why negative frequency need in the spectrum
Listo said:
ysenthilece said:
frequency basically is no of rotations (or cycles) per second
and there are two possible directions of rotations ..one clockwise and one anticlockwise
so we can associate one direction to +ve frequencies and the other direction to -ve..
for differentiation
but is not this the phase concept ?
I know if fc is the carrier frequency and fm is modulant and if in AM I have fc, fm and fc+fm and fc-fm then if fm>fc I have a negative frequency. But this is a math speculation. I am wrong ?
//Felipe
it is not phase concept ..like phase concept is ..having a reference and the relative shift with respect to that is phase....
but moving in anticlockwise and clockwise direction corresponds to positive frequencies...u can understand better physically considering rotation ..the simple harmonic theory concept...
u cannot visualise this much in real time signal's case..as they possibly move along the positive time axis..in this case negative frequencies can be considered only for
mathematical convenience...
like we will involve with sinusoids like cos(wt) ..this correspons to superposition of
exp(jwt) and exp(-jwt) superposition of postive and negative frequencies...
""""""""""""I know if fc is the carrier frequency and fm is modulant and if in AM I have fc, fm and fc+fm and fc-fm then if fm>fc I have a negative frequency. But this is a math speculation. I am wrong ?"""""""""""""
ya if fm>fc one frequency will go to the negative side...correspondingly one from the negative side will come from the negative side to positive side..to maintain the
conjugate pairs......and it is just that as fc is usually higher it is taken as reference and there are 2 additional frequencies fc+fm and fc-fm appear...if fm is greater
we will get fm+fc and fm-fc ..
but this won't happen in practical cases...as the spectrum overlaps and results in distortion..it won't be an AM wave...