Spectrum of FM signal
From page 8-5 of these class notes from UMD (using Hz instead of radians/sec), the spectrum of an FM tone can be written as

$$s(t) = A_c \sum_{n=-\infty}^{\infty}J_n(\beta)\cos[2\pi(f_c+nf_m)t]$$

where \$A_c\$ is the carrier amplitude, \$f_c\$ is the carrier frequency in Hz, and \$f_m\$ is the frequency of the modulating tone in Hz. Moving this to the frequency domain gives us:

$$S(f) = \frac {A_c} 2 \sum_{n=-\infty}^{\infty} J_n(\beta) [\delta(f - (f_c + n f_m) + \delta(f + (f_c + n f_m)]$$

We can plot this FM spectrum as delta functions with "height" (more accurately, area) \$\frac {A_c} 2 J_n(\beta)\$. Thus, the Bessel function values form the basis of the coefficients of the frequency components.

If you're doing power calculations don't forget to include the negative frequencies as well!