WSPR/FST4W/FST4
https://www.wsprnet.org/drupal/
https://www.wsprnet.org/drupal/wsprnet/map
https://www.youtube.com/watch?v=KYlaLT5HLkM
https://wsjt.sourceforge.io/FST4_Quick_Start.pdf
https://jl1jvt.cocolog-nifty.com/blog/files/fst4_quick_start.pdf
https://www.sigidwiki.com/wiki/FST4W
https://www.pa8s.nl/knowledge-base/frequencies-for-digital-modes/