man with drill
An air capacitor is an adjustable capacitor consisting of a series of semicircular rotating aluminum plates on a central axis placed between a set of similarly spaced static aluminum plates. When the moving plates are rotated, the amount of overlap between the moving and static plates changes. The air between the plate assemblies acts as an effective dielectric, insulating the assemblies from each other. As the capacitance of any capacitor depends on the combined size of its plates, this adjustment allows the value of the air capacitor to be adjusted. Air capacitors are commonly used in resonant circuits where adjustable capacitance is required.
Capacitors are electronic components that store electrical energy for short periods. Capacitors consist of thin-film plates of metal separated by a dielectric or insulating material, such as composites of glass, paper, or air. The capacitance, or extent of energy storage capacity, of any capacitor is largely dictated by the total area of its plates. Most capacitors have a fixed capacitance value, requiring replacement of components to decrease or increase the value. Some types of electronic circuits, however, require the values of certain capacitors to be changed repeatedly as part of the circuit’s function.
In these cases, components such as the air condenser, also known as variable condenser or variable air condenser, are used. They are typically considerably larger than conventional capacitors and are not included in a housing. The air capacitor consists of a series of semicircular discs with a hole in the center, through which a control rod passes. Alternate disks are attached to the control rod as it passes freely through the others. This means that the disk array is effectively divided into two groups, one rotating with each other with an insulating body of air between them.
These two groups of disks collectively form the two areas of the capacitor plate. As the disks are semicircular in shape, rotating the movable assembly causes the amount of overlap of the two groups to change, thus changing the total area of the plate. Since the capacitance of a capacitor depends on the total area of the plate, this change in area causes a corresponding change in the capacitance of the components, allowing an operator to change the value of the component at will. The air capacitor is often used in LC, or resonant, circuits that require changes in capacitance. These circuits include frequency mixers, radio tuners, and the impedance-matching components of antenna tuners.