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Thread: Demodulators question

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    Demodulators question

    From many years ago, I have a basic understanding of modulation as an ex Radio Ham. That was for voice transmissions and receiving.

    What do , for example, x8 demodulators for a satellite signal . Googling tells me roughly that they multiply the signal.

    I would appreciate a bit of basic information on this if possible.

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    Huevos's Avatar
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    The job of any demodulator is to recover the information content from the carrier... so for AM/FM the demodulator recovers the analogue audio content from the carrier... In the case of DVB-S/S2 the modulation is PSK (Phase-Shift Keying) and the demodulator returns binary digits, which go through error correction and are finally converted digital packets. One demodulator is needed per tuned frequency.

    DVB can either be monoplex (normally feeds) or multiplex (which means a group of channels is combined and packed onto one single frequency). Also packed on the same carrier is program synopsis and TV program guide.
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    Have a look at things like this:
    Code:
    https://www.open.edu/openlearn/science-maths-technology/exploring-communications-technology/content-section-1.7
    The theory is best explained by complex numbers (hence it looks like an Argand diagram) as tit's phase-based.
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    Quote Originally Posted by birdman View Post
    Have a look at things like this:
    Code:
    https://www.open.edu/openlearn/science-maths-technology/exploring-communications-technology/content-section-1.7
    The theory is best explained by complex numbers (hence it looks like an Argand diagram) as tit's phase-based.
    Except QAM is not used for satellite, it is used for cable and terrestrial. Satellite is almost always QPSK, 8PSK or sometimes APSK.
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    Quote Originally Posted by Huevos View Post
    Except QAM is not used for satellite, it is used for cable and terrestrial. Satellite is almost always QPSK, 8PSK or sometimes APSK.
    OK, so try the Wkipedia entry:
    Code:
    https://en.wikipedia.org/wiki/Phase-shift_keying#Quadrature_phase-shift_keying_(QPSK)
    or
    Code:
    https://core.ac.uk/download/pdf/61800941.pdf
    There are many results for a QPSK search.
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    @Heuvos:
    yes I can recall monoplex and multiplex particularly with bulletin board servers.

    @birdman:
    Thanks for the links and some of the information there takes me back a good few years.

    Thanks to both of you.

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