| 'Engineering', January 18, 1907, Page 89 : TRANS-ATLANTIC WIRELESS TELEGRAPHY In 1904 The National Electric Signalling Company decided to erect two stations for trans-Atlantic working, the antennę to consist of cylindrical steel tubes, 400 ft. high, with the National Electric Signalling Company's patent umbrella capacity at the top, each tube to rest at the bottom on a pivoted insulated base and to be supported by sectionally insulated wire-rope guys of the company's standard type. This type of antennę, which was invented and designed by The National Electric Signalling Company and patented by it, has proved quite successful and has been copied in Germany at the Nauen wireless station, a lattice-work, however, being used instead of a steel cylinder.
The sites selected were Brant Rock, 30 miles south of Boston, Massachusetts, U.S.A. and at Machrihanish, on the far side of The Mull of Cantyre from Campbelltown, Scotland. These two points were selected because The Great Circle (course) joining them passes up the Bay of Fundy, over the Isthmus of Chignecto and across Newfoundland at a point where it is comparatively low. The contract for the steelwork and erection of these towers was let to The Brown Hoisting Machinery Company, of Cleveland, Ohio, U.S.A. and for the insulators to The Locke Insulator Company, of Victor, N.Y., U.S.A. Owing to delays on the part of the contractors, the towers were not completed until December 28, 1905. On Friday, December 29, 1905, Brant Rock sent to Machrihanish, but nothing was received, owing, as it was afterwards learned, to a miscalculation in the wave-length. On January 2, 1906, Brant Rock sent again and Machrihanish received the messages. Communication was maintained one way until about the middle of January, when, the sending apparatus at Machrihanish having been completed, Machrihanish sent and Brant Rock received messages from there at the first trial. Very satisfactory communication was then maintained for some time and code messages containing as many as forty cipher words were received without a single error, or the necessity of any repetitions. It was found that the amount of atmospheric absorption had been miscalculated. From tests made on shipboard at distances of 1500 miles, the atmospheric absorption had been found to be about 90 per cent i.e. 10 per cent. of the radiation got through. It was considered that, by assuming the atmospheric absorption to be 99 per cent i.e. that 1 per cent. of the radiation got through, a sufficient factor of safety would be provided. As the design was conservative, it was found that in practice the factor of safety was larger than this and equivalent to an absorption of 99.8 per cent i.e. that messages could be received although only one-fifth of per cent. got through. Over this distance of 3000 miles, partly over land, it was found that the absorption was considerably greater than this and that as a matter of fact, during daylight, not more than one-tenth of 1 per cent. of the energy got through and that a factor of safety of at least 100,000 must be provided. As an illustration, with the same sending power, on some nights messages were received 480 times stronger than was necessary for audibility and the messages could be read with the receiver 6 in. away from the ear. On other nights with the same sending power the messages were so faint that they could not be read. A number of tests were made, which were witnessed by scientific experts from The General Electric Company in America and Mr. Shields, the technical expert of Messrs. Abel and Imray and others but, as it was evident that the stations were not sufficiently powerful for commercial work, they were shut down early in 1906 for reconstruction. Owing to the impossibility of getting aluminium for the compressed-air condensers the stations were not opened again until October, 1906, when they were operated at a factor of safety of 2000, only half of the condensers being in place. With the full amount of condensers the factor of safety would have been 4000 and a new form of receiving apparatus, which it was intended to use, would have brought up the factor of safety to 400,000. The stations operated continuously, barring shut-downs for a couple of nights for mechanical reasons, until December 5, when the tower at Machrihanish blew down. This accident came at a very unfortunate time, as work had just been begun on a new method for eliminating the atmospheric absorption, which had given very promising results, the absorption having been already reduced to one-tenth of what it was formerly. Moreover, the new receiving apparatus had only been partly installed and no opportunity had been afforded of trying it between the trans-Atlantic stations. The specifications on which the contractors bid called for the tower to stand a wind-pressure of 50 lb. per square foot on a flat surface and for the tower to be capable of being extended to a height of 500 ft. later, if desired and to be capable of standing a pressure of 50 lb. per square foot on a flat surface even if one set of guys broke. The design was carried out in a very creditable manner by The Brown Hoisting Machinery Company. In a future issue we shall illustrate the installation and describe the jointing of the guy-ropes, to the failure of which the fall of the mast is attributed. This jointing was carried out by a subcontractor. | 
Friday, October 6, 2006 was Reginald Fessenden's 140th Birthday (born 1866)