This set of Basic Software Defined Radio Questions and Answers focuses on “ADC Tradeoffs – 2”.
1. 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
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.
2. 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
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.
3. ____ 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
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.
4. 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
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.
5. 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
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.
6. 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
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.
7. 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
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.
8. 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
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.
9. 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
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.
10. 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
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.
11. 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
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.
12. 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
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
13. 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
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.
14. 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
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.
15. 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
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.
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