Re: [Discuss-gnuradio] Interpolation in siggen.py

[Angilberto Muniz Sb]

Thank you very much for the explanation, Charles.
That explains what I see on the Spectrum Analyser and
why I was getting some weird signals in Matlab...

Thank you,

Angilberto.

--- Charles Swiger <address@hidden>
wrote:

> On Tue, 2006-07-18 at 08:57 -0700, Angilberto Muniz
> Sb wrote:
> > Folks,
> > I'm confused with -i option in siggen.py...
> > 
> > If I want to generate a pure 1MHz sine wave
> centered
> > at 10MHz carrier is it correct to use:
> > 
> > siggen.py --const --sine -f 1e6 -c 10e6
> > 
> > or should I use:
> > 
> > siggen.py --const --sine -f 1e6 -c 10e6 -i 32
> > 
> > or neither one ???
> > 
> > Would somebody elaborate on that?
> > 
> 
> [ posting to list in case I make any mistakes, pls
> correct ]
> 
> Quick answer: Either one, and don't use --const,
> just --sine.
> 
> That must be an older version of usrp_siggen.py as
> the
> latest does not have a -c option. You would use just
> --sine,
> as --const is for a constant (DC) signal.
> 
> In that version you could specify waveform frequency
> before
> upconverting to the output frequency, the
> upconverter (DUC)
> frequency and the interpolation.  It looks like
> this:
> 
> (waveform) ----> (duc) -----> (output freq)
>              ^           ^
>            usb_rate     128e6 
> 
> Interpolation is the ratio of DAC rate (128e6) to
> the usb_rate,
> default is 64 and you ask for 32 above. So for an
> interpolation
> of 32 the usb_rate would be 4MHz (128e6 / 32)  so
> your waveform
> could be anything from -2 to +2Mhz and the output
> would be the
> DUC freq plus the waveform frequency.
> 
> If you use  siggen.py --sine -f 1e6 -c 10e6 -i 32
> 
> you would get an output at 11Mhz. IF you use default
> interp = 64
> you might want to use a smaller waveform freq as
> 1MHz would be
> right at the edge of the usb_rate and it loses
> amplitude some.
> Something like    siggen.py --sine -f 50e3 -c
> 10.95e6 
> 
> In the newer versions -f is the DUC frequency and -w
> is the
> waveform frequency.
> 
> 
> 
> 


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