I am not sure where your information comes from but I don't really agree = with it. Heres some food for thought... Draw two simple series circuits near each other one consisting of = source, source resistance a track then a load resistasnce. The other = circuit having a source resistance a track then a load resitance. Lets = call one the source and the other the victim. Now first off link the two = tracks in the middle of the circuits together with a capacitor to model = parasitic capacitance or electric field coupling between the two = circuits. You will find that the maximum signal transfer from one = circuit to the other occurs with a high impedance circuit at the victim. Now change the coupling so you have an inductor in series in each = circuit which is coupled to the other circuit (transformer coupling if = you like). This time when you do the sums you will find that the low = impedance at the victim circuit is the one to avoid. This coupling = mechanism is magnetic of H field coupling. This occurs with low = impedance high current things near each other. There is one other type of coupling which you need to be aware of. This = is antenna coupling. In very simple terms you will have structures on = your board that are resonant at certain frequencies. At this frequency = the structure behaves like a good antenna to signals at the resonant = frequency and is therefore prone to pick up or to radiate energy at that = frequency.=20 The High impedance problem is normally quite easy to avoid given that = electric fields are easily screened by thin metal screening cans around = any circuits prone to this affect. The low impedance magnetic field = problem on the other hand can be a little more problematic. If the = energy is low frequency energy the shielding required can be = inpractically large.=20 In all cases the best way out is to put physical distance between source = and victim. You will also note if you have done the sums on the circuits = mentioned above that the source and load impedances can be changed to = help.=20 We could go of forever on this one The subject is covered will in all good EMC / RF books Hope my input gave you a start Steve Rogers B.Eng (Hons) C.Eng IEE RF Design Engineer Micromill Electronics Limited Leydene House Waterberry Drive=20 Waterlooville Hampshire PO7 7XX Tel: +44 (0) 23 9236 6600 Fax: +44 (0) 23 9236 6673 Registered No. 1456922 (England). =20 Registered Office Brook Road Wimborne, Dorset BH21 2BJ *********************************************************************** "This email and any attached files are confidential and may be legally = privileged.If you are not the addressee, any disclosure, = reproduction,copying, distribution,, or other dissemination or use of = this communication is strictly prohibited. If you have received this = transmission in error please notify the sender immediately and then = delete this email. It is the policy of Micromill Electronics Limited that no legally = binding statements, representations or commitments (collectively = 'statements') may be made by email. Any such statements must be = confirmed either by facsimilie or by post before they will have legal = effect. The sender of this email is not authorised to commit the company = in any way and the addressee is hereby formally notified of that fact." *********************************************************************** -----Original Message----- From: Lim Guan Choon [mailto:guanchoon.lim@xxxxxxxxxxxxxxxx] Sent: Friday, September 26, 2003 9:31 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] High Impedance Traces are prone to Radio Frequency Interference Hi, all. Could anyone help to explain why high impedance traces are = =3D prone to Radio frequency interference? I have come across this kind of = =3D remark in articles, but no explanation why it is so. Please help. Warmest regards Lim ------------------------------------------------------------------ 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 Email Security System. 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