Communication System JEE Main previous year questions with solutions

5 solved JEE Main questions on Communication System, free to read — no sign-in needed. The full chapter has 107 questions; sign in to attempt the remaining 102 in the exam simulator.

1. Q1JEE Main 2023 (15 Apr, Shift 1)
   The height of transmitting antenna is $180m$ and the height of the receiving antenna is $245m$. The maximum distance between them for satisfactory communication in line of sight will be: (given $R=6400km$)
   1. A.$96km$
   2. B.$56km$
   3. C.$48km$
   4. D.$104km$
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   Answer: (D)

   The maximum distance for line of sight communication is $d=\sqrt{2hR}+\sqrt{2h'R}$ The given data is $R=6400km h=180m$ $h'=245m$ Thus, the value is $d=\sqrt{2\times 180\times 6400\times {10}^{3}}$ $+\sqrt{2\times 245\times 6400\times {10}^{3}}$ $=6\times 80\times {10}^{2}+7\times 80\times {10}^{2}$ $=104km$
2. Q2JEE Main 2023 (13 Apr, Shift 2)
   To radiate EM signal of wavelength $\lambda$ with high efficiency, the antennas should have a minimum size equal to:
   1. A.$2\lambda$
   2. B.$\dfrac{\lambda }{2}$
   3. C.$\dfrac{\lambda }{4}$
   4. D.$\lambda$
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   Answer: (C)

   For efficient radiation and reception, the height of transmitting and receiving antennas should be comparable to a quarter of wavelength of the frequency used. So for efficient transmission of signals of wavelengths$\lambda$ the minimum length of antenna should be $\dfrac{\lambda }{4}$.
3. Q3JEE Main 2023 (13 Apr, Shift 1)
   Match List-I with List-II List-I (Layer of atmosphere) List-II (Approximate height over earth's surface) $(A)$ ${F}_{1}-$Layer $(I)$ $10km$ $\left(B\right)$ $D-$Layer $\left(II\right)$ $170-190km$ $\left(C\right)$ Troposphere $\left(III\right)$ $100km$ $\left(D\right)$ $E-$Layer $\left(V\right)$ $65-75km$ Choose the correct answer from the options given below.
   1. A.$A–II,B–IV,C–I,D–III$
   2. B.$A–II,B–IV,C–III,D–I$
   3. C.$A–III,B–IV,C–I,D–II$
   4. D.$A–II,B–I,C–IV,D–III$
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   Answer: (A)

   The ${F}_{1}$ layer is above the E layer and the ionization is less compared to E layer. It ranges to $170-190km$. The D layer is located above the stratosphere. It ranges from $60-90km$ above the earth's surface. The troposphere starts from the ground and ranges to $100km$. The E layer is located above the D layer. The intensity of ionization is less than the D layer. It ranges from $100-125km$ above the earth's surface.
4. Q4JEE Main 2023 (12 Apr, Shift 1)
   The amplitude of $15\sin (1000\pi t)$ is modulated by $10\sin (4\pi t)$ signal. The amplitude modulated signal contains frequencies of A. $500Hz$ B. $2Hz$ C. $250Hz$ D. $498Hz$ E. $502Hz$ Choose the correct answer from the options given below
   1. A.A and B only
   2. B.A and C only
   3. C.A and D only
   4. D.A, D and E only
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   Answer: (D)

   The carrier wave frequency is given by $\begin{matrix}{f}_{c} & = & \dfrac{1000\pi }{2\pi } \\ & = & 500Hz\end{matrix}$ The modulating wave frequency is given by $\begin{matrix}{f}_{m} & = & \dfrac{4\pi }{2\pi } \\ & = & 2Hz\end{matrix}$ Hence, the frequencies contained in the modulated signal are given by $\begin{matrix}f & = & {f}_{c}-{f}_{m},{f}_{m},{f}_{c}+{f}_{m} \\ & = & 498Hz,500Hz,502Hz\end{matrix}$
5. Q5JEE Main 2023 (11 Apr, Shift 2)
   In satellite communication, the uplink frequency band used is:
   1. A.$420-890MHz$
   2. B.$5.925-6.425GHz$
   3. C.$76-88MHz$
   4. D.$3.7-4.2GHz$
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   Answer: (B)

   In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite. Uplink frequency band for satellite communication is $5.925-6.425GHz$.