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Re: [softrock40] How to measure IMD?

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  • Chris Wilson
    ... 14/06/2013 12:33 Thanks Sid and Alan. I made an Audacity dual tone file with combined frequencies of 1330 Hz and 550 Hz, and checked the resulting file
    Message 1 of 61 , Jun 14 4:36 AM
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      >
      > http://www.funkamateure-dresden-ov-s06.de/index.php?article_id=259&clang=0
      > http://www.home.agilent.com/upload/cmc_upload/All/ENA_IMD_Measurement_Summary.pdf?&cc=GB&lc=eng
      > http://www.maurymw.com/pdf/applib/5C-043.pdf

      > Not comprehensive guides but should give some insights.
      > Two-tone test and look at the Spectrum Analyser for additional products.
      > 5C-043.pdf shows what you should see and the difference between the
      > carrier peak and the 3rd order product peak as seen on the Spectrum
      > Analyser gives you the figure.
      > 73 ... Sid.





      14/06/2013 12:33


      Thanks Sid and Alan.


      I made an Audacity dual tone file with combined frequencies of 1330
      Hz and 550 Hz, and checked the resulting file looked clean from the
      audio card, on a `scope. I then ran it into the Softrock Ensemble II
      RXTX audio input. I measured the TX output at the aerial socket via a
      30dB attenuator into the SA. I played with RBW and reference level
      settings as I wasn't sure of the best way to show the results. The
      image *55.jpg is with the Softrock at full 1 Watt power with sensible
      modulation levels. The earlier SA scans are with about 750 mW output.
      The `scope scan is with the Softrock at full power. I can't see any
      clipping. I sniffed the output into a dummy load. I am sure I am
      doing some things wrong, criticism welcome. Thanks! Once I am more
      confident of technique I want to look at the output after power
      amplification.

      http://www.gatesgarth.com/IMD-SCANS/imd.zip


      --
      Best Regards,
      Chris Wilson. 2E0ILY
    • warrenallgyer
      cause IMD, as measured using the ARRL protocol, is specified with reference to PEP, which is accepted to be 6 dB higher than the two tone level. I would be
      Message 61 of 61 , Jun 18 4:31 AM
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        'cause IMD, as measured using the ARRL protocol, is specified with reference to PEP, which is accepted to be 6 dB higher than the two tone level.

        I would be interested to see the mil protocol and specification if you have it.

        Lucy
        (AKA Warren Allgyer - 9V1TD)


        --- In softrock40@yahoogroups.com, FRANCIS CARCIA <carcia@...> wrote:
        >
        > The ARRL spec is the 6dB gift method not the mil method. If you add 6dB to the two tone level why don't you add 6dB to the IP3 also since it is the result of the two tones. Splain that Lucy.
        > I'm attending the school of hard knocks trying to modify a 1200 watt MRI board to HF. Fairly easy to make power but a different issue to get good IMD on all bands.
        > Frank WA1GFZ
        >
        >
        >
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