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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 distances by means of the so-called electrical telegraph via electric wires. The transmitting operator used a morse key (switch) to turn the electric current on and off in the rithm of the morse characters.

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 device on a paper strip in morse code.

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 speech 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 very little bandwidth, it was ideal for transmission via Short Wave Radio (HF). A skilled morse operator could take barely readable text that was obscured by static noise and interferences. Morse code was heavily used for (covert) transmissions during WWI and WWII.

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 the speed of his morse signals to the skills of the operator at the other end.

Morse code remained popular throughout the Cold War, but was eventually superceeded by other trans­mission methods, such as voice and (digital) telegraphy. In international shipping, morse code was used as a backup measure for many years, with the well known SOS ··· --- ··· as the internationally recognized emergency signal. Today, morse code is no longer officially used for commercial and military radio traffic. It remains relatively popular however with radio ama­teurs (HAMs), al­though in most countries – including the US and Europe – it is no longer a man­da­tory requirment for obtaining an Amateur Radio Licence. For most people it is relatively easy to learn.

Shortening messages
Sending messages in morse codes is slow compared to other transmission methods, which means that a radio station is 'on air' for a relatively long time. This has several disadvantages. In com­mer­cial radio telegraphy, messages were usually charged per letter or word, which means that long messages were more expensive than short ones. In addition, longer messages occupied the radio and its operator for a longer period of time, which could lead to congestion on the network.

Long messages were dangerous for clandestine radio stations, such as resistance fighters during WWII and secret agents during the Cold War. The longer they were 'on air', the higher the chance of detection and the higher the risk of being located by means of Radio Direction Finding (RDF).

One way to reduce the 'on air' time, was to shorten the message by means of a codebook. Various books were developed for international trading companies, such as the Peterson Inter­national Code (1929) and the Boe Code (1937).

Similar books were developed for military use, such as the SP-02201 (1935) and the short mesasge books of the German Navy that were used during WWII.

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A good example of internationally harmonised codes, is the so-called Q-code, introduced around 1909 by the British Government for use by British Ships and licenced coast stations. It was soon adopted by the rest of the world and is still used internally today.

The Q-codes were expanded during WWII, as demonstrated by the Combined Operating Signals (1944) shown in the image on the right.

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Burst encoders
Another way to reduce the 'on air' time is to send the message at a much higher speed, known as a burst transmission. This was accomplished by first recording the message on­to a medium — e.g. paper tape, film or magnetic tape — and then playing it back at very high speed.

At the receiving end, the message was recorded and then played back at a much lower speed so that it could be written out again.

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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, also known as 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.

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.

Although the Russian language uses a differerent alphabet (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 token. As the Russian alphabet has more characters (33) than 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.

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.

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.

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:

  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.
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Crypto Museum. Created: Monday 01 February 2016. Last changed: Tuesday, 30 January 2024 - 10:03 CET.
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