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Dither

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  • Greg Gilbert
    Hi All, What does the Dither radio button perform on the Perseus? How was the name Perseus chosen for the unit? Nice radio, enjoying learning from the Group.
    Message 1 of 4 , Jul 1, 2009
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      Hi All,

      What does the Dither radio button perform on the Perseus?

      How was the name Perseus chosen for the unit?

      Nice radio, enjoying learning from the Group.

      Take care,

      Greg
      Marietta, GA USA
    • Nico iv3nwv
      ... Hi Greg, the dither button enables the dithering circuits contained in the receiver A/D converter. These circuits help greatly reducing the
      Message 2 of 4 , Jul 1, 2009
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        --- In perseus_SDR@yahoogroups.com, Greg Gilbert <glg1@...> wrote:
        >
        > Hi All,
        >
        > What does the Dither radio button perform on the Perseus?
        >
        > How was the name Perseus chosen for the unit?
        >
        > Nice radio, enjoying learning from the Group.
        >
        > Take care,
        >
        > Greg
        > Marietta, GA USA
        >

        Hi Greg,

        the dither button enables the dithering circuits contained in the receiver A/D converter. These circuits help greatly reducing the intermodulations level in a pipelined A/D converter at the price of a slight increase of its noise floor. You will find a lot of resources on the net about this issue and, if you are interested in learning something more, I suggest you to give a look to what Leif, SM5BSZ wrote on his web pages.
        Better to leave the button always on, unless you need to get out of your receiver one or two dB more sensitivity.

        The Perseus name came out of an amazing discussion I had with Alberto, I2PHD, the author of Winrad, and others in the SDR Italia Yahoo group and it is the acronym of "Pretty Excellent Receiver for Software Eager Unperceivable Signals" or the italian "Piccolo Eccellente Ricevitore per Segnali Elaborati Unicamente dal Software" (which has the slightly different meaning of "small, excellent receiver for signals processed uniquely by the software").

        Regards,
        Nico - iv3nwv
      • Michael
        Can someone explain in Laymans term what dither does and really what are the benefits? This radio is amazing listening to Radio Amazonia(6,180) with all the
        Message 3 of 4 , May 29, 2012
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          Can someone explain in Laymans term what dither does and really what are the benefits? This radio is amazing listening to Radio Amazonia(6,180) with all the splatter from the Voice of Vietnam on 6,175 with 20 -30 Db signal.... AGC off LSB all at 1.6BW and readable.

           

          Mike Manning

          KB3IUL

        • lasse moell
          The A/D will show weak spurios signals and by applying noise (that is usually ouside of the frequency passband you are using) you will force the A/D to toggle
          Message 4 of 4 , May 30, 2012
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            The A/D will show weak spurios signals and by applying noise (that is usually ouside of the frequency passband you are using) you will force the A/D to toggle some of the least significant bits and spreading out the energy from the spurious signals. This may give a few dB higher noise figure, but substancially less spurs!

            Now, *IF* you do have enough noise from your antenna, this will serve as dither, and you may not need the built-in noise!

            But as you only loose a dB or two in sensitivity, you may leave it on as when you listen on a very low noise band, you still need the built-in dither to remove those false signals.

            My own experience is that if the A/D is behind a tuner i.e. stages with gain this will generate enough noise to act as dither. But if you are direct sample (like the Perseus) you may have to add dither. Especially if you are trying to evaluate the specs of your receiver in a lab with-out antenna attached.

            As a side note... I even ran into troubble using dither, that were casuing problems reading absolute values from the A/D prior to FFT stages. The dither was stronger (but outside the FFT filtered band) than the signals we were looking for.

            /Lasse SM5GLC

            --- In perseus_SDR@yahoogroups.com, "Michael" <kyw1060@...> wrote:
            >
            > Can someone explain in Laymans term what dither does and really what are the
            > benefits? This radio is amazing listening to Radio Amazonia(6,180) with all
            > the splatter from the Voice of Vietnam on 6,175 with 20 -30 Db signal....
            > AGC off LSB all at 1.6BW and readable.
            >
            >
            >
            > Mike Manning
            >
            > KB3IUL
            >
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