The phenomonon you are speaking of is the quasi-static assumption. B. Young estimates in his book that the maximum circuit dimension must be less than the wavelength/10 or wavelength/30. This maximum circuit dimension would be the equivalent electrical length. approx.= Er*Mechanical length... I'm not sure if this relates directly to the Td of the line. Optimization of the lumped element models, and increasing degree of complexity will extend the used of simplified models. Merrick ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu