The FM signal (see image 1) is applied to a 50 Ohms antenna, and I am seeking the required bandwith with the Bessel table (image 2). From the FM signal, I deduced that the information frequency is equal to 5 kHz and that the modulation index is equal to 2. So I also know that I have to look in the row of the table where mf = 2.0 and that j0, j1, j2, j3 and j4 exist in this case (significant sidebands).
The solution first says 4 x 5 kHz = 20 kHz, this I still understand (4 because components up to j4 exist and 5 kHz because that is the information frequency). Finally it says that BW = 2 x 20 kHz = 40 kHz. Why do we have to multiply the found bandwith by two? Is this always the case or does the found bandwith have to be multiplied by the modulation index?
Image 1: FM signal
Image 2: Bessel table