The success of the cross channel radio communications lead Marconi to believe that transmissions could be made across the Atlantic.
The possibility of making a transatlantic transmission seemed impossible to many because it was not certain at this time whether radio signals could travel beyond the line of sight. In addition to this, the distance was over twenty times the distances that had been achieved to date.
Yet Marconi saw the possibility of a trans-Atlantic transmission to establish long range radio communications as challenge to which he could rise despite the fact that funds were starting to become tight within his company.
To Marconi the Atlantic transmission seemed necessary because of the possible new business it could bring, especially with the maritime business as no other form of communications was possible once they left port. Establish the possibility of long range radio communications to him was essential.
Marconi prepares for the Atlantic
The first stage of his preparation for a transatlantic transmission was for Marconi to convince his fellow directors that this test, which would have enormous expense associated with it would be worthwhile. Marconi faced a tough battle to convince them, but eventually he succeeded in gaining their reluctant agreement for this massive project.
To enable the long range radio communications to be established, it was essential to choose the correct sites to provide the best chance of success. Sites were selected either side of the Atlantic at Poldhu in Cornwall and Cape Cod in Massachusetts.
The Poldhu station was the first to be set up. A massive antenna consisting of a ring of twenty masts over sixty metres high was erected. This supported a cone of wires that formed the actual antenna.
One of Marconi's assistants, a man named Vyvyan expressed concern over the design of the antenna. His reservations were dismissed, but unfortunately he was proved to be right as the whole structure collapsed in a gale.
The antenna at Cape Cod was of the same design, and even became distorted in a strong breeze. Later it suffered the same fate as the one the other side of the Atlantic. By a strange quirk of fate one of the masts narrowly missed Marconi's assistant Vyvyan.
In order to meet the requirements for a transatlantic transmission, a totally new form of transmitter would be required. One with a far greater power generation capacity was needed.
The task of designing and developing this new radio transmitter fell to Ambrose Fleming. He was Professor at University College London and a consultant to Marconi's company.
Fleming's transmitter design for Marconi's transatlantic transmission
In Fleming's transmitter an alternator charges the capacitor C1 through a circuit that is resonant at the alternator frequency. Spark-gap S1 discharges to create a higher frequency signal and the step up transformer then steps up the voltage to charge C2 to a much higher voltage. Spark gap C2 which is wider then discharges C2 through a circuit that is resonant at the radiated frequency to which the aerial is also tuned.
Marconi rebuilds the transatlantic stations
The collapse of the antennas at Poldhu and Cape Cod dealt a devastating blow to Marconi. He had invested enormous sums into the building of these two stations and their antennas.
But Marconi did not let this setback defeat him. With typical resilience he set about the task of rebuilding. This time he made the Poldhu antenna smaller and more robust.
He also decided to move the site of the American station to Newfoundland to shorten the distance of the path. At this location he decided the antenna would have to be kept as simple as possible consisting of a wire supported by kites or balloons - this was no doubt in some degree due to the cost of rebuilding a full antenna system. This also meant that a transmission could only be made in one direction from England to Newfoundland.
Tests commenced in December 1901 with the Poldu station transmitting the letter "s" consisting of three dots, for three hours every day. This letter was chosen for two reasons. The first was that it would be easy to recognise. The second was probably more important. The transmitter was a very new design and it could not be trusted to transmit dashes without the risk of a breakdown.
The weather in Newfoundland was bad for these tests. On the first two days kites were lost because of the strength of the wind. A third kite was tried, but this moved rapidly in the wind causing the resonance of the antenna to change rapidly, and it was not possible to counteract this with the receiver tuning sufficiently fast.
In order to be able to detect the signals under these difficult conditions Marconi reverted to an un-tuned circuit and what was called a self-restoring coherer. Despite its name this was not a coherer at all, but an early example of a detector that operated by rectifying the signal in the same basic manner as diode detectors do in amplitude modulation, AM receivers. This was used with a sensitive telephone earpiece to enable Marconi to listen to the signals.
Despite these difficulties, Marconi was convinced that he could hear the signals. He asked his assistant Kemp to confirm this which he did. Marconi's notebook indicates that he heard signals at 12.30 pm, 1.10 and at 2.20 on 12 December 1901.
The weather worsened and with no sign of a let-up in the conditions an elated Marconi released the information to the press despite the fact that he had no independent witness, nor any instrumental record. This news was received enthusiastically by the press, although the scientific community was more sceptical. They thought he might have mistaken static cracks for the Poldhu transmissions.
Further Atlantic transmissions
While Marconi genuinely believed that he had heard the radio signals from Poldu, they were so weak that it would not have been possible to send a full message across the Atlantic. Unfortunately Marconi was not allowed to repeat the experiment because the local telegraph company exerted its rights to a monopoly and forced him to close his station there.
Again Marconi had to move, and this time he set up a new radio communications station on Cape Breton Island. When the station entered service it was difficult to assess its performance because propagation conditions were varying so widely. However it was found that increasing the wavelength improved the performance. As the wavelengths were already of the order of 2000 metres this meant that even larger radio antennas were necessary.
The transatlantic project was costing the company vast sums of money, and despite the problems it was decided that it was necessary to use it to bring in some finance. To achieve this, a news transmission service was introduced in conjunction with the Times newspaper. Messages were sent across the Atlantic and it meant that news could be received more quickly than by other methods. However this service only lasted for nine days as the aerial on Cape Breton Island collapsed.
Accordingly Marconi returned to his idea of providing services to ships to gain some revenue, and instigated a service to provide news to liners crossing he Atlantic.
To try to resolve the problem with antennas, Marconi experimented with new antennas at Poldhu. Whilst he was doing this he noticed that a wire on the ground pointing towards Glace Bay gave a stronger signal than his other antennas. Further development resulted in the inverted L antenna used to this day.
With the introduction of this antenna it was possible to maintain a better level of service even if it was still painstakingly slow to send messages across the Atlantic without errors.
The main area of business for Marconi's company was to provide communications systems for ships. With the transatlantic link established more ships took the Marconi system on board. The first commercial installation on a merchant ship was completed in 1900, and by 1902 seventy ships had Marconi systems on board.
More Famous Scientists in Electronics and Radio:
Volta Ampere Armstrong Appleton Babbage Bardeen Brattain Edison Faraday R A Fessenden Fleming Heaviside Hertz Ohm Oersted Gauss Hedy Lamarr Lodge Marconi Maxwell Morse H J Round Shockley Tesla
Return to History menu . . .