I will write my theory about usrp working and some math in Am modulation, because I want to be sure before continuing: If I want to modulate in DSB amplitude a carrier of saying 1GHz ,with a m(t) signal (in this case a simple 1kHz cosine tone) the carrier is sourcing by USRP module, and I have to set up the freq of usrp in 1GHz and based on Leon Couch Book the complex envelope for DSB AM should be I=Ac(1+m(t)) Q=0. (In my case Ac=1). This is equivalent to (1+m(t))(e^0) eq.1 I and Q are a complex signal that I connect to the usrp sink. Internally the usrp multiplies eq.1 by e^(2*pi*1GHz*t) resulting (1+m(t))e^(2*pi*1GHz*t) eq.2 Eq2. travels by the air to the receiver. In the USRP receiver, Eq. 2 is multiplied by e^-(2*pi*1GHz*t) resulting (1+m(t))(e^0) whose I and Q components are 1+m(t) and 0 respectively , and I can obtain the magnitude with a complex to magnitude block, this magnitude is 1+m(t). This my theory and I want to be sure if this is correct. Thanks.
on 2013-01-08 04:04
on 2013-01-08 05:03
> > to magnitude block, this magnitude is 1+m(t). > > This my"theory"and I want to be sure if this is correct....... > > Thanks. > > > _______________________________________________ > Discuss-gnuradio mailing list > Discussemail@example.com > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio So, here's a more complicated example, that factors in additive noise, which is the actual, realistic scenario. The Q term is never actually really zero, only "conceptually" zero. The real world is *never* as neat and tidy as your simulations. Also this has a -1.5kHz frequency offset, which is also realistic. complex-am