THE
MORSE CODE
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The Amateur Radio Service is the only officially recognised service that still uses Morse code on a regular basis, although it is still used by some military and commercial agencies throughout the world and as a system for indicating the identity of automatic beacons and similar devices. The use of Morse by Radio Amateurs should not be seen as the use of an obsolete technology by a group of individuals who have been left behind by the advance of science. Quite the reverse, as a skilled operator using Morse code will be able to achieve reliable contact under incredibly difficult conditions of interference and poor propagation causing weak and variable signals, which would result in the failure of automatic systems.
Also, the equipment required does not need to be complicated or expensive, but the speed of Morse communication is slow and the type of data transmitted is limited to upper case alpha-numeric text. Furthermore, the system relies on the human brain for coding and decoding and therefore suffers from the possibility of errors occurring, particularly when the operator is tired or stressed. Obviously, this is not the case with machine based systems.
The various former users of Morse from commercial and military agencies have turned to other systems, as equipment cost is relatively unimportant, whereas reliability, accuracy, high speed, data volume and content and no necessity to employ trained telegraphists, is of paramount importance. Also, these links often employ satellites, but even the terrestrial links do not suffer from weak signals and interference, as the optimum frequency and power levels for a particular purpose can be chosen. Additionally, excellent antenna systems and station locations can be selected to ensure strong signals. Few, if any, of these luxuries are available to the Radio Amateur, who has to rely on his own skill, limited power and whatever antenna he can erect in his own back yard.
The line telegraph was invented in the USA by Samuel Finley Breese Morse (1791-1872) but it was Alfred Vail (1807-1859) who actually invented the coding system that is now known as the Morse code. The Morse telegraph system using Vail's original code was used extensively on the telegraph circuits of the American railways. Some code groups were different to those currently forming the International Morse Code, and thanks are due to Denzil, G3KXF, for providing the listings of these American landline telegraph code groups which are included below. It is interesting to note that the Amateur Radio codes "73" (best wishes) and "88" (love and kisses), are believed to have been first used by American railway telegragh operators during the nineteenth century and the CW abbreviation for "and" is "es", which is actually the old American land-line telegraphy code group for the ampersand (&).
Morse code was also ideal for use with early radio transmitters before methods of modulating an RF carrier became available with the invention of the radio valve. Many marine installations employed spark transmitters which, by their very nature, could not be modulated, but they could be easily interrupted, or keyed, to form code groups.
Unlike the Murray Code used by teleprinters, where the code groups always contain the same number of bits, the Morse code uses varying length code groups. The letters occurring most frequently in English are represented by short groups, whereas the lesser used letters are represented by longer groups. This variable length makes automatic error detection and correction by electronic means virtually impossible. There are many computer programmes available to send and receive Morse code automatically, but these are not error correcting and are therefore prone to decoding problems if the received signal is suffering from fading or interference or is badly spaced hand-sent Morse. However, Morse that is hand-sent by a skilled operator is virtually indistinguishable from machine sent Morse.
Normal practice is to refer to a Morse "dot" as "di" or "dit", depending on its position in the group, and a Morse "dash" as "dah". When spoken, these words give a good impression of what the Morse signal actually sounds like. An example of actual Morse can be heard by clicking "sound of Morse". This is an off-air recording of Morse being used by skilled Amateur Radio operators during a contest.
The normally accepted timings for International Morse Code signals are:-
dot 1 time unit
dash 3 time units
space between elements of a letter 1 time unit
space between letters of a word 3 time units
space between words 5 time units
Obviously, the value of "1 time unit" depends on the overall speed of transmission. Speeds are normally expressed in "words per minute" or "wpm". As words can vary in length, the word "PARIS" is normally accepted as being the standard length word used for speed calculation. This means that if the word "PARIS" were to be sent twenty times in one minute, with spaces between the words, the transmission speed would be 20wpm. Obviously, if shorter words were to be sent, but the same element timings were used, the speed would still be 20wpm but more than twenty words would be sent in one minute. The original landline Morse code, which is described later, did not specify timings.
Certain phrases, when sent by Morse code, have a rhythm, similar to simple musical tunes or to elementary poetry. Probably the best known of these phrases is "BEST BENT WIRE / G", which is often sent as a message to instill a sense of code rhythm into people learning Morse. Unlike the phrase "THE QUICK BROWN FOX JUMPED OVER THE LAZY DOGS BACK 1234567890 TIMES", which is much used on teleprinter circuits as it uses all the letters of the alphabet, all the figures, checks the figures / letters shift and exactly fills one full line of text on a standard mechanical teleprinter, the Morse code phrase is chosen for its sound, as the need to check the operation of electro-mechanical sending and receiving devices is not normally required when using Morse code.
The International Morse
Code, as defined by the ITU Radiocommunication Sector (ITU-R) Study Group 8,
is shown below, together with the Russian Alphabet, special accented letters
used in languages other than English and Russian, abbreviated codes for numbers
and various procedural signals. All characters in the Morse code
are assumed to be upper case. There are no separate codes for lower
case letters.
THE INTERNATIONAL MORSE CODE A didah .- 1 didahdahdahdah .---- B dahdididit -... 2 dididahdahdah ..--- C dahdidahdit -.-. 3 didididahdah ...-- D dahdidit -.. 4 dididididah ....- E dit . 5 dididididit ..... F dididahdit ..-. 6 dahdidididit -.... G dahdahdit --. 7 dahdahdididit --... H didididit .... 8 dahdahdahdidit ---.. I didit .. 9 dahdahdahdahdit ----. J didahdahdah .--- 0 dahdahdahdahdah ----- K dahdidah -.- L didahdidit .-.. . didahdidahdidah .-.-.- M dahdah -- , dahdahdididahdah --..-- N dahdit -. ? dididahdahdidit ..--.. O dahdahdah --- - dahdididididah -....- P didahdahdit .--. = dahdidididah -...- Q dahdahdidah --.- : dahdahdahdididit ---... R didahdit .-. ; dahdidahdidahdit -.-.-. S dididit ... ( dahdidahdahdit -.--. T dah - ) dahdidahdahdidah -.--.- U dididah ..- / dahdididahdit -..-. V didididah ...- " didahdididahdit .-..-. W didahdah .-- $ didididahdididah ...-..- X dahdididah -..- ' didahdahdahdahdit .----. Y dahdidahdah -.-- ¶ didahdidahdidit .-.-.. Z dahdahdidit --.. _ dididahdahdidah ..--.- @ didahdahdidahdit .--.-. (Note 1) ! See Note 2 below + See Note 3 below Error didididididididit ........ (Note that this is sometimes abbreviated to three or four dots sent at a much slower speed than that currently being used in the message)Notes
1. Originally, there was no code group for the e-mail address "at" sign (@) in the International Morse Code, but didahdahdidah .--.- (À) was often used in French speaking countries. However, in December 2003, the ITU recommended that didahdahdidahdit .--.-. (AC) should be adopted for international use. With the agreement of all member states, this new code group has now been added to the official International Morse Code character set.2. There is no code group for the exclamation mark (!) in the International Morse Code, but dahdahdahdit ---. (the code originally used over landlines in the USA and Canada) is sometimes also used over radio links in those countries. Some years ago, the Heathkit Company were advocating the use of -.-.-- (KW) for the exclamation mark. 3. Although not included in the official listings, didahdidahdit .-.-. is often used to represent the plus sign (+). 4. When sending numbers having integer and fractional parts, the fractional part is preceded and followed by hyphens. (e.g. 2½ would be sent as 2-1/2-). 5. Amateur Radio operators often use the letter "R" (didahdit .-.) to represent a decimal point, but this convention is not generally followed by other Services.
LETTERS USED IN THE RUSSIAN ALPHABET (CYRILLIC)А didah .- Р didahdit .-. Б dahdididit -... С dididit ... В didahdah .-- Т dah - Г dahdahdit --. У dididah ..- Д dahdidit -.. Ф dididahdit ..-. Е dit . Х didididit .... Ё dit . Ц dahdidahdit -.-. Ж didididah ...- Ч dahdahdahdit ---. З dahdahdidit --.. Ш dahdahdahdah ---- И didit .. Щ dahdahdidah --.- Й ditdahdahdah .--- Ъ dahdididah -..- К dahdidah -.- Ы dahdidahdah -.-- Л didahdidit .-.. Ь dahdididah -..- М dahdah -- Э dididahdidit ..-.. Н dahdit -. Ю dididahdah ..-- О dahdahdah --- Я didahdidah .-.- П didahdahdit .--.
LETTERS USED IN THE GREEK ALPHABET
Α (alpha) didah .- Ν (nu) dahdit -.
Β (beta) dahdididit -... Ξ (xi) dahditditdah -..-
Γ (gamma) dahdahdit --. Ο (omicron) dahdahdah ---
Δ (delta) dahdidit -.. Π (pi) didahdahdit .--.
Ε (epsilon) dit . Ρ (rho) didahdit .-.
Ζ (zeta) dahdahdidit --.. Σ (sigma) dididit ...
Η (eta) didididit .... Τ (tau) dah -
Θ (theta) dahdidahdit -.-. Υ (upsilon) dahdidahdah -.--
Ι (iota) didit .. Φ (phi) dididahdit ..-.
Κ (kappa) dahdidah -.- Χ (chi) dahdahdahdah ----
Λ (lamda) didahdidit .-.. Ψ (psi) dahdahdidah --.-
Μ (mu) dahdah -- Ω (omega) didahdah .--
LETTERS USED IN THE HEBREW ALPHABET
א (alef) didah .- ל (lamed) didahdidit .-..
ב (bet) dahdididit -... ם (mem) dahdah --
ג (gimel) dahdahdit --. נ (nun) dahdit -.
ד (dalet) dahdidit -.. ס (samekh) dahdidahdit -.-.
ה (he) dahdahdah --- ע (ayin) didahdahdah .---
ו (vav) dit . פ (pe) didahdahdit .--.
ז (zayin) dahdahdidit --.. צ (tsadi) didahdah .--
ח (het) didididit .... ק (qof) dahdahdidah --.-
ט (tet) dididah ..- ר (resh) didahdit .-.
י (yod) didit .. ש (shin) dididit ...
כ (kaf) dahdidah -.- ת (tav) dah -
LETTERS USED IN THE ARABIC ALPHABET
ا (alef) didah .- ض (dad) dididitdah ...-
ب (beh) dahdididit -... ط (tah) dididah ..-
ت (teh) dah - ظ (zah) dahditdahdah -.--
ث (theh) dahdidahdit -.-. ع (ain) didahdidah .-.-
ج (jeem) didahdahdah .--- غ (ghain) dahdahdit --.
ح (hah) didididit .... ف (feh) dididahdit ..-.
خ (khah) dahdahdah --- ق (qaf) dahdahdidah --.-
د (dal) dahdidit -.. ك (kaf) dahdidah -.-
ذ (thal) dahdahdidit --.. ل (lam) didahdidit .-..
ر (reh) didahdit .-. م (meem) dahdah --
ز (zain) dahdahdahdit ---. ن (noon) dahdit -.
س (seen) dididit ... و (waw) didahdah .--
ش (sheen) dahdahdahdah ---- ي (yeh) didi ..
ص (sad) dahdididah -..- ('ayn) dit .
Ä, Ą didahdidah .-.- Ö, Ó dahdahdahdit ---.
Â, À, Á, Å didahdahdidah .--.- Ñ dadahdidahdah --.--
Ç, Ć dahdidahdidit -.-.. Ü dididahdah ..--
É, Ę dididahdidit ..-.. Ż dahdahdidit --..
È didahdididah .-..- Ź dahdahdididah --..-
Ê dahdididahdit -..-. CH, Ş dahdahdahdah ----
ACCENTED LETTERS USED IN ESPERANTO
Ĉ dahdidahdidit -.-.. Ĵ didahdahdahdit .---.
Ĝ dahdahdidahdit --.-. Ŝ didididahdit ...-.
Ĥ dahdidahdahdit -.--. Ŭ dididahdah ..--
PROCEDURAL SIGNALS
__
Wait (AS) __ didahdididit .-...
Understood (SN) __ didididahdit ...-.
End of message__(AR) didahdidahdit .-.-.
End of work (SK) __ didididahdidah ...-.-
Starting signal (KA) dahdidahdidah -.-.-
Invitation to transmit (K) dahdidah -.-
Short pause (for thought?) (II) didit didit .. ..
General call to any station (CQ) dahdidahdit dahdahdidah -.-. --.-
Closing down (CL) dahdidahdit didahdidit -.-. .-..
The following procedural signals are not used by the Amateur Radio Service:-
_____
Break-in signal (TTTTT) __ dahdahdahdahdah -----
Executive message signal (IX) dididahdididah ..-..-
Interrogatory signal (INT)__ dididahdidah ..-.-
Emergency silence signal (HM) dididididahdah ....--
Emergency Distress signal (SOS) didididahdahdahdididit ...---...
This signal replaced the original
distress signal CQD, which was
used in the early years of the
twentieth century. ___
Relay of distress message (DDD) dahdididahdididahdidit -..-..-..
An interesting point to note is that reporters, when using the American land-line telegraph system, were in the habit of sending "30" to indicate the end of a story. They would have been using the land-line code (see below) where "3" is ...-. and "0" is ——— (a long dash). Therefore, "30" would be sent as ...-.——— which becomes ...-.- when sent with standard Morse Code timing, which is the normal "end of work" signal SK.
ABBREVIATED NUMBERS
1 didah .- 6 dahdidididit -....
2 dididah ..- 7 dahdididit -...
3 didididah ...- 8 dahdidit -..
4 dididididah ....- 9 dahdit -.
5 dit . 0 dah -
ORIGINAL AMERICAN LANDLINE MORSE CODE (NOW OBSOLETE)
Note that L is a long
dash and T is a short dash, while C, O, R, Y, Z, :, ;, -, ', /, (, ), "
and & are composed of dots and spaces. Zero (0) is a very long
dash and was usually abbreviated to T. As C comprises I and E it
is difficult to see how words such as "FRIED" or "FRIEND"
would, or could, be sent, especially as there is no specific timing quoted
for this code. If you thought that mastering the normal International
Morse Code was difficult, try learning this!!!
A didah .- 1 didahdahdit .--.
B dahdididit -... 2 dididahdidit ..-..
C didit dit .. . 3 didididahdit ...-.
D dahdidit -.. 4 dididididah ....-
E dit . 5 dahdahdah ---
F didahdit .-. 6 didididididit ......
G dahdahdit --. 7 dahdahdidi --..
H didididit .... 8 dahdidididit -....
I didit .. 9 dahdididah -..-
J dahdidahdit -.-. 0 daaaah ——— (very long
K dahdidah -.- dash)
L daah —— (long dash)
M dahdah -- . dididahdahdidit ..--..
N dahdit -. , didahdidah .-.-
O dit dit . . ? dahdididahdit -..-.
P dididididit ..... : dahdidah dit dit -.- . .
Q dididahdit ..-. ; dididit didit ... ..
R dit didit . .. - didididit didahdidit .... .-..
S dididit ... ! dahdahdahdit ---.
T dah - ' dididahdit didahdidit ..-. .-..
U dididah ..- / dididah dah ..- -
V didididah ...- ( dididididit dahdit ..... -.
W didahdah .-- ) dididididit didit didit ..... .. ..
X didahdidit .-.. “ dididahdit dahdit ..-. -.
Y didit didit .. .. ” dididahdit dahditdahdit ..-. -.-.
Z dididit dit ... . & dit dididit . ...
US NAVY "MORSE" CODE (NOW OBSOLETE)
According to the 1911 edition of the "Cyclopedia of Applied Electricity", the US Navy once used a rather bizarre coding system for sending messages based on "dots" and "dashes" but having different code groups from normal Morse code. This system used a limited number of code groups and some letters and numbers shared the same group. There were no punctuation signs or procedural signals, apart from "error" and "understand". The message context was supposed to indicate which letter or figure was actually being sent. This could obviously lead to ambiguities and use of this code system was eventually discontinued.
A dahdah -- 1 didididit ....
B, 0 dahdididah -..- 2, Z dahdahdahdah ----
C didahdit .-. 3 didididah ...-
D dahdahdah --- 4, F dahdahdahdit ---.
E didah .- 5 dididahdah ..--
F, 4 dahdahdahdit ---. 6, G dahdahdidit --..
G, 6 dahdahdidit --.. 7, V didahdahdah .---
H didahdah .-- 8 dahdididit -...
I dit . 9 didahdahdit .--.
J dididahdah ..-- 0, B dahdididah -..-
K dahdidahdit -.-.
L dahdahdit --.
M, 9 didahdahdit .--.
N didit ..
O dahdit -. Error didah didah didah .- .- .-
P didahdidah .-.- Understand dahdah dahdah -- --
Q didahdidit .-..
R dahdidit -..
S dahdidah -.-
T dah -
U dididah ..-
V, 7 didahdahdah .---
W dididahdit ..-.
X dahdidahdah -.--
Y dididit ...
Z, 2 dahdahdahdah ----
KEYING DEVICES
Manual Morse code is hand-sent using a special switch called a key. There are several types of Morse key, some of which are purely mechanical, while others combine mechanical contacts and electronic circuitry. There are also computer programmes that generate the Morse code corresponding to the keyboard key being depressed and then key the transmitter accordingly, via the computer's serial port. These programmes can also decode incoming morse code signals applied as audio to the computer's sound card, displaying the message on the computer's screen.
Original Morse keys consisted of a single contact actuated by a vertically operated lever fitted with a knob, which was used to control the transmitter. A version of this type of key included the fitting of a "back contact" which was used to control the receiver. These types of key are referred to as "straight keys" and hundreds of different designs have been produced, and are still being produced, all over the world.
A variation of the straight key was developed that used a horizontal, rather than a vertical, operating lever. These keys were often referred to as "side-swipers", although this term also came to be used for electronic bug-keys. Mechanical bug-keys may be used in this mode by using only the dash (left) side of the key and some electronic bug-keys may be configured to function in a similar manner.
In the 1930s, mechanical bug-keys were developed by several US manufacturers, noteably Vibroplex and McElroy. The name "bug-key" derives from the red beetle used as the trade mark of the Vibroplex Company. Between 1947 and 1952, a version of this type of key was manufactured in the UK by Stratton and Co. Ltd. (Eddystone Radio), but these were not greeted with much enthusiasm by the CW fraternity and only about 400 were made. Mechanical bug-keys are operated by a horizontally acting "paddle" and send a string of dots when the paddle is pushed to the right but a continuous dash when pushed to the left. The timing of the dots is determined by the position of a weight along a spring loaded lever and therefore relies on the mechanical resonance of the system. Although used on ships and aircraft, movement and vibration made the action of mechanical bug-keys a little unpredictable in these circumstances.
With the advent of transistors, and more particularly integrated circuits, various types of electronic bug-key were developed. These usually employ twin parallel horizontal paddles, one generating a string of automatic dots, the other generating a string of automatic dashes. Modern tranceivers often have internal keying circuits, often a "Curtis keying chip", which only requires the connection of a suitable twin lever paddle. This type of key is often referred to as a "squeeze keyer" and the precise operation depends on whether the paddles are pressed and released separately or are squeezed together prior to release. The element length and spacing times are electronically controlled and are therefore unaffected by ambient conditions of temperature, vibration and movement etc.
Most modern electronic bug-key systems employ "iambic" keying. There are two versions of iambic keying, namely mode-A and mode-B. The original Curtis chip utilised mode-A, whereas the WB4VVF Accukeyer employs mode-B. The latest version of the Curtis chip, now manufactured by MFJ, can be programmed to use either mode. The difference between the two modes lies in what the keyer does when both paddles are released. In mode-A, the keyer completes the element being sent when the paddles are released prior to completion of the element, whereas in mode-B the keyer sends an additional element opposite to that being sent if the paddles are released prior to completion of an element. This all sounds very complicated but Morse experts insist that it is fairly easy to master and allows the sending of high speed morse for long periods without undue fatigue.
THE BAUDOT CODE
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The original, true, baudot code was a five bit code invented by the Frenchman
Emile Baudot in 1870 and was used extensively in telegraph systems. Baudot's
code was replaced by Murray's code in 1901. CCITT Alphabet No.2,
also known as ITA2 in the USA, replaced both by the early 1930's. This
is the code that is now used in all commercial radio and land-line teleprinter
applications and by the Amateur Radio Service when using RTTY.
Using five bits allows 32 different characters. To accommodate all the letters of the alphabet, the numerals 0 to 9 and some punctuation and special characters, two implementations of the 32 combinations are used to select alternate character sets. The figures character set is used after a figures shift character has been received and this state remains in effect until a letters shift is received, after which the letters character set is used (and vice-versa).
Two "Baudot codes" are in common usage. One is used in the USA and is often termed in that country, the International Telegraph Alphabet No.2 (ITA2). The one used in Europe is the international standard and is termed the CCITT Alphabet No.2. The "letters" character sets are identical in both alphabets, but the "figures" character sets differ.
In use, each five-bit word is preceeded by a start bit (space) and followed by a stop bit (mark). The stop bit is often actually one and a half bits in length, making the complete code group for each character seven and a half bits long. Words are transmitted LSB first. The duration of each bit obviously depends on the rate at which the code is being transmitted, but at the international standard speed of 50 Bauds, the bit duration is 20mS.
When idling, a continuous stream of letter shift characters is sent. System test transmissions often consist of sending test phrases such as "THE QUICK BROWN FOX JUMPED OVER THE LAZY DOGS BACK 1234567890 TIMES" or test sequencies such as "RY64RY64RY64RY". The test phrase contains all the letters and figures, checks the letter and figures shift functions and has a length of 67 characters, which is the maximum line length of a mechanical teleprinter. The test sequence ensures all bits "reverse" and also checks the letter and figure shift functions. These tests were more important when using mechanical teleprinters than now, when computerized signal decoding is usually employed. As all characters in the code are the same number of bits in length, electronic error detection is possible, although standard teleprinter links are not inherently error correcting. Variations such as SITOR and AMTOR are error correcting systems because "handshaking" between the sending and receiving stations is employed.
As with the Morse code, the character set is limited to upper case letters, figures, the space and some punctuation marks. There are also some special "characters", which perform functions such as carriage return, line feed, figures shift, letters shift, a character which is used to sound a bell and one that the receiving station initiates that causes the sending of an identifying code by the transmitting station. This latter function is only implemented in the CCITT No.2 alphabet.
In the table below, a binary 1 represents a "mark" signal and a binary 0 represents a "space" signal. For interest, the decimal, hexadecimal, and octal equivalents are also given, but teleprinter transmissions are invariably binary. The character code group is preceeded by a start bit (0) and followed by stop bit (1). The start bit has a duration of one character bit and the stop bit has a duration of one and a half character bits. Normally, land-line systems employ DC voltage levels of 0V to represent the space signal and a positive voltage to represent the mark signal. Radio teleprinter transmissions normally employ FSK, with two specific frequencies representing the mark and space signals.
Binary Decimal Hex Octal Letters CCITT No.2 Figures U.S. Figures 00000 0 0 0 Not used Not used Not used 00001 1 1 1 E 3 3 00010 2 2 2 Line Feed Line Feed Line Feed 00011 3 3 3 A - - 00100 4 4 4 Space Space Space 00101 5 5 5 S ' Bell 00110 6 6 6 I 8 8 00111 7 7 7 U 7 7 01000 8 8 10 Carriage Return Carriage Return Carriage Return 01001 9 9 11 D Who are you (WRU) $ 01010 10 A 12 R 4 4 01011 11 B 13 J Bell ' 01100 12 C 14 N , , 01101 13 D 15 F ! ! 01110 14 E 16 C : : 01111 15 F 17 K ( ( 10000 16 10 20 T 5 5 10001 17 11 21 Z + " 10010 18 12 22 L ) ) 10011 19 13 23 W 2 2 10100 20 14 24 H £ # 10101 21 15 25 Y 6 6 10110 22 16 26 P 0 0 10111 23 17 27 Q 1 1 11000 24 18 30 O 9 9 11001 25 19 31 B ? ? 11010 26 1A 32 G & & 11011 27 1B 33 Figures Shift Figures Shift Figures Shift 11100 28 1C 34 M . . 11101 29 1D 35 X / / 11110 30 1E 36 V = ; 11111 31 1F 37 Letters Shift Letters Shift Letters Shift
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