1
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 10th January Morning Slot

A TV transmission tower has a height of 140 m and the height of the receiving antenna is 40 m. What is the maximum distance upto which signals can be broadcasted from this tower is LOS (Line of Sight) mode ? (Given : radius of earth = 6.4 × 106 m).
A
40 km
B
65 km
C
48 km
D
80 km

Explanation

Maximum distance upto which signal can be broadcasted is

dmax = $$\sqrt {2R{h_T}} + \sqrt {2R{h_R}} $$

where hT and hR are heights of transmitter tower and height of reserver respectively. Putting all values -

dmax = $$\sqrt {2 \times 6.4 \times 106} \left[ {\sqrt {104} + \sqrt {40} } \right]$$

on solving, dmax = 65 km
2
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 10th January Evening Slot

The modulation frequency of an AM radio station is 250 kHz, which is 10% of the carrier wave. If another AM station approaches you for license what broadcast frequency will you allot ?
A
2900 kHz
B
2750 kHz
C
2250 kHz
D
2000 kz

Explanation

fcarrier = $${{250} \over {0.1}}$$ = 2500 KHZ

$$ \therefore $$   Range of signal = 2250 Hz to 2750 Hz

Now check all options : for 2000 KHZ

fmod = 200 Hz

$$ \therefore $$   Range = 1800 KHZ to 2200 KHZ
3
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 11th January Morning Slot

An amplitude modulated signal is given by V(t) = 10[1 + 0.3cos(2.2 $$ \times $$ 104 t)] sin(5.5 $$ \times $$ 105 t). Here t is in seconds. The sideband frequencies (in kHz) are, [Given $$\pi $$ = 22/7]
A
892.5 and 857.5
B
89.25 and 85.75
C
1785 and 1715
D
178.5 and 171.5

Explanation

V(t) = 10 + $${3 \over 2}$$ [2cos A sinB]

= 10 + $${3 \over 2}$$ [sin(A+B) $$-$$ sin(A $$-$$ B)]

= 10+$${3 \over 2}$$[sin (57.2 $$ \times $$ 104 t) $$-$$ sin(52.8 $$ \times $$ 104 t)]

$$\omega $$1 = 57.2 $$ \times $$ 104 = 2$$\pi $$f1

f1 = $${{57.2 \times {{10}^4}} \over {2 \times \left( {{{22} \over 7}} \right)}} = 9.1 \times {10^4}$$

$$ \simeq $$ 91KHz

f2 = $${{52.8 \times {{10}^4}} \over {2 \times \left( {{{22} \over 7}} \right)}}$$

$$ \simeq $$ 84 KHz



Side band frequency are

f1 = fc $$-$$ fw = $${{52.8 \times {{10}^4}} \over {2\pi }}$$ $$ \simeq $$ 85.00 kHz

f2 = fc + fw = $${{57.2 \times {{10}^4}} \over {2\pi }}$$ $$ \simeq $$ 90.00 kHz
4
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 11th January Evening Slot

An amplitude modulated signal is plotted below :



Which one of the following best describes the above signal ?
A
(1 + 9sin (2$$\pi $$ $$ \times $$ 104 t)) sin(2.5$$\pi $$ $$ \times $$ 105t) V
B
(9 + sin (4$$\pi $$ $$ \times $$ 104 t)) sin(5$$\pi $$ $$ \times $$ 105t) V
C
(9 + sin (2$$\pi $$ $$ \times $$ 104 t)) sin(2.5$$\pi $$ $$ \times $$ 105t) V
D
(9 + sin (2.5$$\pi $$ $$ \times $$ 104 t)) sin(2$$\pi $$ $$ \times $$ 104t) V

Explanation

Analysis of graph says

(1)   Amplitude varies as 8 $$-$$ 10 V or 9 $$ \pm $$ 1

(2)  Two time period as

100 $$\mu $$s (signal wave) & 8 $$\mu $$s (carrier wave)

Hence signal is $$\left[ {9 \pm 1\sin \left( {{{2\pi t} \over {{T_1}}}} \right)} \right]\sin \left( {{{2\pi t} \over {{T_2}}}} \right)$$

= 9 $$ \pm $$ 1sin (2$$\pi $$ $$ \times $$ 104t) sin 2.5$$\pi $$ $$ \times $$ 105 t

Questions Asked from Communication Systems

On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Name Indicates No of Questions
AIEEE 2003 (1)
keyboard_arrow_right
AIEEE 2011 (1)
keyboard_arrow_right
AIEEE 2012 (1)
keyboard_arrow_right
JEE Main 2015 (Offline) (1)
keyboard_arrow_right
JEE Main 2016 (Offline) (1)
keyboard_arrow_right
JEE Main 2016 (Online) 9th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2016 (Online) 10th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2017 (Offline) (1)
keyboard_arrow_right
JEE Main 2017 (Online) 8th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2017 (Online) 9th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2018 (Offline) (1)
keyboard_arrow_right
JEE Main 2018 (Online) 15th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2018 (Online) 15th April Evening Slot (1)
keyboard_arrow_right
JEE Main 2018 (Online) 16th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 9th January Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 10th January Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 11th January Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 12th January Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 8th April Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Morning Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 9th April Evening Slot (1)
keyboard_arrow_right
JEE Main 2019 (Online) 10th April Morning Slot (2)
keyboard_arrow_right
JEE Main 2019 (Online) 12th April Evening Slot (1)
keyboard_arrow_right
JEE Main 2021 (Online) 25th February Morning Slot (1)
keyboard_arrow_right
JEE Main 2021 (Online) 25th February Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 16th March Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 17th March Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 22th July Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 25th July Morning Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 26th August Evening Shift (1)
keyboard_arrow_right
JEE Main 2021 (Online) 27th August Evening Shift (1)
keyboard_arrow_right

EXAM MAP

Joint Entrance Examination

JEE Advanced JEE Main

Graduate Aptitude Test in Engineering

GATE CSE GATE EE GATE ECE GATE ME GATE CE GATE PI GATE IN

Medical

NEET