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Relation between bandwidth and ssamplig rate

  1. Oct 20, 2012 #1
    greetings,
    how a sampling rate can define bandwidth required for transmission of that signal.if sampling rate is high then bandwidth requirement is also high,how?
     
  2. jcsd
  3. Oct 20, 2012 #2
    In order not to have spectral aliasing of the discrete signal, you need to have a sampling rate that is 2 times the bandwidth. So the relationship is simple

    F = 2B
     
  4. Oct 20, 2012 #3
    In order not to have spectral aliasing of the discrete signal, you need to have a sampling rate that is 2 times the bandwidth. So the relationship is simple

    F = 2B
     
  5. Oct 20, 2012 #4

    sophiecentaur

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    There is a small problem with using that basic definition for practical sampled systems. Bandwidth is not usually defined in terms of the difference between the maximum and minimum frequencies involved. The value of B, in the quote would be defined as above but system bandwidth is usually defined in different terms.
    Because all communications systems (transmitters and receivers) have 'real' channel-defining filters, which will never have a completely 'sharp cut' characteristic, the bandwidth is usually defined in terms of 'half power bandwidth' - that is the interval between points on the filter where the admitted power is half. There are always 'skirts' which allow a finite level of components to fall outside this bandwidth value. Hence, if you want to avoid aliasing, your sampling frequency needs to be somewhat in excess of twice the bandwidth. The more fussy you have to be about the phase response of the analogue channel, the wider the skirts of anti aliasing filters need to be - so the more excess sampling rate you need.
     
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