An interesting side note: FM Multiplexing is as old as FM itself. Here's a link to Major Armstrong's paper, "A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation" (Proceedings of the IRE, May, 1936):
https://michael.industrynumbers.com/fm.pdf
Toward the end, he discusses multiplex operation. And, not surprisingly, he found that an FM subscarrier was far superior to an AM subcarrier. What would he have thought of the FCC's 1961 decision to adopt the Zenith system instead of Murray Crosby's FM subcarrier system (with the same sum-and difference stereo matrix)?
(Warning: Unless you're a died-in-the-wool technoid, this one may make your head swim!)
https://michael.industrynumbers.com/fm.pdf
Toward the end, he discusses multiplex operation. And, not surprisingly, he found that an FM subscarrier was far superior to an AM subcarrier. What would he have thought of the FCC's 1961 decision to adopt the Zenith system instead of Murray Crosby's FM subcarrier system (with the same sum-and difference stereo matrix)?
(Warning: Unless you're a died-in-the-wool technoid, this one may make your head swim!)