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Re: [Discuss-gnuradio] Log power FFT block - bug?

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Log power FFT block - bug?
Date: Thu, 24 May 2012 15:41:44 -0400

On Mon, May 21, 2012 at 4:52 AM, Urban Kuhar <address@hidden> wrote:
> Hi everyone!
> I've been using log power FFT block for signal power estimation. I've fed
> the output of Log Power block to my custom block in which I search for peak
> in power spectrum and then I sum up bins left and right from that peak until
> the turn is reached. C++ code for power estimation:
>     // move right from the max
>     iCount = iMax_index + 1;
>     while (in[iCount] < in[iCount-1])
> fTotalPower += in[iCount++];
>     // move left from the max
>     iCount = iMax_index;
>     while (in[iCount] > in[iCount - 1])
> fTotalPower += in[iCount--];
> I've set the frame rate property to 10 frames per second (each 32768
> samples) and I use sample rate of 200kSPS. What happens is that every fourth
> power estimate sample has magnitude for about 1dB lower than the other
> three. I've looked deeper into situation and I found out that every fourth
> power spectrum from log power FFT block has about three of four bins thinner
> signal and that's why the total magnitude of the signal is lower. I've tried
> lower frame rate (2 frames per second) but situation doesn't change.
> Next I tried the FFT block instead of log power FFT and the problem
> disappears. So I am guessing that there is some kind of problem in Log Power
> FFT block. Has anyone experienced similar problem?
> Regards,
> Urban

Hey Urban,
Any chance you could send along a simulation that could be easily run
that shows the bug? That'd help us understand the problem and find a


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