The next product is a bit more interesting, because it is something that has the potential to be useful: a power-line filter
. It is made and marketed by Quantum Products, and is called the ElectroClear, QRT Enhancement System.
"Engineers should position a power-line filter so incoming power lines connect to it with short leads.
Engineers may think they will have difficulty removing low-frequency EMI on a PCB, so they design in a power-line filter. "But the magnetic components get much larger when you have EMI at 150 kHz or below, so control low-frequency EMI at its source."
To keep that type of conducted electromagnetic interference (EMI) within the limits specified by government agencies, engineers rely on good design techniques and power-line filters. A typical filter removes unwanted signals by providing them with a low-impedance path to ground, or it blocks them with a high-impedance connection and "forces" them into a lower impedance path.