Rusty bolt effect

rdf:langString Rusty bolt effect

rdf:langString The rusty bolt effect is a form of radio interference due to interactions of the radio waves with dirty connections or corroded parts. It is more properly known as passive intermodulation, and can result from a variety of different causes such as ferromagnetic conduction metals, or nonlinear microwave absorbers and loads. Corroded materials on antennas, waveguides, or even structural elements, can act as one or more diodes. (Crystal sets, early radio receivers, used the semiconductor properties of natural galena to demodulate the radio signal, and copper oxide was used in power rectifiers.) Galvanised fasteners and sheet roofing develop a coating of zinc oxide, a semiconductor commonly used for transient voltage suppression. This gives rise to undesired interference, including the generation of harmonics or intermodulation. Rusty objects that should not be in the signal-path, including antenna structures, can also reradiate radio signals with harmonics and other unwanted signals. As with all out-of-band noise, these spurious emissions can interfere with receivers. This effect can cause radiated signals out of the desired band, even if the signal into a passive antenna is carefully band-limited.