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Homework Help: Finding the bandwidth of an FM signal

  1. Apr 2, 2017 #1
    1. The problem statement, all variables and given/known data
    Consider the frequency-modulated (FM) signa A(t)=A0sin[2πfct+Δfsin(2πfmt)/fm] , where fc = 3.5 kHz, fm = 88.1 MHz. What is the bandwidth of the signal? [Note: You may take sin≅ and cos≅1 for x (in radian) << 1.]

    2. Relevant equations
    3. The attempt at a solution
    for finding bandwidth, isn't it (fc+fm)-(fc-fm)?
  2. jcsd
  3. Apr 2, 2017 #2


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    I think the question has mixed up fc and fm, which should be probably be 88.1MHz and 3.5kHz respectively. It also does not specify the deviation, which you need to find the bandwidth.
  4. Apr 6, 2017 #3

    rude man

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    I agree with post #2. Also, the required bandwidth depends on the (constant) frequency deviation Δω; then a bandwidth BW can be computed from a normalized bandwidth curve BW/2Δω vs. β.
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