Indeed, 'tis a puzzlement. I can draw three continuous sine waves of apppropriate amplitude, frequency and phase, corresponding to carrier, upper sideband and lower sideband, and I can add them point by point, and I can duplicate a 100% modulated AM signal waveform as we understand it. I have to believe that this works backwards; if I make this waveform by modulating a carrier in an AM transmitter, then I am synthesizing the same continuous sine waves. It seems to me that an on-off sequence would only differ from the sine wave modulated condition in the complexity of the sideband spectrum.
But in the real world, sometimes theory does not produce results. For example, if there was some FM audio subchannel modulating the on-off carrier, I would simply not be able to receive it while the transmitter was off, even if I was positive that the carrier was theoretically still present. So as Dennis asked on the amradio mailing list - if a tree falls in the forest, and nobody sees it or hears it... did it really fall? When I am receiving zero, I can only know that I am receiving zero. And if there is interference, I may not even be sure I am receiving zero! And as Don pointed out, there is the question of reality, and the appearance of reality. If I took the time scale to infinity, then if a carrier was EVER transmitted, even for only a second, I would have to say that it existed for all of time. That's ridiculous! I only think that because I am integrating over all time, and then generalizing. I guess it's off when it's off, and it's signalling us when it's on. So the question becomes, at what time scale do we stop seeing beat notes, and start seeing variations and on-off switching? Bacon, WA3WDR
