Automatic frequency control (AFC) is a circuit used in some electronic devices to maintain a particular frequency automatically. Modern devices that are digitally tuned do not use AFC. A familiar use of AFC is to keep a radio tuned to a specific station. In some FM receivers, a device called an oscillator helps zero in on the frequency of the desired station. However, the oscillator can drift off the frequency as the radio heats up. The AFC circuit detects this frequency drift and develops a correction voltage in response. This voltage acts on the oscillator to reverse the drift and hold it on frequency. Without an AFC circuit, a listener would have to retune the radio manually each time a station began to fade.