The Radio Station That Bridge Built (opens in new tab)

Those are shortwave, that has vastly wider propagation than the 833 khz that the Bridge radio company was using.

For the broadcast station, one key to very long distance is the 250 foot towers.

Around 1920 my great-grandfather, I am told, built a 1w radio transmitter in his basement in San Francisco, with an aerial running up the outside of the chimney. I've no idea what frequencies he used, but he regularly spoke with fellow enthusiasts in Europe and New Zealand - several of them came to visit, when my grandfather was a child. By 1930 there was enough interference that was no longer possible with such a low-power set.