Bessel function if frequency modulation and modulating index
Narrow Band FM, spectrally, looks similar to AM, in that only a carrier and two sidebands carry most of the energy.
Have you defined the &quot;data eye&quot; your system requires, to have acceptable Bit Errors?
Once you have done so, the presence or absence of the further_out Bessel components will become easier to compute.
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I think the modulating index is also called &quot;beta&quot;, and is the phase deviation.