Chris, Try using a PI filter made out of two caps and a resistor (or at least a resistor and then the cap). This combination will work at low RF freqs. and is relatively inexpensive. For higher RF frequencies try changing the resistor to a ferrite. Depending on the frequency you are having problems with, you might have to change the value of the capacitors. I am sure you already know to keep the capacitor leads short, as those leads are inductive and are also antennas.
Sometimes the wires from the back panel to the board can pick up the RF, in which case you can twist the signal wire with a ground wire (or use shielded wire). If your product is in a shielded case put the capacitors on the connectors that are on the back panel, rather than on the board. In some cases I have seen people use what ever parts that happened to be handy when designing audio circuits. The catch is the transistors they were using were RF transistors. They did an excellent job of amplifying the unwanted RF as well as the audio. In really sever cases, Murata makes some ferrite PI filters that I have used. You can also get some absorbing material to put on leads as well. Jim Jim Bacher, Senior Engineer Paxar - Monarch e-mail: jim_bac...@monarch.com voice: 1-937-865-2020 fax: 1-937-865-2048 ____________________Reply Separator____________________ Subject: RE: EN 55024 Annex A.1 Author: "Colgan; Chris" <chris.col...@tagmclarenaudio.com> List-Post: emc-pstc@listserv.ieee.org Date: 5/25/01 12:44 PM David Oh dear, I was going to post a similar help message. Same problem except it is an audio amplifier and the test is radiated immunity. I can't possibly fathom out the demodulation process so I have to stop the RF getting in to the product. It doesn't help having the input and output grounds isolated from the chassis (for so called sonic reasons). I have made a significant improvement by a liberal sprinkling of 100n caps from signal ground points to chassis and secure EMC bonding of the chassis components. Hopefully a few more 100ns should clear the problem completely. >From this experience I guess you too might have a grounding problem. Try the magic wet finger and a few caps. Regards Chris Colgan Compliance Engineer TAG McLaren Audio Ltd The Summit, Latham Road Huntingdon, Cambs, PE29 6ZU *Tel: +44 (0)1480 415 627 *Fax: +44 (0)1480 52159 * Mailto:chris.col...@tagmclarenaudio.com * http://www.tagmclarenaudio.com ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
