There are international agreements that regulate the radio frequencies and modes of operation (voice, digital, Morse code, etc.) that may be utilized by different classes of license holders; although there are some differences in different countries. For the most part, one must hold a class of license that includes the ability to transmit and receive Morse code at a certain speed before being allowed to operate at frequencies less than 30 MHz. It is these lower (or HF, i.e. short wave) frequencies that are able to be propagated around the world (because they bounce off the upper layers of the atmosphere).
The code less license is usually limited to above 30 MHz (VHF & UHF). These frequencies are usually limited in range to just beyond the horizon. To extend the range, repeaters are often placed into operation by local hams. In addition, there are many satellites used by hams at VHF and UHF frequencies that allow for global communications; but schedules must be coordinated so that communications between any two locations can occur; and the time that these communications can take place is quite short due to the movement of the satellite.
So, given the proper license, equipment (HF), antenna system (usually tower with large antenna atop it), and propagation (affected by ionization of the upper atmosphere), you and I could chit chat for hours. We can even do that now, using Internet phone or IRC software.
Offered by Ron.
WB5KAN - General Class