Dear Marcus, On Sat, Mar 15, 2014 at 11:14 AM, Marcus D. Leech <mle...@ripnet.com> wrote: > The SBX does analog downconversion, nothing more. It knows nothing about > the incoming signal, and doesn't demodulate it in any way.
Please be clarified what do you mean by "analog downconversion". At the transmitter side, complex-based (I/Q) signal is fed into USRP. Says, the signal is x(t) = I(t) + j.Q(t) I think this is performed at transmitter SBX: y(t) = I(t).cos(wt) - Q(t).sin(wt) where w = central frequency, t = time here the y(t) is the output of SBX to the antenna. Is this what you meant by "analog upconversion" ? Whereas at the receiver side, the received signal from antenna is real signal, says, z(t) = c.y(t) = c.I(t).cos(wt) - c.Q(t).sin(wt) where c = channel attenuation The receiver SBX performs this: Retrieved I(t) = LPS( z(t).cos(wt) ) where LPS = low pass filter Retrieved Q(t) = LPS( z(t). sin(wt) ) With this process the receiver SBX is able to produce complex-based (I/Q) signal from the real signal from antenna. Is this what you meant by "analog downconversion"? If not, please describe what you mean by "analog upconversion" and "analog downconversion", because I have no idea of what you are trying to explain. It is impossible that SBX only mix the incoming complex-based signal with a central frequency and then send directly to antenna for transmission, because the simple mixing (analog upconversion) produces another complex-based signal which cannot be transmitted through antenna. A physical antenna can only transmit real signal, not complex-based signal. Please clarify, thanks. Regards, Activecat > That is what SDR is all about--the signals are represented as > complex-baseband (i/Q) format for processing by computer algorithms. > > The SBX (or any other daughtercard) is simply doing downconversion (or, > upconversion for TX). > Frequency offset in a digital demodulator implemented in software generally > drives a local correction--not the hardware. You achieve this by > bringing in a bit more bandwidth than you actually need, and then applying > frequency corrections in software. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
