COnfusion About Complex Signals

[aryajur]

Hello,
I am new to RF Design and I was introduced to the concept of complex signals and filters. But I cannot seem to understand the concept as to how do we have a complex signal in the real world.
For example when we multiply a real signal with a complex signal like exp(jωt) we are multiply the signal's spectrum with just a delta at frequecy ω and thus the entire spectrum just shifts to the right by ω as opposed to both right and left shifting if we multiply it with a real signla like a sine or a cosine. So how do we get the complex signal in the real world.
I found out that a book by Jan Crols Wireless CMOS Transceiver Design talks about this, but I cannot seem to find it anywhere.
If somebody can explain the concept to me or give me links or material where I can clarify this, it would be really helpful.

 

[wt70707]

In the real world a complex signal is two orthogonal signals. There are some instrument that can generate complex signal. Here is one article. May it help you.

Best Regards

 

[chihhao]

For example,

If you would like to transmit a signal like A+jB.
You just need to transmit a Acos(wt) + Bsin(wt)
that's becasue cos and sin are orthogonal.

No "j" in real world but you can use orthorgonal signal
to achieve it.

 

[aryajur]

Ok, but still the main source of my confusion is, that like if we multiply a real signal with a complex signal like exp(jωt) (which is cosωt + j sinωt) we are multiplying the signal's spectrum with just a delta at frequecy ω and thus the entire spectrum just shifts to the RIGHT by ω.
But now consider multiplying the real signal by a sinωt and a cosωt separately. This will give us 2 spectrums which on magnitude addition give us a spectrum which is equivalent to LEFT shifting of the signal's spectrum !
I don't understand this discrepancy.

Another thing is that in such a structure where we multiply a signal by a sinωt and cosωt separately, we can freely take either sinωt or cosωt as the real part and hence more possibilities...
What does all this mean??