Cynthia, This is a problem that never seems to go away. What I have found to be something of a conscious saver when shipping products with marginal results is to always test more then one sample of the "Manufactured" product. I really don't believe that 6 dB margin on one sample means much anyway.
I have used the statistical method called out in CISPR 22 but the sampling does not have to be that sophisticated. If three samples pass with less then 6 dB margin I think we have done our duty. Many of the low cost low margin designs out there can't handle some of the added cost 6 dB margin represents. Some will say, well that adds time and cost to the approval cycle. For high volume products the "Money" saved in the cost of manufacturing the product will way out weigh the cost of testing 3 ( or whatever ) samples. Have you ever tried auditing samples out of manufacturing to see what 6dB margin gets you over time, I really haven't but would be interested in hearing what others have to say about it. Regards and Good luck PS: This is my opinion , usual disclaimers!!!! Paul Zahra Manager, EMC and Safety Laboratories Corporate Compliance Engineering
