The "T" Aerial is the most nearly perfect and gives the best "all around" results.
The "L" or Horizontal type of aerial is used wherever it is desirable for any reason to send the most powerful waves in one direction.
The "V" type is used where the highest point must be near the station.
The wire leading into the station, from the aerial is called the "rat-tail" or "lead-in." It is always very carefully insulated and usually enters the station through a hole in the window or wall by means of a "window pane bushing" or "leading-in insulator."
Certain aerials possess a directive action, that is they radiate and receive messages in some directions better than others. Flat top aerials possess this peculiarity more noticeably than the vertical types. Flat top aerials receive and radiate waves coming from and going towards a direction opposite to that in which the free end points.
FIG. 29. Spiral Aerial.
The free end is the opposite end to that to which the "rat-tail" is connected.
There are two free ends on a "T" aerial and so this form radiates and receives its waves equally well in two directions.
The inverted "L" and "V" types possess a very decided directive action.