Re: [Discuss-gnuradio] Failure of sending square wave over USRPs (back-to-back)

[Marcus D. Leech]

On 03/15/2014 02:57 AM, Activecat wrote:
> Dear Marcus,
>
> Please avoid adding more confusions rather than clarities.
>
> > The term "upconversion" and "downconversion" are common terms used in the
> > radio engineering industry, but may not be common among other technical folks.
> In radio engineering industry, there are more than 1 type of
> upconversion or downconversion. The common types include:
> a).  analog up-conversion:
>        The baseband real signal x(t) will be mixed with a carrier
> frequency, that its output is a real signal of
>         y(t) = x(t).cos(wt)  where w = central frequency
>
> b).  complex up-conversion:
>        The baseband complex-based signal x(t) = I(t) + j.Q(t) will be
> quadrature upconverted so that its output is a real signal of
>         y(t) = I(t).cos(wt) - Q(t).sin(wt)
>
> For clarity sometimes we need to clarify which one you were referring to.
> These two (analog vs complex upconverter) are significantly very
> different from each other.
I was using the term "analog" to distinguish from "digital".   The FPGA 
*also* has up/downconverters for doing offsetting and "mop up"
  operations on the signal stream, and those operations are, 
necessarily, performed on a digital sample stream, rather than on an analog
  electron stream.

A quadrature up (or down) converter is structurally very similar to a 
real-valued converter, and most folks in the industry refer to
  both as "upconversion" and "downconversion".  While the mathematical 
expressions that describe them are, as you note, different,
  they're performing a very similar function, and use nearly-identical 
hardware, except that in the complex (quadrature) case, you have
  two mixers, and a phase-split local oscillator.

You can see the schematics of SBX (and other cards) here:

http://www.ettus.com/files/schematics