`73 once published a detailed schematic of a spark gap transmitter. At the end of the article there was a warning you didn't want to put it on the air. They had another interesting one when fluorescent light bulbs hit the market and they found out the things oscillated at lower end of 80 meters. A complete schematic for a QRP CW rig using one, with the warning "for experienced operators only" at the end. You had to love Wayne Green.
However, the propagation charts by Tomas Hood were dead on.
Anyone want to buy some colloidal silver?