Editing Phase-locked loop (section)

===Spread spectrum===
All electronic systems emit some unwanted radio frequency energy. Various regulatory agencies (such as the [[Federal Communications Commission|FCC]] in the United States) put limits on the emitted energy and any interference caused by it. The emitted noise generally appears at sharp spectral peaks (usually at the operating frequency of the device, and a few harmonics). A system designer can use a spread-spectrum PLL to reduce interference with high-Q receivers by spreading the energy over a larger portion of the spectrum. For example, by changing the operating frequency up and down by a small amount (about 1%), a device running at hundreds of megahertz can spread its interference evenly over a few megahertz of spectrum, which drastically reduces the amount of noise seen on broadcast [[FM broadcasting|FM radio]] channels, which have a bandwidth of several tens of kilohertz.