# Topic: Communications (Test 5)

Topic: Communications
Q.1
During transmission over a certain binary communication channel, bit errors occur independently with probability p. The probability of AT MOST one bit in error in a block of n bits is given by
A. pn
B. 1 - pn
C. np( - p)n + ( + p)n
D. 1 - (1 - p)n
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Q.2
The field in a rectangular waveguide of inner dimension a × b is given by Where H0 is a constant, and a and b are the dimensions along the x − axis and the y − axis respectively. The mode of propagation in the waveguide is
A. TE20
B. TM11
C. TM20
D. TE10
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Q.3
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. A. √2
B. √3
C. 2
D. 3
Explaination / Solution:
No Explaination.

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Q.4
Consider the amplitude modulated (AM) signal For demodulating the signal using envelope detector, the minimum value of Ac should be
A. 2
B. 1
C. 0.5
D. 0
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Q.5
A signal flow graph of a system is given below The set of equalities that corresponds to this signal flow graph is
A. B. C. D. Explaination / Solution: Workspace
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Q.6
A rectangular waveguide of internal dimensions (a = 4 cm and b = 3 cm) is to be operated in TE11 mode. The minimum operating frequency is
A. 6.25 GHz
B. 6.0 GHz
C. 5.0 GHz
D. 3.75 GHz
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Q.7
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
A. K
B. Kfc
C. kπfc
D.

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Q.8
Consider the frequency modulated signal with carrier frequency of 105 Hz. The modulation index is
A. 12.5
B. 10
C. 7.5
D. 5
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Q.9
Which of the following statements is true regarding the fundamental mode of the metallic waveguides shown ? A. Only P has no cutoff-frequency
B. Only Q has no cutoff-frequency
C. Only R has no cutoff-frequency
D. All three have cutoff-frequencies
Explaination / Solution:

Rectangular and cylindrical waveguide doesn’t support TEM modes and have cut off frequency. Coaxial cable support TEM wave and doesn’t have cut off frequency.

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Q.10
The return loss of a device is found to be 20 dB. The voltage standing wave ratio (VSWR) and magnitude of reflection coefficient are respectively
A. 1.22 and 0.1
B. 0.81 and 0.1
C. – 1.22 and 0.1
D. 2.44 and 0.2 