RF Noise from Inverters (VFD)
Frequency inverters drive the motor with very fast voltage transitions, and this high dv/dt produces noise spread over a wide frequency range. The noise is both conducted and radiated via the motor cable; it raises the noise floor at the wireless remote control's receiver and shortens the effective range.
The pulse edges at the inverter output can be shorter than a microsecond. A transition this fast produces harmonic energy far above the fundamental switching frequency, and the motor cable carries that energy.
- Result: the noise floor the receiver sees rises; even if the signal level does not change, the signal-to-noise ratio drops.
- Scale: a 10 dB rise in the noise floor cuts the effective range to roughly one third even if the transmitter power does not change at all, because 6 dB corresponds to a factor of two in distance.
The practical measures, in order, are these: use a shielded motor cable and terminate the shield to the chassis in a low-impedance manner on the driver side, fit a suitable line filter at the inverter input, move the receiver antenna away from the inverter enclosure and the motor cable, and do not take the receiver supply from the same line as the inverter. Bringing the antenna outside the enclosure also makes a noticeable difference; in AXI's IP67 kits the antenna and cable glands are included in the kit contents.
Context where this term is used: Wireless remote control installation: pairing, relay, safety