PIM distortion occurs when two signals pass through a non-linearity in a transmission line, creating an unwanted third signal. The third signal causes problems with transit and receive transmissions, causing noise, interference, and in the worst case a full frequency channel being allocated to a false signal. Non-linearities include ferrous metals, poor contact joints, and loose metallic particles. PIM distortion is typically seen in high-power applications, such as in wireless base stations.