Ratio detector

A FM detector circuit with toroidal cores

Apperence

Circuit

About

I designed a ratio detector circuit which is a classic FM demodulatior. Though you may imagine that requires a complicated special transformer, I tried to construct it with a general-purpose toroidal cores. The transformer is composed of two toroidal cores in order to obtain both loose and tight coupling, which is the key to the ratio detection circuit.
The picture below shows the frequency dependance of output voltage. With 1mW input, the vertical axis is the output voltage (0.1V / div) and the horizontal axis is the frequency (span ~ 5MHz).