Single Sideband, or SSB, has been the predominant amateur radio voice mode for many decades now. It has bee traditionally generated by analogue means, generating a double sideband and filtering awa…
You’re not off the mark. Honestly not a bad overview to squeeze into a few sentences. Here’s some extra detail for those who remain more curious.
The circuit complexity reduction happens by changing the math behind the radio signal. Much like how you can describe a vector in cartesian coordinates (a point in x, y) or in polar coordinates (a point in angle and length), choosing how to represent the radio math allows for different techniques to arrive in the same answer. That’s what the author did: he picked a polar modulating scheme over a quadrature modulation scheme. (Note, there are even more mathy ways to modulate a radio signal, but those are what the author is presenting to us.)
The author’s choice avoids generating unwanted frequencies that must be filtered out before amplifying. That’s components on the board that don’t need to be designed nor exist. A solid win.
The drawback? Polar modulation is non-linear in frequency space. What that means is certain frequencies are over-represented and others are under-represented. Imagine playing notes on a piano where some keys are very loud and others you could hardly hear them. That’s the unwanted non-linearity.
Herein lies the trick: what’s bad can be turned into good. Power amplifiers typically need to be linear. Imagine a piano that works fine but the auditorium’s loud speakers make it sound terrible. Those loud speakers would be a non-linear amplifier. The trick is that it’s possible to match the modulator’s non-linear behavior with a power amplifier’s non-linear behavior to end up with a clean signal! A non-linear piano and a non-linear loud-speaker can produce beautiful music! This engineering trick unlocks all kinds of non-linear power amplifier architectures (that’s the “C/E/F” described in the article) which are drastically more energy efficient than linear ones (linear designs max out around 65% efficient).
You’re not off the mark. Honestly not a bad overview to squeeze into a few sentences. Here’s some extra detail for those who remain more curious.
The circuit complexity reduction happens by changing the math behind the radio signal. Much like how you can describe a vector in cartesian coordinates (a point in x, y) or in polar coordinates (a point in angle and length), choosing how to represent the radio math allows for different techniques to arrive in the same answer. That’s what the author did: he picked a polar modulating scheme over a quadrature modulation scheme. (Note, there are even more mathy ways to modulate a radio signal, but those are what the author is presenting to us.)
The author’s choice avoids generating unwanted frequencies that must be filtered out before amplifying. That’s components on the board that don’t need to be designed nor exist. A solid win.
The drawback? Polar modulation is non-linear in frequency space. What that means is certain frequencies are over-represented and others are under-represented. Imagine playing notes on a piano where some keys are very loud and others you could hardly hear them. That’s the unwanted non-linearity.
Herein lies the trick: what’s bad can be turned into good. Power amplifiers typically need to be linear. Imagine a piano that works fine but the auditorium’s loud speakers make it sound terrible. Those loud speakers would be a non-linear amplifier. The trick is that it’s possible to match the modulator’s non-linear behavior with a power amplifier’s non-linear behavior to end up with a clean signal! A non-linear piano and a non-linear loud-speaker can produce beautiful music! This engineering trick unlocks all kinds of non-linear power amplifier architectures (that’s the “C/E/F” described in the article) which are drastically more energy efficient than linear ones (linear designs max out around 65% efficient).
Big thanks for providing this extra context, that made it a lot clearer for me