Beaglebone Black FCC Testing

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1

Good Afternoon,

First off, thanks to the BB community for making this such a great resource for those working on the BBB and other boards. I have personally spent hours on this forum.

I am hoping that someone monitoring this group may be able to help me and my company solve an EMC problem that we are facing the the BBB. We are open to paid consultations to aid in solving this issue (Gerald?). We are building a product around the BBB that needs to pass FCC part 15 Class B. We are having trouble passing the tests mostly around the 625 MHz range. We were only 1-2dB above the limit in one lab and almost 10dB over at another lab (yes, test equipment makes a big difference!). We tried it with and without our custom shield attached.

There is another thread here: https://groups.google.com/forum/#!searchin/beagleboard/625/beagleboard/Y6BhtzKx2oY/YQ_xjmmkWusJ that seems to have the same problem. That thread seems to have lost attention of the key players in this group so I thought I would create another thread to bring more attention to this critical issue.

We have done some pretty aggressive modifications to the board and the only way we can get the board to pass is by completely disabling (and depowering) the LAN PHY. This was accomplished by removing FB4 and mangling part of the device tree so we don’t get a kernel panic on startup. Not an elegant solution, I know.

As suggested in the other similar thread, we tried shorting R136 but it actually made the noise worse.

We also tried disabling (removing Y4) the McASP oscillator as that was also generating quite a bit of noise. Didn’t help enough.

Has anyone other than CircuitCo been able to successfully pass FCC with the BBBw/Ethernet enabled as part of a system? CircuitCo was probably able to pass because they could isolate the BBB with big filters on all cables because they aren’t selling the BBB as as system but as a component. Because ours is a “Commercial System”, we need to test with all cables as they would be typically installed. No giant chokes for us.

Thoughts? Comments? Suggestions?

Thanks!

Jon

2

A lot depends on SW as well. Best way to pass is to put it in a box, but thee are some other things you can try that involve $$.

You can contact me directly and we can have a lively discussion about your issues.

Gerald

3

Gerald,

Thanks for the speedy response. We do have an enclosure for our product but it is made of PC so it doesn’t help much with EMC. The test lab also tried “painting” it with this conductive paint but it didn’t help enough. I’ll take up your offer and take this offline and contact you directly.

Thanks,

Jon

4

I suggest you add common mode chokes on HDMI, Ethernet, and USB. And on any additional connectors you have coming from the board.

Gerald

5

Was the culprit for the 625Mhz noise found? We have a similar issue and we suspect the USB.

6

This was a long time ago but I believe it was the HDMI clock. We were able to disable HDMI clock output by recompiling the device trees.

Hope this helps.

Jon