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

(image source wspr.aprsinfo.com)

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