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Morse code
Morse code is a method for encoding text into a series of dashes and dots, that can be sent (transmitted) by means of sound, light or radio waves, and that can be decoded be a skilled listener without special equipment. The system is named after the American artist Samuel Finley Breese Morse [2] who co-developed an electrical telegraph system at the beginning of 1836 [1].
 
In his original design, Samuel Morse had only planned to use numbers (0-9). The code was later adapted for more general use by Alfred Vail, who added letters, special characters and punctuation marks to the code, in such a way that the most frequently used characters (in the English language) were represented by the shortest codes (e.g. the letter 'e' is a single dot).

In the early days, morse code was used to send short text messages over long distance by means of the so-called electrical telegraph via (long) wires. The transmitting operator used a morse key (switch) to turn the electric current on and off in the rithm of the morse codes.
  
Samuel Finley Breese Morse, the co-inventor of the Morse Code. Click for a larger image. Copyright unknown.

At the receiving end, the electric current engaged an electro-magnet, that would 'click' in the rithm of the morse signals. In most cases the codes were directly written to paper by attaching a pen to the electro-magnet, resulting in the original series of dots, dashes and spaces. The image below shows the word MESSAGE printed by a telegraph in morse code on a paper strip.


This way, a message could be recorded, even if the operator was not present at the receiving station. The dots and dashes were later translated into text again. Some operators were trained to recognize the 'clicks' of the electro-magnet, translate them to text and write them down directly.
 
In the 1890s, morse code began to be used for radio communication as well, as it was not possible to transmit voice at the time. When used over radio, the dots and dashes are represented by a series of short and long tones, often called dits and dahs by the operators.

As morse code requires limited bandwidth, it was ideal for transmission via Short Wave Radio (HF). A skilled morse operator could still 'read' the text even if the signal was noisy and disturbed. Morse code was heavily used for (secret) transmissions during WWI and WWII.
  
Former radio interceptor Louis van Erck using a wartim B2 spy set for communication in morse.

The image above shows former Dutch radio interceptor Louis van Erck using a wartime Type 3 Mk.II (B2) spy radio set, during a demonstration at Museum Jan Corver in November 2008, as part of the exhibition Secret Messages. Being an experienced radio operator, Louis is capable of smoothly adapting his sending speed to the skills of the operator at the other end.

Morse code remained popular during the major part of the Cold War, but was eventually replaced by other transmission methods. In the Navy, morse code was used as a backup measure for many years, with the well known SOS ··· --- ·· being internationally recognized as an emergency signal. Today, morse code is no longer officially used, but it remains relatively popular with radio amateurs (HAMs), although it is no longer mandatory for a HAM Radio Licence is most countries, including the US and most European countries. For most people it is rather easy to learn.
 
Direction Finding (DF)
As it takes relatively long to send a message in morse code, transmitting stations, such as WWII clandestine agents, were prone to detection by means of Direction Finding. During WWII, both the Germans and the allies developed sophisticated methods for such Direction Finding (DF).
 
In the later part of WWII, but more predominantly during the Cold War, this was partly solved by the development of the so-called Burst Encoder, a device that could record a message in morse code and play it back at very high speed.

This shortened the transmission significantly and reduced the risk of detection and direction finding. At the receiving end, the message was recorded (e.g. on a wire-recorder), played back at much lower speed, and written out again. The image on the right shows an example of a Cold War burst encoder that was used by the USSR.
  
Russian burst encoder using during the Cold War. Click for more information about burst encoders.

Such devices generally consisted of a recording device (the actual burst encoder), a storage medium (often a cassette of some kind), and a play back device (the burst transmitter). They were used extensively by the USSR and its Warsaw Pact allies, but also by the Western Allies. The US also used them during the Vietnam War, to make efficient use of the limited frequency space.
 
Expanded Latin alphabet
In the International Morse Code, each character of the basic ISO Latin alphabet is represented by a a series of dots and dashes, sometimes called dits and dahs, in such a way that the most frequently used letters (in the English language) are represented by the shortest codes. The table below shows the Latin characters that are most commonly used (by radio amateurs) today.

Extended Latin morse code alphabet. Click to download as PDF file.  Crypto Museum.

 
Dichotomic chart
The branched table below shows how the morse code of each Latin character is constructed. The letters with the highest frequency (i.e. the letters are used the most in English) are higher up in the table. A left-branch represents a dot, whilst a right-branch represents a dash. Special characters and punctuation marks are at the bottom. Click the image to download it as a PDF file.

Dichotomic chart of morse characters. Click to download as PDF file.  Crypto Museum.

 
Russian
Although the Russian language requires a differerent character set (Cyrillic), the same morse mode as for the Latin-oriented languages is used. The characters that have a Latin equivalent (e.g. the Russian letter 'Б' is the Latin letter 'B') use the same morse code. As the Russian alphabet has more characters (33) that the Latin alphabet (26), some additional codes are used. The table below can be used as a reference. Click the table to download it as a PDF file.

Russian (Cyrillic) morse code alphabet. Click to download as PDF file.  Crypto Museum.

 
Learning morse code
When learning morse code, one first has to memorize the basic alphabet, starting with the letters (A-Z) and numbers (0-9). While the tables above can be used as a guide, some people require a visual aid when trying to memorize the morse characters. The diagram below is an example of such a visual symbolic aid. Click the image to download it as a PDF file.

Visual symbolic representation of the morse code alphabet. Click to download as PDF file.

Over the years, many methods for learning morse code have been developed. Some methods start with sending and receiving at a very slow speed, which is then gradually increased over time, whilst other methods claim that is is better to start sending the characters at the target speed, with long spaces in between them. The spaces are than gradually reduced.
 
Timing
Although morse code can be transmitted at any given speed, the relative timing between the various elements is fixed. Generally speaking, morse code consists of five elements: a dot (one unit), a dash (three units), an inter-element gap (one unit), a gap between letters (three units) and the gap between words (7 units). The diagram below shows the timing for each of the elements.


In the above diagram, the text 'MESSAGE TO' has been used as an example. It is also possible to represent morse code by a constant stream of digital bits (ones and zeros). If we define a tone as a '1' and a silence as a '0', the above example would produce the following bit-stream:

111011100010001010100010101000101110001110111010001000000011100011101110111

 
References
  1. Wikipedia, Morse code
    Retrieved February 2013.

  2. Wikipedia, Samuel Morse
    Retrieved February 2013.

  3. Crypto Museum, Extended Latin Morse Code Alphabet
    Crypto Museum, November 2008.

  4. Crypto Museum, Dichotomic chart of morse characters
    Crypto Museum, November 2008.

  5. Crypto Museum, Russian (Cyrillic) morse code alphabet
    Crypto Museum, November 2008.

  6. Crypto Museum, Visual symbolic representation of the morse code alphabet
    © Copyright 1989, AG Reinhold, Cambridge, UK. Crypto Museum, November 2008.

Further information

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Crypto Museum. Created: Monday 01 February 2016. Last changed: Sunday, 15 January 2017 - 12:32 CET.
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