Loading ...
Sorry, an error occurred while loading the content.
 

Re: Trying to understand FFT

Expand Messages
  • sm5le
    Fine Wolf , understand. I keep away from minus then. Tnx /Sven
    Message 1 of 4 , Jul 21, 2011
      Fine Wolf , understand.
      I keep away from minus then.

      Tnx /Sven

      --- In SpectrumLabUsers@yahoogroups.com, wolf_dl4yhf <dl4yhf@...> wrote:
      >
      > Hi Sven,
      >
      > (aargh.. the stupid 'Send' button should be disabled as long as no
      > text has been typed - sorry for my 'empty response')
      >
      > Negative overlap indeed makes little sense, and (as a percentage) is a
      > bit hard to explain.
      > Actually this is just the result of a calculation.
      > "Zero percent overlap" means that the time between two FFT
      > calculations is exactly the same as the time required to acquire enough
      > samples (to fill the input block for one FFT).
      >
      > Positive overlap means the FFT is calculated more often than the time
      > required to acquire enough samples. Thus the samples used at the end of
      > the previous FFT are used *again* at the beginning of the next FFT.
      >
      > Negative overlap actually means "no overlap", PLUS a longer gap between
      > two FFTs. Example:
      > 1024 points per FFT, 11025 samples per second -> 92 milliseconds to
      > collect enough samples for one FFT.
      > If the screen update interval (or "waterfall scroll interval") is larger
      > than 92 ms, there will be samples taken from the soundcard (or similar)
      > which do NOT enter the FFT at all, i.e. there's a gap, and you may lose
      > information for the display.
      >
      > Hope this explains it, half way.
      >
      > All the best,
      > Wolf .
      >
      >
      > Am 21.07.2011 10:43, schrieb sm5le:
      > >
      > > Hi Wolf
      > > Q. abt " overlap % " :
      > >
      > > I understand that I schall try to have about 50% overlap
      > > when using waterfall.
      > > But what happens when the overlap goes minus ( -% ) ?
      > > Is -50% the same as +50% ?
      > >
      > > I still have readings on waterfall when the overlap is minus.
      > >
      > > Tnx Sven
      > >
      > >
      >
    Your message has been successfully submitted and would be delivered to recipients shortly.