exceeds the maximum limit, causing distortion. This distortion results in the creation of harmonics, which are additional frequencies that are multiples of the original signal frequency. These harmonics contribute to an increase in bandwidth because they add extra frequencies to the signal. Therefore, overmodulating a signal increases its bandwidth.

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• 9.

### Reducing modulation to less than 100 percent gives

• A.

More total power

• B.

A reduction to 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 percent, it means that the amplitude of the carrier signal remains constant. This means that there is no reduction in the power of the carrier signal. The modulation only affects the sidebands, which are the additional frequency components added to the carrier signal. Therefore, reducing modulation does not result in a reduction in carrier power.

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• 10.

### 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 modulating signal

• D.

Durectly 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 wave also increases, and vice versa. This relationship is what allows for the encoding and decoding of information in FM signals, as changes in the modulating signal's amplitude can be used to represent different data or signals.

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• 11.

### In frequency modulation (FM), what is considered a significant sideband?

• A.

Sidebands containing at least 1 percent of the total transmitted power

• B.

Sidebands containing at least 3 percent of the total transmitted power

• C.

Sidebands containing at least 10 percent of the total transmitted power

• D.

Sidebands containing at least 0.1 percent of the total transmitted power

A. Sidebands containing at least 1 percent of the total transmitted power
Explanation
A significant sideband in frequency modulation (FM) is considered to be one that contains at least 1 percent of the total transmitted power. This means that the sideband carries a significant portion of the signal and contributes to the overall transmission. Sidebands with less than 1 percent of the total transmitted power may not be strong enough to effectively carry the signal and may result in a weaker transmission.

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• 12.

### What is the formula to find the modulating index?

• A.

Deviation divided by frequency of modulation

• B.

Deviation times frequency of modulation

• C.

Sideband divided by carrier frequency

• D.

Sideband times carrier frequency

A. Deviation divided by frequency of modulation
Explanation
The formula to find the modulating index is deviation divided by frequency of modulation. This means that the extent of the deviation from the carrier frequency is divided by the rate at which the modulation signal varies. The modulating index is a measure of the strength or depth of modulation in a signal.

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• 13.

### 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

A. Phase is shifted at the rate of the modulating signal
Explanation
In phase modulation (PM), the phase of the carrier signal is shifted at the rate of the modulating signal. This means that the instantaneous phase of the carrier signal changes in accordance with the modulating signal. The amount of phase shift is directly proportional to the amplitude of the modulating signal. Therefore, as the modulating signal varies, the phase of the carrier signal also varies, resulting in phase modulation.

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• 14.

• 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 unique symbols to be transmitted within a given bandwidth. This means that more data can be encoded and transmitted in the same amount of time, resulting in higher data rates. By increasing the number of phase shifts, the system can differentiate between a larger number of symbols, allowing for more information to be transmitted per unit of time.

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• 15.

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

• A.

Discrete amplitudes are assigned to the sampling pulse

• B.

A binary code number is assigned to the smaple.

• C.

The quantizer limits the amplitude of the pulses.

• D.

The analog signal is band limited

D. The analog signal is band limited
Explanation
The first step in the pulse code modulation (PCM) process is to band limit the analog signal. This means that the analog signal is filtered to remove any frequencies outside of a certain range, which helps to reduce noise and ensure accurate representation of the signal.

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• 16.

### 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 this process, the continuous signal is sampled at regular intervals to obtain a series of discrete samples. These samples represent the amplitude of the original signal at specific time points. By converting the continuous signal into discrete samples, PCM allows for efficient digital representation and transmission of the signal.

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• 17.

### A type of pulse modulation (PM) that changes 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

• C.

Pulse duration modulation

• D.

Pulse amplitude modulation

D. Pulse amplitude modulation
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. This means that the height or intensity of the pulses in the pulse train changes to represent the varying amplitude of the input signal.

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• 18.

### 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.

Synchcroniztion (SYNC) bit

B. Block of data
Explanation
In synchronous transmission, data is sent in blocks. Each block contains multiple characters or bits of information. If an error occurs during transmission, it can cause the entire block of data to be lost. Therefore, the correct answer is "Block of data."

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• 19.

### 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 determines the parity. Parity is a form of error checking in which an extra bit is added to a data bit pattern to ensure that the number of ones in the pattern is either always even (even parity) or always odd (odd parity). By checking the parity bit, the receiver can detect if any errors occurred during transmission.

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• 20.

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

• A.

Checksum and cyclic redundancy checkin

• 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
Vertical redundancy check (VRC) and longitudinal redundancy check (LRC) are two error detection methods that, when used together, are 98 percent effective in detecting errors. VRC involves adding an additional bit to each character or byte of data, which is then used to check for errors during transmission. LRC involves adding a parity bit to each block of data, which is used to detect errors in the entire block. By combining these two methods, a high level of error detection can be achieved.

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• 21.

### 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 adds up all the characters in a stack, divides the sum by 255, and only considers the remainder. This remainder is then sent along with the data. At the receiving end, the same process is applied to the received data, and if the remainder matches the one sent, it indicates that there are no errors in the data transmission.

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• 22.

### 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

• B.

Forward error control

• C.

Redundant data transfer

• D.

Automatic retransmit on request

D. Automatic retransmit on request
Explanation
Automatic retransmit on request is the 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 the receiver to notify the sender about the error and request the retransmission of the frame, ensuring the accurate delivery of data.

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• 23.

### 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
In forward error control, error correction takes place at the receiving end. This means that when data is transmitted, any errors that occur during transmission are detected and corrected at the receiving end before the data is processed or used. This ensures that the received data is accurate and reliable.

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• 24.

### What does an optical source do?

• A.

Terminates fiber optic cables

• B.

Converts electrical energy into optical energy

• C.

Extend 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 converts 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 is an essential function in optical communication systems, as it allows for the transmission of data over long distances with high signal integrity.

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• 25.

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

• A.

Photo transistors

• B.

Hybrid photodiodes

• C.

Semiconductor laser diodes

• D.

Integrated photodiode/preamplifiers

C. Semiconductor laser diodes
Explanation
Semiconductor laser diodes are applicable to fiber optic waveguide because they can generate a coherent and focused beam of light. This makes them suitable for transmitting data over long distances through the fiber optic cable. LED and photo transistors are not as suitable as they do not produce a coherent beam of light. Hybrid photodiodes and integrated photodiode/preamplifiers are used for receiving the light signal in fiber optic communication, but they are not used as the light source itself.

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• 26.

### What type of light is emitted from a laser?

• A.

Incoherent

• B.

Coherent

• C.

Ordinary

• D.

Invisisble

B. Coherent
Explanation
A laser emits coherent light. Coherent light is characterized by its consistent wavelength, phase, and direction. Unlike incoherent light, which consists of multiple wavelengths and phases, coherent light has all its waves in phase with each other, resulting in a narrow beam of light that travels in a straight line. This property of coherence allows lasers to produce a concentrated and powerful beam of light that can be used in various applications such as cutting, welding, and medical procedures.

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• 27.

### 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 milliwatts. This unit of measurement is used to quantify the power output of a laser diode when it is coupled with an external device or system. Milliwatts are a smaller unit of power compared to kilowatts and megawatts, indicating that laser diodes typically have lower power outputs. Microwatts are also a smaller unit, but milliwatts are a more commonly used and appropriate measurement for laser diode power coupling.

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• 28.

### A device that accepts optical signals from an optical fiber and converts them into electrical signals is called an optical

• A.

Regenerator

• B.

Transmitter

• C.

Amplifier

• D.

Explanation
An optical receiver is a device that accepts optical signals from an optical fiber and converts them into electrical signals. This allows for the transmission of data over long distances through the use of optical fibers. The receiver plays a crucial role in the communication process by receiving and decoding the optical signals, allowing the information to be processed and utilized by other devices.

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• 29.

### 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
The small current that flows from a photodiode even with no light is called dark current. This current is generated due to the random movement of charge carriers within the photodiode's semiconductor material. It is independent of the incident light and can be caused by factors such as temperature or impurities in the material. Dark current can affect the accuracy and sensitivity of photodiodes, especially in low-light conditions, and needs to be minimized for optimal performance.

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• 30.

### The responsivity of a photo detector is dependent on the

• A.

Emitter rise time

• B.

Wavelength of light

• C.

Signal-to-noise ratio

• D.

Emitter modulation speed

B. Wavelength of light
Explanation
The responsivity of a photo detector refers to its ability to convert incident light into an electrical signal. The wavelength of light plays a crucial role in determining the responsivity of a photo detector. Different detectors have different responsivity curves, meaning they are more sensitive to certain wavelengths of light than others. Therefore, the wavelength of light is a key factor in determining the responsivity of a photo detector.

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• 31.

### What are the two main types of photodetectors

• A.

Positive intrinsic negative and avalanche photodiode

• B.

Light-emitting diode (LED) and avalanche photodiode

• C.

LED and semiconductor laser

• D.

Tunnel and zener diodes

A. Positive intrinsic negative and avalanche photodiode
Explanation
The correct answer is positive intrinsic negative and avalanche photodiode. These are the two main types of photodetectors commonly used in various applications. Positive intrinsic negative (PIN) photodiodes are made of three layers of semiconductor material and are used for high-speed and low-noise applications. Avalanche photodiodes (APDs) are also made of three layers of semiconductor material but have an additional layer that allows for the multiplication of photocurrent, making them suitable for low-light detection and high-gain applications.

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• 32.

### 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 photodioe/preamplifier (IDP)

C. Positive intrinsic negative (PIN) diode
Explanation
A positive intrinsic negative (PIN) diode is a type of photo detector that converts one photon to one electron. This type of diode has a heavily doped p-type region and a heavily doped n-type region separated by an intrinsic (undoped) region. When a photon is absorbed by the intrinsic region, it creates an electron-hole pair. The electric field applied across the diode then separates the electron and hole, allowing the electron to be collected as a current. Therefore, the PIN diode is capable of converting individual photons into electrons.

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• 33.

### 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 optical signal, converts it into an electrical signal, amplifies it, and then retransmits it as an optical signal. This process helps to overcome signal loss and maintain signal integrity over long distances. By regenerating the signal, repeaters allow for longer transmission distances in fiber optic communication systems.

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• 34.

### 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 amplify optical signals without converting them to and from the electrical domain. Unlike repeaters and regenerators which regenerate and amplify electrical signals, optical amplifiers directly amplify the optical signals. Receivers, on the other hand, are responsible for converting optical signals into electrical signals. Therefore, the correct answer is optical amplifiers.

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• 35.

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

• A.

Pigtail

• B.

Patch cord

• C.

Jumper

• D.

Breakout cable

B. Patch cord
Explanation
A patch cord is a short section of single fiber cables that has a connector at each end. It is commonly used to connect devices in a network or telecommunications system. Patch cords are typically used to connect equipment to a patch panel or to connect two devices directly. They are often color-coded for easy identification and can be easily plugged and unplugged, making them convenient for quick connections and changes in network configurations.

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• 36.

### Which fiber-optic connector uses 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 type of connector provides a secure and reliable connection, while also allowing for easy installation and removal. The quick-release feature allows for quicker and easier connections and disconnections, making it ideal for situations where frequent changes or adjustments may be required. The keyed bayonet couplings ensure proper alignment and prevent accidental disconnections. Overall, the ST connector is a popular choice in applications where stability and ease of use are important factors.

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• 37.

### 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) Back to top