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Noise Blanker

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  • edgar
    Hi, I would like to get some help in understanding the noise blanker. The spectrum signal strength is set to dBfs, on the FFT tab, and visually the signal
    Message 1 of 3 , Feb 12, 2013
      Hi,
        I would like to get some help in understanding the noise blanker.

      The spectrum signal strength is set to dBfs, on the FFT tab,

      and visually the signal average is less than -60.0 dBfs.

      In the noise blanker says that the current average is -32.5 dBfs.

      Although is can not be seen in the image the peak signal is not 32.5 dB

      over the average, but is around 20 dBfs.

      What is the explanation for these differences?





      Regards, Edgar
      Moonah, Tasmania.

    • wolf_dl4yhf
      ... The difference is that the 20 dB shown in the noiseblanker s setup menu are the ratio between the a simple average in the time domain (i.e. broadband,
      Message 2 of 3 , Feb 12, 2013
        Am 12.02.2013 11:55, schrieb edgar:
        Hi,
          I would like to get some help in understanding the noise blanker.

        The spectrum signal strength is set to dBfs, on the FFT tab,

        and visually the signal average is less than -60.0 dBfs.

        In the noise blanker says that the current average is -32.5 dBfs.

        Although is can not be seen in the image the peak signal is not 32.5 dB

        over the average, but is around 20 dBfs.

        What is the explanation for these differences?
        The difference is that the 20 dB shown in the noiseblanker's setup menu are the ratio between the a simple average in the time domain (i.e. broadband, covering all frequencies, seen at the blanker's own input) and the peaks in the time domain (also seen at the noise blanker's own input). The noiseblanker has no connection to the spectrum analyser at all. The visual average in a certain frequency range (usually the 'displayed' frequency range) is not related to the average calculated internally by the noiseblanker.
        The reason for this non-existing relation is modularity of the software. Futhermore, the noiseblanker shall operate totally independent of the FFT settings in the spectrum analyser - especially its FFT gain.

        Average in a certain part of the spectrum depends on the FFT size, while the (broadband) average measured by the noiseblanker does not.

        Cheers,
          Wolf .
      • edgar
        Hi Wolf, Thank you for the prompt reply. Regards, Edgar Moonah, Tasmania.
        Message 3 of 3 , Feb 12, 2013
          Hi Wolf,
          Thank you for the prompt reply.

          Regards, Edgar
          Moonah, Tasmania.
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