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Re: Rob Sherwood tests Perseus

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  • Leif Asbrink
    Hi Henry, ... I did not see any response to your posting. Have you seen fig. 1 here? http://www.sm5bsz.com/perseus/perseus.htm I do not remember whether
    Message 1 of 121 , May 1, 2009
      Hi Henry,

      > Do you have a plot of the IMD response of the Perseus at 2nd, 3rd and
      > higher orders, with dithering and without, as per figs 4 and 5 in Lief
      > Asbrink's QEX paper (IMD in Digital Receivers)?

      I did not see any response to your posting.
      Have you seen fig. 1 here?
      http://www.sm5bsz.com/perseus/perseus.htm

      I do not remember whether switching off dithering made any difference
      on IM3 measurements, but it does affect IM2 slightly as you can see in fig 3.


      73

      Leif / SM5BSZ
    • DF9IC
      ... Simulation (p. 21) via measurement (p. 22)? -90 dBc/Hz is so far from anything useable - -120 dBc/Hz is ugly, -140 dBc/Hz is acceptable and -160 dBc/Hz is
      Message 121 of 121 , May 11, 2009
        --- In perseus_SDR@yahoogroups.com, Henry <hjrech@...> wrote:
        >
        > Leif,
        >
        > Can you explain the difference (viz. the level of the noise floor)
        > between the plot with predistortion on p. 21 with the plot on page 22
        > also with predistortion?

        Simulation (p. 21) via measurement (p. 22)?

        -90 dBc/Hz is so far from anything useable - -120 dBc/Hz is ugly, -140 dBc/Hz is acceptable and -160 dBc/Hz is good. At least in my metric (VHF driven) :-)

        Maybe he really makes a direct feedback (in this low bandwidth, a concept called "Carthesian feedback loop" is viable) and picks up lots of noise from anywhere with the ADC. Instead of using an adaptive predistortion based upon a series approach with adjustable coefficients.

        BTW do not expect too much from this radio - it has still the old generation ADC in the RX (like the SDR14 - see other thread). I could get one for testing since last year but did not yet find the time to prepare a competition.

        73 Henning
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