Ratio detector

[1][2][3][4] The ratio detector is a variant of the Foster–Seeley discriminator, but one diode conducts in an opposite direction, and using a tertiary winding in the preceding transformer.

The output across the diodes is connected to a large value capacitor, forming a dynamic limiter.

The suppression of the effect of amplitude variation of the incoming signal on the output of the ratio detector is based on the principle of RF dynamic limiting: A large value reservoir capacitor (C4) and bleeding resistor(s) (R1, R2) are connected across the diodes.

This results in a constant steady load and a moderate damping effect on the tuned circuit.

The values of the reservoir capacitor and the bleeding resistor(s) are chosen so that the combined time constant of these components is below the audio spectrum.