Re: [Discuss-gnuradio] Intermediate Frequency of RFX2400

[Eric Blossom]

On Wed, Jan 28, 2009 at 04:09:54PM -0800, Yong J. Chang wrote:
> 
> Hi all,
> 
> Now I'm confusing intermediate frequency of RFX2400. I cannot find any
> references about that.
> As I know so far, RFX2400 converts carrier frequency(we selected it on
> python script) band freq to 10Mhz intermediate freq. This 10Mhz signal is
> passed to FPGA. Therefore, DDC frequency is fixed on 10Mhz. Is it right?
> 
> Any help is appreciated.
> 
> Y.C

The RFX boards are quadrature direct conversion.  We feed them complex
basebase within a few MHz of DC.  The DDC/DUC are used for fine tuning since
the VCO on the daughterboards have a non-zero step size.

You can see what's happening by examining the result from u.tune().

I highly recommend the USRP FAQ:

  http://gnuradio.org/trac/wiki/UsrpFAQ
  
http://gnuradio.org/trac/attachment/wiki/UsrpFAQ/USRP_Documentation.pdf?format=raw

See also the nice diagrams on this page:

  http://gnuradio.org/trac/wiki/UsrpRfxDiagrams

Eric