Communication Engineering - Online Test
Q1. Two magnetically uncoupled inductive coils have Q factors q1 and q2 at the
chosen operating frequency. Their respective resistances are R1 and R2. When
connected in series, their effective Q factor at the same operating frequency is
Answer : Option C
Explaination / Solution:
The quality factor of the inductances are given by
So, in series circuit, the effective quality factor is given by
Q2. A continuous-time function x(t) is periodic with period T. The function is sampled uniformly
with a sampling period TS. In which one of the following cases is the sampled signal periodic?
Answer : Option B
Explaination / Solution:
Q3. Match the inferences X, Y, and Z, about a system, to the corresponding properties of the elements of first column in Routh‟s Table of the system characteristic equation
X: The system is stable … P: … when all elements are positive
Y: The system is unstable … Q: … when any one element is zero
Z: The test breaks down … R: … when there is a change in sign of coefficients
Answer : Option D
Explaination / Solution:
No Explaination.
Q4. A first-order low-pass filter of time constant T is excited with different input signals (with zero
initial conditions up to t = 0). Match the excitation signals X, Y, Z with the corresponding time
responses for t ≥ 0:
X: Impulse P: 1 – e-t/T
Y: Unit step Q: t – T(1 – e(-t/T)
Z :Ramp R: e-t/T
Answer : Option C
Explaination / Solution:
In general the first order, L.P.F filter transfer function is 
because G(0) = k and G(∞) = ∞ if we take this transfer function as reference and give different input such as
s(t).r(t).u(t)
because G(0) = k and G(∞) = ∞ if we take this transfer function as reference and give different input such as
s(t).r(t).u(t)
Q5. The impulse response of a continuous time system is given by 
The value of the step response at t = 2 is
The value of the step response at t = 2 is
Answer : Option B
Explaination / Solution:
