Sunday, 1 January 2017

How Marconi bridged the Atlantic Ocean

The first morse code message sent across the Atlantic Ocean by radio, as opposed to cable, was received by Guglielmo Marconi (1874-1937) on 12th December 1901. He was stationed at Signal Hill, near St John’s, Newfoundland, and the signal was sent by a transmitting station at Poldhu, near Lizard Point in Cornwall, England.

Early experiments

Marconi first started experimenting with wireless telegraphy in 1895 in his native Italy, but moved to England in 1896 because he hoped to attract more interest and support, which was indeed the case. He developed gradually more sophisticated transmitting and receiving equipment and achieved progressively greater distances over which signals could be transmitted.

He was particularly interested in establishing ship-to-shore radio communications, and many of his early experiments were from ships and yachts to receiving stations that he had built onshore. There was clearly a business opportunity here because ships could not be connected by undersea cables in the way that fixed stations could. During the course of these experiments it became clear that radio signals could be picked up even when the transmitter and receiver were not within line of sight of each other, as would be the case when a ship was below the horizon as far as the shore station was concerned. If radio signals could “bend”, what limit could there be to how far they could travel?

Marconi became convinced that it should be possible to send a radio signal for thousands of miles, provided that the transmitting equipment was powerful enough. However, up to this point the best distance achieved had been no greater than about 90 miles (from near Boulogne on the French coast to Chelmsford in Essex, where Marconi had established his business headquarters). Nevertheless, he pressed on with his project to leap the Atlantic.

Preparatory work

Work on the transmitting station at Poldhu Cove began in October 1900, the plan being to build a similar station at Cape Cod, Massachusetts, and the work on this station began in March 1901. Each station was to comprise 20 masts, each being 200 high, set in a circle that was 200 feet in diameter. In terms of transmitting equipment, Marconi calculated that the energy needed to send a signal the required distance would be around 20,000 volts, and this was to be provided by a Hornsby-Ackroyd oil-driven engine that would drive a 25 kilowatt alternator and a pair of transformers that would boost the alternator’s 2,000 volts to the necessary 20,000 volts. The final output of the plant, in terms of signal energy, would be 100 times greater than that of any previously built transmitter.

All seemed to be going well until 17th September 1901. By this time the aerials at both Poldhu and Cape Cod were nearly complete and Marconi was carrying out tests on the parts of the system that were serviceable, getting very satisfactory results. However, on that day a storm blew up and wrecked the circle of masts. This was clearly a massive setback, but it proved possible to create a temporary aerial, based on only two masts, that was operational only seven days later. Experiments using this aerial showed that strong signals could reach Marconi’s station at Crookhaven in County Cork, Ireland, 225 miles away, so Marconi decided that there was no need to rebuild the station before trying the ultimate test.

The Newfoundland test

He therefore abandoned the original plan to set up two-way communications between Poldhu and Cape Cod and on 26th November 1901 he set sail, with two colleagues, for St John’s, Newfoundland. He had begun to have doubts about whether the signals would reach as far as Cape Cod and decided to bridge a shorter distance, Newfoundland being the closest point of the North American continent to Cornwall. As it happened, just before setting sail he heard news that the Cape Cod station had also been wrecked in a gale.

The party arrived at St John’s with a quantity of balloons, hydrogen cylinders and large kites, apart from their portable receiving apparatus. They were received hospitably by the authorities at St John’s (Newfoundland was a British colony at the time) and offered space in a disused fever hospital on a rocky promontory overlooking the town. The appropriately named Signal Hill had been used in past ages for sending semaphore communications, and was also close to the point at which the first transatlantic cable had reached shore in 1866.

The trio tried various methods for getting an aerial wire airborne using the balloons and kites. The winds were strong and at times threatened to be too strong, but, once in place, the kites were perfectly serviceable for what was needed.

The station at Poldhu had been instructed to transmit a morse code “S” (three dots) for three hours every day. This letter was chosen because it would be unmistakable if picked up on the other side of the ocean. Any letter including a dash could be indistinguishable from atmospheric noise.

The first attempts at reception were made on 11th December. Marconi and his team recorded in their notes that something was detected on the Morse detectors, and as clicks on a telephone monitor, but they could not be definite that they were the Poldhu “S” dots.

However, on the following day there was no mistaking the regular three dots. One of the kites broke free, but, when a second kite was raised with a slightly shorter wire, the signals were heard continuously for more than two hours. Marconi was convinced that the experiment had succeeded.

Conditions on later days proved difficult, such that further tests were not possible and Marconi was concerned that his claims would not be believed. In this he was partially justified, because the London press was slow to accept his word for what was a remarkable claim, given the scientific opinion of the time that radio waves could not be “bent” (actually, the waves were being bounced off the ionosphere, but nobody knew that at the time).

Later work

Ironically enough, what most convinced people that Marconi had succeeded was the vehemence shown by the Anglo-American Telegraph Company, whose undersea cable had transmitted Marconi’s triumphant massage back to England. They immediately threatened legal action against Marconi for breaking their monopoly, and Marconi promptly ended his testing in Newfoundland.

However, he was clever enough to make public his correspondence with the “Anglo” and won immediate support from the Canadian press and government agencies, the news soon spreading to the United States. Many messages of support came his way, including one from Alexander Graham Bell who made Marconi an offer of land at Cape Breton, Nova Scotia, for a permanent transmitting/receiving station.

Marconi packed up his equipment on 23rd December, sending everything back to England with one of his colleagues, while he undertook visits to inspect various possible sites and to meet government officials.

Before he left Canada, Marconi had a draft contract in his pocket to establish a permanent wireless telegraph service, and he was promised government finance towards building a wireless station. Both in Ottawa and New York, Marconi was feted and dined, being hailed as a hero for his magnificent achievement, although his evidence for success was extremely sketchy and impossible to demonstrate without a receiving station being in place.

Fortunately, Marconi had been correct, and later work confirmed what he had claimed. The stations at Poldhu and Cape Cod were quickly rebuilt, with substantial wooden towers instead of flimsy masts, and many technical refinements were to follow.

On 22nd February 1902 Marconi set sail on the SS Philadelphia from Southampton to New York, with a view to sorting out the final details of his Canadian contract. However, he used the voyage to demonstrate his system to the world at large, by transmitting and receiving messages as the ship sailed across the Atlantic. The ship’s mast acted as an excellent aerial (albeit much shorter than that used at Signal Hill) and various improvements allowed for dashes as well as dots to be received.

The result was that readable messages could be transmitted for up to 700 miles during daylight and more than 1500 miles at night. The three-dot “S” signal could be detected at more than 2000 miles distance. With this very public demonstration the critics were finally silenced.

Marconi’s equipment was to prove its worth in two very notable instances within the following ten years. In July 1910 a radio message to the SS Montrose led to the arrest of Dr Hawley Crippen, who had murdered his wife and attempted to escape to Canada. Radio messages from RMS Titanic in April 1912 led to the saving of many lives due to the signals being picked up by other ships within steaming distance.

© John Welford