In a basic AFC circuit, an increase in oscillator frequency results in which type of control voltage?

In a basic AFC (Automatic Frequency Control) circuit, the purpose is to maintain the output frequency of an oscillator at a desired level by adjusting its control voltage based on frequency changes. When the oscillator frequency increases, the control voltage must also increase to ensure that the oscillator frequency is brought back down to the intended value.

Therefore, the correct answer highlights that an increase in oscillator frequency results in a positive change in control voltage. This positive control voltage allows the circuit to react by adjusting the oscillator downwards in frequency, thereby stabilizing the output frequency against undesired deviations.

The other options do not accurately represent this dynamic: a negative control voltage would suggest a reduction in output frequency rather than a corrective measure; a neutral answer implies no change, which is not aligned with the feedback mechanism of AFC; and a constant control voltage would not accommodate the necessary adjustments made in response to frequency variations.