For the very best results, the top or horizontal portion of a "T" aerial should be slightly shorter than the vertical section.
The umbrella type of antenna is very efficient. Instead of a wooden mast, an iron pipe terminating above in a system of wires, inclining downward and serving both as part of the aerial and as guys to support the pole, is often used. The bottom of the pole is placed on an insulating base, protected from the rain by a small shelter. The wires are insulated near the lower ends by strain-insulators. The action of the wires is to serve as a capacity extension to the aerial.
FIG. 22.—An amateur aerial (flat-top).
Vertical aerials are not as efficient as either of those forms just mentioned. They require to be 50 per cent. higher than a flat-top aerial, in order to be of the same value.
The "L" and "V" types are somewhat directional. They are used where the highest point must be near the station, with a lower point some distance away. It is possible to secure excellent results with either type.
The terms straightaway and loop denote the method of connecting the aerial wires. In the first form the upper or free ends of the wires terminate at the insulators. In the loop form they are all connected together, and divided into two sections, each of which is led separately into the operating room.
FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.
The straightaway aerial is the most efficient in most cases, but wherever great height cannot be obtained, or the aerial is necessarily short, the loop aerial will give the best results.