[Discuss-gnuradio] USRP Complex Demodulation

[Roee Bar]

Hello,

I am trying to understand how the USRP performs the 
modulation/demodulation to/from higher frequencies.

Let's say I have a complex signal s(t). When I feed it to the USRP 
block, my understanding is that the USRP performs something like 
s(t)*exp(i*w*t), and transmit the real part of it, i.e.,
r(t) = 1/2 * (s(t)*exp(i*w*t) + s_c(t)*exp(-i*w*t)),
where s_c is the complex conjugate of s(t).

However, I couldn't find any explanation how the receiver brings the 
signal back to its original representation. My experiments show that 
it's not just multiplication with exp(-i*w*t) followed by low pass 
filter, but something else. The USRP source complex output is not the 
original s(t). Can someone please clarify this issue?

Thanks in advance!
Roee