| Nominal FrequencyClassification | Frequency | Wavelength |
| VLF- Very Low Frequency | 3-30 kHz | 100,000-10,000 meters |
| LF - Low Frequency | 30-300 kHz | 10,000-1,000 meters |
| MF - Medium Frequency | 300-3,000 kHz | 1,000-100 meters |
| HF - High Frequency | 3-30 MHz | 100-10 meters |
| VHF - Very High Frequency | 30-300 MHz | 10-1 meters |
| UHF - Ultrahigh Frequency | 300-3,000 MHz | 100-10 centimeters |
| SHF - Superhigh Frequency | 3-30 GHz | 10-1 centimeters |
| EHF - Extremely High Frequency | 30-300 GHz | 10-1 millimeters |
Line-of-sight waves:
Above, approximately, 1 GHz electromagnetic waves behave much like light propagating through a clear, reasonably uniform atmosphere. When originating from a point source, they propagate in all directions and, since the area of the wavefront spreads out spherically, the intensity decreases roughly as the square of the distance from the source.
Surface waves:
Below, approximately, 500 kHz electromagnetic waves tend to follow the curvature of the earth, being guided between the earth and the ionized layers of the upper atmosphere (i.e. the ionosphere). Early experimenters soon discovered this advantage of the lower frequencies and exploited it for overseas and ship-to-shore transmission.
Sky waves:
In the 1920s it was discovered that HF waves (3-30 MHz) are reflected by the ionosphere and, thus, they are also usable for long range communication.500 kHz to 3 MHz and 30 MHz to 1 GHz are transition bands where the propagation characteristics are more complex.