JEE Main & Advanced Physics Communication System / संचार तंत्र Question Bank Self Evaluation Test - Communication System

  • question_answer
    A modulated signal \[{{C}_{m}}(t)\] has the form \[{{C}_{m}}(t)=30\]\[\sin 300\pi t+10(\cos 200\pi t-\cos 400\pi t)\]. The carrier frequency \[{{f}_{c}},\] the modulating frequency (message frequency) \[{{f}_{\omega }}\] and the modulation index \[\mu \] are respectively given by :     

    A) \[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{1}{2}\]

    B) \[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{2}{3}\]

    C) \[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{3}\]

    D) \[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{2}\]

    Correct Answer: B

    Solution :

    [b] Comparing the given equation with standard modulated signal wave equation, \[m={{A}_{c}}\sin {{\omega }_{c}}t+\frac{\mu {{A}_{c}}}{2}\cos ({{\omega }_{c}}-{{\omega }_{s}})t\] \[-\frac{\mu {{A}_{c}}}{2}\cos ({{\omega }_{c}}+{{\omega }_{s}})t\] \[\mu \frac{{{A}_{c}}}{2}=10\Rightarrow \mu =\frac{2}{3}\] (modulation index) \[{{A}_{c}}=30\] \[{{\omega }_{c}}-{{\omega }_{s}}=200\pi \] \[{{\omega }_{c}}+{{\omega }_{s}}=400\pi \] \[\Rightarrow \,\,\,\,\,\,\,\,{{f}_{c}}=150,\,\,{{f}_{s}}=50\,Hz.\]


You need to login to perform this action.
You will be redirected in 3 sec spinner