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Questions On EMC Pre-Compliance Testing for Radiated Emissions

7/31/2013 09:00 AM EDT
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elctrnx_lyf
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Detailed
elctrnx_lyf   7/31/2013 1:19:56 PM
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These extensive details are definitely helpful to understand the basic of Emc precompliance testing.

Kenneth Wyatt
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Re: Detailed
Kenneth Wyatt   8/4/2013 10:37:00 AM
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Thanks elctrnx_lyf. You might also check The EMC Blog at: http://www.edn.com/electronics-blogs/4376432/The-EMC-Blog for additional Q&A following my webinar.

Sanjib.A
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EMC Questions
Sanjib.A   8/4/2013 2:45:16 AM
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Hello,

I missed the webinar, but thanks for sharing the link and Q&A. I have the following questions for which I have not got satisfactory answers:

1. Is it okay to use a GTEM cell to do the pre-compliance testing? I saw a big difference in the results when we tried to fix a power supply issue in GTEM cell vs when we tried the same fix in an anechoic chamber. Would you suggest avoiding GTEM cell for pre-compliance testing?

2. How to interpret about the source of the noise (PCB or Cable; Common-mode or diff mode) if a frequency component is appears in Horizontal scan but not in the vertical scan or vice-versa or appears in both?

Best Regards, 

Kenneth Wyatt
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Re: EMC Questions
Kenneth Wyatt   8/4/2013 10:46:32 AM
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Hi Sanjib.A, you pose several questions and I'll answer the best I can. As I'm not completely familiar with GTEMs, except from what I've read, you may need to consult other experts in the field.

I believe there is a "best" lower limit with GTEMS, depending on their size. So assuming the product you're testing does not exceed the size recommendation and the frequencies in question are - say - above 150 MHz, I've read they can be accurate enough for pre-compliance testing. Please correct me if I'm wrong...

As for your second question, there are "sources" of RF energy, such as devices producing fast edges (oscillators, buffers, ASICs, A/D, D/A, etc.) and these sources can couple via conductive, radiative, inductive or capacitive means to "radiating structures", such as cables, enclosure seams, etc.

Typically, it is common-mode currents that radiate via these radiating structures. As long as the loop area between the differential mode source and return currents is small, then DM emissions is usually a second-order effect.

A horizontal emission might come from a horizontal cable or a vertical seam, and visa versa with vertical emissions. You can also have a combination of the two.

JanineLove
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IEEE EMC2013
JanineLove   8/5/2013 3:25:35 PM
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Ken's in Denver this week for EMC. Ken, be sure to let us know how it goes.

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