Re: [Discuss-gnuradio] fft sink x-axis units

[Eric Hill Matlis]

Thanks for the response.  I guess my question is: where is that 
information carried?  Is it in the definition of the source?  The 
two definitions of the sinks look virtually identical to me:

am_rcv.py:
            pre_demod = fftsink.fft_sink_c (self, panel,
            title="Pre-Demodulation", fft_size=1024, sample_rate=if_rate)
            self.connect (src, pre_demod)
            vbox.Add (pre_demod.win, 1, wx.EXPAND)

usrp_wfm_rcv_pll.py:
            self.src_fft = fftsink.fft_sink_c (self, self.panel,
            title="Data from USRP",fft_size=512, sample_rate=usrp_rate)
            self.connect (self.u, self.src_fft)
            vbox.Add (self.src_fft.win, 4, wx.EXPAND)

eric

On Fri, 1 Dec 2006, Eric Blossom wrote:

> On Fri, Dec 01, 2006 at 03:53:36PM -0500, Eric Hill Matlis wrote:
> > I'm trying to figure out how the x-axis units work on the fftsinks.  In
> > the application "am_rcv.py", the first plot shows the incoming data
> > plotted as an fft, however the units are centered about 0 kHz.  In another
> > application, say usrp_wfm_rcv_pll.py the units are centered about the
> > actual frequency of the carrier.  Why is this?  The fft sink in both cases
> > is plotting the fft of the source, so I don't see why there should be a
> > difference.
> >
> > thanks,
> >
> > eric
>
> It depends on who coded them when.  Originally there was no interface
> for telling the FFT sink what RF frequency corresponded to DC in the
> FFT output.  Now there is.  Feel free to submit a patch for am_rcv.py.
>
> Eric