Single frequency spikes at a multiple of 25 Mhz are almost always Phy related. You did not mention if they are smallband (single spikes)
or wideband, nor if your box is of metal and if it is really closed.... Gert Gremmen Van: Derek Walton [mailto:[email protected]] Verzonden: zaterdag 7 december 2013 16:28 Aan: [email protected] Onderwerp: [PSES] Puzzle Good day folks, I'm faced with a challenge that's confusing me a bit, and I'm concerned I'm overlooking something. I have a small box, about 4" by 6" by 2" that contains some Ethernet circuitry. Normally there are cables that come and go from this box. During RE testing, there are several very strong emissions ( above 200 MHz ) that exceed all other noise made by the box. As yet, we have not been able to link them with any of the anticipated frequencies one would expect. In chasing the source down I have taken a number of steps which are: 1) Disconnect all cables except the power. There was no change on the large spikes, other noise came down as anticipated. 2) Added several ferrites on the power cable. No change. 3) Added two feed through type caps at the power entry point. No change. 4) Wrapped the box completely in Aluminium foil. No change. 5) Checked Ambients... Nothing, quiet. 6) Replaced power source. No change. 7) Rotated box, very minor change in amplitude. This box is a new version of an existing design that does not have the same issue and close field probing is very difficult inside the box. My suspicion is that a small daughter board is the source, but this cannot be removed from the box without destruction. A new box has been ordered build without that board. That may not arrive for a few weeks. In the meantime, can anyone make suggestions about what may cause this noise, besides parasitic oscillations/faulty parts, and what radiating mechanisms can be uninfluenced with the protection measures I took. Many thanks, Derek Walton. L F Research. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
