The Vertical Wire or Aerial.— Marconi's first experiments in wireless telegraphy were made with a vertical wire 20 feet high at the sending and receiving stations. With this height of wire he transmitted signals one mile. With wires 40 feet high signals were transmitted four miles and with wires 80 feet high 16 miles.
Many different arrangements of the aerial wires are now employed. For instance, in a number of wireless installations 20 wires about No. 16 gauge are suspended from a long strip of wood, which is upheld by insulators sup ported by a rope between the tops of two masts about 150 or 200 feet high. The wires, two feet apart, drop vertically to a similar wooden strip, where the wires are joined together and led into the instrument room. In other cases the wires are suspended from towers by well insulated arms and are kept apart by wooden spreaders until near the ground, where the wires are connected and thence are carried into the operating room. In still other cases a single mast is employed, from the top of which a number of wires are suspended. Each wire is attached, at a distance of about 50 feet from the top of the mast, to a guy-rope, which is itself attached to an anchor post in the earth, 40 feet or more from the base of the mast. The guy-rope thus first draws the wires away obliquely from the mast, then at its point of connection with the guy-rope each wire is drawn toward the foot of the mast, where all the wires converge and are thence led into the operating room; the wires forming a >, with the mast as a base and no spreaders are re quired.
In Fig. 8 are shown various ways in which two or more aerial wires may be employed as antenna. The wires may be of varying length depending on requirements. In the figure, a may represent two wires open or closed at top, c indicates a four-wire arrangement; f is a cage arrangement of four, six or more wires in which the wires are held apart by hoops; g is, a box method in which the wires are separated by a wooden frame.
The plan shown at c is much used. The wires in this case are held apart by wooden spreaders at the top and bottom and also at the middle if the wires are very long; a represents an Eddy Kite arrangement for supporting an aerial; two or more of these kites may be used in tandem.
Again two high masts or towers 100 and more feet apart are employed, having a num ber of horizontal wires strung between them at their tops. Vertical wires are attached to the horizontal wires and are dropped to a wooden strip and thence are led into the in strument room. On shipboard horizontal wires are usually strung between the tops of one fore-mast and one aft-mast, from which hori zontal wires the vertical wires of the antenna are conducted to the operating room.
For the very powerful wireless stations much more elaborate antenna than those described are necessary. For instance, at the Belmar, N. J., station on the Atlantic Coast four iron masts are usually arranged in alignment at right angles to the coast. These masts are 300 feet high and are about one-quarter of a mile apart. Horizontal wires are supported by these masts and vertical wires are connected therewith, which are led into the station.
Kites and captive balloons for supporting the vertical wires have frequently been availed of for temporary use and for military opera tions. The material of the vertical wire does not appear to affect the results. Iron, copper and aluminum wires have been used. Wire netting has. also been employed. The insulation of the vertical wires from the mast is, however, very important. Good earth connection for the verti cal wire has been found very essential in prac tice, especially at the transmitting end. Cop per plates 30 feet long and 4 feet wide, em bedded two or three feet in damp earth, glv 'ing about 2,400 feet of plate surface, are some times used for this puirpose. When feasible the ground plate is sunk in the sea. On ship board the aeartho is secured by attaching a wire to botts on the iron frame of the vessel.