Examples of EMI Issues in real Products

[timb]

I bet you a donut that they implemented the USB shield ground in utterly the most wrong way possible.

Tim

Would you mind elaborating what scheme you prefer? I've seen so many different options online and in app notes - solid connection; connection through ferrite; connection through resistors sometimes with a cap in parallel; not connected at all...

AFAIK, it has to go to chassis GND directly, if chassis GND is missing, then it has to go GND directly.

I've always connected the USB shield to the board's ground through a 100k resistor and 100nF cap in parallel and never had an issue. I'm pretty sure I picked it up from several app notes many years ago.

I assume the idea is to filter any noise out. Though I'm not sure how effective it really is...

[tautech]

Joe mentions EMI problems with his LeCroy in this post and on other occasions in this thread:
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1128792/#msg1128792

But he playing with some pretty nasty stuff.

[coppice]

A few years ago we were working to harden utility meters against attacks from noise generating devices, obtained from back street sources, which are designed to cause the processors in these meters to lock up, and not register consumption. Over time the noise generators escalated, and the hardness we achieved responded to this escalation. The difficult point came when the noise sources were crashing every Tek and Agilent instrument on the workbench. Its hard to continue development of your product when its the only thing you have which doesn't fall over.

[FlyingHacker]

I'll just drop this here:

http://www.compliance-club.com/archive/old_archive/Bananaskins.htm

This is awesome! Lots of examples...

I got into Amateur Radio starting last year, and this has really opened my eyes to RF interference both from other devices and to other devices. The ham bands are just a small sliver of the spectrum too. It is a very interesting topic.

[mmagin]

I'll just drop this here:

http://www.compliance-club.com/archive/old_archive/Bananaskins.htm

This is awesome! Lots of examples...

I got into Amateur Radio starting last year, and this has really opened my eyes to RF interference both from other devices and to other devices. The ham bands are just a small sliver of the spectrum too. It is a very interesting topic.

Soon you'll hate just about every piece of consumer electronics beyond a wristwatch or an (incadescent) light bulb.

[KE5FX]

I assume the idea is to filter any noise out. Though I'm not sure how effective it really is...

The idea behind the parallel-RC connection is to break low-frequency ground loops that might introduce AC line noise into sensitive equipment like audio gear, without sacrificing RF ground integrity.  It's better than leaving the shield floating or putting a bead or inductor in series with it, but I personally prefer a solid ground bond at all points of entry.  That means that whatever goes wrong is somebody else's fault.

The USB signal itself is differential and doesn't really care about shielding one way or another, but there's one potential exception to that.  The handshaking that takes place during enumeration, when the host first recognizes the presence of a device, is single-ended in nature.  If there are common-mode signal integrity problems for whatever reason, this is when they'll typically show up.  About the only SI problems I've ever seen with USB (2.0 HS) have been related to handshaking.

[FlyingHacker]

Soon you'll hate just about every piece of consumer electronics beyond a wristwatch or an (incadescent) light bulb.

No doubt. It really makes me look for devices in (shielded) metal cases, as they have far fewer issues in either direction. There are so many devices with no RF shielding of any kind these days. I used to complain about all that metal shielding getting in the way when I took things apart. Now I find myself adding it to new products!

And this is the easy stuff to block... higher frequencies must be a real nightmare.