Low power long range radio communication

By combining several factors, you really can achieve amazing results;

Collect the RF power to an extremely narrow bandwidth
Low modulation rate allowing the receiver to integrate over time
Using a frequency high enough to penetrate the D-layer with low losses
Using a frequency low enough to refract in the F2 layer
Timing the ionospheric conditions according to D- and F2 layers
Generous forward error correction coding

This above is a digital transmission of 0.1 watt (20dBm) from Sweden to Australia, over 15000km using the WSPR protocol. For comparison, your cell phone uses many times this transmission power. :-)

6 Hz (sic) modulation bandwidth
Modulation 4-FSK
50 bits payload transmitted over just under 2 minutes time
Modulation speed ~1.5 baud
Data speed ~0.5 bps
28 MHz carrier
Vertical (omnidirectional) antenna

Not any data rates you may surf the web with, but I find it amazing you actually can transmit messages literary across half the world, without any infrastructure, using almost undetectable RF power and equipment available to more or less everyone.

/By Mikael Q Kuisma