Communications (Test 5)

Gate Exam : Ec Electronics And Communication Engineering

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Communications

Communications
| Communications | | Communication Systems |
Q.1
Which of these is an example of broadcast communication?
A. FAX
B. Telephony
C. Radio
D. Mobile
Answer : Option C
Explaination / Solution:

In broadcast mode of communication a large number of receivers are linked to a single transmiiter.Radio works as receiver which converts the transmiited information/message into the original form of the information.

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Q.2
Transmitter is a device that
A. clips the message signal
B. inverts the message
C. makes the message contain parts of the spectrum
D. makes the message suitable for transmission and reception
Answer : Option D
Explaination / Solution:

A transmitter is a set up that transmits the message to the receiving end through a communication channel.its main function is to modify the message signal in a form suitable for transmission over the channel and to transmit it.The transmitter is able to generate a radio frequency alternating current that is then applied to the antenna, which, in turn, radiates this as radio waves. There are many types of transmitters depending on the standard being used and the type of device; for example, many modern devices that have communication capabilities have transmitters such as Wi-Fi, Bluetooth, NFC and cellular.

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Q.3
Repeater is used for
A. increasing the signal fidelity
B. extending communication range
C. changing the language of communication
D. limit the frequencies in communication
Answer : Option B
Explaination / Solution:

In telecommunications, a repeater is an electronic device that receives a signal and retransmits it.Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction.

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Q.4
To radiate signals with high efficiency, the antennas should have a size
A. comparable to the wavelength λ of the signal (at least λ4)
B. much smaller than the wavelength λ of the signal
C. none of these
D. much greater than the wavelength λ of the signal
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.5
need for modulation arises from antenna considerations. If base band signal is to be transmitted then
A. size of antenna would be huge
B. none of these
C. size of antenna would be very small
D. shape of antenna would be complex
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.6
In the following scheme, if the spectrum M(f) of m(t) is as shown, then the spectrum Y(f) of y(t) will be

A.
B.
C.
D.
Answer : Option B
Explaination / Solution:





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Q.7
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
A. 4a2
B. 4
C. 2
D. 8
Answer : Option B
Explaination / Solution:



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Q.8
In the design of a single mode step index optical fibre close to upper cut-off, the single-mode operation is not preserved if
A. radius as well as operating wavelength are halved
B. radius as well as operating wavelength are doubled
C. radius is halved and operating wavelength is doubled
D. radius is doubled and operating wavelength is halved
Answer : Option C
Explaination / Solution:
No Explaination.


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Q.9
In the following network, the switch is closed at t = 0- and the sampling starts from t = 0. The sampling frequency is 10 Hz.

The samples x(n), n = (0, 1, 2, ...) are given by
A.

5(1 - e-0.05n)

B. 5e-0.05n
C. 5(1 e-5n)
D. 5e-5n
Answer : Option B
Explaination / Solution:
No Explaination.


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Q.10
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).
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.

The value of the parameter α (in V-1) is
A. 1010
B. 107
C. 1. 414 × 10-10
D. × 10-20
Answer : Option B
Explaination / Solution:

Let response of LPF filters

Noise variance (power) is given as


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EC Electronics and Communication Engineering