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.
The complex upconverter simply sums the two components after mixing, to
produce a valid real-valued analog signal.
Are you saying SBX performs this complex upconversion? But earlier
you said SBX just performed analog upconversion and nothing more.
But, again, none of the daughtercards that Ettus produces are designed to
extract information from the signal–they merely manipulate it
so that it is represented in a complex baseband form that can easily be
digitized by the ADCs.
You are saying the output of SBX is in complex baseband. This means
SBX perform complex down-conversion.
But earlier you said SBX performed just analog down-conversion and
nothing more.
One impresses information on an RF carrier by modulating it–doing “stuff”
to that carrier so that the information can be recognized by
a suitable receiver. There are hundreds of different ways of doing this,
depending on the required attributes of the resulting signal, etc.
Are you saying SBX daughtercard will automatically select the correct
way depending on the received signal?
In my flow graph there is no configuration to tell the SBX which way to
use.
You square-wave example is roughly similar to so-called OOK–on/off keying.
Such techniques are generally only used for very-low-speed
data transmission, owing to the unpleasant spectral properties of signals
with sharp edges.
There are no documentation of what SBX performs on incoming or
outgoing signals. SBX-40 400 MHz - 4.4 GHz Rx/Tx, 40 MHz BW - Ettus Research | Ettus Research, a National Instruments Brand | The leader in Software Defined Radio (SDR)
If Ettus support personnel doesn’t clear things up, the Ettus products
continue to remain mystery to many newcomers.
