Amplitude Modulation and Sideband Simulator

A gear mesh or bearing frequency is amplitude-modulated by load that varies with shaft rotation. In the spectrum, sidebands appear on both sides of the carrier, spaced by the modulating frequency. Their spacing points to the source, their height to the severity.

Sideband frequencies — · —

Amplitude of each sideband: —
Sideband / carrier: —
Modulation period: —
State: —

Waveform and envelope

Spectrum: carrier and sidebands

These tools are intended for preliminary assessment and training. Decisions on critical equipment should be based on on-site measurement and expert evaluation.

How to use

Pick an example or enter the carrier and modulating frequencies.
Increase the modulation depth and watch the sidebands rise and the envelope deepen.
In a real spectrum, measure the sideband spacing to find which shaft or part causes the modulation.

Theory & formulas

x(t) = A·[1 + m·cos(2πf_mt)]·cos(2πf_ct).

Expanding gives three lines: f_c (A) and f_c ± f_m (A·m/2 each).

In gearboxes, the spacing of sidebands around the gear mesh frequency (GMF = teeth × speed) equals the speed of the shaft carrying the faulty gear.

m > 1 (overmodulation) means the envelope goes below zero, matching the abrupt amplitude changes of impacting and loose systems.

Frequently asked questions

Are sidebands always a fault?

No. Healthy gears also show low sidebands. A growing number and height of sidebands over time indicates eccentricity, wear or tooth damage.