1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks."> 1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks.">
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    Narrowband and Wideband FM

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    Islam Candle
    Narrowband FM (NBFM) has a modulation index β ≤ 1, resulting in only the carrier signal and two significant sidebands. This gives it a bandwidth of 2fm. Wideband FM (WBFM) has a modulation index β > 1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks.

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    Narrowband and Wideband FM

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    Islam Candle
    1K views18 pages
    Narrowband FM (NBFM) has a modulation index β ≤ 1, resulting in only the carrier signal and two significant sidebands. This gives it a bandwidth of 2fm. Wideband FM (WBFM) has a modulation index β > 1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks.

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    NBFM WBFM

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    Narrowband FM (NBFM) has a modulation index β ≤ 1, resulting in only the carrier signal and two significant sidebands. This gives it a bandwidth of 2fm. Wideband FM (WBFM) has a modulation index β > 1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks.

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    Download as pptx, pdf, or txt
    1K views18 pages

    Narrowband and Wideband FM

    Uploaded by

    Islam Candle
    Narrowband FM (NBFM) has a modulation index β ≤ 1, resulting in only the carrier signal and two significant sidebands. This gives it a bandwidth of 2fm. Wideband FM (WBFM) has a modulation index β > 1, producing more than two sidebands. As β increases, more sidebands are produced, increasing the bandwidth. Phase modulation (PM) varies the phase of the carrier signal based on the modulating signal, while frequency modulation (FM) varies the frequency of the carrier. PM has maximum phase deviation at zero crossings of the modulating signal, while FM has maximum frequency deviation at the peaks.

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    © All Rights Reserved
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    of 18

    Narrowband and Wideband FM

    Narrowband FM NBFM

    From the graph/table of Bessel functions it may be seen that for small , (  0.3)
    there is only the carrier and 2 significant sidebands, i.e. BW = 2fm.

    FM with   1 is referred to as narrowband FM (NBFM) (Note, the bandwidth is


    the same as DSBAM).

    Wideband FM WBFM

    For  > 1 there are more than 2 significant sidebands. As  increases the number of
    sidebands increases. This is referred to as wideband FM (WBFM).

    1
    Narrowband FM

    2
    Narrowband FM

    The expression for AM and NBFM will be same except 180 degree phase shift at
    the lower frequency side.

    3
    Narrowband FM

    4
    WIDEBAND FM
    The features of Wideband FM are as follows

    •This frequency modulation has infinite bandwidth.

    •The modulation index is large, i.e., higher than 1.

    •Its spectrum consists of a carrier and infinite number of sidebands, which


    are located around it.

    •This is used in entertainment broadcasting applications such as FM radio,


    TV, etc
    •General Expression for single tone Wideband FM:

    5
    WIDEBAND FM
    𝑛𝑓𝑖𝑡
     
    𝑓𝑖𝑡
      𝑓  𝑜 (𝑡 )=𝑛𝑓 𝑐 +𝑛 𝐴𝑚𝑘𝑓 cos(¿2𝜋 𝑓𝑚𝑡)¿
    𝑓  𝑖 ( 𝑡 )=𝑓 𝑐 +𝐴𝑚𝑘𝑓 cos(¿ 2 𝜋 𝑓𝑚𝑡)¿ ⨯𝑛
     

    6
    WIDEBAND FM
    𝑠  ( 𝑡 ) = 𝐴𝑐cos(2 𝜋 𝑓 𝑐 𝑡)+ 𝛽sin (2¿𝜋 𝑓𝑚𝑡)¿
    Cos(θ)= Re[ej θ]

    S(t) is periodic function of time with


    fundamental frequency fm, using complex
    Fourier series

    𝑑  𝑡=𝑑𝑥/2π 𝑓𝑚
    𝑑  𝑥=2π 𝑓𝑚𝑑𝑡 7
    WIDEBAND FM
    Bessel function of first kind order n

    Nth coefficient of DFT s(t)

    8
    Phase Modulation

    • In the phase modulation, we vary the carrier signal


    in accordance with the phase of the modulating
    signal or message signal

    • If the amplitude of message or modulating signal is


    huge then the phase shift will also be greater.

    9
    Phase Modulation

    10
    Mathematical Expression of PM

    i  t  = kp m t 
    The standard equation of angle modulated wave is

    s (t ) = Ac cos( 2f c t  i )
    Substitute, ϕi value in the above equation.

    s (t ) = Ac cos( 2f c t  kp m t  )
    If modulating signal
    m(t ) = Am cos( 2fmt )
    s (t ) = Ac cos( 2f c t  kp Am cos( 2fmt ))
     =   kp Am
    s (t ) = Ac cos( 2f c t   cos( 2fmt ))
    Δϕ is phase deviation 11
    Average Power of a FM or PM
    Wave
    • The amplitude A is constant in a phase modulated
    or a frequency modulated signal. RF power does
    not depend upon the frequency or the phase of the
    waveform.
    A2
    Average power =
    2R

    12
    FM and PM
    • FM – maximum frequency deviation (change in the carrier freq.) occurs during
    the maximum positive and negative peaks (zero slope) of the modulating
    signal (freq. deviation is proportional to the amplitude of the modulating
    signal)
    • PM – the maximum phase deviation occurs during the zero crossings (maximum
    slope) of the modulating signal (the freq. deviation is proportional to the slope or
    first derivative of the modulating signal)

    FM PM
    Instantaneous frequency of the carrier is Phase angle of the carrier is varied
    varied from its reference value by from its reference value by an
    an amount proportional to the amount proportional to the
    modulating signal amplitude modulating signal amplitude
    Freq. carrier - - - > directly varied Phase carrier - - - > directly varied
    Phase carrier - - -> indirectly varied Freq. carrier - - -> indirectly varied
    13
    14
    Relation b/w Frequency and
    Phase modulation

    15
    16
    17
    Frequency spectrum for FM

    Frequency spectrum for PM

    18

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