Radio alphabet

A spelling alphabet, voice procedure alphabet, radio alphabet, or telephone alphabet is a set of words used to stand for the letters of an alphabet in oral communication.

Each word in the spelling alphabet typically replaces the name of the letter with which it starts (acrophony). It is used to spell out words when speaking to someone not able to see the speaker, or when the audio channel is not clear. The lack of high frequencies on standard telephones makes it hard to distinguish an 'F' from an 'S' for example. Also, the lack of visual cues during oral communication can cause confusion. For example, lips are closed at the start of saying the letter "B" but open at the beginning of the letter "D" making these otherwise similar-sounding letters more easily discriminated when looking at the speaker. Without these visual cues, such as during announcements of airline gate numbers "B1" and "D1" at an airport, "B" may be confused with "D" by the listener. Spelling out one's name, a password or a ticker symbol over the telephone are other scenarios where a spelling alphabet is useful.

A spelling alphabet is also often called a phonetic alphabet, especially by amateur radio enthusiasts, recreational sailors in the US and Australia, and NATO military organizations. However, this conflicts with the usage of the same phrase in phonetics to mean a notation used for phonetic transcription or phonetic spelling, such as the International Phonetic Alphabet, which is used to indicate the sounds of human speech.

Prior to spelling alphabets, the words used to indicate English letters were "a", "bee", "cee", "dee", "e", etc. Their spoken sounds are difficult to discriminate, particularly over a limited-bandwidth and noisy communications channel, hence the use by armed services of unambiguous phonetic alphabets for electrical voice communication (telephone and radio, but not telegraph). Confusion between letters may not be problematical in some circumstances but, particularly in some military contexts, it can have lethal consequences.

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