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Developments in High-Power Radio
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that is possible above the earth, to insulate effectively the antenna from its supports, and to iliver the greatest possible current value from ic transmitter into the antenna for communiiting over long distances such as distances 2,000 to 6,000 miles.
Three types of antenna supports were avail)le from which a selection could be made, imely guyed wooden lattice masts, guyed teel pipe or steel lattice masts, and self-sup>rting steel towers.
A variety of factors must be considered in the election of the type of antenna supports to be sed, particularly at high-power stations, where ic initial cost and subsequent upkeep must given careful consideration, such as the area the ground available for the station site id the cost required to purchase, if not alidy available, the availability, locally or therwise, of suitable timber, in the case of /ood masts, transportation facilities and labor )sts, intensity of prevailing winds, nature of >il in connection with foundations, etc. The Navy decided on self-supporting steel towers as antenna supports in preference to steel or guyed wood lattice masts in the interests of permanency, dependability, and comparative low cost of upkeep, notwithstanding the fact that the effective antenna height would be reduced thereby in the order of 1 5 per cent, as compared with guyed wood masts.
The tower height was fixed at 600 feet and to be of sufficient strength to withstand a hori
zontal antenna pull at the top of 20,000 pounds. Three towers were decided upon for each station, the towers to be erected at the apices of a triangle i ,000 feet on a side.
Broadly speaking, there were only two classes of radio transmitters available for selection, one the damped wave system, and the other, the undamped or continuous wave system. The first question to be decided was which of the two systems should be adopted, whether the system of damped waves, or the system of undamped or continuous wave transmission, and the second queston was the selection of a type of transmitter of the system decided upon.
The damped wave system as originally used by Marconi, based on the earlier experiments of Hertz, had been in general use in the radio services of Great Britain, the British Marconi Company and its various affiliated companies, including the Marconi Wireless Telegraph Company of America, for low power and medium power stations but it had not been successfully demonstrated for use in high power stations to work reliably over long distances.
In the damped or spark system of radio telegraphy the antenna is given a series of electrical impulses of considerable intensity but of very short duration at comparatively infrequent intervals, and the average power is thus a very small fraction of the maximum. If communications are to be exchanged over extremely long distances, the energy to be handled during one of these impulses becomes
View of the Cavite and Pearl Harbor arc converters under manufacture and assembly at the Federal Telegraph Company's factory at Palo Alto, California