långwire

Långwire, in radio engineering commonly referred to as a longwire antenna, is a type of single, extended conductor used for transmitting or receiving radio signals. It is typically suspended between two support points such as masts or trees and fed at one end or near the end. The arrangement favors simplicity and wide operating bandwidth, especially when used with an antenna tuner.

The electrical length of a långwire is the key factor in its behavior. Impedance and radiation pattern vary with the wire length relative to the wavelength, the height above ground, and nearby structures. Resonant conditions occur near half-wavelength or full-wavelength lengths, but a longwire will generally present a highly reactive impedance when not at resonance. Because of this, most installations use some form of impedance matching at the feed point, such as a balun, an unun, or an antenna tuning unit, to make the antenna usable across multiple bands.

Common variants include the end-fed longwire, the center-fed longwire with a balanced feeder, and the inverted-V or sloper configurations. A “random wire” refers to a non-resonant length used with an automatic tuner to access many bands. The wire may be a simple single conductor or a paired feeder arrangement, with insulation at the ends and appropriate support hardware to maintain clearance from obstacles and power lines.

Advantages of långwire antennas include low cost, simple construction, and potential multi-band operation with a tuner. Disadvantages include large physical footprint, sensitivity to orientation and terrain, and potential RF interaction with support structures and nearby equipment. They remain a practical option where space is available and ease of setup is prioritized.