The following report appeared in the newsletter of the Blackheath Scientific Society and is reproduced with permission
Enderby Wharf by Richard Buchanan on 21st November 2014
Mr Buchanan began by showing pictures of Enderby Wharf in its heyday when it was the site of the Telegraph Construction and Maintenance Company (Telcon) in Greenwich. The company had been formed 150 years ago in 1864, and was the first to make a successful trans-Atlantic telegraph cable in 1866. It remained the principal subsea telegraph cable manufacturer in the world, despite competition, until the mid-20C.
Its site is midway along the riverfront between the Old Royal Naval College and the 02. Historically marshland, the Navy first used the site in 17C for a gunpowder store, but the people of Greenwich did not think it was sufficiently remote, and it was closed. It was eventually acquired by the Enderbys, who were a seafaring family, and used it for sail and rope making. In 1845 their works were destroyed by a fire, from which they recovered long enough to build Enderby House as we now know it, but sold afterwards to cable makers Glass-Elliot & Co – who merged in 1864 with the Gutta-Percha Co to form Telcon.
Gutta-Percha is a latex obtained from a species of tree found in Malaya. It was first brought to London in 1842, and found to be water resistant and easily worked. An early application was to insulate telegraph wires whose ducts could be flooded when it rained. Its subsea use followed – a cable was successfully laid from Dover to Calais in 1850 (but soon failed, but was followed by a better one the next year).
Cable making is a lengthy, continuous process and is done before loading the cable laying ship – so on-site storage is necessary. In the early days this was done in the open, a central drum formed of wooden posts with a ring of posts centred on it to form a reel. It was soon found that the cable degraded in these conditions, particularly in hot summer weather, and steel storage tanks were constructed in which the cable could be stored and sprayed with water. The tanks were, and are, still wood lined to avoid damage to the cable.
The 1850 cable comprised a thick copper wire core with gutta-percha insulation. The 1851 cable had the addition of armour wires, and lasted over a decade.
Not only was gutta-percha a new material, so was the steel for armour wires. Purities of materials were not then measurable as they have become in the late-20C. Suitable heat treatment for armour wires (to avoid brittleness) was not developed before the mid 1850s.
Cyrus West Field (1819-1892), an American entrepreneur, promoted a trans-Atlantic cable in 1857 – he had it made by Glass Elliott & Co. This involved several suppliers of copper and steel wires from around the country, the logistics comparable to Paxton building the Crystal Palace for the Great Exhibition. The cable was laid by HMS Agamemnon & USS Niagara. The cable broke during the lay – but more was produced and in 1858 the connection was made – but just for a few weeks before the cable failed. A third attempt was made in 1865. It used the Great Eastern as the cable layer – better in every way than sailing ships. This cable too broke before land was reached. The next year saw a fourth cable laid successfully – and the third cable also completed.
Transmission over the cable was by Morse Code, dots & dashes being sent; and a waggly line received. A high power signal was sent; microwatts arrived. The received signal was passed through a moving coil galvanometer with a tiny mirror attached. A beam of light was reflected onto a screen which the operator watched. The (male) operator would interpret this and use a Morse Key to repeat the message. (The received signal would include the effects of magnetic currents in the sea picked up via the cable armour wires.)
Matching the terminal equipment to the cable (equalisation) by adding electrical networks was soon found to improve the performance. In 1880s Oliver Heaviside set out the mathematical theory for this, but it is said that when it was applied to the equaliser circuits they were found to be already fully optimised.
The limiting factor for the rate of transmission was the capacitance between the copper core and the outer armour wires (though even without armouring sea water would make an effective outer). The earliest long distance cables only managed 4 words/minute. Adding inductance reduced the cable loss (up to a cut-off frequency above which the loss would be greater), and enabled transmission up to 100 words/minute.’ This became possible when the Americans developed Permalloy in 1921,followed by Telcon who developed Mumetal which was easier to use.
The next development was to make coaxial cable, where an outer conductor, usually aluminium, was added over the insulation – under the armour wires – which made it possible to define the impedance of the cable and improve the equalisation. Short distance cables could be used for telephony, several two way channels becoming possible. By 1950s repeaters were being added at intervals in long distance cables for telephony. These had amplifiers to offset the loss of the cable, power fed by a direct current sent down the cable. Development led to transoceanic systems for over 5000 telephone channels in 1970s.
Then optical fibre was developed – by Charles Kao of STC – and the first experimenta11engths made at the Greenwich site (by then a part of STC). Externally these are similar to coaxial cables. However the inner is a tube with fibres inside and round that high tensile steel segmental wires. Polythene insulation is provided, as the inner still has to carry the power feed current, and an aluminium outer sheath prevents sea life from eating the polythene. Traffic now is digital, mainly for the internet, and capacity is quoted in megabitlsec or gigabitlsec.
Branching Units enable a main cable to have a branch to a coastal town with traffic connected in either direction; or for a main cable to have alternative landing sites in case oneis lost (to terrorists).
Enderby House was an important. part of Telcon who had their board room in it, with a fine view of the Thames. Subsea cable system manufacture started there, and was joined by rival firms both locally: Henleys, Siemens, BICC, STC- and elsewhere. The Greenwich site is now host to Alcatel-Lucent (into which STC was merged) still producing terminal equipment for subsea cabie systems – all the other businesses having gone. However, the riverside half of the site, which includes Enderby House, is being redeveloped with blocks of flats. The House is Grade 2 listed and is to be refurbished, with a large annex built on the landward side. The Enderby Group has been formed to encourage use of at least a part of the House as a museum of Subsea Telecommunications.
R J Buchanan
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