Wireless Telegraphy and Telephony

 l8 WIRELESS TELEGRAPHY and located on land are usually housed in a small building in the immediate neighborhood of the tall wooden mast which supports the aerial. Commercial stations are usually situated on the top floor of a high office building, or a hotel, and the aerials supported by a steel lattice-work tower. Amateurs place a small pole on the roof of the house, or in a tree, and locate their station in any convenient room near the top of the house. Fig. 15.—Vertical aerials of the “grid,” “fan” and “inverted pyramid” types. Aerials are of numerous classes and forms, but the most prominent types can be divided into two main groups, called respectively, the “flat-top” and “vertical” antenna. The vertical aerials are the older form, and are usually employed for long-distance work or ultra-powerful stations. The aerials intended for transmission from Europe to America, installed by Marconi, consisted of huge inverted pyramids, supported by four heavy lattice-work towers, over 200 feet high. Vertical aerials also sometimes take the form of an umbrella, or fan, where only one support- ing pole is available. Iron pipe masts may be employed for the purpose, by setting on an insulating base. The um- brella aerial is used extensively in the army and portable sets.