Re: [Discuss-gnuradio] really get to zero Hz

[Eric Blossom]

On Wed, Sep 05, 2007 at 09:12:53AM -0700, Hans Glitsch wrote:
> Hi,
> 
> I want to frequency shift my signal down to zero Hz.  I can do that
> with the ddc and a freq_xlating_fir_filter block, but there is
> always some frequency error.  Is there a block that will auto fine
> tune the shift frequency so the output is as close as possible to 0
> Hz?
> 
> If so, is there an example of how to use it?
> 
> Another potential complication is that there is no constant carrier
> for the signal I'm receiving.
> 
> Thanks,
> Hans

Generally people use some kind of PLL or FPLL to track out the
frequency offset.  There must be some way to generate an error signal
in your case, even with no carrier, otherwise you wouldn't know that
you're not at zero ;)

There are some existing pll blocks;  take a look in
gnuradio-core/src/lib/general/gr_*pll*.{h,cc}


Eric