I have two WSPR beacons running, one in Sunnyvale CA and the other in Binyamina-Giv'at Ada, Israel. Both are running 200 mw into EFHW antennas just 6 meters off the ground. I can routinly pick up the signals between the two sites.

I get signal reports everwhere from a US military base at the South Pole, Australia, and throughout Europe and Asia.

The transmitters are homemade, a Rapsperry Pi Pico, and a small external circuit of a Si5355, a couple of MOSFETS and a lowpass filter -- maybe $30 in parts.

It's fascinating how the amount of electrons needed to light up a few LEDs can be heard around the world when modulated correctly.