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Exercise Problems · Q21

Q.A FM wave is represented by 10sin[2π×10⁸t+5sin2π×200t ] Determine

(a) the carrier and modulating frequency
(b) the modulation index and maximum deviation.
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[!TLDR]

Matching to the standard FM equation gives fc=100 MHzf_c = 100\ \text{MHz}, fm=200 Hzf_m = 200\ \text{Hz}, mf=5m_f = 5 and Δf=1 kHz\Delta f = 1\ \text{kHz}.

Compare 10sin⁡[2π×108t+5sin⁡(2π×200t)]10\sin[2\pi\times10^{8}t + 5\sin(2\pi\times200t)] with the standard form v=Vcsin⁡(ωct+mfsin⁡ωmt)v = V_c\sin(\omega_c t + m_f\sin\omega_m t).

(a) The carrier term is 2π×108t2\pi\times10^{8}t, so fc=108=100 MHzf_c = 10^{8} = 100\ \text{MHz}; the inner modulating term is 2π×200t2\pi\times200t, so fm=200 Hzf_m = 200\ \text{Hz}. …

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