# communication basics

Discussion in 'Wireless & RF Design' started by raks_universe, Mar 22, 2010.

1. ### raks_universe Thread Starter Active Member

Mar 15, 2009
67
0
What does complex quantity present in the signal represents,,,,,,,

why we use complex terms in signal.....

and im so confused with this complex quantity,,,,In communication too we r taking complex envelope etc.

what is need for using complex variables...

2. ### Papabravo Expert

Feb 24, 2006
10,022
1,760
The use of complex numbers and complex algebra allows us to deal with behavior that would otherwise be difficult to describe and keep track of. It accurately describes the effect on AC voltage and AC current of reactive components. The properties of the imaginary unit (i or j) make the calculations come out correctly.

If you know of another, simpler method of doing the same thing, then by all means tell us. I'm all ears!

3. ### Duane P Wetick Active Member

Apr 23, 2009
408
19
Probably the simplest explanation is that there are phase orientations involved in adding AC signals, thus the need for complex numbers when signals are combined; modulated for another word.

Cheers, DPW [ Everything has limitations...and I hate limitations.]

4. ### Thevenin's Planet Active Member

Nov 14, 2008
183
1
This is a good suject in which I was baffled until long trials and frustrations but finally I came to find out that complex number is dealing with voltage lead and lag in capacitors and inductors mainly.You should remember this teaching in electricty level of learning.In capacitors the current leads the voltage by 90 degree if its considered by it self.And in Inductors the current leads the voltage by 90 degrees if considered by it's self.But with a combination of resistors and reactances then the degrees become less then 90 degrees.Check out the allaboutcircuits E-book on complex numbers for futher instructions on how to use the equations. Good Luck

5. ### raks_universe Thread Starter Active Member

Mar 15, 2009
67
0
What does the negative frequency denotes...??

Pls explain the concept of negative frequency.....

Fourier transform of unit impulse function(delta) function gives d.c(constant) value in frequency domain, what it is denoting...??....what it explains for the component at negative frequency region.....

Pls explain the negative frequency with above example...