Re: [Discuss-gnuradio] gnuradio 101

[Krzysztof Kamieniecki]

Quoting Martin Dvh <address@hidden>:

> cswiger wrote:
> > One thing I don't understand tho: if a typical mux of
> > 0xF0F0F0F0 feeds zeros to all DDC Q inputs, and ADC 0
> > to all DDC I inputs, nchannels = 1 sends data from DDC 0
> > only, and looking at the DDC block diagram in figure 3 at:
> > 
> > http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html
> > 
> > how is it we can a complex stream to the software? Why aren't
> > all the Q values also 0 ( zero * nco-cos ) ?    Is the
> > decimating low pass filter also a hilbert?
> I think simple complex math:
> out.complex=ADC.complex * NCO.complex
> out.real=ADC.real*NCO.real - ADC.imag*NCO.imag
> out.imag=ADC.imag.NCO.real + ADC.real*NCO.imag
> 
> ADC.imag=0 ==>
> out.real=ADC.real*NCO.real
> out.imag=ADC.real*NCO.imag
> 

And NCO.imag is only zero if the NCO frequency has not been changed from zero
since USRP powerup.