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Types of Radio Waves

๐Ÿ›ฉ️Radio waves of different frequencies have unique characteristics as they propagate through the atmosphere. VLF, LF, & MF waves have relatively long wavelengths and utilize correspondingly long antennas.

๐Ÿ›ฉ️Radio waves produced at these frequencies ranging from 3kHz to 3mHz are known as ground waves or surface waves. They follow the curvature of the earth as they travel from the broadcast antenna to the receiving antenna. Ground waves are particularly useful for long distance transmissions. Automatic direction finders (ADF) & LORAN navigational aids use these frequencies.

✈️High frequency (HF) radio waves travel in a straight line & do not curve to follow the earth’s surface. This would limit transmissions from the broadcast antenna to receiving antennas only in the line-of-sight of the broadcast antenna except for a unique characteristic. HF radio waves bounce off of the ionosphere layer of the atmosphere. This refraction extends the range of HF signals beyond line-of-sight. As a result, transoceanic aircraft often use HF radios for voice communication. The frequency range is between 2 to 25 MHz. These kinds of radio waves are known as sky waves.

✈️Above HF transmissions, radio waves are known as space waves. They are only capable of line-of-sight transmission & do not refract off of the ionosphere. Most aviation communication & navigational aids operate with space waves. This includes VHF (30-300MHz), UHF (300MHz-3GHz), & super high frequency (SHF) (3Ghz-30Ghz) radio waves.

✈️VHF communication radios are the primary communication radios used in aviation. They operate in the frequency range from 118.0 MHz to 136.975MHz. 700 & 20 separate and distinct channels have been designated in this range with 25 kilohertz spacing between each channel. Further division of the bandwidth is possible, such as in Europe where 8.33 kilohertz separate each VHF communication channel. VHF radios are used for communications between aircraft & ATC as well as air-to-air communication between aircraft. When using VHF, each party transmits & receives on the same channel. Only one party can transmit at any one time

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