Radio skip is a natural phenomenon in which broadcasts arrive from places you do not normally expect -- sometimes hundreds or thousands of miles away. Although the maximum range for high-frequency radio and television broadcasts is normally about sixty miles, changing conditions in the upper atmosphere dramatically increase that distance. Ham radio operators and other broadcasters are familiar with radio skip, but you can experience it with any pocket radio.

Radio Signals
Radio waves are part of the electromagnetic spectrum -- radiant energy that also includes X-rays and visible light. In the vacuum of space and in the part of the atmosphere closest to the Earth, radio signals travel in straight lines; however, large objects, such as mountains and high-rise buildings, can block or reflect radio transmissions.

Ionosphere
In the upper parts of the Earth's atmosphere, ultraviolet and other radiation from the Sun strips electrons from oxygen atoms, turning them into electrically-charged ions. These ions conduct electricity and interfere with radio waves. The ionosphere is much thinner than the air you breathe, and it forms complex and turbulent layers that move with temperature and weather.

Line Of Sight Transmission
Because a radio signal travels in straight lines, the farthest it normally travels is to the horizon; it cannot go past the curve of the Earth, which becomes a significant factor about 60 miles from the transmitting antenna. Radio technicians call this the "line-of-sight" limit; if you cannot see the antenna because it's past the horizon, you cannot receive the broadcast.

Wavelength And Frequency
Radio waves have a wavelength, as water waves do, and a frequency. The wavelength depends on the speed of light and the radio frequency: the higher the frequency, the shorter the wavelength. Relatively low-frequency radio waves, such as those from AM broadcasts, have long wavelengths that easily bounce off of the ionosphere; this is why you can pick up AM stations well past the normal 60-mile limit. Higher-frequency signals, such as FM radio and television, have shorter wavelengths that normally pass through the ionosphere, so these transmissions have a limited range.

Signal Reflections And Skip
When parts of the ionosphere become denser and have more electrical charge, its ability to reflect all types of radio waves increases. In particular, heavy sunspot activity and solar flares dramatically affect the ionosphere in this regard. Radio transmissions experience more skip, and you can receive broadcasts from distant locations. You can receive more distant stations at night than during the day because of the Sun's influence on the ionosphere.

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