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signal

-              v79
+              v80
 S(t) = I(t) + Q(t)''i''
 S(t)*sin(wt) -> low pass filter -> I(t)
 S(t)*cos(wt) -> low pass filter -> Q(t)
+- S(t)*sin(wt) -> low pass filter -> I(t)
+- S(t)*cos(wt) -> low pass filter -> Q(t)
 However, we don't know the phase of the sine wave. Another way to think about this is we don't know when to start receiving the signal. AND, even though the machine might tell us that the carrier is 1 GHz, there's no way it can send EXACTLY 1 GHz and might actually be something like 999.9 MHz. If we don't account for these, we get an IQ plot that looks like below. This signal is BPSK so we expect IQ to be across the real axis, though that's clearly not what we received.