Morse code

Morse code is a telecommunications method which encodes text characters as standardized sequences of two different signal durations, called dots and dashes, or dits and dahs.

The dit duration can vary for signal clarity and operator skill, but for any one message, once established it is the basic unit of time measurement in Morse code.

[1][5][a] Morse code can be memorized and sent in a form perceptible to the human senses, e.g. via sound waves or visible light, such that it can be directly interpreted by persons trained in the skill.

[13] To increase the efficiency of transmission, Morse code was originally designed so that the duration of each symbol is approximately inverse to the frequency of occurrence of the character that it represents in text of the English language.

By making the two clicks sound different (by installing one ivory and one metal stop), transmissions on the single needle device became audible as well as visible, which led in turn to the Double Plate Sounder System.

Vail estimated the frequency of use of letters in the English language by counting the movable type he found in the type-cases of a local newspaper in Morristown, New Jersey.

[citation needed] In the original Morse telegraph system, the receiver's armature made a clicking noise as it moved in and out of position to mark the paper tape.

Early telegraph operators soon learned that they could translate the clicks directly into dots and dashes, and write these down by hand, thus making the paper tape unnecessary.

[19] With the advent of tones produced by radiotelegraph receivers, the operators began to vocalize a dot as dit, and a dash as dah, to reflect the sounds of Morse code they heard.

In the late 19th and early 20th centuries, most high-speed international communication used Morse code on telegraph lines, undersea cables, and radio circuits.

Although previous transmitters were bulky and the spark gap system of transmission was dangerous and difficult to use, there had been some early attempts: In 1910, the U.S. Navy experimented with sending Morse from an airplane.

[30] However, the Federal Communications Commission still grants commercial radiotelegraph operator licenses to applicants who pass its code and written tests.

In July 1939 at a contest in Asheville, North Carolina in the United States, Theodore Roosevelt McElroy (W1JYN) set a still-standing record for Morse copying, 75.2 WPM.

Today among amateur operators there are several organizations that recognize high-speed code ability, one group consisting of those who can copy Morse at 60 WPM.

Members of the Boy Scouts of America may put a Morse interpreter's strip on their uniforms if they meet the standards for translating code at 5 WPM.

Through May 2013, the First, Second, and Third Class (commercial) Radiotelegraph Licenses using code tests based upon the CODEX standard word were still being issued in the United States by the Federal Communications Commission.

However, the code exams are currently waived for holders of Amateur Extra Class licenses who obtained their operating privileges under the old 20 WPM test requirement.

In some countries, during periods of maintenance, the facility may instead transmit the signal TEST ( ▄▄▄   ▄  ▄ ▄ ▄  ▄▄▄ ), or the identification may be removed, which tells pilots and navigators that the station is unreliable.

Until 2003, the International Telecommunication Union mandated Morse code proficiency as part of the amateur radio licensing procedure worldwide.

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.

Automatic Transmitter Identification System (ATIS) uses Morse code to identify uplink sources of analog satellite transmissions.

[46][47][f][49] For example, the Android operating system versions 5.0 and higher allow users to input text using Morse Code as an alternative to a keypad or handwriting recognition.

[53][54] Another example occurred in 1966 when prisoner of war Jeremiah Denton, brought on television by his North Vietnamese captors, Morse-blinked the word TORTURE.

A more efficient binary encoding uses only two-bits for each dit or dah element, with the 1 dit-length pause that must follow after each automatically included for every 2 bit code.

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.

For example, Morse G ( ▄▄▄ ▄▄▄ ▄  + 2 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 nibbles) (as does every three-element code).

The very long time constants of 19th and early 20th century submarine communications cables required a different form of Morse signalling.

They are only used when both the sender and the receiver understand that numbers, and not letters, are intended;[citation needed] for example, one often sees the most common R-S-T signal report rendered as 5NN[‡] instead of 599.

[citation needed] Prosigns for Morse code are special (usually) unwritten procedural signals or symbols that are used to indicate changes in communications protocol status or white space text formatting actions.

In popular culture, this is mostly remembered in the book The Codebreakers by David Kahn and in the national archives of the UK and Australia (whose SIGINT operators copied most of this Morse variant).

Chart of the Morse code 26 letters and 10 numerals [ 1 ]
This Morse key was originally used by Gotthard railway , later by a shortwave radio amateur [ 2 ]
Single needle telegraph instrument
Telegraph key and sounder ; the signal is "on" when the knob is pressed, and "off" when it is released, length and timing of the dits and dahs are entirely controlled by the telegraphist
Morse code receiver that records on paper tape
Comparison of historical versions of Morse code with the current standard. Left : Later American Morse code from 1844. [ 17 ] Center : The modified and rationalized version used by Friedrich Gerke on German railways. Right : Current ITU standard.
A U.S. Navy Morse Code training class in 2015. The sailors will use their new skills to collect signals intelligence .
A commercially manufactured iambic paddle used in conjunction with an electronic keyer to generate high-speed Morse code, the timing of which is controlled by the electronic keyer. [ c ]
A U.S. Navy signalman sends Morse code signals in 2005.
Cayo Largo Del Sur VOR-DME
The sound of non-directional beacon WG , on 248 kHz, located at 49.8992 North, 97.349197 West, [ 38 ] near Winnipeg's main airport
Vibroplex brand semiautomatic key [ d ] (informally called a "bug" since it vaguely resembles a stick insect ).
Morse code recorded on the 40 meter ham radio band (31 sec).
Representation of Morse code SOS
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 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 are circled in red with red text and are complete; unofficial prosigns are orange and are mostly complete.
Scout movement founder Baden-Powell's mnemonic chart from 1918