Software Defined Radio Questions and Answers – RF and IF Processing Tradeoffs – 1

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This set of Software Defined Radio Multiple Choice Questions & Answers (MCQs) focuses on “”.

1. Which of the following is not present in the conversion stages of super heterodyne receiver?
a) Local oscillator
b) Additional filter
c) Step attenuator
d) Amplifier
View Answer

Answer: c
Explanation: Each conversion stage of super heterodyne receiver has one LO, additional filters and amplifiers. Step attenuator is present after the pre-selector filters. It confines the total power at the input of first conversion stage within its linear range.

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2. Which of the following is used in base station applications?
a) Super heterodyne receiver
b) Direct conversion receiver
c) Digital-RF receiver
d) Homodyne receiver
View Answer

Answer: a
Explanation: Super heterodyne receiver is used in base station applications. Direct conversion receiver is used in handsets. Digital-RF receiver performs demodulation at RF.

3. Direct conversion receiver is a heterodyne receiver.
a) True
b) False
View Answer

Answer: b
Explanation: The direct conversion receiver is a homodyne receiver which may use non-zero baseband center frequency.
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4. Which of the following is a challenge for direct conversion receiver?
a) GaAs circuitry
b) CMOS circuitry
c) LO leakage and DC bias
d) Difference between CMOS and GaAs circuitry
View Answer

Answer: c
Explanation: LO leakage and DC bias are a challenge for wide band digital signal processing using direct conversion receiver.

5. In which technique RF is amplified until it is hard-limited into a square wave?
a) Super heterodyne receiver
b) One-bit direct conversion digital receiver
c) Two-bit direct conversion digital receiver
d) Phase crossing counter receiver
View Answer

Answer: b
Explanation: One-bit direct conversion digital receiver amplifies RF until it is hard limited into a square wave. An advantage of this architecture is that the channel states are stored in lookup tables.
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6. When ____ of N zero crossings count becomes small, a signal is considered to be present.
a) mean
b) correlation
c) standard deviation
d) variance
View Answer

Answer: d
Explanation: When zero crossings are simply counted, a small variance of N zero crossings indicate a signal to be present. A disadvantage of this technique is the presence of high speed logic and lack of equalization.

7. Which of the following is not used to control interference at RF?
a) Programmable digital notch filters
b) Active cancellation
c) Frequency separation
d) Antenna separation
View Answer

Answer: a
Explanation: Physical antenna separation, frequency separation, programmable analog notch filters and active cancellation are the steps used to control interference at RF.
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8. The ______ of out-of-band signal with bandpass characteristic of the receiver gives the interference in the receiver owing to out-of-band energy at the transmitter.
a) correlation
b) correlation and convolution
c) integral
d) convolution
View Answer

Answer: d
Explanation: The convolution of out-of-band signal with bandpass characteristic of the receiver gives the interference in the receiver owing to out-of-band energy at the transmitter.This type of interference can affect the roll-offs. Frequency separation is employed to suppress this type of interference.

9. ____ separates uplink and downlink.
a) Frequency Division Duplexing
b) Time Division Duplexing
c) Frequency Division Multiplexing
d) Time Division Multiplexing
View Answer

Answer: a
Explanation: Frequency Division Duplexing separates uplink and downlink to minimize interference. SDR operating on TDD can create dynamic FDD nets by a protocol that dynamically defines uplink, downlink and frequency separation.
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10. A _____filter establishes maximum and minimum possible level for processing.
a) adaptive
b) flooring
c) roofing
d) content
View Answer

Answer: c
Explanation: A roofing filter establishes the maximum (roof) and minimum (floor) linearly possible level for processing. It is also referred to as co-site filter.

11. Which of the following is a characteristic to be possessed by a roofing filter?
a) Low insertion loss
b) Fixed bandwidth
c) High insertion loss and fixed bandwidth
d) High insertion loss
View Answer

Answer: a
Explanation: A roofing filter must have low insertion loss, programmable bandwidth and programmable center frequency for effective interference suppression.

12. Active cancellation is the process of introducing transmitted signal in the _____ for subtraction from the input signal.
a) transmitter
b) low pass filter
c) equalizer
d) receiver
View Answer

Answer: d
Explanation: Active cancellation is the processing of introducing transmitted signal in the receiver for subtraction from the input signal. It is a part of interference suppression process.

13. In active radar blanking, communication between RF stage and rest of the communication system is ___ while the control line is ____
a) on, inactive
b) off, inactive
c) off, active
d) on, absent
View Answer

Answer: b
Explanation: In active blanking, communication between RF stage and rest of the communication system is off while the control line is inactive. This is an example for active cancellation.

14. The required active cancellation is equal to ____ between the maximum non distorting input signal and the radiation level at the antenna.
a) half the difference
b) the difference
c) twice the difference
d) the correlation
View Answer

Answer: b
Explanation: The amount of active cancellation to be provided is equal to the difference between the maximum non distorting input signal and the radiation level at the antenna. It is also given by the ratio of peak energy at the output of the receiver antenna terminal to the maximum linear energy.

15. The number and characteristics of roofing filter are determined by modulation of the subscriber signal.
a) True
b) False
View Answer

Answer: a
Explanation: The modulation of the subscriber signal and bandwidth of the passband interference determine number and characteristics of roofing filter. The use of roofing filter establishes a noise floor and prevents dropped calls.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter