digital communication

Discussion in 'Wireless & RF Design' started by vivek kumar singh, Nov 8, 2013.

  1. vivek kumar singh

    Thread Starter New Member

    Nov 8, 2013
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    hii..frnds,
    i have a doubt regarding the digital modulation technique i.e in pcm method we are not using any carrier signal, but in bask, bpsk... we are using analog carrier signal what is the advantages of using this analog signal????please answer it....
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,143
    1,790
    Your terminology is a bit confused to me. I'm not sure what you are referring to when you speak of an "analog carrier". I am familiar with PSK31 as an example. I believe there are three signals of interest.

    1. The RF carrier located in one of the amateur bands 80M, 40M, 30M, 20M, 15M, 10M, 6M and so forth. This carrier is modulated by the "multiplication" of the next two signals.
    2. The analog signal whose phase is changed, depending on the bits of the character. These characters are formed with Viterbi encoding and decoding to make sure the continuous strings of ones and zeros are limited. This might be what you refer to as the "analog" carrier.
    3. A cosine multiplying signal, at the bit rate (31 bits per second), with its zero crossings at the phase changes so that phase changes with a discontinuous derivative (a "corner") will only happen at a very low amplitude.
     
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