Is this EMI shielding missing on purpose? - Page 1
Forum section: electronics / rf-microwave

author: PeterFW
author_rank: Frequent Contributor
timestamp: June 21, 2016, 08:11:18 pm
content: Hello!I got this new WiFi device today, it emits a fairly loud buzz/hum so i opened it to have a look were to put some nail varnish in case the offending part is accessible.I expexted a tin can to cover most of the PCB but i was a bit surprised when i found this:http://imgur.com/a/jAg1KThere are traces for the EMI shield on the board but it is not populated.This can not be right, right?I thougth RF stuff has to be shieldet for various reasons.Greetings,Peter

author: ataradov
author_rank: Super Contributor
timestamp: June 21, 2016, 08:49:44 pm
content: If you can pass regulations without it, then shield is not needed.The reason designers always put footprint for the shield is that some markets (US included) will require a shield even if it is not needed technically and does absolutely nothing.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 21, 2016, 10:53:08 pm
content: Is that actually a requirement? Do you have the standards that say so?Tim

author: ataradov
author_rank: Super Contributor
timestamp: June 21, 2016, 11:05:06 pm
content: Quote from: T3sl4co1l on June 21, 2016, 10:53:08 pmIt is a very strict requirement for modules and modular approval. Here is a document, for examplehttps://apps.fcc.gov/eas/comments/GetPublishedDocument.html?id=50&tn=916170It has following text:Quote.FCC is a bit vague on device approval, but in general certification labs like to see shields around RF components, but it is possible to do without a shield.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 22, 2016, 08:11:14 am
content: Hmm, interesting.The horse's mouth is here:http://www.ecfr.gov/cgi-bin/text-idx?SID=65383194e02b51c7035811b81823af69&mc=true&node=pt47.1.15&rgn=div5#se47.1.15_1212It's not at all clear to what length "shielding" constitutes, or what a "crystal" is and why it's implicitly required. Or "buffering", though I assume they mean to constrain the input voltage range and bandwidth (or data rate, or anything that gets turned into radio modulation, in any case). Not that it should just have an op-amp or logic buffer, which would do little...But go figure, the FCC is underfunded these days...In any case, the pictured device at least doesn't appear to meet the definition of a modular transmitter -- it doesn't have a self-contained antenna, and doesn't appear to use a "non-standard" connector (not that that's a point in favor of its legality in the US..).Tim

author: ataradov
author_rank: Super Contributor
timestamp: June 22, 2016, 03:56:58 pm
content: If not US, some other country may require mandatory shielding. And it costs nothing to design it in, but costs a lot to retrofit somethings later.

author: janekm
author_rank: Unknown
timestamp: June 22, 2016, 10:55:51 pm
content: That "non-standard connector" phrasing is why RP-SMA connectors exist, because they are non-standard... Of course by now antennas in RP-SMA are probably more common than SMA onesThat wifi gadget you've got is probably using RP-SMA connectors to keep the FCC happy (not that there's FCC approval on the label anyway it seems).