Communications - Online Test
Q1. A load of 50 Ω is connected in shunt in a 2-wire transmission line of Z0 = 50Ω as shown in the figure. The 2-port scattering parameter matrix (s-matrix) of the
shunt element is
Answer : Option C
Explaination / Solution:
Q2. The parallel branches of a 2-wire transmission line re terminated in 100Ω and
200Ω resistors as shown in the figure. The characteristic impedance of the
line is Z0 = Ω and each section has a length of λ/4. The voltage reflection
coefficient Γ at the input is
Answer : Option D
Explaination / Solution:
Q3. A λ/2 dipole is kept horizontally at a height of λ0/2 above a perfectly conducting
infinite ground plane. The radiation pattern in the lane of the dipole (
plane)
looks approximately as
plane)
looks approximately as
Answer : Option B
Explaination / Solution:
Q4. A right circularly polarized (RCP) plane wave is incident at an angle 600 to the
normal, on an air-dielectric interface. If the reflected wave is linearly polarized,
the relative dielectric constant ξr is.
Answer : Option D
Explaination / Solution:
No Explaination.
Q5. Two 4-array signal constellations are shown. It is given that φ1 and φ2 constitute
an orthonormal basis for the two constellation. Assume that the four symbols
in both the constellations are equiprobable. Let N0/2 denote the power spectral
density of white Gaussian noise.
The if ratio or the average energy of Constellation 1 to the average energy of
Constellation 2 is
Answer : Option B
Explaination / Solution:
Q6. Two 4-array signal constellations are shown. It is given that φ1 and φ2 constitute an orthonormal basis for the two constellation. Assume that the four symbols in both the constellations are equiprobable. Let N0/2 denote the power spectral density of white Gaussian noise.
If these constellations are used for digital communications over an AWGN channel, then which of the following statements is true ?
Answer : Option A
Explaination / Solution:
No Explaination.
Q7. For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is
Answer : Option C
Explaination / Solution:
The beam-width of Hertizian dipole is 1800 and its half power beam-width is 900
Q8. Consider the amplitude modulated (AM) signal 
For demodulating the signal using envelope detector, the minimum value of Ac should be
For demodulating the signal using envelope detector, the minimum value of Ac should be
Answer : Option A
Explaination / Solution:
Q9. The driving point impedance of the following network is given by
The component values are
Answer : Option D
Explaination / Solution:
Q10. The circuit shown in the figure is used to charge the capacitor C alternately
from two current sources as indicated. The switches S1 and S2 are mechanically
coupled and connected as follows:
Assume that the capacitor has zero initial charge. Given that u(t) is a unit step function , the voltage vc(t) across the capacitor is given by
Answer : Option C
Explaination / Solution:
