Bird Cage Antenna

A linear loaded vertical is what an amateur builds when the garden will not take a full-size antenna for the lower bands. Instead of a single tall radiator, the conductor is folded so that the electrical length stays long while the physical height stays short, and the page here describes one homebuilt version of that idea, named for the obvious thing it resembles: two large hoops held apart on a vertical insulating axle with wires running between them, like the frame of a bird cage.

Every part of the design answers a problem. The hoops set the spacing of the conductors and keep the loading distributed rather than lumped, so losses stay low. The metal disc beneath the lower hoop gives the coaxial feedline something to terminate against and doubles as the mounting plate for the radial rods, which are what a vertical needs in place of ground. A fibreglass axle carries the mechanical load without appearing in the electrical picture at all. The result stands about the height of a person and is light enough for one person to lift, which matters to anyone who has to take an antenna down before a storm.

The page is kept as it was published on this domain by its builder. The dimensions and photographs are his; anyone copying the design should expect to tune it to their own ground and surroundings.