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Re: [SpectrumLabUsers] Pulse broadened

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  • wolf_dl4yhf
    Hi Sven, That s exactly as the maths dictate: 65536 point FFT, at 11025 samples per second: - each FFT (- window) is approxiately 5.9 seconds long. In other
    Message 1 of 4 , Apr 16, 2013
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      Hi Sven,

      That's exactly as the maths dictate: 65536 point FFT, at 11025 samples per second:
      ->  each FFT (- window) is approxiately 5.9 seconds long.
      In other words, an enormous overlap between the FFT windows.

      This is the price to be paid for a good frequency resolution.
      Besides using a shorter FFT (to improve the time resolution), you could try the *REASSIGNED* spectrogram display.
      It uses the phase between consecutive FFTs to improve the resolutions.
      Details:

      http://www.qsl.net/dl4yhf/speclab/ra_spectrogram.htm


      73,
        Wolf DL4YHF



      Am 16.04.2013 17:33, schrieb sm5le:
       

      Hi all

      How to explain this:
      A 10mS pulse is feeded into EM-U 0202 and then in to SpecLab.
      On the time domain scope the pulse is OK BUT on watherfall
      it is broadened up to 5 second. Soundcard 11025 and sample 16 Bit and FFT 65536 scroll 150 mS. Picture in SM5LE folder/files.

      Tnx Sven


    • Mark McCarron
      With FFT you can either have accurate time resolution, or accurate frequency resolution. But not both at the same time. The mathematical formula does not
      Message 2 of 4 , Apr 16, 2013
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        With FFT you can either have accurate time resolution, or accurate frequency resolution.  But not both at the same time.

        The mathematical formula does not allow this.

        Regards,

        Mark McCarron


        To: SpectrumLabUsers@yahoogroups.com
        From: dl4yhf@...
        Date: Tue, 16 Apr 2013 18:27:27 +0200
        Subject: Re: [SpectrumLabUsers] Pulse broadened

         

        Hi Sven,

        That's exactly as the maths dictate: 65536 point FFT, at 11025 samples per second:
        ->  each FFT (- window) is approxiately 5.9 seconds long.
        In other words, an enormous overlap between the FFT windows.

        This is the price to be paid for a good frequency resolution.
        Besides using a shorter FFT (to improve the time resolution), you could try the *REASSIGNED* spectrogram display.
        It uses the phase between consecutive FFTs to improve the resolutions.
        Details:

        http://www.qsl.net/dl4yhf/speclab/ra_spectrogram.htm


        73,
          Wolf DL4YHF



        Am 16.04.2013 17:33, schrieb sm5le:
         
        Hi all

        How to explain this:
        A 10mS pulse is feeded into EM-U 0202 and then in to SpecLab.
        On the time domain scope the pulse is OK BUT on watherfall
        it is broadened up to 5 second. Soundcard 11025 and sample 16 Bit and FFT 65536 scroll 150 mS. Picture in SM5LE folder/files.

        Tnx Sven




      • sm5le
        Thank you Mark and Wolf. So it dont matter how thin or broad the puls is; the FFT will show the same. So maybe I will use one A/D - SpecLab for frequncy (high
        Message 3 of 4 , Apr 17, 2013
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          Thank you Mark and Wolf.
          So it dont matter how thin or broad the puls is; the FFT will show the same. So maybe I will use one A/D - SpecLab for frequncy (high FFT) and then one A/D - Speclab for the waterfall (lov FFT).
          It is Schumann 3-30 Hz my interest. I have alot of pulse noise at my sight.

          Sven

          --- In SpectrumLabUsers@yahoogroups.com, Mark McCarron <mark.mccarron@...> wrote:
          >
          > With FFT you can either have accurate time resolution, or accurate frequency resolution. But not both at the same time.
          >
          > The mathematical formula does not allow this.
          >
          > Regards,
          >
          > Mark McCarron
          >
          > To: SpectrumLabUsers@yahoogroups.com
          > From: dl4yhf@...
          > Date: Tue, 16 Apr 2013 18:27:27 +0200
          > Subject: Re: [SpectrumLabUsers] Pulse broadened
          >
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          > Hi Sven,
          >
          >
          >
          > That's exactly as the maths dictate: 65536 point FFT, at 11025
          > samples per second:
          >
          > -> each FFT (- window) is approxiately 5.9 seconds long.
          >
          > In other words, an enormous overlap between the FFT windows.
          >
          >
          >
          > This is the price to be paid for a good frequency resolution.
          >
          > Besides using a shorter FFT (to improve the time resolution), you
          > could try the *REASSIGNED* spectrogram display.
          >
          > It uses the phase between consecutive FFTs to improve the
          > resolutions.
          >
          > Details:
          >
          >
          >
          > http://www.qsl.net/dl4yhf/speclab/ra_spectrogram.htm
          >
          >
          >
          >
          >
          > 73,
          >
          > Wolf DL4YHF
          >
          >
          >
          >
          >
          >
          >
          > Am 16.04.2013 17:33, schrieb sm5le:
          >
          >
          >
          >
          >
          >
          > Hi all
          >
          >
          >
          > How to explain this:
          >
          > A 10mS pulse is feeded into EM-U 0202 and then in to
          > SpecLab.
          >
          > On the time domain scope the pulse is OK BUT on watherfall
          >
          > it is broadened up to 5 second. Soundcard 11025 and sample
          > 16 Bit and FFT 65536 scroll 150 mS. Picture in SM5LE
          > folder/files.
          >
          >
          >
          > Tnx Sven
          >
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