Counterweight (radio technology)

Amateur radio antenna of the "Inverted-L" type from the 1920s. The lower "clothes lines" just above the roof form the counterweight.

Rod antenna on a car . Here the metallic roof of the vehicle serves as a counterweight.

A counterweight ( English Counterpoise ) is in the radio engineering an electrically conductive surface, in particular in the unbalanced excited antennas to provide a good is needed adjustment with a low standing wave ratio to achieve (VSWR) and efficient radiation.

principle

According to the definition, it is an electrically conductive metallic surface separated from the earth or a mostly radial arrangement of conductors that are excited in phase opposition to the emitter at the base of the emitter .

The counterweight corresponds in a certain way to an earth network , but differs from it in that it is not or at least not necessarily connected to the earth. Counterweights isolated from the earth often work better than earth nets, especially at lower frequencies where the earth has a significantly higher resistance than a metallic surface.

application

Especially in vertical - monopoles ( neudeutsch ground plane mentioned), ie perpendicular to rod antennas, the counterweight is essential to a useful functionality to reach the antenna system. The antenna rod ideally has a length corresponding to a quarter wavelength (λ / 4). "Mirrored" on the counterweight, it is electrically supplemented to form a λ / 2 dipole antenna with good radiation properties.

Elaborately designed counterweights can be found in transmission systems for medium waves , long waves and especially for long waves . Here, around the base of the antenna, radial metal strips are arranged (also called radials ), which are usually chosen to be at least as long as the antenna is high. If the antenna is on a platform in the sea, the surrounding sea water forms the counterweight. In the case of a simple telescopic antenna for a car (picture) , the metal car roof serves as a counterweight.

literature

Archibald C. Doty et al .: Efficient Ground Systems for Vertical Antennas. QST 1983, pp. 20-25. W1NPP.org (PDF; 1.2 MB).
Alois Krischke : Rothammels Antennenbuch. DARC- Verlag, 2013, pp. 585-593, ISBN 978-3-88692-065-5 .

Web links

Commons : Counterpoise - album with pictures, videos and audio files

Guy Olinger: The FCP - A 160 Meter Counterpoise for a Postage-Stamp Lot. K2AV.com (PDF; 680 kB)
Counterpoise Systems (English)

Individual evidence

^ Alois Krischke: Rothammels Antennenbuch. DARC-Verlag, 2013, p. 585, ISBN 978-3-88692-065-5 .

[1] Alois Krischke: Rothammels Antennenbuch. DARC-Verlag, 2013, p. 585, ISBN 978-3-88692-065-5 .