Communications (Test 2)

Gate Exam : Ec Electronics And Communication Engineering

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Communications

Communications
| Communications | | Communication Systems |
Q.1
The three elements of a generalized communication system are
A. Transmitter, transmission channel and receiver
B. Transmitter, multiplier and receiver
C. Transmitter, noise generator and receiver
D. Transmitter, transmission channel and detector
Answer : Option A
Explaination / Solution:

In communication the Transmitter helps in transmitting the signal through communication channel which acts as a physical path that connects transmitter to a receiver.And the receiver receives the transmitted signal and converts those signals in their original form.

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Q.2
In Analog type signals
A. the signal value is available every 1 second
B. the value of the signal varies continuously with time
C. the voltages are fixed at 0 and 5 V
D. the voltages are fixed at -5 V and 5 V
Answer : Option B
Explaination / Solution:

A signal in which current or voltage varies with time is called analog signal.A vibrating fork produces such a sound signal of single frequency.Every speech or music is a complex signal formed by the superposition of several sinusoidal signals of different amplitudes and frequencies.

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Q.3
Modulation is
A. superimposing high frequency message on a low frequency wave carrier
B. superimposing low frequency message on a high frequency wave carrier
C. alternating low frequency message and a high frequency wave carrier
D. alternating high frequency message and a low frequency wave carrier
Answer : Option B
Explaination / Solution:

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Most radio systems uses frequency modulation (FM) or amplitude modulation (AM) to make the carrier carry the radio broadcast.

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Q.4
Audio signals have a maximum bandwidth of about
A. 2000 kHz
B. 2 kHz
C. 200 kHz
D. 20 kHz
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.5
With reference to the figure the value of  can be calculated by

A.  dM=2RhT
B. dM=2RhR
C.  dM=2RhT+2RhR
D.  dM=2RhT+RhR
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.6
If S(f) is the power spectral density of a real, wide-sense stationary random process, then which of the following is ALWAYS true?
A. S(0)≤S(f)
B. S(f)≥0
C. S(-f) = -S(f)
D.
Answer : Option B
Explaination / Solution:
No Explaination.


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Q.7
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

A. -j-
B. -5/7
C. j-
D. 5/7
Answer : Option D
Explaination / Solution:




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Q.8
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.
Answer : Option C
Explaination / Solution:



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Q.9
The signal  is
A. FM only
B. AM only
C. both AM and FM
D. neither AM nor FM
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.10
The Nyquist sampling rate for the signal  is given by
A. 400 Hz
B. 600 Hz
C. 1200 Hz
D. 1400 Hz
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

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EC Electronics and Communication Engineering