Minor Question regarding Amplitude Modulation

Discussion in 'Homework' started by juraculation, Jan 26, 2016.

  1. juraculation

    juraculation Well-Known Member

    [​IMG]
    Why does wc > 2ws? I understand why that needs to be the case for sampling but not for amplitude modulation. In this case, as long as wc > ws, the two frequency-domain signals don't add together (because they're both on different sides of the y-axis), and the original signal can be retrieved.
     
  2. HHHNNNGGG

    HHHNNNGGG Well-Known Member

    The information in the pic is weird.

    You are right about wc > ws part, but it just works in theory.

    Generally, low-pass filters can't suppress totally the -2wc and 2wc bands in demodulated signal, just attenuate them. So wc, in practice, is vastly superior to ws so that the low-pass filters can extract the information with lowest distortion from the higher frequencies. The low-pass filters also do not strictly use the same cutoff frequency as the carrier's frequency.

    Transmissions also usually use carriers at different frequencies depending on the type and distance of transmission as well, but they are usually at higher frequency than information.
     
    Last edited: Feb 8, 2016