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Re: [Discuss-gnuradio] FFT Scaling


From: Jeff Long
Subject: Re: [Discuss-gnuradio] FFT Scaling
Date: Thu, 13 Aug 2015 21:04:11 -0400
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On 08/12/2015 05:39 PM, West, Nathan wrote:
On Wed, Aug 12, 2015 at 12:31 PM, West, Nathan
<address@hidden <mailto:address@hidden>> wrote:

    On Wed, Aug 12, 2015 at 10:51 AM, Gerome Jan L
    <address@hidden <mailto:address@hidden>> wrote:

        There is an internal scaling effect of |fftlen| (the length of
        your FFT) in the FFT block. How do I unscale or remove the
        scaling factor in the python generated by thr GRC? I tried the
        one suggested in the faq,

        |... forward FFT --> multiply_const_cc(fftlen*[1.0/fftlen,]) -->
        reverse FFT ...

        |
        |but it doesn't seem to work. I know I am missing something. How
        do I insert this into this line of code in my python?

        1. self.fft_vxx_0 = fft.fft_vcc(1024, True,
        (window.rectangular(1024)), True, 1)
        |
        |or here?
        2. self.blocks_complex_to_mag_squared_0 =
        blocks.complex_to_mag_squared(1024)

        |
        |Thank you in advance.
        |
        |
        |
        |Attached is my flow graph.


        |

        Best,

        *Gerome Jan M. Llames *


        "Design is not just what it looks like and feels like. Design is
        how it works."  - Steve Jobs


    What do you expect the constant to be? fftlen*[1.0/fftlen,] = [1],
    unless I'm having a really slow day.


It's been pointed out to me that I am having a slow day. Taking a step
back... when you say "it doesn't seem to work", what exactly does that
mean? What do you observer that is different from what you expect?



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Try multiply_const_cc( 1.0/fftlen, vlen=fftlen )

- Jeff






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