https://www.sciencefocus.com/future-technology/solving-mh370-mystery
"Maskell and his team are analysing data from a technology called Weak Signal Propagation Reporter (WSPR, pronounced "whisper"). The WSPR network was set up in 2008 and involves amateur radio operators sending low-power test signals to receivers up to 10,000km (6,200 miles) away. These signals are stored in a huge database called WSPRnet."