Switching Noise
It is the wideband electrical noise produced by the discontinuous current and voltage edges of the power stage. Although its fundamental component is at the switching frequency, because of the sharpness of the edges its energy spreads up to the megahertz range, and the motor cable acts like an antenna and amplifies the emission.
The noise has two propagation paths. By conduction it reaches devices sharing the same line via the supply and motor cables; by radiation it spreads into the air via the loop formed by the cables. The larger the loop area, that is, the further apart the outgoing and returning conductors are, the stronger the radiation.
That is why the most effective measures are concentrated in the cable layout. Twisting the motor supply pair largely cancels the magnetic fields of the opposing currents. Shortening the cables reduces both the loop area and the inductance. Routing the motor cable and the analog, digital and RF signal cables along separate paths, leaving at least 50 mm between them or crossing them at 90 degrees, noticeably reduces interference; in an enclosure with an inverter and on the antenna cable this separation is increased to about 20 cm. The shield of a low-frequency signal cable is earthed at one end, preferably at the driver side; on the motor power cable, where high-frequency noise dominates, 360° termination at both ends is preferred.
In brushed DC motors the driver is not the only source; brush arcing also produces wideband noise. Adding a capacitor and a ferrite bead at the motor terminals suppresses this component. In an RF remote-controlled system, the range dropping while the motor runs is most often the combined effect of these two sources.
Context where this term is used: DC Motor Driver Selection Guide