Radio Waves

1.  At what frequency does alternating current start propagating as a wave?

It always propagates as a wave as long as the frequency is not at zero.

2.  What is the range of short wave frequencies that propagate as skywaves?  

The range of wave frequencies that propagate as skywaves is between 3 and 30 megahertz.

3.  What causes ions to develop in the ionosphere?  

Ions are created when atoms and molecules lose their electrons in the ionosphere.