Power filters are electronic circuits designed to locate and eliminate surges, harmonic transient currents, spikes, and other unwanted signals in power distribution systems and electrical equipment such as computers, television sets, and other devices. There are many different types of power filters. Examples include power line filters, power supply filters, microwave filters, and harmonic line filters. A power line filter removes impurities and artifacts from an alternating current (AC) that energizes components. In addition, power line filters protect equipment from potentially damaging voltage surges. A power supply filter helps reduce conducted noise to acceptable limits for equipment. A microwave filter is used to eliminate unwanted frequency components in the output from microwave transmitters. Microwave filters are typically inserted between a power amplifier and an antenna. Higher harmonics generated by phase control firing of thyristors require the implementation of a harmonic filter, so that the harmonics do not break through the AC distribution system. Harmonic filters require tuning to line and load conditions. Other power filters are also commonly available.