Editing Morse code (section)

===Amateur radio===
[[File:VibroplexBug.jpg|thumb|right|[[Vibroplex]] brand semiautomatic key{{efn|name=bug_op_note}} (informally called a "bug" since it vaguely resembles a [[stick insect]]). ]]
International Morse code today is most popular among [[amateur radio]] operators, in the mode commonly referred to as "[[continuous wave]]" or "CW".{{efn|
The name ''[[continuous wave]]'' was chosen to distinguish the single-frequency [[List of amateur radio modes|transmission mode]] from the sliding-frequency [[damped wave (radio transmission)|damped wave signals]] from now-banned [[spark-gap transmitter]]s. Although the modern {{sc|on}} / {{sc|off}} signal itself is interrupted, not continuous, it does (ideally) maintain a single, constant frequency [[carrier wave]] throughout any one transmission.
}}
Other, faster keying methods are available in radio telegraphy, such as [[frequency-shift keying]] (FSK).

The original amateur radio operators used Morse code exclusively since voice-capable radio transmitters did not become commonly available until around 1920. Until 2003, the [[International Telecommunication Union]] mandated Morse code proficiency as part of the amateur radio licensing procedure worldwide. However, the [[World Radiocommunication Conference]] of 2003 made the Morse code requirement for amateur radio licensing optional.<ref name=IARU-2003-07-03/> Many countries subsequently removed the Morse requirement from their license requirements.<ref name=ARRL-Letter-2005-08-12/>
[[File:2022-11-06 0204 40 Meter CW.ogg|thumb|Morse code recorded on the [[40-meter band|40&nbsp;meter ham radio band]] (31&nbsp;sec).]]
Until 1991, a demonstration of the ability to send and receive Morse code at a minimum of five words per minute ({{sc|wpm}}) was required to receive an amateur radio license for use in the United States from the [[Federal Communications Commission]]. Demonstration of this ability was still required for the privilege to use the [[shortwave|shortwave bands]]. Until 2000, proficiency at the 20&nbsp;{{sc|wpm}} level was required to receive the highest level of amateur license (Amateur Extra Class); effective April 15, 2000, in the FCC reduced the Extra Class requirement to 5&nbsp;{{sc|wpm}}.<ref name=ARRL-2000-Part-97-amended/> Finally, effective on February 23, 2007, the FCC eliminated the Morse code proficiency requirements from all amateur radio licenses.

While voice and data transmissions are limited to specific amateur radio bands under U.S. rules, Morse code is permitted on all amateur bands: [[2200-meter band|LF]], [[630-meter band|MF low]], [[160-meter band|MF high]], [[High frequency|HF]], [[VHF]], and [[UHF]]. In some countries, certain portions of the amateur radio bands are reserved for transmission of Morse code signals only.

Because Morse code transmissions employ an [[on-off keying|on-off keyed]] radio signal, it requires less complex equipment than other [[List of amateur radio modes|radio transmission modes]]. Morse code also uses less [[signal bandwidth|bandwidth]] (typically only 100–150&nbsp;[[hertz|Hz]] wide, although only for a slow data rate) than voice communication (roughly 2,400~2,800&nbsp;Hz used by [[single-sideband modulation|SSB voice]]).

Morse code is usually received as a high-pitched audio tone, so transmissions are easier to copy than voice through the noise on congested frequencies, and it can be used in very high noise / low signal environments. The fact that the transmitted power is concentrated into a very limited bandwidth makes it possible to use narrow receiver filters, which suppress or eliminate interference on nearby frequencies. The narrow signal bandwidth also takes advantage of the natural aural selectivity of the human brain, further enhancing weak signal readability.{{citation needed|date=December 2020}} This efficiency makes CW extremely useful for [[DXing|DX (long distance) transmissions]], as well as for low-power transmissions (commonly called "[[QRP operation]]", from the [[Q-code]] for "reduce power"). There are several amateur clubs that require solid high speed copy, the highest of these has a standard of 60&nbsp;{{sc|WPM}}. The [[American Radio Relay League]] offers a code proficiency certification program that starts at 10&nbsp;{{sc|wpm}}.

The relatively limited speed at which Morse code can be sent led to the development of an extensive number of abbreviations to speed communication. These include prosigns, [[Q code]]s, and a set of [[Morse code abbreviations]] for typical message components. For example, '''{{sc|CQ}}''' is broadcast to be interpreted as "seek you" (I'd like to converse with anyone who can hear my signal). The abbreviations '''{{sc|OM}}''' (old man), '''{{sc|YL}}''' (young lady), and '''{{sc|XYL}}''' ("ex-young lady" – wife) are common. '''{{sc|YL}}''' or '''{{sc|OM}}''' is used by an operator when referring to the other operator (regardless of their actual age), and '''{{sc|XYL}}''' or '''{{sc|OM}}''' (rather than the expected '''{{sc|XYM}}''') is used by an operator when referring to his or her spouse. '''{{sc|QTH}}''' is "transmitting location" (spoken "my Q.T.H." is "my location"). The use of abbreviations for common terms permits conversation even when the operators speak different languages.

Although the traditional [[telegraph key]] (straight key) is still used by some amateurs, the use of mechanical semi-automatic [[keyer]]s{{efn|
name=bug_op_note|
The semiautomatic key paddle, when pressed to the right by the thumb, kicks a clockwork-like horizontal pendulum that generates a series of ''dits'', the length and timing of which are controlled by a sliding the pendulum weight toward the rear of the unit. When pressed to the left by the knuckle of the index finger, the paddle generates a single ''dah'', the length of which is controlled by the operator. Multiple ''dahs'' require multiple presses. Left-handed operators may use a key built as a mirror image of this one.
}}
(informally called "bugs"), and of fully automatic electronic [[keyer]]s (called "single paddle" and either "double-paddle" or "iambic" keys) is prevalent today. [[Software]] is also frequently employed to produce and decode Morse code radio signals. The [[ARRL]] has a readability standard for robot encoders called ''ARRL Farnsworth spacing''<ref name=ARRL-x9004008-Farnsw/> that is supposed to have higher readability for both robot and human decoders. Some programs like WinMorse<ref name=Winmorse-custom-Farnsw/> have implemented the standard.