Editing Morse code (section)

==Representation, timing, and speeds==
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'''International Morse code is composed of five elements:'''<ref name=ITU-R-M-1677/>{{rp|at=§3}}

# short mark, dot or ''dit'' ({{morse|dot}}): "dit duration" is one time unit long
# long mark, dash or ''dah'' ({{morse|dash}}): three time units long
# inter-element gap between the ''dits'' and ''dahs'' within a character: one dot duration or one unit long
# short gap (between letters): three time units long
# medium gap (between words): seven time units long (formerly five<ref name=TR-Cairo-1938/>)

===Transmission===
Morse code can be transmitted in a number of ways: Originally as electrical pulses along a [[telegraph]] wire, but later extended to an audio tone, a radio signal with short and long tones, or high and low tones, or as a mechanical, audible, or visual signal (e.g. a flashing light) using devices like an [[Aldis lamp]] or a [[heliograph]], a common flashlight, or even a car horn. Some mine rescues have used pulling on a rope - a short pull for a dot and a long pull for a ''dah''. Ground forces send messages to aircraft with panel signalling, where a horizontal panel is a dah and a vertical panel a dit.<ref>[https://www.nato.int/nato_static_fl2014/assets/pdf/pdf_2018_01/20180111_nato-alphabet-sign-signal.pdf NATO phonetic alphabet, codes & signals.] Poster, 2018.</ref>

Morse messages are generally transmitted by a hand-operated device such as a [[telegraph key]], so there are variations introduced by the skill of the sender and receiver — more experienced operators can send and receive at faster speeds. In addition, individual operators differ slightly, for example, using slightly longer or shorter ''dahs'' or gaps, perhaps only for particular characters. This is called their "fist", and experienced operators can recognize specific individuals by it alone. A good operator who sends clearly and is easy to copy is said to have a "good fist". A "poor fist" is a characteristic of sloppy or hard to copy Morse code.

==== Digital storage ====
Morse code is transmitted using just two states (on and off). Morse code may be represented as a binary code, and that is what telegraph operators do when transmitting messages. Working from the above ITU definition and further defining a [[bit]] as a dot time, a Morse code sequence may be crudely represented a combination of the following five bit-strings:

# short mark, dot or ''dit'' ({{morse|dot}}): '1'b
# longer mark, dash or ''dah'' ({{morse|dash}}): '111'b
# intra-character gap (between the ''dits'' and ''dahs'' within a character): 0
# short gap (between letters): '000'b
# medium gap (between words): '0000000'b

The marks and gaps alternate: ''Dits'' and ''dahs'' are always separated by one of the gaps, and that the gaps are always separated by a ''dit'' or a ''dah''.

A more efficient binary encoding uses only two-bits for each ''dit'' or ''dah'' element, with the 1&nbsp;''dit''-length pause that must follow after each automatically included for every 2&nbsp;bit code. One possible coding is by number value for the length of signal tone sent one could use '01'b for a ''dit'' and the automatic single-dit pause after it, and '11'b for a ''dah'' and the automatic single-''dit'' following pause, and '00'b for the ''extra'' pause between letters (in effect, an end-of-letter mark). That leaves the code '10'b available for some other purpose, such as an escape character, or to more compactly represent the ''extra'' space between words (an end-of-word mark) instead of '00 00 00'b (only 6&nbsp;''dit'' lengths, since the 7th is automatically inserted as part of the prior ''dit'' or ''dah''). Although the ''dit'' and inter-letter pauses work out to be the same, for any letter containing a ''dah'', the two-bit encoding uses digital memory more compactly than the direct-conversion bit strings mentioned above. Including the letter-separating spaces, all International Morse letter codes pack into 12&nbsp;bits or less (5&nbsp;symbols), and most fit into 10&nbsp;bits or less (4&nbsp;symbols); most of the [[prosigns for Morse code|procedural signs]] fit into 14&nbsp;bits, with a few only needing 12&nbsp;bits (5&nbsp;symbols); and all digits require exactly 12&nbsp;bits.

For example, Morse '''{{sc|g}}''' ({{morse|dash|dash|dot}} + 2&nbsp;''extra'' empty dits for "end of letter") would binary-encode as '11'b, '11'b, '01'b, '00'b; when packed it is '1111 0100'b = 'F4'x, which stores into only one [[byte]] (two [[nibble]]s) (as does every three-element code). The bit encoding for the longer method mentioned earlier the same letter would encode as '1110'b, '1110'b, '1000'b = '1110 1110 1000'b = 'EE8'x, or one-and-a-half bytes (three nibbles). The space saving allows small devices, like portable memory keyers, to have more and longer International Morse code sequences in small, conventional device-driver [[microprocessor]]s' [[random access memory|RAM]] chips.

===Cable code===
The very long [[time constant]]s of 19th and early 20th&nbsp;century [[submarine communications cable]]s required a different form of Morse signalling. Instead of keying a voltage on and off for varying times, the dits and dahs were represented by two polarities of voltage impressed on the cable, for a uniform time.<ref name=Beauchamp-2001/>

===Timing===
Below is an illustration of timing conventions. The phrase '''{{sc|MORSE CODE}}''', in Morse code format, would normally be written something like this, where {{code|–}} represents ''dahs'' and {{code|·}} represents ''dits'':

<syntaxhighlight lang="text">
 −− −−− ·−· ··· ·       −·−· −−− −·· ·
  M  O   R   S  E        C   O   D  E
</syntaxhighlight>

Next is the exact conventional timing for this phrase, with {{code|▓}} representing "signal on", and {{code|˽}} representing "signal off", each for the time length of exactly one dit:
{{disable VE top}}
{{smalldiv|1=
<syntaxhighlight lang="text">

          1         2         3         4         5         6         7         8
 12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789

  ———M———   —————O—————   ———R———   ——S——   E       —————C—————   —————O—————   ———D———   E

  ▓▓▓˽▓▓▓˽˽˽▓▓▓˽▓▓▓˽▓▓▓˽˽˽▓˽▓▓▓˽▓˽˽˽▓˽▓˽▓˽˽˽▓˽˽˽˽˽˽˽▓▓▓˽▓˽▓▓▓˽▓˽˽˽▓▓▓˽▓▓▓˽▓▓▓˽˽˽▓▓▓˽▓˽▓˽˽˽▓
     ↑          ↑       ↑       ↑            ↑
   symbol      dah     dit   letter        word
   space                     space        space

</syntaxhighlight>
}}
{{disable VE bottom}}

===Spoken representation===
Morse code is often spoken or written with ''dah'' for dashes, ''dit'' for dots located at the end of a character, and ''di'' for dots located at the beginning or internally within the character. Thus, the following Morse code sequence:
{{small| {{blockquote|
<syntaxhighlight lang="text">
M   O   R   S  E          C    O   D  E
−− −−− ·−· ··· · (space) −·−· −−− −·· ·
</syntaxhighlight>}} }}
is spoken (or sung):

{{small| {{blockquote|''{{nobr|Dah dah {{spaces|3}} dah dah dah {{spaces|3}} di dah dit {{spaces|3}} di di dit {{spaces|3}} dit, {{spaces|3}} }} {{spaces|3}} {{nobr| {{spaces|3}} Dah di dah dit {{spaces|3}} dah dah dah {{spaces|3}} dah di dit {{spaces|3}} dit. }}''}} }}

For use on radio, there is little point in learning to read ''written'' Morse as above; rather, the ''sounds'' of all of the letters and symbols need to be learned, for both sending and receiving.

===Speed in words per minute===
All Morse code elements depend on the dot / ''dit'' length. A ''dah'' is the length of 3&nbsp;dits (with no gaps between), and spacings are specified in number of ''dit'' lengths. An unambiguous method of specifying the transmission speed is to specify the ''dit'' duration as, for example, {{val|50|ul=milliseconds}}.

Specifying the ''dit'' duration is, however, not the common practice. Usually, speeds are stated in words per minute. That introduces ambiguity because words have different numbers of characters, and characters have different ''dit'' lengths. It is not immediately clear how a specific word rate determines the ''dit'' duration in milliseconds.

Some method to standardize the transformation of a word rate to a ''dit'' duration is useful. A simple way to do this is to choose a ''dit'' duration that would send a typical word the desired number of times in one minute. If, for example, the operator wanted a character speed of 13&nbsp;words per minute, the operator would choose a ''dit'' rate that would send the typical word 13&nbsp;times in exactly one minute.

The typical word thus determines the ''dit'' length. It is common to assume that a word is 5&nbsp;characters long. There are two common typical words: '''{{sc|PARIS}}''' and '''{{sc|CODEX}}'''. '''{{sc|PARIS}}''' mimics a word rate that is typical of natural language words and reflects the benefits of Morse code's shorter code durations for common characters such as '''{{sc|e}}''' and '''{{sc|t}}'''. '''{{sc|CODEX}}''' offers a word rate that is typical of 5&nbsp;letter code groups (sequences of random letters). Using the word '''{{sc|PARIS}}''' as a standard, the number of ''dit'' units is 50 and a simple calculation shows that the ''dit'' length at 20&nbsp;words per minute is {{val|60|u=milliseconds}}. Using the word '''{{sc|CODEX}}''' with 60&nbsp;dit units, the ''dit'' length at 20&nbsp;words per minute is {{val|50|u=milliseconds}}.

Because Morse code is usually sent by hand, it is unlikely that an operator could be that precise with the ''dit'' length, and the individual characteristics and preferences of the operators usually override the standards.

For commercial radiotelegraph licenses in the United States, the Federal Communications Commission specifies tests for Morse code proficiency in words per minute and in code groups per minute.<ref name=US-CFR-Title-47/>{{rp|at=§13.207(c), §13.209(d)}} The [[FCC]] specifies that a "word" is 5&nbsp;characters long. The Commission specifies Morse code test elements at 16&nbsp;code groups per minute, 20&nbsp;words per minute, 20&nbsp;code groups per minute, and 25&nbsp;words per minute.<ref name=US-CFR-Title-47/>{{rp|at=§13.203(b)}} The word per minute rate would be close to the '''{{sc|PARIS}}''' standard, and the code groups per minute would be close to the '''{{sc|CODEX}}''' standard.

While the Federal Communications Commission no longer requires Morse code for amateur radio licenses, the old requirements were similar to the requirements for commercial radiotelegraph licenses.<ref name=US-CFR-Title-47/>{{rp|at=§97.503, 1996}}

A difference between amateur radio licenses and commercial radiotelegraph licenses is that commercial operators must be able to receive code groups of random characters along with plain language text. For each class of license, the code group speed requirement is slower than the plain language text requirement. For example, for the Radiotelegraph Operator License, the examinee must pass a 20&nbsp;word per minute plain text test and a 16&nbsp;word per minute code group test.<ref name=FCC-radiotelegraph/>

Based upon a 50&nbsp;dit duration standard word such as '''{{sc|PARIS}}''', the time for one ''dit'' duration or one unit can be computed by the formula:

:{{math|''T'' {{=}} {{sfrac|{{val|1200|fmt=commas}}|''W''}}}}

where: {{mvar|T}} is the unit time, or ''dit'' duration in milliseconds, and {{mvar|W}} is the speed in [[words per minute|{{sc|wpm}}]].

[[High-speed telegraphy]] contests are held; according to the ''[[Guinness Book of Records]]'' in June&nbsp;2005 at the [[International Amateur Radio Union]]'s 6th&nbsp;World Championship in High Speed Telegraphy in [[Primorsko]], Bulgaria, Andrei Bindasov of [[Belarus]] transmitted 230&nbsp;Morse code marks of mixed text in one minute.<ref name=Guinness-records-Morse/>

===Farnsworth speed===
Sometimes, especially while teaching Morse code, the timing rules above are changed so two different speeds are used: A character speed and a text speed. The character speed is how fast each individual letter is sent. The text speed is how fast the entire message is sent. For example, individual characters may be sent at a 13 words-per-minute rate, but the intercharacter and interword gaps may be lengthened so the word rate is only 5&nbsp;words per minute.

Using different character and text speeds is, in fact, a common practice, and is used in the Farnsworth method of [[#Learning methods|learning Morse code]].

===Alternative display of common characters in International Morse code===
{{See also|Huffman coding}}
Some methods of teaching Morse code use a [[dichotomic search]] table.
[[File:Morse code tree3.png|thumb|center|upright=3.5|International Morse code [[binary search]] tree: The graph branches left for each ''dit'' and right for each ''dah'' until the character representation is reached. Official [[International Telecommunication Union|ITU]] codes are shown as black letters on dark grey, and are complete, including punctuation; a few non-ITU extensions are shown in grey letters on light grey, but many others are left out. ITU [[Prosigns for Morse code|prosigns]] are circled in red with red text and are complete; unofficial prosigns are orange and are mostly complete.]]