Table 3: Bell-206-B4 gearbox modulation sidebands (assuming planets are evenly spaced).

Sidebands

−50(99 − 5)/4 (NI)
−40(99 − 4)/4 (NI)
3 (550.52 Hz)1(993)/4 (I)
−20(99 − 2)/4 (NI)
−1 (561.97 Hz)0(99 − 1)/4 (NI)
0 (567.71 Hz)0(99 − 0)/4 (NI)
1 (573.74 Hz)1(99 + 1)/4 (I)
20(99 + 2)/4 (I)
30(99 + 3)/4 (NI)
40(99 + 4)/4 (NI)
5 (596.36 Hz)1(99 + 5)/4 (I)

0: suppressed. 1: dominance: nonzero vibration. : number of teeth on the ring gear (99 teeth). : number of planetary gears (4 planets). I: integer. NI: noninteger.