Heres my input... Putting metal things near a coil is generally not a good idea. The time = varying fields from the coil induce currents in the metal which will = flow to oppose the current in the coil (good old lenz law). The effect = of this (for conventional round solenoids) is to reduce the inductance = of the coil. However, this is not the whole story. You must also = consider the electric field effects. In practice you will also increase = the capacitance to ground from the coils turns. If you think of this in = very simple terms you have a coil with lots of capacitors in parallel = with it to ground. At some frequency you will see a parallel resonance = of the coil inductance and this stray capacitance. The reactance = increase at high frequency you are seeing could be the coil resonance = with the stray capacitance.=20 Theres also the fact that in reality the humble coil actually exhibits = transmission line behaviour. You can see this from the multiple = resonances you get from it...... I will let you investigate this = yourself -----Original Message----- From: GEORGE VARGHESE [mailto:rfengg@xxxxxxxxx] Sent: 07 March 2003 11:39 To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Inductance variation. Hi All, I have one more very interesting observation regarding inductors at RF = when in the presence of a conducting shield.=20 =20 When I put a high valued inductor close to a copper shield and observe = the reactance on a VNA , the reactance seems to decrease at lower = frequencies and the reactance increases at higher frequncies when the = shield is put near the inductor. What I mean is that , the presence of = the copper shield causes the reactance to decrease at the lower = frequencies (20Mhz) and increase at higher frequencies (100Mhz) . Can = anybody tell me the reason for this? Regards, George. =20 _____________________________________________________________ Get 25MB, POP3, Spam Filtering with LYCOS MAIL PLUS for $19.95/year. http://login.mail.lycos.com/brandPage.shtml?pageId=3Dplus&ref=3Dlmtplus ------------------------------------------------------------------ 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: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ________________________________________________________________________ This email has been scanned for all viruses by the MessageLabs SkyScan service. For more information on a proactive anti-virus service working around the clock, around the globe, visit http://www.messagelabs.com ________________________________________________________________________ ------------------------------------------------------------------ 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