|
The rusty bolt effect is radio interference due to interactions with dirty connections or corroded parts.〔Lui, P.L., ''Passive intermodulation interference in communication systems,'' IEEE Electronics & Communication Engineering Journal, Vol. 2, No. 3, pp.109-118, Jun 1990. (Available online ).〕 It is more properly known as passive intermodulation,〔 and can result from a variety of different causes such as ferromagnetic conduction metals,〔Henrie, J., Christianson, A. and Chappell, W. ''Engineered passive nonlinearities for broadband passive intermodulation distortion mitigation,'' Microwave and Wireless Components Letters, Vol. 19, pp.614-616, 2009. (Available online ).〕 or nonlinear microwave absorbers and loads.〔Christianson, A. and Chappell, W. J. ''Measurement of ultra low passive intermodulation with ability to separate current/voltage induced nonlinearities,'' in IEEE Microwave Theory and Techniques Society International Microwave Symposium, Boston, MA, 2009, pp. 1301-1304. (Available online ).〕 Corroded materials on antennas, waveguides, or even structural elements, can act as a diode. (Crystal sets, early radio receivers, used the semiconductor properties of galena to demodulate the radio signal, and copper oxide was used in power rectifiers.) This gives rise to undesired interference, including the generation of harmonics or intermodulation.〔(【引用サイトリンク】title=Preventing 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.〔Lui, P.L.; Rawlins, A.D., ''The field measurement of passive intermodulation products.'' Fifth International Conference on Mobile Radio and Personal Communications, 1989. pp.199-203, 11-14 Dec 1989. (Available online ).〕 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.〔Johannessen, R.; Gale, S.J.; Asbury, M.J.A., ''Potential interference sources to GPS and solutions appropriate for applications to civil aviation.'' IEEE Aerospace and Electronic Systems Magazine, Vol. 5, No. 1, pp.3-9, Jan 1990 (Available online ).〕 ==Possible cures== If one experiences this problem, one should check both the transmitter and the receiver for dirty connections or corroded parts. One should also check for signs of corrosion in the cables which link the equipment to the antennae and for badly made joints. Beyond this, one might check any metal objects near the antenna for rust or corrosion. Any of these could be the source of the problem. It is possible to cure this problem in several ways: * Remove the corroded object. This is often the best cure because if you can eliminate the object then the interference it generates will cease entirely. * Clean the object - if the rust is superficial, the diode behavior might be eliminated by removing the surface rust. * Place an insulator between the two objects which are causing the issue. This might reduce the RF current. * Lower the RF field strength. Intermodulation becomes much worse with amplitude, so small amplitude reduction can greatly reduce the intensity of the effect. See the mathematics section below for details. * Get a better antenna which is more directional. It may be possible to point the aerial in such a direction that it does not pick up the unwanted signal coming from the "rusty bolt." 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rusty bolt effect」の詳細全文を読む スポンサード リンク
|