Why does a frequency inverter (VFD) reduce remote control range?
An inverter output switches with very fast voltage changes (high dv/dt) and this produces a wideband noise spectrum. An unshielded motor cable turns that energy into an antenna and radiates it, raising the receiver's noise floor. If the noise floor rises by 10 dB the effective range shortens by about 3.16 times even if the transmitter power does not change at all; the fact that 6 dB doubles the distance is calculated from the same scale.
What determines range is not the absolute signal level but the difference between signal and noise. The inverter gnaws at that difference from below: the received signal stays the same while the noise rises, the SNR falls and the receiver stops decoding. The complaint typically appears while the machine is running and disappears when it stops; that is the strongest clue for diagnosis.
Mitigation methods:
- Change the motor cable to a shielded type and earth the shield only at the inverter end, with a short and wide connection.
- Do not route the motor cable through the same duct as the antenna cable and signal cables; use a separate duct, and a right-angle crossing where unavoidable.
- Move the receiver antenna as far as possible from the inverter enclosure and from the motor cable route.
- Fit a suitable EMC filter on the input side of the inverter and consider lowering the switching frequency as far as the manufacturer permits.
- If you take the receiver supply from the same line as the inverter, separate it or filter it; the noise can carry part of the way along the conductive path.
Each of these measures gains a few dB; when combined it is common for them to exceed 6 dB, and that alone doubles the range.
Full topic: 433 MHz or 2.4 GHz?