Dublin – EI0MAR
EIØMAR
HOWTH MARTELLO TOWER, DUBLIN
Howth Marconi Station in 1905
The tower’s association with radio dates back to 1903, when Lee deForest, the American radio pioneer and inventor of the triode valve, carried out experimental transmissions from there. He demonstrated his system to engineers from the British Post Office. Two years later a Marconi station was installed in the tower and signal strength tests were carried out with the HMS Monarch as she navigated her way from Howth to Holyhead (see below). The Martello has been recently refurbished by Fingal County Council.
W. Duddell and J.F. Taylor carried out tests (range versus receiver antenna current) for the British Postal Telegraphy Department in Bushy Park, London, in June 1904 and later, in 1905, extended the range of these tests by carrying out sea trials between a transmitter on H.M. telegraph ship “Monarch” and a receiving station in the Martello Tower, Howth. The significance of the trials was that there was at last available an accurate instrument, a thermogalvanometer designed by Duddell, sensitive enough to measure the small currents in the receiving antenna.
The sea trials, carried out at a wavelength of some 200m, corroborated the results of the Bushy Park tests and showed that away from land (up to about 60 miles) the product of antenna current and distance was always quite constant. Furthermore the difference observed between day and night transmission was less than one per cent.
At this period in radio engineering, transmitters based on a sparking system were used. The significance of different rates of sparking is that there were upper and lower values which allowed stable power output in the particular transmitter used. An r.m.s. current of 2.31 amperes was produced in the antenna for a rate of sparking of 42 per second and this increased to 2.83 amperes when the rate of sparking was increased to 67 per second. A natural sequel to the Duddell and Taylor trials was the American Navy Department’s tests on the Atlantic in 1909 and 1910.
