Communication Engineering - Online Test
Q1. In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved if
Answer : Option C
Explaination / Solution:
No Explaination.
Q2. Consider a continuous-time system with input x(t) and output y(t) given by
y(t) = x(t) cos(t)
This system is
Answer : Option C
Explaination / Solution:
Q3. At 20 GHz, the gain of a parabolic dish antenna of 1 meter and 70% efficiency is
Answer : Option D
Explaination / Solution:
Q4. Suppose x1(t) and x2(t) have the Fourier transforms as shown below
Which one of the following statements is TRUE?
Answer : Option C
Explaination / Solution:
Q5.
Noise with double-sided power spectral density on K over all frequencies is passed through a RC low pass filter with 3 dB cut-off frequency of fc. The noise power at the filter output is
Answer : Option C
Explaination / Solution:
Q6. The output of a continuous-time, linear time-invariant system is denoted by T{x(t)} where x(t) is
the input signal. A signal z(t) is called eigen-signal of the system T , when T{z(t)} = γz(t),
where γ is a complex number, in general, and is called an eigenvalue of T. Suppose the impulse
response of the system T is real and even. Which of the following statements is TRUE?
Answer : Option D
Explaination / Solution:
Q7. Consider a Binary Symmetric Channel (BSC) with probability of error being p. To transmit a bit, say 1, we transmit a sequence of three 1s. The receiver will interpret the received sequence to represent 1 if at least two bits are 1. The probability that the transmitted bit will be received in error is
Answer : Option D
Explaination / Solution:
No Explaination.
Q8. Consider a causal LTI system characterized by differential equation 
The response of the system to the input 
where u(t) denotes the unit step
function, is
The response of the system to the input where u(t) denotes the unit step
function, is
Answer : Option D
Explaination / Solution:
Q9. Four messages band limited to W,W,2W and 3W respectively are to be multiplexed using Time Division Multiplexing (TDM). The minimum bandwidth required for transmission of this TDM signal is
Answer : Option D
Explaination / Solution:
Bandwidth of TDM is
= 1/2 (sum of Nyquist Rate)
= 1/2 [2W + 2W + 4W + 6W] = 7W
Q10. Consider the function ݂f(z) = z + z* where z is a complex variable and z* denotes its complex
conjugate. Which one of the following is TRUE?
Answer : Option B
Explaination / Solution:
