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how generate two frequency a quadrature in propeller — Parallax Forums

how generate two frequency a quadrature in propeller

lcyepizlcyepiz Posts: 26
edited 2009-06-12 19:48 in Propeller 1
i download FrequencySynth from object exchange
but· i traying to generate two frequency from 0 to 125mhz
in quadrature 90 grades.

any ideas?


thanks a lot

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-12 04:32
    You need to make clear whether you want sine waves in quadrature or square waves. FrequencySynth is used to generate square waves. For sine waves, you need to use a table of sine values and step through that table to generate the sine wave. You can easily generate two signals in quadrature by using a word table of two sine values each with the values in quadrature relationship.
  • lcyepizlcyepiz Posts: 26
    edited 2009-06-12 15:19
    thanks for the replay

    I need a square frequency , i try to make tayloe·mixer,·so square signal ok.



    My target is to design a shortwave receiver with propeller

    some info of tayloe mixer

    http://www.oe1ira.at/sl/mix.html

    thanks a lot
  • Mike GreenMike Green Posts: 23,101
    edited 2009-06-12 15:31
    You can't do it without external hardware.

    The problem is that the cog counters can produce a pulse train at frequencies up to around 160MHz with true and complement outputs. To get phase angles of 90 degrees, you have to divide the interval into four pieces which would limit the frequency to 30-40MHz.

    Keep in mind that there's a PLL involved in the frequency generation and there's some jitter in the output, particularly as you get away from multiples of the crystal frequency. I wouldn't recommend it without a lot of cleanup.
  • LeonLeon Posts: 7,620
    edited 2009-06-12 16:36
    If you want a reasonable quality receiver you could use an Si570 controlled by the Propeller (via I2C) and a couple of D flip-flops to get your quadrature signals. It shouldn't be called a Tayloe mixer, BTW, the quadrature sampling detector was around for a long time before he got his patent.

    Leon

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-06-12 19:48
    Leon

    the articles that flow from a search on those mixers instantly took me back to the late 70s. VHF Comms were full of ccts that were lovingly constucted in milled out solids, only to be built by me in a mustard tin. Bloody things seldom worked.
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