Communication System – JEE Main Previous Year Questions with Solutions

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Q. This questions has Statement-1 and Statement-2. Of the four choice given after the statements, choose the one that best describes the two statements. Statement-1 : Sky wave signals are used for long distance radio communication. These signals are in general, less stable than ground wave signals. Statement-2 : The state of ionosphere varies from hour to hour, day to day and season to season. (1) Statement-1 is true, Statement-2 is true, Statement-2 is the correct explanation of statement-1 (2) Statement-1 is true, Statement-2 is true, Statrment-2 is not the correct explanation of Statement-1 (3) Statement-1 is false, Statement-2 is true (4) Statement-1 is true, Statement-2 is false [AIEEE-2011]

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Sol. (2)

Q. A radar has a power of 1 kW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance up to which it can detect object located on the surface of the earth (Radius of earth $\left.=6.4 \times 10^{6} \mathrm{m}\right)$ is : (1) 40 km (2) 64 (3) 80 km (4) 16km [AIEEE-2012]

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Sol. (3) $\mathrm{d}=\sqrt{2 \mathrm{Rh}}=\sqrt{2 \times 6400 \times 0.5}=80 \mathrm{km}$

Q. A diode detector is used to detect an amplitude modulated wave of 60% modulation by using a condenser of capacity 250 pico farad in parallel with a load resistance 100 kilo ohm. Find the maximum modulated frequency which could be detected by it. (1) 10.62kHz (2) 5.31 MHz (3) 5.31 kHz (4) 10.62MHz [JEE Main-2013]

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Sol. (3) $\mathrm{f}_{\mathrm{max}} \leq \frac{\sqrt{\frac{1}{\mathrm{m}^{2}}-1}}{2 \pi \mathrm{RC}}$ $\mathrm{f}_{\max } \leq \frac{8}{6 \times 2 \pi \times 100 \times 10^{3} \times 250 \times 10^{-12}}$ $\mathrm{f}_{\max } \leq \frac{8 \times 10^{6}}{12 \pi \times 25}$ $\mathrm{f}_{\max } \leq 8.4925 \mathrm{kHz}$

Q. A single of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. The frequencies of the resultant signal is/are – (1) 2005 kHz, 2000 kHz and 1995 kHz (2) 2000 kHz and 1995 kHz (3) 2 MHz only (4) 2005 kHz and 1995 kHz [JEE Main-2015]

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Sol. (1) Frequency present after modulation $\mathrm{f}_{\mathrm{c}}, \mathrm{f}_{\mathrm{c}} \pm \mathrm{f}_{\mathrm{s}}$ $\Rightarrow 2000 \mathrm{KHz}, 2005 \mathrm{KHz}$ and $1995 \mathrm{KHz}$

Q. Choose the correct statement : (1) In frequency modulation the amplitude of the high frequency carrier wave is made to vary in proportion to the frequency of the audio signal. (2) In amplitude modulation the amplitude of the high frequency carrier wave is made to vary in proportion to the amplitude of the audio signal. (3) In amplitude modulation the frequency of the high frequency carrier wave is made to vary in proportion to the amplitude of the audio signal. (4) In frequency modulation the amplitude of the high frequency carrier wave is made to vary in proportion to the amplitude of the audio signal. [JEE Main-2016]

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Sol. (2)

Q. In amplitude modulation, sinusoidal carrier frequency used is denoted by $\omega_{\mathrm{c}}$ and the signal frequency is denoted by $\omega_{\mathrm{m}}$. The bandwidth $\left(\Delta \omega_{\mathrm{m}}\right)$ of the signal is such that $\Delta \omega_{\mathrm{m}}<<\omega_{\mathrm{c}}$. Which of the following frequencies is not contained in the modulated wave ? [JEE Main-2017]

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Sol. (3) Refer NCERT Page No. 526 Three frequencies are contained $\omega_{\mathrm{m}}+\omega_{\mathrm{c}}, \omega_{\mathrm{c}}-\omega_{\mathrm{m}} \& \omega_{\mathrm{c}}$

Q. A telephonic communication service is working at carrier frequency of 10 GHz. Only 10% of it is utilized for transmission. How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of 5 kHz ? [JEE Main-2018]

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Sol. (2) Since the carrier frequency is distributed as band width frequency, so 10% of 10 GHz = n × 5 kHz where n = no of channels $\frac{10}{100} \times 10 \times 10^{9}=n \times 5 \times 10^{3} \mathrm{n}=2 \times 10^{5}$ telephonic channels

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Comments
  • March 27, 2021 at 9:44 pm

    hi

    1
  • Rij
    February 23, 2021 at 6:59 pm

    yes

    3
  • October 5, 2020 at 8:23 pm

    Key is wrong i think

    1
    • Rij
      February 23, 2021 at 6:56 pm

      yes

      0
  • September 2, 2020 at 5:33 am

    Thank you. It is really useful

    11
  • August 30, 2020 at 7:26 pm

    These questions are ever before and never after

    8
  • August 25, 2020 at 11:59 am

    It’s good but I’m not satisfied with the questions .only few years questions are included.its better to add some more questions.

    33
  • August 25, 2020 at 10:59 am

    S it is good thing .but add some privious year question s

    11
    • April 13, 2021 at 3:49 pm

      Yes even i am not satisfied

      0
  • August 24, 2020 at 8:10 pm

    If you people can convert it into PDF that will be of great help.

    5
  • August 21, 2020 at 2:23 pm

    It was a useful collection of questions. But please, include the recent questions also( jee mains 2020,2019….). Then it would be a , perfect source to do PYQ’s

    3
  • August 18, 2020 at 12:32 pm

    Sukriya

    0
  • August 12, 2020 at 1:05 am

    Thank you so much for providing questions with answers

    0
  • August 2, 2020 at 7:57 pm

    Explanation is to be provided if possible

    2
  • August 2, 2020 at 7:56 pm

    Super

    1
  • July 26, 2020 at 6:52 pm

    i want you to include more questions from previous year papers .kindly look into this matter urgently

    1
  • July 25, 2020 at 4:17 pm

    Last question explanation is not clear to understand

    1
  • July 2, 2020 at 8:21 pm

    Explanation should be mention clearly look into this

    0
  • July 2, 2020 at 8:19 pm

    I have been saying u to keep more questions but u are not kindly look into this

    0
  • June 20, 2020 at 3:24 pm

    Detailed solutions must be given to understand the student clearly and easily

    0
  • June 16, 2020 at 5:08 pm

    answers must be sloved so we can go through this without a problem

    1
    • .
      February 17, 2021 at 4:26 pm

      Yes

      0
  • May 1, 2020 at 5:05 pm

    This questions are very nice

    2
  • April 14, 2020 at 2:28 pm

    More concept &formulas on communication systems

    3
  • March 22, 2020 at 5:38 pm

    Answers must be solved

    4