automatic frequency control (AFC)

The automatic frequency control (AFC) is a voltage-controlled oscillator ( VCO) whose frequency is readjusted via a negative feedback with a control voltage in case of deviations due to ageing or temperature influences, so that it is always correctly tuned. The level of the control voltage depends on the frequency deviation from the set frequency. The higher the frequency deviation, the higher the control voltage and thus the frequency readjustment.