frequency spectrum plot (frequency modulation)

when freq.spectrum is plotted for FM signals such as the pic below, how
would I go about calculating the power? 
Is it sum of |X(f)|^2 (i.e. square each individual compnent and add)

The solution has the solution squares each indivial compnents adds it then
halves (i.e. 1/2 . A_c^2). Why did they do this? 

>when freq.spectrum is plotted for FM signals such as the pic below, how
>would I go about calculating the power? 
>Is it sum of |X(f)|^2 (i.e. square each individual compnent and add)
>
>The solution has the solution squares each indivial compnents adds it
then
>halves (i.e. 1/2 . A_c^2). Why did they do this? 
>
>[IMG]http://i49.tinypic.com/xmoj6g.jpg[/IMG]
>

Given a sinewave with magnitude A and frequency F0 a normalized DFT will
contain two components (assuming that the sinewave have an integer number
of cycles over N samples, N is the DFT size) at +-F0 each having magnitude
of A/2. 
Sum of |X(f)|^2 will  give you 2*((A/2)^2) = (A^2)/2.
In your picture only the positive side of the spectrum is plotted. I guess
this is where the 1/2 coefficient comes from.

Alexander

>>when freq.spectrum is plotted for FM signals such as the pic below, how
>>would I go about calculating the power? 
>>Is it sum of |X(f)|^2 (i.e. square each individual compnent and add)
>>
>>The solution has the solution squares each indivial compnents adds it
>then
>>halves (i.e. 1/2 . A_c^2). Why did they do this? 
>>
>>[IMG]http://i49.tinypic.com/xmoj6g.jpg[/IMG]
>>
>