Digital Communications Multiple Choice Questions on “Pseudo-noise sequence and jamming”.
1. Pseudorandom signal ________ predicted.
A. Can be
B. Cannot be
C. maybe
D. None of the mentioned
Answer: A
Clarification: Random signals cannot be predicted whereas pseudorandom sequence can be predicted.
2. The properties used for pseudorandom sequence are
A. Balance
B. Run
C. Correlation
D. All of the mentioned
Answer: D
Clarification: The three basic properties that can be applied for pseudorandom sequence are balance, run and correlation properties.
3. The shift register needs to be controlled by clock pulses.
A. True
B. False
Answer: A
Clarification: The shift register operation is controlled by clock pulses.
4. A linear feedback shift register consists of
A. Feedback path
B. Modulo 2 adder
C. Four stage register
D. All of the mentioned
Answer: D
Clarification: A linear feedback shift register consists of four stage register for storage and shifting, modulo 2 adder and feedback path.
5. If the initial pulse of 1000 is fed to shift register, after how many clock pulses does the sequence repeat?
A. 15
B. 16
C. 14
D. 17
Answer: A
Clarification: If the initial pulse 1000 is given to shift register, the foregoing sequence repeats after 15 clock pulses.
6. The sequences produced by shift register depends on
A. Number of stages
B. Feedback tap connections
C. Initial conditions
D. All of the mentioned
Answer: D
Clarification: The sequences produced by shift register depends on the number of stages, the feedback tap connections and initial conditions.
7. For maximal length sequence, the sequence repetition clock pulses p is given by
A. 2n + 1
B. 2n -1
C. 2n
D. None of the mentioned
Answer: B
Clarification: For maximal length sequence, produced by n stage linear feedback shift register the sequence repetition clock pulses p is given by 2n -1 .
8. For any cyclic shift, the auto-correlation function is equal to
A. 1/p
B. -1/p
C. –p
D. p
Answer: B
Clarification: For any cyclic shift the auto-correlation function is equal to -1/p.
9. Which method is better?
A. To share same bandwidth
B. To share different bandwidth
C. To share same & different bandwidth
D. None of the mentioned
Answer: B
Clarification: If the jammer noise shares the same bandwidth, the result could be destructive.
10. Pulse jammer consists of
A. Pulse modulated excess band noise
B. Pulse modulated band-limited noise
C. Pulse width modulated excess band noise
D. Pulse width modulated band-limited noise
Answer: B
Clarification: Pulse jammer consists of pulse modulated band-limited noise.
11. Which are the design options for anti jam communicator?
A. Time diversity
B. Frequency diversity
C. Special discrimination
D. All of the mentioned
Answer: D
Clarification: The design options for anti-jam communicator are time diversity, frequency diversity and special discrimination.
12. The ratio (J/S)reqd gives the measure of
A. Vulnerability to interference
B. Invulnerability to interference
C. All of the mentioned
D. None of the mentioned
Answer: B
Clarification: The ratio (J/S)reqd gives the measure of how invulnerable the system is to interference.
13. The system should have
A. Larger (J/S)reqd
B. Greater system’s noise rejection capability
C. Larger (J/S)reqd & Greater system’s noise rejection capability
D. None of the mentioned
Answer: C
Clarification: The system will be efficient if it has greater (J/S)reqd and larger system’s noise rejection capability.
14. The broadband jammer jams the entire
A. W
B. Wss
C. W & Wss
D. None of the mentioned
Answer: B
Clarification: The broadband jammer or wide-band jammer is the one which jams the entire Wss with its fixed power.
15. To increase error probability, the processing gain should be
A. Increased
B. Decreased
C. Exponentially increased
D. Exponentially decreased
Answer: A
Clarification: In a system, to increase the error probability the processing gain should be increased.
16. Which jamming method produces greater degradation?
A. Broadband jamming
B. Partial jamming
C. Broadband & Partial jamming
D. None of the mentioned
Answer: B
Clarification: Greater degradation is possible more with partial jamming than broadband jamming.
17. The jammer which monitors a communicator’s signal is known as
A. Frequency follower jammers
B. Repeat back jammers
C. Frequency follower & Repeat back jammers
D. None of the mentioned
Answer: C
Clarification: The smart jammers which monitor a communicator’s signals is known as frequency follower or repeat back jammers.