Question 1
____ and ____ are the parameters that define software defined radio applications.
A. Linearity, SNR
B. Dynamic range, SNR
C. Linearity, Dynamic range
D. Bandwidth, SNR
View Answer
Answer: Option C
Explanation:
Linearity and Dynamic range are the parameters that define software defined radio applications. SNR is measured to determine the dynamic range. The SNR and DNR value is computed from the antenna to end user.
Question 2
____, ____ and ____ must be properly matched for effective representation of input signal in quadrature sampling.
A. Modulators, signal paths, correlator
B. Signal paths, modulators, zero crossing detector
C. Low pass filters, zero crossing detector, correlator
D. Low pass filters, modulators, signal paths
View Answer
Answer: Option D
Explanation:
Low pass filters, modulators,and signal paths must be properly matched for effective representation of input signal in quadrature sampling. Amplitude mismatch, inconsistent time duration in filters may lead to degradation of complex signal.
Question 3
If Wais the receiver bandwidth and NF is the noise figure, the noise power of a noise limited receiver is given by the expression ____
A. Pm=-184dBm+10log(Wa)+NF
B. Pm=-174dBm+10log(Wa)+NF
C. Pm=-174dBm+10log(NF)+Wa
D. Pm=-184dBm+10log(NF)+Wa
View Answer
Answer: Option B
Explanation:
If Wa is the receiver bandwidth and NF is the noise figure, the noise power of a noise limited receiver is given by the expression Pm=-174dBm+10log(Wa)+NF. The noise power of the noise limited receiver must be matched to power of the least significant bit of ADC.
Question 4
In non-monotonic filters, attenuation increases with frequency.
A. True
B. False
View Answer
Answer: Option B
Explanation:
In monotonic filters, attenuation increases with frequency. Non-monotonic filter has less attenuation. It allows energy beyond the passband and exhibits phase distortion.
Question 5
In Nyquist sampling, the ____ frequency is ______to the duration of the observation interval.
A. maximum recoverable, proportional
B. minimum resolvable, inversely proportional
C. maximum recoverable, inversely proportional
D. minimum resolvable, proportional
View Answer
Answer: Option B
Explanation:
In Nyquist sampling, the maximum recoverable frequency is given by the expression fs/2. The minimum resolvable frequency is inversely proportional to the duration of the observation interval. The observation interval is given by the number of time domain points.
Question 6
Limited dynamic range in digital RF system can be improved by _____
A. digital filter
B. digital amplifier
C. digital equalizer
D. digital suppressor
View Answer
Answer: Option A
Explanation:
RF ADC has a high sampling rate and it oversamples the bandwidth of the signal. The oversampling gain increases the dynamic range with the help of digital integrating filters.
Question 7
Noise must be less than _____ of the ADC.
A. half of the LSB
B. LSB
C. half of the MSB
D. MSB
View Answer
Answer: Option A
Explanation:
The effect of aliasing, spurious response in IF/RF processing and other noise must be less than half of the least significant bit of the ADC. If this condition is satisfied, then all the bits of ADC give only the useful signal power.
Question 8
Quadrature sampling uses ____ to ____ the bandwidth available for a particular sampling rate.
A. integration, quadruple
B. complex numbers, quadruple
C. complex numbers, double
D. integration, double
View Answer
Answer: Option C
Explanation:
Quadrature sampling uses complex numbers to double the bandwidth available for a particular sampling rate. It is a polyphase filter. Real signals are combined with cosine and sine reference signal generated by a local oscillator.
Question 9
Signal to noise ratio is the preferred metric when ____
A. desired signal bandwidth is less than Nyquist bandwidth
B. desired signal bandwidth is approximately equal to Nyquist bandwidth
C. desired signal bandwidth is greater than Nyquist bandwidth
D. bandpass sampling is used
View Answer
Answer: Option B
Explanation:
Signal to noise ratio is the preferred metric for ADC performance when the desired signal bandwidth is approximately equal to Nyquist bandwidth. Radar matched filter is an example for this condition. The matched filter optimally operates with the square shape of the radar pulses.
Question 10
The NPR for an SDR can be determined by matching the radio noise floor to the ADC input noise level.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The SNR and DNR can be determined by matching the radio noise floor to the ADC input noise level. This imposes the design rule that the total noise power should be less than half of the least significant bit of ADC. The ratio of spectral density outside the notch filter to the maximum spectral density inside the notch filter gives the Noise Power Ratio.
Question 11
The point at which the output noise power of the fundamental signal shifts away from the ideal output power by 1-dB is called 1-dB expansion point.
A. True
B. False
View Answer
Answer: Option B
Explanation:
The increase in the third-order intermodulation product eventually results in the intersection of the fundamental signal with the power of third-order intermodulation product. This is referred as IP3. The output power of the fundamental signal saturates before IP3.The point at which the output noise power of the fundamental signal shifts away from the ideal output power by 1-dB is called 1-dB compression point.
Question 12
The point of intersection of the fundamental signal with the power of third-order intermodulation product is called as _____
A. input-referenced third-order intercept point
B. output-referenced third-order intercept point
C. input-referenced third-order intermodulation point
D. output-reference third-order intermodulation point
View Answer
Answer: Option A
Explanation:
The increase in the third-order intermodulation product eventually results in the intersection of fundamental signal with the power of third-order intermodulation product. This is referred as input-reference third-order intercept point (IP3). The output power of the fundamental signal saturates before IP3.
Question 13
The principle behind Sigma-Delta ADC is oversampling.
A. True
B. False
View Answer
Question 14
The ratio of ______ the notch filter to the ____ the notch filter gives the Noise Power Ratio.
A. maximum spectral density inside, spectral density outside
B. spectral density inside , maximum spectral density outside
C. spectral density outside, maximum spectral density inside
D. maximum spectral density outside, spectral density inside
View Answer
Answer: Option C
Explanation:
The ratio of spectral density outside the notch filter to the maximum spectral density inside the notch filter gives the Noise Power Ratio. Noise Power Ratio is the preferred metric when the number of narrow band channels in the signal spectrum is high. It is measured by flooding the Nyquist bandwidth with white noise.
Question 15
The sampling rate of promising SDR technology ranges between _____
A. 1 MHz – 100 MHz
B. 10 MHz – 100 MHz
C. 1 MHz – 1 GHz
D. 1 MHz – 10 GHz
View Answer
Answer: Option B
Explanation:
The sampling rate of promising SDR technology ranges between 10 MHz – 100 MHz. The resolution falls in the range of 30 dB– 60 dB. Frequency division multiplexing uses few MHz IF-bandwidth. PCM, cellular band allocation, 3G, and air navigation signals use hundreds of MHz.
Question 16
The shape factor of an anti-aliasing filter is given by the ratio of the frequency at ___ dB attenuation point to the frequency at ___ dB point.
A. 80, 3
B. 3, 80
C. -80, -3
D. -3, -80
View Answer
Answer: Option C
Explanation:
Anti -aliasing filters require large shape factor for suppression of signals closer to the upper band-edge of ADC passband. The shape factor of an anti-aliasing filter is given by the ratio of the frequency at -80 dB attenuation point to the frequency at -3 dB point.
Question 17
To avoid aliasing, the wideband ADC is ____ by anti-aliasing filters to suitably alter the _____ waveform.
A. succeeded, digital
B. preceded, digital
C. succeeded, analog
D. preceded, analog
View Answer
Answer: Option D
Explanation:
Aliasing prevents faithful restoration of the signal. To avoid aliasing, the wideband ADC is preceded by anti-aliasing filters to suitably alter the analog waveform. The filters must have satisfactory stop-band attenuation.
Question 18
Which among the following filters has the slowest roll-off?
A. Cauer
B. Chebychev
C. Butterworth
D. Bessel
View Answer
Answer: Option D
Explanation:
Bessel function has the slowest roll-off factor among the four filters. The approximate value of shape factor is 6. It is a monotonic filter.
Question 19
Which of the following applications takes only SFDR as its performance metric?
A. Spread spectrum access
B. Wideband digital receiver
C. Cellular Phone
D. Spectrum analysis
View Answer
Answer: Option B
Explanation:
Spurious Free Dynamic Range is used in wideband digital receiver to quantify the reliability of detection of weak signals in the presence of strong in-band interference.
Question 20
Which of the following conditions does not affect SNR?
A. Small signals in an environment of strong interference
B. Wide band channelized receiver
C. High fidelity instrumentation
D. High dynamic range
View Answer
Answer: Option D
Explanation:
SNR is affected by small signals in an environment of strong interference in spread spectrum technique. Wide band channelized receiver affect SNR in Mobile Cellular applications. In spectrum analysis, SNR is influenced by high-fidelity instrumentation
Question 21
Which of the following expressions give the relation between power and quantization step size (q)?
A. p=q2/2R
B. p=q/2R
C. p=q2/R
D. p=q2*2R
View Answer
Answer: Option A
Explanation:
p=q2/2R is the relation between power and quantization step size. R is the input resistance.
Question 22
Which of the following expressions give the SNR at the output of ADC?
A. SNR=6.02*B+1.76+10log(fs/2fmax)
B. SNR=6.02*B+1.76+10log(2fmax/fs)
C. SNR=12.04*B+1.76+10log(2fmax/fs)
D. SNR=6.02*B+1.76
View Answer
Answer: Option A
Explanation:
SNR=6.02*B+1.76+10log(fs/2fmax) is the expression for SNR at the output of ADC. B is the number of bits. fs is the sampling frequency. fmax is the maximum frequency component of the signal.
Question 23
Which of the following influences the spurious free dynamic range?
A. Second-order intercept
B. Second-order intermodulation product
C. Third-order intercept
D. Third-order intermodulation product
View Answer
Answer: Option D
Explanation:
The point at which the output noise level is tangential to the power of the third-order intermodulation product of ADC determines the spurious free dynamic range of ADC.
Question 24
Which of the following is not a characteristic of DAC?
A. Linearity
B. Level conversion
C. Grounding
D. Sample and hold circuit
View Answer
Answer: Option D
Explanation:
DAC does not use sample and hold circuit. However it does make use of setup and hold circuit which is similar to sample and hold circuit. Linearity, level conversion, grounding, and isolation of digital from analog waveform are characteristics of a DAC.
Question 25
Which of the following is not a characteristic of IC implementation of quadrature sampling ADC?
A. Thermal difference is less than lumped components
B. Matching of passive component on IC substrate is easy
C. Matching of passive component on IC substrate is difficult
D. Thermal difference among filters is not large
View Answer
Answer: Option C
Explanation:
The integrated circuit implementation of quadrature sampling ADC is effective because of short signal paths, easy matching of passive components on IC substrate and low thermal difference among filters.
Question 26
Which of the following is not a part of traditional RF subsystems?
A. Filter
B. Low noise amplifier
C. Multiplexer
D. Frequency translation
View Answer
Answer: Option C
Explanation:
The traditional RF subsystems comprise of preamplifier, low noise amplifier, filters, RF distribution, frequency translation, and filtering stages that convert RF signals to IF signals. Multiplexer is used in digital RF systems.
Question 27
Which of the following is the first step in establishing acceptable aliasing power?
A. Establish the relation between CIR and BER
B. Fix BER threshold
C. Convert BER threshold to CIR threshold
D. Apply the instantaneous dynamic range requirement of ADC
View Answer
Answer: Option B
Explanation:
The first step in establishing acceptable aliasing power is to fix the BER threshold based on QOS requirements of the waveform. The second step is to establish a relationship between CIR and BER. Then the BER threshold is converted to CIR threshold. The fourth and the final step is to apply the instantaneous dynamic range requirement of ADC.
Question 28
Which of the following is the preferred metric when the desired signal bandwidth is less than Nyquist bandwidth?
A. Noise Power Ratio
B. Spurious Free Dynamic Range (SFDR)
C. Full Power Analog Input Bandwidth
D. Half Power Analog Input Bandwidth
View Answer
Answer: Option B
Explanation:
Spurious Free Dynamic Range is the preferred metric when the desired signal bandwidth is less than Nyquist bandwidth. First generation cellular base station is an example for this condition. The AMPS signal is much smaller in bandwidth when compared to the spectrum allocation accessed by a cell site ADC.
Question 29
Which of the following is untrue about Sigma-Delta ADC?
A. fs>2fmax
B. Zero crossing detector consists of a sample and hold circuit
C. Aperture jitter is minimized due to integration
D. The integrating filter is preceded by a zero crossing detector
View Answer
Answer: Option B
Explanation:
Sigma-Delta ADC does not require a sample and hold circuit. The zero-crossing detector can be implemented by threshold logic.
Question 30
Which of the following metrics is considered for spread spectrum method?
A. SNR
B. SNR, SFDR
C. SNR, SFDR, NPR
D. SNR, NPR
View Answer
Answer: Option C
Explanation:
Spread spectrum uses SNR, SFDR and NPR for performance analysis. SNR is affected by small signals in an environment of strong interference. SFDR is degraded due to spatial filtering. NPR is affected by inter-channel cross talk.