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^(2pi1GHzt) resulting
(1+m(t))e^(2pi1GHzt) eq.2
Eq2. travels by the air to the receiver.
In the USRP receiver, Eq. 2 is multiplied by e^-(2pi1GHz*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.