CDC 3D153 Rf Journeyman Volume 1, Unit 1
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Questions and Answers
- 1.
(001) What is one reason for modulation that involves modulating low frequency signals for transmission over long distances?
- A.
Spectrum conservation
- B.
Channel allocation
- C.
Ease of radiation
- D.
Companding
Correct Answer
C. Ease of radiationExplanation
Modulating low frequency signals for transmission over long distances provides ease of radiation. This is because low frequency signals have longer wavelengths, allowing them to propagate further without significant loss. By modulating these signals, they can be easily transmitted over long distances, ensuring efficient and effective communication.Rate this question:
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- 2.
(001) 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
Correct Answer
C. Amplitude, frequency, and phaseExplanation
The three general categories used to produce modulation in radio frequency (RF) transmission today are amplitude, frequency, and phase. Modulation is the process of varying one or more properties of a carrier signal in order to transmit information. In amplitude modulation (AM), the amplitude of the carrier signal is varied to encode the information. In frequency modulation (FM), the frequency of the carrier signal is varied. In phase modulation (PM), the phase of the carrier signal is varied. These three types of modulation are commonly used in RF transmission to carry information efficiently.Rate this question:
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- 3.
(002) When the modulating signal and carrier signal are combined within a modulator, the output signal contains
- A.
Modulating signal, upper sideband, and lower sideband
- B.
Carrier, upper sideband, and lower sideband
- C.
Upper sideband and modulating signal
- D.
Carrier and modulating signal
Correct Answer
B. Carrier, upper sideband, and lower sidebandExplanation
When the modulating signal and carrier signal are combined within a modulator, the output signal contains the carrier signal, as well as the upper sideband and lower sideband. This is because the modulating signal affects the carrier signal by shifting its frequency, resulting in the creation of sidebands. The upper sideband has frequencies higher than the carrier frequency, while the lower sideband has frequencies lower than the carrier frequency. Therefore, the correct answer is carrier, upper sideband, and lower sideband.Rate this question:
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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 include
- 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, 0.000 MHz
Correct Answer
A. 1.01 MHz, 1 MHz, and 0.99 MHzExplanation
When a carrier frequency of 1 MHz and a modulating tone of 10 kHz are combined in a modulator, the output signal will include the carrier frequency (1 MHz) and the sidebands resulting from modulation. In this case, the sidebands will be at frequencies of 1.01 MHz (1 MHz + 10 kHz) and 0.99 MHz (1 MHz - 10 kHz). Therefore, the correct answer is 1.01 MHz, 1 MHz, and 0.99 MHz.Rate this question:
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- 5.
(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
Correct Answer
A. Two times the modulating signalExplanation
The correct answer is "two times the modulating signal." In amplitude modulation, the bandwidth refers to the range of frequencies required to accurately transmit the modulating signal. Since the modulating signal is multiplied by both its positive and negative copies, the bandwidth is two times the modulating signal.Rate this question:
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- 6.
(002) Use the formula on page 1-3. If an oscilloscope displays a modulation envelope having an EMax of 200 volts and an EMin of 20 volts, what is the modulation percentage?
- A.
81.8
- B.
85.5
- C.
88
- D.
122
Correct Answer
A. 81.8Explanation
The modulation percentage can be calculated using the formula: (EMax - EMin) / (EMax + EMin) * 100. In this case, the EMax is 200 volts and the EMin is 20 volts. Plugging these values into the formula, we get (200 - 20) / (200 + 20) * 100 = 180 / 220 * 100 = 81.8. Therefore, the modulation percentage is 81.8.Rate this question:
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- 7.
(002) Which statement concerning bandwidth is true?
- A.
Overmodulating increases bandwidth because the distortion produces harmonics
- B.
Undermodulating increases bandwidth because the distortion produces harmonics
- C.
Overmodulating increases bandwidth because the output's increased amplitude
- D.
Undermodulating increases bandwidth because the output's decreased amplitude
Correct Answer
A. Overmodulating increases bandwidth because the distortion produces harmonicsExplanation
Overmodulating refers to the process of increasing the amplitude of a signal beyond its normal range. This causes distortion in the signal, which in turn produces harmonics. Harmonics are additional frequencies that are multiples of the original signal frequency. As a result, the bandwidth of the signal increases because it now contains these additional frequencies. Therefore, the statement "Overmodulating increases bandwidth because the distortion produces harmonics" is true.Rate this question:
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- 8.
(003) The output of the oscillator in a frequency modulation (FM) modulator increase in frequency with each
- A.
Positive half cycle of the carrier
- B.
Negative half cycle of the carrier
- C.
Positive half cycle of the modulating signal
- D.
Negative half cycle of the modulating signal
Correct Answer
A. Positive half cycle of the carrierExplanation
In frequency modulation (FM), the output of the oscillator increases in frequency with each positive half cycle of the carrier. This means that as the carrier wave goes through its positive half cycle, the frequency of the oscillator increases. This change in frequency is what carries the information in FM modulation.Rate this question:
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- 9.
(003) In frequency modulation, a significant sideband contains at least what percentage of the total transmitted power?
- A.
1
- B.
3
- C.
10
- D.
0.1
Correct Answer
A. 1Explanation
In frequency modulation, a significant sideband contains at least 1% of the total transmitted power. This means that when a signal is modulated in frequency, at least 1% of the power is distributed in the sidebands that are created around the carrier frequency. These sidebands contain the information being transmitted and are important for the receiver to demodulate the signal accurately.Rate this question:
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- 10.
(003) What is the formula to find the modulating index?
- A.
Deviation divided by frequency of modulation
- B.
Deviation times frequency of modulation
- C.
Sideband divide by carrier frequency
- D.
Sideband times carrier frequency
Correct Answer
A. Deviation divided by frequency of modulationExplanation
The modulating index is the ratio of the frequency deviation (the difference between the carrier frequency and the highest frequency in the modulating signal) to the frequency of modulation (the frequency of the modulating signal). Therefore, the formula to find the modulating index is deviation divided by frequency of modulation.Rate this question:
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- 11.
(003) A 5 kHz modulating signal has enough peak voltage to cause a deviation of 15 kHz. What is the modulation index?
- A.
5
- B.
0.5
- C.
0.3
- D.
3
Correct Answer
D. 3Explanation
The modulation index is a measure of the extent of frequency deviation in a modulated signal. In this question, the modulating signal has a frequency of 5 kHz and it causes a deviation of 15 kHz. The modulation index can be calculated by dividing the peak frequency deviation by the modulating signal frequency. Therefore, the modulation index in this case would be 15 kHz / 5 kHz = 3.Rate this question:
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- 12.
(003) What is it called when a narrow frequency band between adjacent stations prevent frequency modulated sidebands from overlapping?
- A.
Space
- B.
Guard band
- C.
Buffer zone
- D.
Prevention field
Correct Answer
B. Guard bandExplanation
A guard band is a narrow frequency band that is used to prevent frequency modulated sidebands from overlapping between adjacent stations. It acts as a buffer zone, ensuring that there is enough space between the frequencies of different stations to avoid interference and maintain clear communication. This helps to prevent signal distortion and maintain the integrity of the transmitted information.Rate this question:
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- 13.
(004) In phase modulation, what part of the carrier signal is varied?
- A.
Frequency
- B.
Amplitude
- C.
Height
- D.
Phase
Correct Answer
D. PhaseExplanation
In phase modulation, the part of the carrier signal that is varied is the phase. This means that the timing of the carrier signal is altered, resulting in a change in the position of the signal on the waveform. The amplitude and frequency of the carrier signal remain constant, but the phase is adjusted to encode the information being transmitted.Rate this question:
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- 14.
(004) In phase modulation, 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
Correct Answer
A. Phase is shifted at the rate of the modulating signalExplanation
In phase modulation, 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 is varied in accordance with the changing amplitude of the modulating signal. As the modulating signal changes, the phase of the carrier signal also changes, resulting in a phase-shifted carrier signal. This phase shift is what carries the information of the modulating signal.Rate this question:
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- 15.
(005) What is the first step in the pulse code modulation 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.
Correct Answer
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 involves restricting the frequency range of the analog signal to prevent aliasing and ensure accurate representation in the digital domain. This is done by applying a low-pass filter to remove any high-frequency components that are beyond the Nyquist limit. By band limiting the analog signal, it becomes suitable for the subsequent steps of sampling, quantization, and encoding into binary code numbers.Rate this question:
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- 16.
(005) What part of the pulse code modulation process converts a continuous time signal into a discrete time signal?
- A.
Sampling
- B.
Rectifying
- C.
Oscillating
- D.
Band limiting
Correct Answer
A. SamplingExplanation
Sampling is the part of the pulse code modulation 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, it becomes easier to process, transmit, and store the signal digitally.Rate this question:
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- 17.
(006) In asynchronous transmissions, what bit is used by the receiving device to verify that the transmission was received correctly?
- A.
Control
- B.
Parity
- C.
Start
- D.
Stop
Correct Answer
B. ParityExplanation
Parity bit is used in asynchronous transmissions to verify the accuracy of the received data. It is an extra bit added to the data being transmitted that helps in error detection. The receiving device checks the parity bit to determine if any errors occurred during transmission. If the parity bit does not match the expected value, it indicates that an error has occurred. Therefore, the correct answer is Parity.Rate this question:
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- 18.
(006) If an error should occur, what transmission is lost in an synchronous transmission?
- A.
One character
- B.
Block of data
- C.
A parity bit
- D.
A stop bit
Correct Answer
B. Block of dataExplanation
In synchronous transmission, data is transmitted in blocks. Each block of data consists of multiple characters. If an error occurs during transmission, it means that the entire block of data is lost, not just one character. Therefore, the correct answer is "Block of data".Rate this question:
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- 19.
(007) When using vertical redundancy check, 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 ASCII format
- D.
Determines whether transmission is synchronous or asynchronous
Correct Answer
A. Determines parityExplanation
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 the data to ensure that the number of ones in the pattern is either even (even parity) or odd (odd parity). This allows the receiver to detect if any errors occurred during transmission by comparing the received parity bit with the calculated parity. If the number of ones in the received pattern does not match the expected parity, an error is detected. Therefore, the amount of ones in the data bit pattern is significant in determining the parity.Rate this question:
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- 20.
(007) What error detection method is used for checking a data block greater than 512 and is about 99 percent effective in most applications?
- A.
Checksum
- B.
Cyclic redundancy check
- C.
Vertical redundancy check
- D.
Longitudinal redundancy check
Correct Answer
B. Cyclic redundancy checkExplanation
Cyclic redundancy check (CRC) is an error detection method used for checking a data block greater than 512 and is about 99 percent effective in most applications. CRC involves dividing the data block by a predetermined divisor and appending the remainder as a checksum to the original data. Upon receiving the data, the recipient performs the same division and compares the remainder with the received checksum. If they match, it is highly likely that the data has been transmitted correctly. CRC is widely used in various communication protocols to ensure data integrity.Rate this question:
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- 21.
(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
Correct Answer
A. Receiving endExplanation
Error correction takes place at the receiving end when using forward error control as a method of error correction. This means that the errors in the transmitted data are detected and corrected by the receiving device before the data is processed or displayed. The receiving end analyzes the received data and uses error correction techniques to correct any errors that may have occurred during transmission.Rate this question:
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- 22.
(008) Light sources that are applicable to fiber optic waveguide are light-emitting diodes and
- A.
Photo transistors
- B.
Hybrid photodiodes
- C.
Semiconductor laser diodes
- D.
Integrated photodiode/preamplifiers
Correct Answer
C. Semiconductor laser diodesExplanation
Semiconductor laser diodes are applicable to fiber optic waveguides because they can emit light that is coherent and focused, allowing for efficient transmission through the fiber optic cables. Unlike light-emitting diodes (LEDs), which emit incoherent light, semiconductor laser diodes produce a single wavelength of light that can be easily coupled into the fiber optic waveguide. This makes them ideal for long-distance communication and high-speed data transmission applications. Photo transistors, hybrid photodiodes, and integrated photodiode/preamplifiers are not typically used as light sources in fiber optic waveguides.Rate this question:
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- 23.
(008) What type of light is emitted from a laser?
- A.
Incoherent
- B.
Coherent
- C.
Ordinary
- D.
Invisible
Correct Answer
B. CoherentExplanation
A laser emits coherent light. Coherent light is characterized by its waves having a constant phase relationship with each other, meaning that the peaks and troughs of the waves align perfectly. This results in a concentrated, focused beam of light that is highly directional and has a single wavelength. Unlike ordinary light sources, such as a light bulb, which emit incoherent light with random phase relationships, lasers produce a highly organized and synchronized light beam.Rate this question:
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- 24.
(009) What are the two main types of photodetectors?
- A.
Positive intrinsic negative and avalanche photodiode
- B.
Light-emitting diode and avalanche photodiode
- C.
Light emitting diode and semiconductor laser
- D.
Tunnel and zener diodes
Correct Answer
A. Positive intrinsic negative and avalanche photodiodeExplanation
The correct answer is positive intrinsic negative and avalanche photodiode. Photodetectors are devices that convert light energy into electrical signals. Positive intrinsic negative (PIN) photodiodes are widely used in optical communication systems due to their high sensitivity and low noise characteristics. Avalanche photodiodes (APDs) are also commonly used in applications that require high gain and high-speed detection. These two types of photodetectors are essential in various fields such as telecommunications, imaging, and sensing.Rate this question:
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- 25.
(009) What photo detector converts one photon to one electron?
- A.
Light emitting diode
- B.
Avalanche photodiode
- C.
Positive intrinsic negative diode
- D.
Integrated photodiode/preamplifier
Correct Answer
C. Positive intrinsic negative diodeExplanation
A positive intrinsic negative (PIN) diode is a type of photo detector that converts one photon to one electron. It is designed to have a high sensitivity to light and is commonly used in applications such as optical communication systems and photovoltaic devices. The other options mentioned in the question, such as light emitting diode, avalanche photodiode, and integrated photodiode/preamplifier, do not specifically convert one photon to one electron.Rate this question:
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- 26.
(010) Which repeater amplifies optical signal without converting to and from the electrical domain?
- A.
Receiver
- B.
Repeater
- C.
Regenerators
- D.
Optical amplifiers
Correct Answer
D. Optical amplifiersExplanation
Optical amplifiers are devices that enhance the strength of an optical signal without converting it to an electrical signal. They use a process called stimulated emission to amplify the signal directly in the optical domain. This allows for long-distance transmission of optical signals without the need for frequent conversion to and from electrical signals. Unlike repeaters, which regenerate and reshape the electrical signal, optical amplifiers solely focus on amplifying the optical signal, making them more efficient and cost-effective for optical communication systems.Rate this question:
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- 27.
(011) A short section of single fiber cable that has a connector at each end is called a
- A.
Pigtail
- B.
Jumper
- C.
Patch cord
- D.
Breakout cables
Correct Answer
C. Patch cordExplanation
A short section of single fiber cable that has a connector at each end is called a patch cord. A patch cord is used to connect devices or components together in a network or telecommunications system. It provides a temporary or permanent connection and allows for easy installation, maintenance, and reconfiguration of the network.Rate this question:
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- 28.
(011) 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 (FC)
- C.
Straight tip (ST)
- D.
Sub-miniature, type A (SMA)
Correct Answer
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, but it may not be suitable for environments with high levels of vibrations that could potentially loosen the connection. Therefore, in situations where severe vibrations are not expected, the ST connector is a suitable choice.Rate this question:
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