Radio Broadcast (May-Oct 1922)

56 RADIO BROADCAST communicate between themselves by employing the small portable "stations" we are considering. Signals from headquarters may be received over rather long distances, depending, of course, upon the power at the transmitting station and such other variable factors as the size and height of the receiving antenna and the particular natural characteristics of the land over which the communication is carried on. • The most important consideration in field operations is the aerial, or "antenna" as it is sometimes called. There is a great deal of misunderstanding concerning .this very important part of a radio station, so let us decide this case once and for all. Perhaps we may best know what to do by knowing what not to do. For ordinary communication a wave length of two hundred meters should not be exceeded, therefore the best form of aerial is a single wire, having a total length, from the binding post on the set to its outer end, of about fifty feet. This wire may be made of almost any metal and may be bare or insulated. For outdoor work, the best aerial wire is aluminum, be.cause it is very light, but it is rather brittle and requires a little care in handling, which is not the case when copper or galvanized iron wire is employed. If the additional weight makes no difference, copper is most suitable. RECEIVING MESSAGES FROM TROOP HEADQUARTERS The equipment shown in the previous picture in operation. No ground connection was possible so an insulated wire thrown on top of the snow was used as a counterpoise Various locations require aerials of different classes, but no definite rules may be given, governing this phase of field radio communication and the following generalities may be followed, as nearly as is reasonably possible, with satisfaction. Wherever possible, the aerial should be very well insulated and should be isolated from all possible surrounding objects. A very suitable aerial may be erected in a few minutes by attaching an insulator to a string and casting the insulator over a high tree, letting the string unravel as the insulator takes its course, in somewhat the same fashion as the gun used for life-saving purposes. A little practise is necessary for this work, but it is not a very difficult task for a boy to cast a line over the top branch of a fifty foot tree. When the insulator comes down, on the opposite side of the tree, it is merely necessary to fasten one end of the wire to it, pull in on the string until the insulator is in a position approximately fifteen feet from the leaves, drive a stake in the ground and make the string fast to it. The remaining end of the aerial wire should then be connected to the outfit and drawn up taut. The ideal condition is found where there is a single tree without foliage, but if an effort is made to keep the aerial wire as far from other objects as possible, this ideal condition is not entirely necessary. In making the aerial do not make the very common mistake of using too long or too many wires. More than two should not be used, nor should the aerial be more than fifty feet in length, for this class of communication. Wherever possible, advantage should be taken of a natural ground connection, that is, one in which it is possible to place a large sheet of metal directly into some body of water or soggy soil. If it is possible to locate a water pipe it is doubtful that a more suitable ground could be had. A water supply hydrant is frequently available along most of our highways. Where use is to be made of the natural ground, a sheet of metal approximately one foot by three feet should be buried in moist earth after a wire is soldered to it or attached by a binding post. The latter method is frequently found more convenient. Where operation is to be carried on over a stretch of dry territory and it is impossible to locate a water pipe or some soggy ground, it is necessary to employ what is known as a counterpoise. A very con