Hi Patrick, > The calculation is good however, you must consider that inside the bandwidth > covered by I and Q, you have an upper side transmission, let's say: > A.(cos(wt1+phi1)+jsin(wt+phi1)) or A. exp(jwt+Phi1) but also a lower side > transmission lets' say: > B.(cos(-wt+phi2)+jsin(-wt+phi2)) or B. exp(-jwt+Phi2). > If you suppose only A.(cos(wt1+phi1)+jsin(wt+phi1)) you restrict the problem > to a pure USB transmission without LSB side. > > So the analytic mixing will shift: > > * w to 0: A. exp(jwt+Phi1) * exp(-jwt)=A exp(Phi1) > > * and -w to -2*w with a possibility of folding if -2*w<wsampling/2 (folding > outside the baseband so...): > B. exp(-jwt+Phi2) * exp(-jwt)=B exp(-2jwt+Phi2)
I am afraid that some people might find this confusing. Sure you are right - but what I wanted to point out is that ANY frequency w will be shifted to a single new frequency. This shift equals the frequency of the complex LO. The algebra is linear so one may have any number of frequencies present simultaneously - they will all be shifted by the same amount in the same direction (and some perhaps across the Nyquist limit.) It is valid for w as well as for -w with the results describe. The origin of this thread was whether one needs a filter to remove the mirror frequency as one does in ordinary mixers. The answer is NO. 73 leif
