>> John Chowning refined the concept, moved from frequency to phase modulation, and brought FM into the digital realm.

> ?? Chowning's paper doesn't mention phase modulation at all, does it? His equation is for frequency modulation. > >https://web.eecs.umich.edu/~fessler/course/100/misc/chowning... > > I would presume that the relationships between phase and frequency modulation were known a half-century before Chowning.

Chowning says his equation is for frequency modulation, but the equation is actually phase modulation.

Chowning's equation(1):

    e = A sin(𝛼t + I sinβt)

That's phase modulation. Frequency modulation would be:

    e = A sin((𝛼 + I sinβt) t)

Very different.

That's okay; it's the first academic paper on the topic, and things were still a little wobbly.

After the paper, he and others refined the concept, moved from frequency to phase modulation, and built digital implementations.