3d1x2 Skt Book 1

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  • 1/109 Questions

    What is the process, or result of the process, of modifying any characteristic of an information singal or carrier signal so that it varies in step with the instantaneous value of another information signal?

    • Multiplexing
    • Modulation
    • Conversion
    • Manipulating
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Electronics Quizzes & Trivia
About This Quiz

Explore key modulation techniques in '3D1X2 SKT Book 1'. This quiz assesses understanding of signal modification methods like Modulation, Analog Modulation, and Binary Phase-Shift Keying, vital for professionals in electronics and communication engineering.

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  • 2. 

    What is the conversion of an analog signal into another analog signal?

    • Analog Modulation

    • Pulse Duration Modulation

    • Digital Modulation

    • Pulse Code Modulation

    Correct Answer
    A. Analog Modulation
    Explanation
    Analog modulation is the process of converting an analog signal into another analog signal. This is achieved by varying one or more properties of the carrier signal in accordance with the input signal. This modulation technique is commonly used in communication systems to transmit analog signals over long distances without significant loss or distortion.

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  • 3. 

    Which of these is not a form of analog modulation?

    • Frequency Modulation

    • Phase Modulation

    • Amplitude Modulation

    • Bandwidth Modulation

    Correct Answer
    A. Bandwidth Modulation
    Explanation
    Bandwidth modulation is not a form of analog modulation because it does not involve varying any of the fundamental properties of the carrier signal, such as its frequency, phase, or amplitude. Instead, bandwidth modulation refers to the process of varying the width of the frequency band that is used to transmit the signal. In other words, it involves changing the range of frequencies that are allowed to pass through a filter or channel, rather than directly manipulating the carrier signal itself.

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  • 4. 

    Which of these is not a basic type of digital conversion techniques?

    • Amplitude Shift Keying(ASK)

    • Binary Shift Keying(BSK)

    • Frequency Shift Keying(FSK)

    • Phase Shift Keying(PSK)

    Correct Answer
    A. Binary Shift Keying(BSK)
    Explanation
    Binary Shift Keying (BSK) is not a basic type of digital conversion technique. Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK) are all commonly used techniques in digital communication systems. ASK involves varying the amplitude of the carrier signal to represent digital data. FSK involves varying the frequency of the carrier signal, and PSK involves varying the phase of the carrier signal. In contrast, BSK is not a recognized technique in digital communication.

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  • 5. 

    Amplitude Shift Keying(ASK) is also know as ______ because the amplitude of the carrier was either on or off depending on the state of the digital input.

    • On-Off Keying(OOK)

    • On Keying(OK)

    • Off Keying(OK)

    • Duplex Keying(DK)

    Correct Answer
    A. On-Off Keying(OOK)
    Explanation
    Amplitude Shift Keying (ASK) is a digital modulation technique where the amplitude of the carrier signal is varied to represent digital data. In ASK, the carrier amplitude is either on or off depending on the state of the digital input. This modulation scheme is also known as On-Off Keying (OOK) because the carrier amplitude is switched on and off to represent the digital information.

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  • 6. 

    ____ is the simplest form of Phase Modulation. There are two phase shifts (0 degrees or 180 degrees) for data transmission depending on whether a binary 1 or 0 is to be transmitted.

    • Phase Shift Keying(PSK)

    • Differential Phase-Shift Keying(DPSK)

    • Quadrature Phase-Shift Keying(QPSK)

    • Binary Phase-Shift Keying(BPSK)

    Correct Answer
    A. Binary Phase-Shift Keying(BPSK)
    Explanation
    Binary Phase-Shift Keying (BPSK) is the simplest form of Phase Modulation. In BPSK, there are two phase shifts (0 degrees or 180 degrees) for data transmission depending on whether a binary 1 or 0 is to be transmitted. This means that the carrier signal is shifted in phase by either 0 degrees or 180 degrees to represent the binary data. BPSK is widely used in various communication systems due to its simplicity and robustness against noise.

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  • 7. 

    What uses four different carrier phases (0 degrees, 90 degrees, 180 degrees, and 270 degrees) to represent two data transmission bits. For example, to send 00, the phase changes by 0 degrees.

    • Differential Phase-Shift Keying(DPSK)

    • Binary Phase-Shift Keying(BPSK)

    • Quadrature Phase-Shift Keying(QPSK)

    • Phase Shift Keying(PSK)

    Correct Answer
    A. Quadrature Phase-Shift Keying(QPSK)
    Explanation
    Quadrature Phase-Shift Keying (QPSK) is the correct answer because it uses four different carrier phases (0 degrees, 90 degrees, 180 degrees, and 270 degrees) to represent two data transmission bits. Each phase shift represents a different combination of bits, allowing for efficient data transmission. This modulation scheme is commonly used in digital communication systems to achieve higher data rates while conserving bandwidth.

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  • 8. 

    ______ encodes different digital values as changes in signal phase. This is easier to implement and is more robust than PSK because____ looks for differences, rather than specific values. This form of modulation can be found in local area network technologies.

    • Differential Phase-Shift Keying(DPSK)

    • Phase-Shift Keying(PSK)

    • Binary Phase-Shift Keying(BPSK)

    • Quadrature Phase-Shift Keying(QPSK)

    Correct Answer
    A. Differential Phase-Shift Keying(DPSK)
    Explanation
    Differential Phase-Shift Keying (DPSK) encodes different digital values as changes in signal phase. This is easier to implement and more robust than PSK because DPSK looks for differences, rather than specific values. In DPSK, the receiver only needs to detect whether the phase has changed or not, rather than determining the exact phase value. This makes DPSK more resistant to noise and other interference. DPSK is commonly used in local area network technologies.

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  • 9. 

    What is a combination of AM and PM? We use this to convert a digital signal to analog form by varying the amplitude and phase of the carrier signal. Using this method of modulation you are able to encode up to four data bits for transmission. This is also similar to QPSK.

    • Dual Modulation(DM)

    • Combined Modulation(CM)

    • Quadrature Amplitude Modulation(QAM)

    • AM-PM Modulation(AMPMM)

    Correct Answer
    A. Quadrature Amplitude Modulation(QAM)
    Explanation
    Quadrature Amplitude Modulation (QAM) is a combination of AM (Amplitude Modulation) and PM (Phase Modulation). It is used to convert a digital signal to analog form by varying the amplitude and phase of the carrier signal. QAM allows for the encoding of up to four data bits for transmission, making it an efficient modulation technique. QAM is also similar to QPSK (Quadrature Phase Shift Keying), another modulation scheme that encodes data by varying the phase of the carrier signal.

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  • 10. 

    What is the conversion of an analog signal into a digital signal? This is done by converting an analog wave into discrete pulses, taking multiple samples, and converting the samples into a digital signal.

    • Digital Modulation

    • Phase Modulation

    • Discrete Pulse Modulation

    • Sample Modulation

    Correct Answer
    A. Digital Modulation
    Explanation
    The correct answer is Digital Modulation. The process of converting an analog signal into a digital signal involves converting the continuous analog wave into discrete pulses. This is done by taking multiple samples of the analog signal at regular intervals and then converting these samples into a digital signal. Digital modulation is the technique used to achieve this conversion, where the discrete pulses are encoded and modulated to represent the original analog signal in a digital format.

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  • 11. 

    What varies one or more parameters of a pulse according to a modulating signal to transmit the desired information?

    • Pulse Modulation

    • Phase Modulation

    • Frequency Modulation

    • Amplitude Modulation

    Correct Answer
    A. Pulse Modulation
    Explanation
    Pulse Modulation is the correct answer because it involves varying one or more parameters of a pulse according to a modulating signal to transmit the desired information. This modulation technique is commonly used in digital communication systems to encode and transmit digital data. By varying the parameters of the pulse, such as its amplitude, duration, or position, the information can be encoded and transmitted in the form of pulses.

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  • 12. 

    ____ is the simplest kind of pulse-modulation technique and is amplitude-modulated. This is used for time-division multiplexing(TDM) and differs from AM mainly in the use of a rectangular pulse train rather than a sine wave for the carrier signal.

    • Pulse-amplitude Modulation

    • Pulse-duration Modulation

    • Pulse-position Modulation

    • Pulse-code Modulation

    Correct Answer
    A. Pulse-amplitude Modulation
    Explanation
    Pulse-amplitude modulation (PAM) is the simplest form of pulse-modulation technique and is amplitude-modulated. It is used for time-division multiplexing (TDM) and differs from amplitude modulation (AM) in that it uses a rectangular pulse train instead of a sine wave for the carrier signal. In PAM, the amplitude of the carrier signal is varied in proportion to the amplitude of the modulating signal, resulting in a series of pulses with varying amplitudes. This allows for the transmission of multiple signals over a single channel by dividing the time into discrete intervals.

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  • 13. 

    This is another method used for TDM. ____ is also known as pulse-width modulation(PWM), pulse-length modulation(PLM), or pulse-time modulation(PTM). In ____ the pulse duration, or width, of each sample pulse is varied to encode an analog signal at the point of sampling. This method is less affected by noise than the PAM method.

    • Pulse-duration Modulation

    • Pulse-amplitude Modulation

    • Pulse-position Modulation

    • Pulse-code Modulation

    Correct Answer
    A. Pulse-duration Modulation
    Explanation
    Pulse-duration modulation (PDM) is another method used for time-division multiplexing (TDM). PDM is also known as pulse-width modulation (PWM), pulse-length modulation (PLM), or pulse-time modulation (PTM). In PDM, the pulse duration or width of each sample pulse is varied to encode an analog signal at the point of sampling. This method is less affected by noise than the pulse-amplitude modulation (PAM) method.

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  • 14. 

    ____ is used in military TDM equipment. ____ uses a pulse time method that represents an analog signal by varying the positioning (the time displacement) of a discrete pulse within a bit interval. The position is varied according to the sampled value of an analog signal.

    • Pulse-position Modulation

    • Pulse-code Modulation

    • Pulse-duration Modulation

    • Pulse-amplitude Modulation

    Correct Answer
    A. Pulse-position Modulation
    Explanation
    Pulse-position modulation (PPM) is used in military TDM equipment. PPM represents an analog signal by varying the positioning (the time displacement) of a discrete pulse within a bit interval. The position is varied according to the sampled value of an analog signal.

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  • 15. 

    _____ is a complete digitization process since it converts an analog signal into one that is discrete with respect to both time and amplitude (or polarity). The signal is based on an analog signal that has already been modulated (by using PAM, PDM, or PPM).

    • Pulse-code Modulation

    • Pre-modulated Modulation

    • Analog Modulation

    • Complete Modulation

    Correct Answer
    A. Pulse-code Modulation
    Explanation
    Pulse-code Modulation (PCM) is the correct answer because it is a complete digitization process that converts an analog signal into a discrete signal in terms of both time and amplitude. PCM is used when the analog signal has already been modulated using techniques like PAM (Pulse Amplitude Modulation), PDM (Pulse Duration Modulation), or PPM (Pulse Position Modulation). PCM samples the analog signal at regular intervals and quantizes the amplitude of each sample, resulting in a digital representation of the original analog signal.

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  • 16. 

    The pulses of PCM are grouped into any of a predefined number of different levels using a ______; each of the possible levels is represented by a unique bit stream. The number of possible values in this stream determines the granularity of the modulation.

    • Quantizer

    • Compander

    • Transformer

    • Converter

    Correct Answer
    A. Quantizer
    Explanation
    In PCM (Pulse Code Modulation), the pulses are grouped into different levels using a quantizer. The quantizer assigns each pulse to a specific level, and each level is represented by a unique bit stream. The number of possible values in this bit stream determines the granularity or resolution of the modulation. A higher number of possible values allows for more precise representation of the signal, while a lower number of values reduces the precision but requires less bandwidth. Therefore, the correct answer is "Quantizer".

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  • 17. 

    This is a variation of PCM. Amplitudes are represented using 4-bit values (rather than the 8 bits used in PCM), and a 32Kbps data-transfer rate is used (rather than 64Kbps, as in PCM).

    • Adaptive differential pulse-code modulation(ADPCM)

    • Amplitude differential pulse-code modulation(ADPCM)

    • Amplitude difference pulse-code modulation(ADPCM)

    • Adaptive difference pulse-code modulation(ADPCM)

    Correct Answer
    A. Adaptive differential pulse-code modulation(ADPCM)
    Explanation
    The given correct answer is Adaptive differential pulse-code modulation (ADPCM). This is because ADPCM is a variation of PCM that uses 4-bit values to represent amplitudes and a data-transfer rate of 32Kbps. ADPCM is an audio compression algorithm that reduces the amount of data required to represent audio signals while maintaining reasonable audio quality. It achieves this by predicting the difference between consecutive audio samples and encoding only the difference rather than the full sample. The adaptive nature of ADPCM allows it to adjust its prediction algorithm based on the characteristics of the audio signal, resulting in more efficient compression.

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  • 18. 

    _____ converts an analog signal (voice signal) by scanning it a specified amount of times (Ex. 32,000 times a second). A sample is taken at a specified time. If the value of the sample is different than it was at the previous scan, the digital signal is modified by a discrete step. If the value is greater, a positive '1' is sent. If the value is smaller, a negative '0' is sent.

    • Delta Modulation(DM)

    • Digital Modulation(DM)

    • Discrete Modulation(DM)

    • Pulse-code Modulation(PCM)

    Correct Answer
    A. Delta Modulation(DM)
    Explanation
    Delta Modulation (DM) converts an analog signal into a digital signal by scanning it a specified number of times per second. It takes a sample of the signal at a specific time and compares it to the previous sample. If the value of the current sample is different, the digital signal is modified by a discrete step. A positive '1' is sent if the value is greater, and a negative '0' is sent if the value is smaller. This process allows for the transmission of analog signals over digital communication systems.

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  • 19. 

    What is a variation of DM where a signal's step size may vary from sample to sample?

    • Adaptive Delta Modulation(ADM)

    • Step Size Modulation(SSM)

    • Differential Modulation(DM)

    • Variation Modulation(VM)

    Correct Answer
    A. Adaptive Delta Modulation(ADM)
    Explanation
    Adaptive Delta Modulation (ADM) is a variation of DM where the step size of a signal can vary from sample to sample. In ADM, the step size is adjusted based on the local characteristics of the input signal, allowing for more efficient encoding and compression of the signal. This adaptive nature of ADM helps in accurately representing the signal by adjusting the step size according to the signal's variations, resulting in improved performance compared to fixed step size modulation techniques.

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  • 20. 

    This modulation varies the signal step size according to the input signal amplitude. At lower input signals, smaller step sizes minimize quantizing noise. At higher signal levels, larger step sizes minimize slope overload.

    • Continuously Variable Slope Delta Modulation(CVSD)

    • Amplitude Modulation(AM)

    • Adaptive Delta Modulation(ADM)

    • Step Size Delta Modulation(SSDM)

    Correct Answer
    A. Continuously Variable Slope Delta Modulation(CVSD)
    Explanation
    The given explanation provides a clear understanding of how the modulation varies the signal step size according to the input signal amplitude. It explains that at lower input signals, smaller step sizes are used to minimize quantizing noise, while at higher signal levels, larger step sizes are used to minimize slope overload. This explanation aligns perfectly with the concept of Continuously Variable Slope Delta Modulation (CVSD), which is the correct answer.

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  • 21. 

    _____ is historically one of the oldest forms of modulation. In this modulation, the amplitude of the carrier signal is varied according to the modulating signal. In the early days of vacuum-tube transmitters, this was achieved by permitting the modulating signal to vary the electrode voltage supplied to one of the elements of the vacuum tube. The result was the amplitude or maximum positive value of the sine-wave carrier signal was caused to vary instant by instant as the modulating signal level varied.

    • Amplitude Modulation

    • Vacuum-Tube Modulation

    • Sine-Wave Modulation

    • Carrier Modulation

    Correct Answer
    A. Amplitude Modulation
    Explanation
    Amplitude modulation is historically one of the oldest forms of modulation. It involves varying the amplitude of the carrier signal according to the modulating signal. In the early days of vacuum-tube transmitters, this was achieved by allowing the modulating signal to change the electrode voltage supplied to one of the vacuum tube elements. As a result, the amplitude or maximum positive value of the sine-wave carrier signal would vary in real-time as the modulating signal level changed.

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  • 22. 

    In Amplitude Modulation, we can show the output of the modulation that contain the following frequencies. Which of these is not an output?

    • F(c)

    • F(c) + F(m)

    • F(c) - F(m)

    • F(c) x F(m)

    Correct Answer
    A. F(c) x F(m)
    Explanation
    In Amplitude Modulation, the output of the modulation contains the sum (F(c) + F(m)) and the difference (F(c) - F(m)) of the carrier frequency (F(c)) and the modulating frequency (F(m)). However, the product (F(c) x F(m)) is not an output in Amplitude Modulation.

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  • 23. 

    In complex Amplitude Modulation, this sideband has the same shape and orientation as the band of modulating signal frequencies.

    • Upper Sideband(USB)

    • Lower Sideband(LSB)

    • Frequency Sideband(FSB)

    • Amplitude Sideband(ASB)

    Correct Answer
    A. Upper Sideband(USB)
    Explanation
    In complex Amplitude Modulation, the upper sideband (USB) has the same shape and orientation as the band of modulating signal frequencies. This means that the USB contains the same frequencies as the modulating signal, but shifted to higher frequencies. In complex AM, the modulating signal is multiplied by a carrier signal and the resulting signal is composed of the carrier frequency, the upper sideband, and the lower sideband. Since the USB has the same shape and orientation as the modulating signal, it carries the same information as the original signal but at higher frequencies.

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  • 24. 

    In complex Analog Modulation, this sideband is the mirror image of the original modulating signal. This sideband is said to be inverted, since its shape is the reverse of the modulating signal.

    • Lower Sideband(LSB)

    • Upper Sideband(USB)

    • Frequency Sideband(FSB)

    • Amplitude Sideband(ASB)

    Correct Answer
    A. Lower Sideband(LSB)
    Explanation
    In complex Analog Modulation, the lower sideband (LSB) is the mirror image of the original modulating signal. This means that the shape of the lower sideband is the reverse of the modulating signal.

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  • 25. 

    We can express the 6-to-1 improvement of SSBSC over DSBSC as __ decibels (dB) of improvement.

    • 8

    • 6

    • 4

    • 2

    Correct Answer
    A. 8
    Explanation
    The 6-to-1 improvement of SSBSC over DSBSC can be expressed as 8 decibels (dB) of improvement.

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  • 26. 

    ______ signals can be detected by reinserting the carrier frequency, when heterodyned with the received signal, produces a sum and a difference output signal. The sum signal is eliminated, and the difference signal corresponds to the original modulating signal.

    • Single-sideband

    • Double-sideband

    • Triple-sideband

    • Quadruple-sideband

    Correct Answer
    A. Single-sideband
    Explanation
    Single-sideband signals can be detected by reinserting the carrier frequency, which when heterodyned with the received signal, produces a sum and a difference output signal. The sum signal is eliminated, leaving only the difference signal, which corresponds to the original modulating signal. This process allows for efficient transmission of signals by eliminating redundant information and reducing bandwidth requirements.

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  • 27. 

    The predominant characterisic of single-sideband modulation is that ___________.

    • All of the transmitter power can be used for the transmission of the information signal located in one sideband without a carrier.

    • It allows multiple links to be spanned over a trunk, thus saving multiple circuits from having to be run.

    • It modulates the signals faster than all forms of modulation.

    • It divides the modulated signal into two sidebands thus allowing more information to be sent.

    Correct Answer
    A. All of the transmitter power can be used for the transmission of the information signal located in one sideband without a carrier.
    Explanation
    Single-sideband modulation is a technique that allows for efficient use of transmitter power by transmitting only one sideband of the modulated signal, while eliminating the carrier and the other sideband. This means that all of the transmitter power can be dedicated to transmitting the information signal located in one sideband, resulting in increased power efficiency. By eliminating the carrier and one sideband, single-sideband modulation allows for more efficient use of bandwidth as well.

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  • 28. 

    The only basic waveform in nature is a pure _____ wave; any other waveform is a "composite" or "resultant" wave.

    • Sine

    • Cosine

    • Tangent

    • Unmodulated

    Correct Answer
    A. Sine
    Explanation
    The correct answer is sine because a sine wave is the only basic waveform in nature. Any other waveform is a combination or result of multiple sine waves. Sine waves are commonly found in natural phenomena such as sound waves, electromagnetic waves, and oscillations in physical systems. They have a smooth and periodic oscillating pattern, making them fundamental in understanding and analyzing wave behavior.

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  • 29. 

    What term do we use for the additional sidebands that cause unwanted bandwidth and distortion in the transmitted AM signal?

    • Splatter

    • Noise

    • Emanations

    • Bad Sidebands

    Correct Answer
    A. Splatter
    Explanation
    Splatter refers to the additional sidebands that cause unwanted bandwidth and distortion in the transmitted AM signal. These sidebands can result from various factors such as nonlinearities in the transmitter, improper modulation, or interference. Splatter can lead to poor signal quality and interference with other nearby frequencies, affecting the overall performance of the transmission.

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  • 30. 

    In ____, the amplitude of the modulated wave does not change---only the frequency is varied.

    • Frequency Modulation

    • Amplitude Modulation

    • Phase Modulation

    • Varied Modulation

    Correct Answer
    A. Frequency Modulation
    Explanation
    Frequency modulation (FM) is a type of modulation in which the frequency of the carrier wave is varied according to the amplitude of the modulating signal. In FM, the amplitude of the modulated wave remains constant while only the frequency changes. This means that as the amplitude of the modulating signal increases, the frequency of the carrier wave also increases, and vice versa. FM is commonly used in radio broadcasting as it provides better noise immunity and signal quality compared to other modulation techniques.

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  • 31. 

    In _____, the information is represented by instantaneous variations in the phase of the carrier wave.

    • Phase Modulation

    • Frequency Modulation

    • Amplitude Modulation

    • Instantaneous Modulation

    Correct Answer
    A. Phase Modulation
    Explanation
    Phase modulation is a method of modulating a carrier wave where the information is represented by instantaneous variations in the phase of the carrier wave. This means that the phase of the carrier wave is changed in accordance with the input signal, allowing for the encoding and transmission of information. In phase modulation, the amplitude and frequency of the carrier wave remain constant, making it different from amplitude modulation and frequency modulation.

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  • 32. 

    In FM, the _______ used to establish the carrier frequency is made to change above and below the carrier frequency with each cycle of the intelligence waveform to produce the modulated wave.

    • Oscillator

    • Quantizer

    • Compander

    • Modulator

    Correct Answer
    A. Oscillator
    Explanation
    In FM (Frequency Modulation), the carrier frequency is established by an oscillator. The oscillator is designed to change above and below the carrier frequency with each cycle of the intelligence waveform. This variation in frequency is what produces the modulated wave in FM.

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  • 33. 

    In FM, the modulating signal causes the oscillator to change frequency. How much the oscillator changes frequency is directly proportional to the amplitude of the modulating signal. The larger the modulating signal voltage, the greater is the deviation. The common term for this is __________. __________ is proportional to the amount (amplitude) of the modulating signal.

    • Amount of Deviation

    • Amount of Change

    • Amount of Difference

    • Amount of Signal

    Correct Answer
    A. Amount of Deviation
    Explanation
    The correct answer is "Amount of Deviation". In FM, the modulating signal causes the oscillator to change frequency, and the amount of frequency change is directly proportional to the amplitude of the modulating signal. This is commonly referred to as the "Amount of Deviation".

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  • 34. 

    ____________ in FM is proportional to the cycle rate (frequency) of the modulating signal.

    • Rate of Deviation

    • Rate of Change

    • Rate of Frequency

    • Rate of Cycles

    Correct Answer
    A. Rate of Deviation
    Explanation
    In frequency modulation (FM), the rate of deviation refers to how much the carrier frequency is varied in response to the modulating signal. The greater the rate of deviation, the more the carrier frequency is changed, resulting in a wider frequency range for the FM signal. Therefore, the rate of deviation is directly proportional to the cycle rate or frequency of the modulating signal. As the modulating signal's frequency increases, the rate of deviation also increases, leading to a higher frequency variation in the FM signal.

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  • 35. 

    In FM, who establishes the amount of deviation?

    • Federal Communications Commission

    • The user

    • The deviation necessary to complete the modulation

    • Government

    Correct Answer
    A. Federal Communications Commission
    Explanation
    The Federal Communications Commission (FCC) establishes the amount of deviation in FM. The FCC is a government agency responsible for regulating communication technologies, including radio broadcasting. In the context of FM modulation, deviation refers to the maximum amount by which the carrier frequency can vary from its original frequency. The FCC sets standards and guidelines for FM broadcasting, including the maximum allowable deviation, to ensure that radio signals are transmitted within the allocated frequency spectrum and do not interfere with other radio services.

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  • 36. 

    The frequency during the constant amplitude portion of each alternation is the ______ frequency.

    • Rest

    • Amplitude

    • Portion

    • Phase

    Correct Answer
    A. Rest
    Explanation
    During the constant amplitude portion of each alternation, the frequency remains unchanged or at rest. This means that the frequency does not fluctuate or vary during this period.

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  • 37. 

    The amount of phase shift is proportional to the ________ of the modulating signal.

    • Amplitude

    • Frequency

    • Phase

    • Rate

    Correct Answer
    A. Amplitude
    Explanation
    The amount of phase shift is proportional to the amplitude of the modulating signal. This means that as the amplitude of the modulating signal increases, the phase shift also increases. Phase shift refers to the delay or advancement of a waveform in relation to a reference waveform. In modulation, the modulating signal affects the phase of the carrier signal, causing it to shift. Therefore, the greater the amplitude of the modulating signal, the greater the effect on the phase of the carrier signal.

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  • 38. 

    The rate of phase shift is porportional to the _________ of the modulating signal.

    • Frequency

    • Amplitude

    • Phase

    • Amount

    Correct Answer
    A. Frequency
    Explanation
    The rate of phase shift is directly proportional to the frequency of the modulating signal. This means that as the frequency of the modulating signal increases, the rate at which the phase shifts also increases. Conversely, if the frequency of the modulating signal decreases, the rate of phase shift will also decrease. This relationship between the rate of phase shift and the frequency of the modulating signal is an important concept in signal processing and modulation techniques.

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  • 39. 

    The output of a PM modulated signal also varies in amplitude. Therefore, the signal is fed to a ______ to remove amplitude variations and maintain the phase shift only.

    • Clipper

    • Modulator

    • Changer

    • Transformer

    Correct Answer
    A. Clipper
    Explanation
    A clipper is used to remove amplitude variations from a PM modulated signal and maintain the phase shift only. By limiting the amplitude of the signal, the clipper ensures that only the desired phase information is preserved, while any variations in amplitude are eliminated. This helps in maintaining the integrity of the phase modulation and allows for accurate demodulation of the signal. A modulator, changer, or transformer are not suitable options for this purpose.

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  • 40. 

    The big advantage of PM over FM is that this circuit uses a _______-controlled oscillator to maintain a stable carrier frequency.

    • Crystal

    • User

    • CPU

    • Uranium

    Correct Answer
    A. Crystal
    Explanation
    The correct answer is Crystal. In frequency modulation (FM), the carrier frequency is generated by a voltage-controlled oscillator (VCO), which can be less stable compared to a crystal-controlled oscillator. On the other hand, phase modulation (PM) uses a crystal-controlled oscillator to maintain a stable carrier frequency. Crystals are known for their high stability and accuracy in generating frequencies, making them a preferred choice in applications where precise frequency control is required.

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  • 41. 

    In FM, the oscillator cannot be crystal controlled, since it is actually made to vary in frequency. That means that an FM oscillator requires a complex _______ circuit to achieve the same degree of stability.

    • Automatic Frequency Control (AFC)

    • Frequency Oscillator (FO)

    • Automated Oscillator (AO)

    • Automated Control Facilitator (ACF)

    Correct Answer
    A. Automatic Frequency Control (AFC)
    Explanation
    In FM, the oscillator needs to vary in frequency, so it cannot be crystal controlled like in other types of oscillators. To ensure stability, an FM oscillator requires a complex circuit called Automatic Frequency Control (AFC). This circuit automatically adjusts the frequency of the oscillator to maintain a stable output.

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  • 42. 

    The important thing to remember about the difference between FM and indirect FM is that modulation occurs at the oscillator stage in FM, while it occurs in a stage _____ the oscillator in indirect FM.

    • After

    • Before

    • During

    • Later

    Correct Answer
    A. After
    Explanation
    In FM, modulation occurs at the oscillator stage, meaning that the frequency of the carrier wave is directly varied by the modulating signal. On the other hand, in indirect FM, modulation occurs after the oscillator stage. This means that the frequency of the carrier wave is first generated by the oscillator and then modulated by the modulating signal. Therefore, the correct answer is "After."

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  • 43. 

    What is one distinct advantage of BPSK?

    • Its insensitivity to level variations.

    • It has a smaller overhead.

    • It is faster than other variation of phase-shift keying.

    • It is less complex than other variations of phase-shift keying.

    Correct Answer
    A. Its insensitivity to level variations.
    Explanation
    BPSK (Binary Phase Shift Keying) has the distinct advantage of being insensitive to level variations. This means that even if the signal strength or amplitude fluctuates, the receiver can still accurately detect and decode the transmitted data. This insensitivity to level variations makes BPSK more robust and reliable in noisy or fading channel conditions. It allows for better performance and reduces the chances of errors in the received signal.

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  • 44. 

    All communication paths show some phase drifts and other kinds of disturbances such as impulse noise, electrical storms, and so forth. These minor and major disturbances create another major problem of PM, ________. If the signal is momentarily interrupted for any reason, the receiver has no way of knowing whether the first data pulse received after the interruption is the reference phase, or whether it represents a mark or a space.

    • Phase Ambiguity

    • Phase Loss

    • Phase Confusion

    • Phase Differential

    Correct Answer
    A. Phase Ambiguity
    Explanation
    The major problem of PM mentioned in the passage is that if the signal is momentarily interrupted, the receiver cannot determine whether the first data pulse received after the interruption is the reference phase or represents a mark or a space. This uncertainty or lack of clarity in determining the phase of the signal is referred to as phase ambiguity.

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  • 45. 

    The two main reasons for _________, despite its complexity, are as follows: 1. A ______ signal is not as seriously degraded as a bi-phase signal when passed through a nonlinear device simultaneously with interference. 2. The RF bandwidth for a _____ signal is half that required by a bi-phase signal, given the same data rate. Alternatively, twice as much data might be transmitted in the same bandwidth with a ______ signal as with a bi-phase signal.

    • Quadriphase (QPSK)

    • Frequency Modulation (FM)

    • Amplitude Modulation (AM)

    • Phase Modulation (PM)

    Correct Answer
    A. Quadriphase (QPSK)
    Explanation
    The two main reasons for choosing Quadriphase (QPSK), despite its complexity, are as follows:

    1. A QPSK signal is not as seriously degraded as a bi-phase signal when passed through a nonlinear device simultaneously with interference. This means that QPSK is more robust and can handle interference better than bi-phase signals.

    2. The RF bandwidth for a QPSK signal is half that required by a bi-phase signal, given the same data rate. Alternatively, twice as much data might be transmitted in the same bandwidth with a QPSK signal as with a bi-phase signal. This means that QPSK is more efficient in terms of bandwidth utilization and allows for higher data transmission rates.

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  • 46. 

    In QPSK, if a "10" is transmitted, how many degrees will the phase shift?

    • 0

    • 90

    • 270

    • 180

    Correct Answer
    A. 270
    Explanation
    In QPSK (Quadrature Phase Shift Keying), the phase shift for a transmitted "10" is 270 degrees. QPSK is a modulation scheme that uses four different phase shifts (0, 90, 180, and 270 degrees) to represent different combinations of bits. In this case, the "1" is represented by a 180-degree phase shift, and the "0" is represented by a 270-degree phase shift. Therefore, when a "10" is transmitted, it will have a phase shift of 270 degrees.

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  • 47. 

    In DPSK, information is not represented by an absolute phase value but by a _______ in phase value.

    • Change

    • Jump

    • Reverse

    • Timing Source

    Correct Answer
    A. Change
    Explanation
    In DPSK (Differential Phase Shift Keying), information is represented by a change in phase value rather than an absolute phase value. This means that instead of directly encoding the phase of the signal, DPSK encodes the difference in phase between consecutive symbols. By detecting these changes in phase, the receiver can decode the transmitted information. Therefore, the correct answer is "Change" as it accurately describes how information is represented in DPSK.

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  • 48. 

    The information-carrying components that occur on either side of a carrier are called _______.

    • Sidebands

    • Sine Waves

    • Frequency Translators

    • Modulating Frequencies

    Correct Answer
    A. Sidebands
    Explanation
    The correct answer is "Sidebands". In a communication system, sidebands refer to the additional frequency components that are produced when a carrier signal is modulated with information. These sidebands carry the encoded information and occur on either side of the carrier frequency. They are essential for transmitting and receiving signals accurately. Sine waves are basic periodic waveforms and not specifically related to information-carrying components. Frequency translators are devices used for frequency conversion, and modulating frequencies are the frequencies used to modulate a carrier signal, but they do not specifically refer to the components occurring on either side of the carrier.

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  • 49. 

    In PAM, the results of this analysis show that a rectangular pulse train contains many frequencies. The frequencies are all multiples of the fundamental frequency of the pulse train, f(o), which is equal to the reciprocal of the period, T(p), of the wave and expressed by the equation: f(o) = 1 / T(p).

    • Fourier Analysis

    • Johnson Analysis

    • Einstein Analysis

    • Douglas Analysis

    Correct Answer
    A. Fourier Analysis
    Explanation
    The given explanation states that in PAM (Pulse Amplitude Modulation), the analysis of a rectangular pulse train reveals that it contains multiple frequencies. These frequencies are all multiples of the fundamental frequency of the pulse train, which is equal to the reciprocal of the period of the wave. This concept is known as Fourier Analysis, which is a mathematical technique used to decompose a complex waveform into its constituent frequencies. Therefore, the correct answer is Fourier Analysis.

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  • Current Version
  • Mar 20, 2023
    Quiz Edited by
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  • Apr 02, 2013
    Quiz Created by
    Esshlman

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