Question 1

_________ is assigning one of a fixed number of numerical values to each pulse.
A)Coding
B)Sampling
C)Quantizing
D)Decoding

Accepted Answer

Quantizing is the process of assigning one of a fixed number of numerical values to each pulse. Coding is the process of converting analog signals to digital signals, sampling refers to the process of taking periodic samples of an analog signal, and decoding refers to the process of converting digital signals back to analog signals.

Question 2

What is the chief disadvantage of analog communication?
A)Simplicity
B)Bandwidth requirements
C)Susceptibility to noise
D)Cost

Accepted Answer

Analog communication systems are more susceptible to noise and interference compared to digital systems. This is because any slight change in the signal, due to noise, can significantly affect the quality of the information being transmitted.

Question 3

Which of the following did Harry Nyquist in 1928 first demonstrate mathematically?
A)An analog signal can be reconstructed from periodic samples.
B)Pulses can be time-division multiplexed over a single communication channel.
C)The sample rate must be at least twice the highest frequency of the intelligence or information signal to be sampled.
D)Analog signals are quantized to the closest binary value provided in the digitizing system.

Accepted Answer

A

Question 4

What technique do Reed-Solomon (RS)codes employ to enable the system to correct multiple data-bit errors?
A)Aliasing
B)Amplitude companding
C)Natural sampling
D)Interleaving

Accepted Answer

Reed-Solomon codes employ the interleaving technique to enable the system to correct multiple data-bit errors. The interleaving technique rearranges the data bits in a way that makes it possible to correct bursts of errors in the signal, which is especially useful in channels affected by noise or interference. Aliasing, amplitude companding, and natural sampling are not techniques used by Reed-Solomon codes to correct errors.

Question 5

PCM is a building block in many digital communication applications and consists of three steps: sampling,quantizing,and __________.
A)decoding
B)coding
C)error-detection
D)retransmission

Accepted Answer

After the analog signal is sampled and quantized, it is encoded into a stream of digital bits, making coding the next step in PCM. Decoding comes later, when the digital signal is received and must be converted back into an analog signal. Error-detection and retransmission are not steps in PCM.

Question 6

What is the primary advantage of the flash ADC?
A)It uses little power.
B)It's simplicity.
C)It is inexpensive.
D)It is very fast.

Accepted Answer

The primary advantage of the flash ADC is its speed. It can provide high-speed conversion and simultaneous sampling of multiple channels. However, it requires a large number of comparators and consumes more power than other ADC architectures.

Question 7

What function does the sample-and-hold circuit perform in a PCM system?
A)Encoder
B)Modulator
C)Filter
D)Decoder

Accepted Answer

The sample-and-hold circuit performs the function of the modulator in a PCM system. It holds the analog signal at each sampling instant, which is then quantized and encoded into digital pulses, thereby converting the analog signal into a digital format. The modulator is responsible for converting the analog signal into digital pulses, and the sample-and-hold circuit is an essential component of the modulator. Therefore, option B is the correct choice.

Question 8

In what terms is dynamic range typically expressed?
A)Decibels
B)Bits
C)Ohms
D)Farads

Accepted Answer

Dynamic range is typically expressed in decibels. Decibels are a logarithmic unit used to measure the ratio of two values, such as the ratio between the loudest and softest sounds that can be captured by a microphone or reproduced by a speaker.

Question 9

With codes and data,error detection is accomplished through some form of ___________.
A)redundancy
B)modulation
C)coding
D)quantization

Accepted Answer

Redundancy is the technique used in error detection, where extra bits are added to the data in order to identify and correct any errors that may occur during transmission. This redundancy facilitates accurate data transfer and ensures that data integrity is maintained.

Question 10

Why do high-quality capacitors have polyethylene,polycarbonate,or Teflon dielectrics?
A)They minimize voltage variations resulting from capacitor characteristics.
B)They limit the maximum input frequency that the S/H circuit can accurately process.
C)They convert quantized waveforms into stepped analog signals.
D)They isolate the input signal from the S/H circuit and provide proper impedance matching.

Accepted Answer

Polyethylene, polycarbonate, and Teflon dielectrics have a low dielectric absorption and high insulation resistance, which result in minimizing voltage variations and maintaining a stable capacitance over time, making them ideal for high-quality capacitors used in applications that require precise and stable voltage values.

Question 11

What is required to increase the resolution of a digitizing system?
A)The number of quantization levels to be increased.
B)The aperture and acquisition times must limit the maximum input frequency.
C)The maximum input or output voltage level to the smallest voltage level be quantized and/or reproduced by the converters.
D)The input amplitude must be increased with reference to the quantizing error.

Accepted Answer

Increasing the number of quantization levels will increase the resolution of a digitizing system by allowing for more precise measurements and representations of the input signal.

Question 12

Techniques that allow correction at the receiver are called forward error-correcting codes.Which of the following is an example of an FEC?
A)Nyquist
B)Hamming
C)Schmitt
D)Fourier

Accepted Answer

Hamming code is an example of a forward error-correcting code (FEC) that is commonly used for error correction in data communication. Nyquist is a sampling theorem, Schmitt is a type of trigger circuit, and Fourier is a mathematical theory for analyzing signals.

Question 13

Conversion of the digital word to analog form consists of three steps: regeneration,decoding,and _______________.
A)modulation
B)reconstruction
C)distortion
D)substitution

Accepted Answer

After the digital signal is converted back to the analog domain through regeneration and decoding, the final step is to reconstruct the original analog waveform. This is done through a process called reconstruction, where the discrete-time signal is transformed into a continuous-time signal. The reconstructed analog waveform is an approximation of the original analog signal and usually requires smoothing or filtering to remove any high-frequency distortion. Therefore, option B, "reconstruction," is the correct answer. Options A, modulation, C, distortion, and D, substitution, are not relevant to this transformation process.

Question 14

What concept is represented by noise corrupted signals being periodically restored to their original values recreating an ideal,perfect representation of data at regular intervals and enabling transmissions over long distances?
A)Regeneration
B)Coding
C)Pulse modulation
D)DSP processing

Accepted Answer

The concept described in the question is regeneration, which involves periodically restoring signals to their original values to create an ideal representation of data. This enables efficient transmissions over long distances by reducing the impact of noise and other distortions. Coding, pulse modulation, and DSP processing are all related concepts, but they do not specifically address the issue of signal regeneration.

Question 15

The process of ____________ is one of reproducing the original analog signal.
A)coding
B)modulation
C)demodulation
D)aliasing

Accepted Answer

Demodulation is the process of obtaining the original analog signal from a modulated waveform. The other options, coding and modulation, involve transforming the original signal into a different form, and aliasing refers to distorting the original signal during the sampling process.

Question 16

Which of the following allows complex,periodic waveforms to be broken down into a series of sine and cosine terms?
A)Flat-top sampling
B)Quantization
C)Reconstruction
D)Fourier analysis

Accepted Answer

Fourier analysis allows for the decomposition of complex, periodic waveforms into a series of sine and cosine terms through the use of Fourier series and transforms. Flat-top sampling is a method of signal processing used to reduce noise, quantization is the process of converting continuous analog signals into discrete digital signals, and reconstruction is the process of converting digital signals back into analog signals.

Question 17

In _______________,the pulse amplitude is made proportional to the amplitude of the modulating signal.
A)pulse-width modulation (PWM)
B)pulse-amplitude modulation (PAM)
C)pulse-position modulation (PPM)
D)pulse-code modulation (PCM)

Accepted Answer

Pulse-amplitude modulation (PAM) is a modulation technique in which the amplitude of the pulse signal is varied in accordance with the amplitude of the modulating signal. This ensures that the information or signal transmitted is properly conveyed to the receiver end without any distortions. The other options, PWM, PPM, and PCM, have different mechanisms of modulation and are not specifically based on the amplitude of the modulating signal.

Question 18

Which of the following forms the basis for class D power amplification?
A)PCM
B)PPM
C)PAM
D)PWM

Accepted Answer

Class D power amplification uses PWM (Pulse Width Modulation) as the basis. This involves rapidly switching the input signal on and off to create a pulse train, which is then amplified to drive the load. This method is very efficient and commonly used in audio amplifiers.

Question 19

Analog signals are quantized to the closest _________ value provided in the digitizing system.
A)waveform
B)bit
C)binary
D)pulse

Accepted Answer

Analog signals are quantized to the closest binary value provided in the digitizing system because the process of digitization involves converting the continuous range of the analog signal into a finite number of discrete values, which are represented in binary form.

Question 20

What is the most common method of error detection?
A)Block check character
B)CRC dividing circuit
C)Parity
D)Cyclic redundancy check

Accepted Answer

Parity is the most common method of error detection. In this method, an extra bit, known as a parity bit, is added to the end of each byte or group of bytes to check whether the transmitted data has been received correctly or not. This method is simple and can detect errors in single-bit transmissions.

Quiz 7: Digital Communications Techniques

_________ is assigning one of a fixed number of numerical values to each pulse.

What is the chief disadvantage of analog communication?

Which of the following did Harry Nyquist in 1928 first demonstrate mathematically?

What technique do Reed-Solomon (RS) codes employ to enable the system to correct multiple data-bit errors?

PCM is a building block in many digital communication applications and consists of three steps: sampling,quantizing,and __________.

What is the primary advantage of the flash ADC?

What function does the sample-and-hold circuit perform in a PCM system?

In what terms is dynamic range typically expressed?

With codes and data,error detection is accomplished through some form of ___________.

Why do high-quality capacitors have polyethylene,polycarbonate,or Teflon dielectrics?

What is required to increase the resolution of a digitizing system?

Techniques that allow correction at the receiver are called forward error-correcting codes.Which of the following is an example of an FEC?

Conversion of the digital word to analog form consists of three steps: regeneration,decoding,and _______________.

What concept is represented by noise corrupted signals being periodically restored to their original values recreating an ideal,perfect representation of data at regular intervals and enabling transmissions over long distances?

The process of ____________ is one of reproducing the original analog signal.

Which of the following allows complex,periodic waveforms to be broken down into a series of sine and cosine terms?

In _______________,the pulse amplitude is made proportional to the amplitude of the modulating signal.

Which of the following forms the basis for class D power amplification?

Analog signals are quantized to the closest _________ value provided in the digitizing system.

What is the most common method of error detection?