FM modulation is so elegant it almost feels like a magic trick. After finally watching a 1940s U.S. Army Signal Corps training film, I realized just how simple frequency modulation really is—both on transmit and receive. Seeing the LC tank, limiter, and discriminator explained visually made everything click. Even better, that understanding immediately paid off in a modern, practical way: fixing an overly aggressive CW sidetone in my video QSLs using nothing more than an audio limiter. I finally understand FM modulation and it's so simple I'm amazed it wasn't developed first. I found an old US Army signal corp video that describes how both FM transmit and receive work. Audio Modulation I had not understood that modulating the transmit frequency was this simple. It all makes sense now that I see it, but I hadn't considered how simple this could be. The video demonstrates the use of an LC tank circuit to generate the required RF. By placing a a condenser mic in p...