Communications - Online Test
Q1.
For a message signal 
and carrier of frequency fc which of thefollowing represents a single side-band (SSB) signal ?
Answer : Option C
Explaination / Solution:
Q2. To increase the range of line of sight communication
Answer : Option B
Explaination / Solution:
No Explaination.
Q3. The Nyquist sampling rate for the signal 
is given by
is given by
Answer : Option C
Explaination / Solution:
S(t) = sinc(500t) sinc(700t)
S(f ) is convolution of two signals whose spectrum covers f1 = 250 Hz and f2 = 350 Hz. So convolution extends
f = 25 + 350 = 600 Hz
Nyquist sampling rate
N = 2f = 2#600 = 1200 Hz
Q4. With reference to the figure the value of can be calculated by
Answer : Option C
Explaination / Solution:
No Explaination.
Q5. X(t) is a stationary process with the power spectral density Sx(f)>0, for all f . The process is passed through a system shown below
Let Sy (f ) be the power spectral density of Y(t). Which one of the following statements is correct
Answer : Option D
Explaination / Solution:
Q6. A transmitting antenna at the top of a tower has a height 32 m and the height of the receiving antenna is 50 m. What is the maximum distance between them for satisfactory communication in LOS mode? Given radius of earth is 6.4 m.
Answer : Option B
Explaination / Solution:
No Explaination.
Q7. 
In the circuit shown, all the transmission line sections are lossless. The Voltage Standing Wave Ration(VSWR) on the 60 Ω line is
Answer : Option B
Explaination / Solution:
Q8. baseband signal refers to the
Answer : Option A
Explaination / Solution:
No Explaination.
Q9. 
Consider a baseband binary PAM receiver shown below. The additive channel noise n(t) is with power spectral density 
The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).
The lowpass filter is ideal with unity gain and cut-off frequency 1 MHz. Let Yk represent the random variable y(tk).Yk = Nk , if transmitted bit bk = 0
Yk = a + Nk if transmitted bit bk = 1
Where Nk represents the noise sample value. The noise sample has a probability density function, 
(This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2
= 10-6 V.
(This has mean zero and variance 2/α2). Assume transmitted bits to be equiprobable and threshold z is set to a/2
= 10-6 V.The value of the parameter α
(in V-1) is
Answer : Option B
Explaination / Solution:
Let response of LPF filters
Noise variance (power) is given as
Q10. need for modulation arises from antenna considerations. If base band signal is to be transmitted then
Answer : Option A
Explaination / Solution:
No Explaination.
