An antenna is a special inverter, which converts a radio frequency field in an alternating current or vice versa. There are two basic types:
- the receiving antenna that receives radio frequency energy and converts it into an AC
- the transmitting antenna, which is fed with an AC current and converts it into a radio frequency field
In its simplest form, an antenna is a conductive, thin wire. The antenna uses the phenomenon that electromagnetic waves in conductors to generate an alternating current (for receiving), and vice-versa alternating current which generates electromagnetic waves (broadcast).
Fixed relation between the length and the frequency range
In the antennas that specific for a given frequency range are provided, these have a fixed relation between the length of the antenna and the desired frequency range. In principle, there are no differences between a transmitting and receiving antenna, in practice, the requirements will determine the performance and construction. A good and undisturbed operation of the antenna is of essential importance for the range of the radio signal. Matters such as corrosion of the wire or a connector, cable breakage or an incorrect wrong placement of the antenna have an immediate negative impact on the scope.
Direction of the Antenna
The direction of polarization (the direction in which the electric field vector vibrates) refers to the emitted and received electric field. For most of the wire antennas, the elements should lie in the plane of the polarization direction.
Impedance can be seen as a complex resistance. The impedance (also called the ‘barrier’ or resistance) is dependent on the frequency of the signal.
The antenna connector has a specific electrical impedance. Antennas are generally designed so that this impedance matches as close as possible to the impedance of conventional antenna cables, such as 50 ohms or 75 ohms.
The length of the antenna
In the case of a rod antenna, the length for the best efficiency is a quarter of the wavelength of the mean frequency.