Physics - Principles of Communication
Exam Duration: 45 Mins Total Questions : 30
A short circuited, uniform, lossless transmission line of 0.04 wavelength long, acts almost like an ideal
- (a)
capacitor
- (b)
inductor
- (c)
series resonant circuit
- (d)
parallel resonant circuit
A commonly used in-band signalling frequency is
- (a)
400 Hz
- (b)
1000 Hz
- (c)
2400 Hz
- (d)
3825 Hz
In amplitude modulation :
A. amplitude of a carrier wave is varied by signal voltage
B. frequency of the carrier wave remains unchanged
C. the wave shape of the modulated signal is different from that of the modulating signal
D. amplitude of the modulated wave varies at the modulating frequency.
- (a)
if A, B, C are correct
- (b)
if B, C, D are correct
- (c)
if C, D, A are correct
- (d)
All the correct
In an amplitrde modulated wave, the amplitude of the side band is
- (a)
indepentent of the carrier amplitude
- (b)
indepentent of the modulation index
- (c)
carrier amplitude \(\times\) modulation index
- (d)
1/2 \(\times\) carrier amplitude \(\times\) modulation index
Detection is done by
- (a)
radio receiver
- (b)
mixer
- (c)
local oscillator
- (d)
transmitter
The medium wave broadcast signals may get propagated via ionosphere. This happens
- (a)
both during day and night
- (b)
only during day
- (c)
only during night
- (d)
during day in winter and during night in summer
The critical frequency of an ionosphere layer is proportional to
- (a)
maximum electron density of the layer
- (b)
square root of maximum electron density of the layer
- (c)
square of the maximum electron density of the layer
- (d)
NONE OF THE ABOVE
Which of the ionospheric layers is termed as the Kennelly-Heaviside layer?
- (a)
D-layer
- (b)
E-layer
- (c)
F1-layer
- (d)
F2-layer
Which layer in ionospheric layer is the most important reflecting medium for high frequency radio waves?
- (a)
D-layer
- (b)
E-layer
- (c)
F1-layer
- (d)
F2-layer
Choose CORRECT statement
- (a)
The D layer of the ionosphere occurs only during the day time.
- (b)
The portion of the atmosphere closest to the ground is called the ionosphere.
- (c)
Troposphere is the upper part of the earth's atmosphere which absorbs large quantities of sun's radiation.
- (d)
The ionosphere plays a significant role in radiowace porapagation at microwave frequencies.
Choose INCORRECT statement
- (a)
The microwave link uses only line-of-sight propagation
- (b)
Television signals are propagated as ground waves
- (c)
The wave 'lies down and dies' is ground wave
- (d)
The skip distance is the maximum distance upto which ionospheric reflection is possible
Wave propagation of high frequency waves is generally better at night than during the day. It is because
- (a)
the critical frequency of the ionospheric layer is less during the daytime
- (b)
the D layer absorbs the radiowave at night
- (c)
the F1 and F2 layers combine into one F layer and the D-layer vanishes
- (d)
the F1 and F2 layers combine into one F layer and the D-layer disappears.
The emission line width will be narrowest for a
- (a)
Ruby laser
- (b)
He-Ne laser
- (c)
LED
- (d)
Hetrojunction laser
Intermodal dispersion in a fibre depends on the refractive index of
- (a)
core
- (b)
cladding
- (c)
surrounding medium
- (d)
both (a) and (b)
The structure of an optical fibre consists of
- (a)
multimode step-index
- (b)
graded index
- (c)
single-mode step-index
- (d)
all of the above
An optical fibre excels at rejecting
- (a)
electromagnetic interference
- (b)
radio-frequancy interference
- (c)
crossstalk
- (d)
all of the above
The range of light wavelength in which the high-quality glass fibres have least losses is
- (a)
820 nm to 880 nm
- (b)
1200 nm to 1320 nm
- (c)
1550 nm to 1610 nm
- (d)
1620 nm to 1710 nm
A plastic-clad fibre has similar characteristics as an all-glass fibre except that it is more sensitive to which kind of damage :
- (a)
chemical
- (b)
moisture
- (c)
corrosion
- (d)
abrasive
Fibre-to-fibre connections are made by
A. splicing
B. connectors
C. twisting
Mark :
- (a)
if A are correct only
- (b)
if A, B are correct only
- (c)
if B, C are correct only
- (d)
if A, B, C all are correct
The performance of an optical fibre is measured in terms of
- (a)
its attenuation
- (b)
its pulse spreading
- (c)
its numerical aperture
- (d)
All of the above
Choose INCORRECT statement :
- (a)
The optic fibres have greater information carrying capacities than metallic conductors
- (b)
The optic fibres are uneffected by lightning and sparking
- (c)
The optic fibres can carry large amount of information in either digital or analog form
- (d)
One of the important characteristecs is accurate signal radiation.
A device which converts one type of energy into is known as
- (a)
attenuator
- (b)
transmitter
- (c)
receiver
- (d)
transducer
3-30 MHz frequency range is known as
- (a)
HF
- (b)
VHF
- (c)
UHF
- (d)
MF
Ozone layer above the earth's atmosphere will not
- (a)
prevent infrared radiations from sun reaching on the earth
- (b)
prevent infrared radiations originated from the earth from escaping the earth's atmosphere
- (c)
prevent ultraviolet rays from sun
- (d)
reflect back radio waves
In earth's atmosphere, for F1- layer; the virtual height and critical frequency are
- (a)
150 km and 3 MHz
- (b)
160 km and 3.5 MHz
- (c)
170 km and 4.5 MHz
- (d)
180 km and 5 MHz
Satellite communication is generally carried out for frequencies above
- (a)
1 MHz
- (b)
1 kHz
- (c)
30 MHz
- (d)
20 kHz
A male voice after modulation transmission sounds like that of female to the receiver. The problem is due to
- (a)
poor selection of modulation index (selected o <.... < 1)
- (b)
poor bandwidth selection of amplifiers
- (c)
poor selection of carrier frequency
- (d)
loss of energy in transmission
Two waves A and B of frequencies 2 MHz and 3 MHz respectively are beamed in the same direction for communication via sky wave. Which one of these is likely to travel longer distance in the ionosphere before suffering total internal reflection?
- (a)
A
- (b)
B
- (c)
Both (a) and (B)
- (d)
None of the above
Which of the following four alternatives is not correct?
- (a)
to increase the selectivity
- (b)
to reduce the time lag between transmission and reception of the information signal
- (c)
to reduce the size of antenna
- (d)
to reduce the fractional bandwidth, that is the ratio of the signal bandwidth to the centre frequency.