The 2000s: The introduction of WSJT, a suite of open-source programs designed for weak-signal digital communication by amateur radio, spurred a wave of propagation observation and investigation using techniques adapted from radio astronomy. Digital voice became popular. Software defined radios (SDRs) offered capabilities that were unimaginable just a few years earlier, at prices amateurs could afford. The 2007 World Radiocommunication Conference (WRC-07) made the first-ever low frequency (LF) amateur allocation at 136 kHz.
The next two WRCs, in 2012 and 2015, allocated new amateur bands at 472 kHz and near 5 MHz respectively. WRC-19 adopted a dramatic improvement of the amateur 50 MHz band in Region 1, providing a degree of global harmonization in this intriguing part of the spectrum.
The amateur experimenters of a century ago would be amazed at what amateurs can do today — and there’s more to come!