Some Basics of Frequency Modulation

Here’s a really great educational project for learning about frequency modulation using your Analog Discovery and Analog Parts Kit.






This is an entirely analog circuit, utilizing several basic analog “building block” sub-circuits, like a voltage follower/buffer, some filters, an envelope detector, and a differentiator. Check out the build instructions here.

We first modulate a carrier wave with a voltage controlled oscillator, or VCO, and a .wav file. We then use a differentiator to convert the signal to an AM wave instead of an FM wave. That allows us to use an envelope detector to pick out the modulation frequency, which is much lower than the carrier frequency. Once we capture the data from the modulated wave, we do some filtering and amplifying until we have fully recovered the original audio from the .wav file and then reproduce it on the speaker.

Have fun building!


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