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Re: [Discuss-gnuradio] Problems with fft_sink_f

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] Problems with fft_sink_f
Date: Thu, 07 Sep 2006 20:48:09 -0700
User-agent: Mozilla Thunderbird 1.0.8-1.1.fc4 (X11/20060501)

Erlend Barstad Strand wrote:


I am quite fresh on GNU Radio so please exscuse me if ask stupid

I simlpy want to view the fft of two sines.
self.src0 = gr.sig_source_f (sampling_freq, gr.GR_SIN_WAVE, 350, ampl)
self.src1 = gr.sig_source_f (sampling_freq, gr.GR_SIN_WAVE, 440, ampl)

self.src = gr.add_ff ()

self.connect(self.src0, (self.src, 0))
self.connect(self.src1, (self.src, 1))

self.scope = fftsink.fft_sink_f (self, panel, 512,
      sampling_freq, fft_rate = 1)

self.connect (self.src, self.scope)
vbox.Add (self.scope.win, 1, wx.EXPAND)

when the window opens there seems to be a sensible spectrum for a very
short period of time, then it flats out and doesnt make much sense.

I have tried changing the fft_rate, sampling_freq and various other
parameters, but the same problem occurs. I have also tried using
fftsink.make_fft_sink_f, but also then a similar problem occurs. After
a very short time the blue line drawing the spectrum disappears.

Have you tried changing the amplitudes and/or the fft scaling? I think your signal is falling below the bottom of the display.


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