Re: [Discuss-gnuradio] Problems with fft_sink_f

[Matt Ettus]

Erlend Barstad Strand wrote:

> Hi
>
> I am quite fresh on GNU Radio so please exscuse me if ask stupid
> questions.
>
> I simlpy want to view the fft of two sines.
> Code:
> "
> 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.

Matt