> The AM band in the United States covers frequencies from 540 kHz up to 1700 kHz

I wonder if there's something useful to do with that range. It's a big chunk of lower frequencies right there, in the range that reliably does over-the-horizon propagation (although better at night perhaps according to wikipedia?)

The benefit of AM being super simple to build a receiver for is less relevant nowadays, FM is trivial to get radios for now, and ham radio uses SSB for voice for the most part in the lower frequency ranges.