Random wire antenna

A wire antenna is an antenna that is comprised of a, relative to the wavelength used, the long wire, and is supplied at one end. In contrast, a dipole antenna is fed in the center.

This design is preferably used in the shortwave range. A wire antenna is at least as long as half the wavelength by definition. For the HF amateur radio band 1.8 MHz (160 m wavelength) a long wire antenna is therefore 80 m long.

Long wire as a receiving antenna

Long wire antennas are particularly interesting for the reception, if they are several wavelengths long. You will then have a clearer directivity along the stretching direction, which can also be done asymmetrically with a matching termination resistor to ground ( Beverage antenna).

Shorter long wire antennas receiving end hardly advantages over much shorter antenna variants, because in the short wave receiver sensitivity is limited by the atmospheric noise and not by the noise of the receiver. The preference is therefore to provide for reception purposes such antennas as far away from noise sources are located and also have a meaningful directional characteristic. This can be, for example, quite easy to achieve with compact magnetic antennas in the reception area.

Long wire as a transmitting antenna

For the transmission mode Long wire antennas have typical dimensions of 0.5 to a few wavelengths. For longer antennas, the efficiency decreases, the effort brings no benefits here, the directional pattern also receives numerous minima. Therefore, the above-mentioned directivity can not use the send side. A plurality of wavelengths is a transmitting antenna, in practice, only long, when it is designed for a lower band (for example, 80 m 40 m band ), but is operated, for example, to 20 m ( two wavelengths). If possible, such a long wire antenna to each supplemented by another for the correspondingly higher bands. In the former Soviet Union, some use radio transmitters long wire antennas ( Zarya antenna).

Fuchs antenna and similar designs

Long wire antennas, exactly 0.5 or 1 or 1.5 (etc.) times as long as the wavelength of the operating frequency are, at the end of high impedance with an impedance of about 2000 Ω. They are therefore supplied with high voltages and minimum currents and therefore require a resonant transformer for adaptation to the much lower impedance of the coaxial cable. Traditionally, a parallel resonant circuit ( " fox circle " ) is used for this. This design is called " Fuchs antenna " (after Josef Fuchs, radio amateur from Austria, had them patented 1927). In recent years spread instead of fox loop transformers with a ratio of eg 1:9 (so-called Magnetic Balun ), whereby the long wire without a vote of the adaptation element can be used for multiple tapes.

The great advantage of Fuchs antenna and related types are:

• In the case of receiving the pre-selection through the tuning circuit,
• Sending the significantly increased bandwidth of about 10% of the Mittenfreqenz,
• The high-impedance power supply reduces the supply current. The grounding system which influences fed at low impedance, unbalanced antennas the antenna efficiency is decisive, not more decisive.

In many antenna ground plane, the typical design of the unbalanced, low -fed antenna, the grounding system is from 100 to several wires, which are each one-quarter wavelength long.

Fuchs antennas and similar designs are especially for smaller transmission powers simple, unobtrusive antennas.