IQ Modulation

Discussion in 'Wireless & RF Design' started by mankmanky1, Feb 13, 2010.

  1. mankmanky1

    Thread Starter New Member

    Feb 13, 2010
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    Hi,

    I am looking for someone to guide me in building an IQ modulator/demodulator using QPSK. Any circuit diagrams, links to good websites, recommended books or explanations would be greatly appreciated!

    Many Thanks
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    As I get older, my IQ naturally modulates. Generally downwards. :)
     
  4. mankmanky1

    Thread Starter New Member

    Feb 13, 2010
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    Thanks very much for the help... However, I do have a few more questions. It states on the diagram on the website that the signal has to be directly upconverted (DUC) and then mixed with signals from the local oscillator for the modulation of the signal.

    Isnt this redundant? If not, why would both steps be necessary because mixing the signals is upping their frequency anyway?

    The other question is would this method be the same if I were to do it using QPSK method? If there are differences would you mind to please tell me what they are.

    Thanks very much
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Good questions. To answer the second one first, yes, this principle is used for QPSK, or any number of PSKs. :)

    To answer the first question...this scheme, as "redundant' as it seems, guarantees that the signal keying occurs precisely at the Zero Crossing, (integral cycle keying). This yields the least possible bandwidth. Absolute phase relation is maintained throughout the process.

    eric
     
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