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Re: [softrock40] Re: How to measure IMD?

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  • Alan
    ... Subject: [softrock40] Re: How to measure IMD? ... Warren, I suppose that makes sense. Single tone CW does not produce IMD but PSK needs more care. I
    Message 1 of 61 , Jun 16, 2013
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      ----- Original Message -----
      Subject: [softrock40] Re: How to measure IMD?


      >
      > Jack and Milt and others who have argued with my assertion that dropping one of the tones on a two tone test would cause the
      > displayed power of the remaining tone to rise; they are correct and I am wrong.
      >
      > I was the victim of my own lying eyes rather than good reasoning. My observations were based on comparing the output spectrum of
      > an RXTX driven by Rocky. And, indeed, when you change the Rocky test tones from two tone to a single tone the peak of the single
      > tone is 6 dB higher than the twin peaks.
      >

      Warren,

      I suppose that makes sense. Single tone CW does not produce IMD but PSK needs more care.
      I suppose any regular user of Rocky would realise Alex made a difference in the levels.

      But the thread has brought up some good information and links, not all is lost!

      Chris,

      I've been looking around.
      Rocky or any PSK program will produce two tones.
      I have not found any other IQ generators.

      http://www.nch.com.au/tonegen/index.html is a multi-tone generator. It looks free as it says it is, just ignore the commercials. And
      do not click "Edit, Buy, or Suite" on the ribbon. It has a good range of noises and full soundcard selection. It could be sent to a
      SDR program with VAC.

      73 Alan G4ZFQ

      > It seems that Jack was dead on in an earlier post when he speculated that the SDR program was changing the level of the two tones.
      > I verified this by connecting the audio out of the RXTX to the audio in of the RXII and viewing the signal directly and confirmed
      > that the recovered audio peaks are 6 dB different.
      >
      > Apparently the single tone test level is boosted 6 dB in order to establish the carrier level reference.
      >
      >
    • 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, 2013
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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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