Samuel Morse’s Legacy – Mike Bedford (G4AEE)

Something is missing from short-wave radio bands. For the first time in over a hundred years, a sound, which would have been familiar to radio operators throughout the twentieth century, has disappeared. What I’m referring to is Morse Code and in particular to its use for maritime communication. This is the end of an era, but what an era this has proved to be, The maritime use of Morse Code lasted for more than a century and its use for landline communication pre-dated that by another sixty years. Morse was first used on-board ship in 1897 when Marconi sent a series of messages between an Italian warship and a shore station 12 miles away. But it was in 1899 that ship-to-shore communication really came to the public attention.

Two American ships were equipped with radio telegraphy equipment so they could relay news by Morse Code, of the America’s Cup yacht race to newspapers on the shore. Within a short period of time the use of Morse Code for the transmission of maritime distress calls was adopted world-wide. Indeed, the international distress call, SOS, is used in everyday speech even today. And despite the introduction of voice communication by radio back in the 20s, the advantages of Morse Code ensured that it would have a long innings at sea. That innings finally came to an end last year whet, the last countries eventually pulled the plug on Morse Code, none more poetically than the French coastguard operator who signed off with the message “Calling all. This is our last cry before our eternal silence.’

Those who had used Morse Code for much of their working lives admitted to a feeling of sadness whet, the end finally came. No doubt many others felt that the Morse Code was just an archaic remnant of a bygone age and its replacement by more sophisticated techniques was well overdue. I’d like to moderate that view somewhat. Despite the rather quaint image of a Western Union telegraph operator hunched over a Morse key in a railroad office in Deadwood, South Dakota, Morse Code was, in fact, the world’s first successful digital coding system. And as such, it’s a direct predecessor of the ASCII code which is so important to modern day digital communication.

Not only this, but Morse Code was remarkably sophisticated, given the fact that it was invented in the mid part of the nineteenth century. In one way, we could argue that it is more sophisticated than ASCII since it uses the principle of variable length encoding which was used much later, in the Huffman scheme for data compression. Rather than consign it to the rubbish bin of history, therefore, I thought it would be interesting to take a look at this, the longest standing encoding scheme of all times and so understand something of the legacy with which it has provided us as computer users.

The Beginnings

Samuel Morse was born in Massachusetts in I 791 and graduated from Yale College in 1810. Following his graduation, Morse left for London to study art. By 1813 his work begun to be recognised and some of his paintings were accepted into an exhibition at the Royal Academy. An interesting background for a man who was to become a key player in the development of the electric telegraph Morse’s interest in telegraphy was roused by a conversation over dinner during his return journey to the USA. Apparently this soon became an all consuming passion, one which occupied much of his thought for the remainder of his trans-Atlantic voyage.

Despite the fact that the name which was to become synonymous with telegraph had only just appeared on the scene, telegraph wasn’t a new concept. However, existing telegraph systems required multiple conductors between the transmitter and the receiver. An obvious example of a multiple-conductor telegraph would be a system with 26 wires, each of which would cause a lamp associated with a particular letter of the alphabet to be illuminated. In fact, the first patented system for telegraphy was developed in 1837 and made us of six wires. By applying an electrical current to different combinations of these wires, a pair of needles was deflected to point to a particular letter.

Morse’s system reduced this cabling requirement to a single conductor (plus a return path through the ground) and so.for the first time, telegraph over long distances became a practical proposition. The fact that just a single channel is required would also be key to its adoption for radio telegraph 60 years or so later. We can view the difference between Morse’s system and earlier telegraph systems as the difference between the serial and the parallel interface on a PC with Morse being equivalent to the serial method of interfacing.

Morse’s solution to sending information on a single conductor is well-known. Combinations of short and long signals (represented in writing as . and – and known colloquially as dots and dashes) were used to represent different letters, figures. and other symbols. The system was first demonstrated in 1837 but littIe interest resulted. Only Alfred Vail showed any interest, an interest which caused him to make a financial investment in Morse’s work and help him to improve and market the system. After year’s of disappointment, Congress finally made finds available for a demonstration and a telegraph line was installed between Washington and Baltimore.

On 24* May 1844, the now famous message “What hath God wrought” was transmitted, using Morse Code, over that 37-mile path. Adoption of the system came very rapidly after that first successful demonstration and by 1851 there were more than 50 telegraph companies in the USA. Morse Code was adopted as a European standard in that same year. By the time of Morse’s death in 1872, there were more than 650,000 mites of telegraph line and 30,000 miles of submarine cable around the world all reeling to the sound of Morse Code.

The picture of a telegraph operator listening to the clicks of the solenoid on a receiver is so familiar that most people don’t realise that this isn’t how Morse originally envisaged his code being used. The original configuration as demonstrated by Morse was a more automated system than this. The transmitter operator passed a stylus over the symbols on a pad in much the same way that hand-scanners read bar-codes today. The symbols were long and short metallic bars set in the insulating pad so dragging the stylus over the symbol would cause corresponding long and short signals to be transmitted. At the receiving end, current on the line would cause a pen to mark a paper tape such that the symbol for the letter received would appear as long and short lines.

Operators soon found that they were able to tell what letter had been received just by listening to the clicks of the receiver and that this was more immediate than interpreting marks from a paper tape. Similarly, the transmitting tablet was also replaced by a manual system a so called Morse key. A Morse key is simply a finely balanced spring-loaded on-off switch. When the key is pressed down an electrical current is injected onto the line; when the key is released the current stops. Surprisingly, operators were soon able to communicate in excess of 40 words per minute using these manual methods of sending and receiving Morse Code. However, the world record for receiving Morse (which is generally accepted to be more difficult than sending) is 75.2 wpm and was achieved by Ted McElroy in 1939.

You will be familiar with the Morse symbols for each of the letters and figures. There are also symbols for punctuation marks, and even for the various accented letters used in foreign languages, but we can ignore those for now. The basic time interval is the duration of the dot. Dashes are three units in length, individual dots and dashes are separated by a single-unit space, letters within a word are separated by a three-unit space, and words are separated by a seven-unit space. It’s immediately obvious, therefore, that unlike ASCII, which was originally a 7-bit code but has been lengthened to eight bits, Morse doesn’t have a fixed character length. At first sight this may seem strange, however the reason ASCII and its predecessor, the 5-bit Baudot Code, had a fixed length was to simplify the design of automated transmitting and receiving equipment. When we bear in mind that the Baudot Code was designed for use with electro-mechanical teleprinters, it’s easy to imagine how difficult things would have been with a variable length code. But if these technological hurdles are absent, as indeed they were with Morse’s telegraph, there are significant advantages to be gained from using a variable character length. Let us look at this in a bit more detail.

If we restrict ourselves, for the moment, to the alphabetic characters we find that the symbol length in Morse Code varies from 4 units (including the three-unit space following the dot) for the letter E to 16 (once again including the space) for the letters I, Q and V. It s no coincidence that the letter E is one of the most frequently encountered in the English language whereas the letters I and Q and, to a lesser extent V. are uncommon. To a first approximation, the lengths of the symbols in the Morse Code are inversely proportional to the corresponding letter’s frequency of occurrence. And it’s not hard to see that this will ensure that the overall length of the message is kept as short as possible.

In fact, a similar technique is used in Huffman encoding, one of the first methods devised for data compression by computer. In Huffman encoding, the file to be compressed is analysed to find out the frequency of occurrence of each of the characters. This first step is necessary to ensure that it will cope with any type of data, not just plain English text for which the frequency of occurrence is already known. Using this information, a coding scheme is calculated such that the shortest codes sic assigned to the most common letters and vice versa. In the case of Huffman compression, this results in the codes for the less common characters being significantly longer than the eight bits of ASCII. However, because the common characters have such sort codes the influence of these long codes is more than cancelled out and, in practice, the file length can often be reduced by 50% or more.

We’ve already seen that the world record for receiving Morse is 72 wpm. This corresponds to receiving ASCII at about 10 bits per second. When we bear in mind that today’s modems operate at 56,000 bits per second we can see that Morse would hardly gain any speed records. However, we’re forgetting one very important fact. The limiting factor in the speed at which Morse could be received was the human brain it certainly wasn’t a imitation of the code.

We could undoubtedly send and receive Morse automatically using 56K modems so a more informative comparison would be of the relative efficiencies of Morse and ASCII. ASCII is, as we all know, an 8-bit code although ten bits are actually transmitted due to the start and stop bits which have to be added. Since Morse is a variable length code we need to come up with some sort of average length to make a comparison. This averaging process clearly needs to take into account the frequency of occurrence of each of the letters.

If we do this, we find that the average length of a Morse character is just over eight bits if plain English text is being transmitted. And since Morse characters have a built-in terminator (the three-unit space) we don’t have to add start and stop bits. At first sight, therefore, Morse looks remarkably efficient and this would suggest that if we used Morse rather than ASCII for sending plain text, we could increase the throughput by about 20%. Not bad for a code invented in 1837.

However, we’re clearly not comparing like with like and if we do try to make the comparison more equitable, things look somewhat less rosy for Morse. For a start, unlike ASCII, Morse has no symbols for the lower case letters. And if we were to devise an ASCII-like code with the same character set as Morse, its symbols would be six bits long rather than eight and Morse’s advantage would be lost. However, we’re forgetting one important point about Morse — the fact that dashes are three times as long as dots. Surely dashes could have been made just twice as long as dots, something which would have had a major impact on its efficiency. And yes, with modern transmitting and receiving equipment based on computers this would have been quite feasible.

I can only assume that the exaggerated difference between the length of dots and dashes (and between the various spaces, for that matter) was to make the code tolerant of errors in an essentially manual system of transmission. Even with the earlier tablet-based transmissions, the relative lengths of the dots and dashes would have been compromised if the operator hadn’t managed to draw the stylus across the pad at a uniform speed. And with a Morse key, of course, the potential for badly sent characters is even greater. In other words, it appears that Morse was deliberately made less efficient than it could have been so that it would cope with human error.

All in, all, therefore, Morse is remarkably sophisticated given the fact that it predates computers, radio communication, the telephone, the electric light bulb and the motor car. Even the railway was in its early days when Morse Code first appeared on the scene.

Enter the Baudot Code.

As a variable length code it would have been unbelievably difficult to produce an automated Morse receiver in the days before digital electronics and computers. By an automated receiver, I mean something which would print letters on paper as opposed to Morse’s original paper tape recorder. The output from this, of course, had to be interpreted manually so we can’t consider it a fully-automated device. There are reports of a genuinely automatic electro-mechanical Morse sender having been produced in the early 1900s but it seems highly unlikely that a receiver would have been viable. So, as the need for a teleprinter — basically an electro-mechanical typewriter
which connects to another teleprinter via a phone line or a radio link — came to the fore, a new code was needed. Unlike Morse, but in common with the ASCII code which would follow it, this had to be a be a fixed length code. The Baudot code was otherwise known as the Murray which was developed for this application was in fact, a binary code. Interestingly the Baudot Code, named after its French inventor Emile Baudot -.from who’s name we get die word baud, a measure of the rate of symbol transmission -.. was introduced in 1875, well before the first practical teleprinter.

Like Morse, the Baudot code made no provision for lower case letters and, at first sight the 5-bit symbol length — even when we add tire mandatory start and stop bits — seems to represent an improvement over Morse. But a bit of binary arithmetic raises the question of how the Baudot Code could possibly have symbols as short as five bits. After all, there are only 32 combination of five binary bits yet there are 36 letters and figures and this figure increases further when we add punctutions. The secret of the Baudot Code’s success was its use of the shift principle. In fact, the character set runs to almost 64 characters and is divided into two sub-sets of 32. One of the sets is referred to as ‘letters’ and the other as ‘figures’ although the figures set also contains a number of punctuations and both sets include a number of control codes including carriage return and line feed. Two other important control codes are the LRS arid the FiGS codes which are common to both sub-sets and which cause the receiving teleprinter to switch into its letters or its figures mode respectively. And the way the receiver interprets a code depends on which mode it’s currently in. This is a reasonably efficient scheme so long as the text being transmitted is mainly textual or mainly numeric. The Baudof Code is also referred to as ITA2, lnternational Telegraph Alphabet #2 so presumably Morse is 1TAl although there don’t seem to be any records of it actually being referred to as such.

The worlds first stored program computer, the Manchester Baby, had a teleprinter based on the 5-bit Baudot code as its input and output device. Little could Baudot have imagined that his creation would. 73 years later, be a key element in an amazing new technology which, would shape the latter halfof the 20th century and beyond. Of course, the Baudot Code is no longer used in computers, but its successor, ASCII. is fundamentally very similar. Accepted as a standard as recently as 1968, ASCII is a 7-bit code arid so has no need for Baudot’s FIGS and LTRS control characters.

Mike Bedford (G4AEE) – April and May 2000.

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