(AFC, Automatic Frequency Control) A circuit that automatically keeps an oscillator on frequency. When present on a TV set, the AFC control usually applies to the TV channel tuning section. It keeps the tuner locked to the channel selected. It could also be labeled AFT for Automatic Fine Tuning. Modern sets with digital tuning often have this capability built in, without an option to turn it on or off. Under normal circumstances this function is desirable and should be left on. An ability to turn it off might be helpful when the TV set is using an antenna to receive distance signals in the face of strong local signals. The function of AFC can be applied to other circuits in a viewing device. In those cases we’ve not seen an ability to turn the AFC on or off. If it exists it is always on.