Do kits w/o RF components require EMI/EMC testing? - Page 1
Forum section: electronics / projects

author: mavericmf
author_rank: Newbie
timestamp: November 21, 2023, 03:52:00 pm
content: Hello all!First; I apologize if this post is in the wrong section, or is a duplicate, but I was unable to find anything that has the same specifications as my project.I am working on a couple projects I would like to sell to hobbyists that connects to a PC via RS-232, it will also connect to a third-party two-way radio (FCC licensed of course, and not a module). I understand that to sell a product, I would need to get compliance testing and file an SDoC. However, even SDoC testing is outside of my budget for this project. I don't want to ignore the law, and in the US some of the rules seem rather vague or are often argued.The reason why I ask this even though there are plenty of topics regarding FCC certifications, is that my product has no intentional radiators; No Bluetooth Modules, WiFi Modules, or anything similar. Does selling these in kit form require FCC compliance? I don't mind doing my own testing to make sure it's not generating harmful interference, but I also have no money or interest in paying for compliance testing. Especially when the profits from this will likely be less than the amount it would cost for even the cheapest compliance testing centers.I am based in the U.S. and I only plan to sell to U.S. only.One more question; I haven't opened the can of worms that is RoHS compliance yet, but does that care if it is a kit as well lol?Is it just me or does it feel like all of these regulations make it extremely difficult for small scale manufacturers? (I understand their purpose, but it feels like they could be less annoying)Thanks guys!(Also one more thing, these devices are either gonna be powered off of USB or just have a +12VDC screw terminal, so no AC/Batteries/UL to deal with)

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 21, 2023, 04:06:03 pm
content: As always, asking for legal advice on an electronics forum is risky, but I believe the answer is yes.Examples can be found in early (pre Wifi and Bluetooth) computers and switch mode power supplies.There may be escape clauses for kits, or for circuits which have no oscillating or switching behavior above a few kHz, but you would need a lawyer to answer that.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 21, 2023, 09:19:10 pm
content: Yup, still cares if it's a kit. Citation:https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-A/section-15.25As for testing, or when law is actually employed... as is almost always the case in the US, it's employed at the behest of any authorized agent that takes notice. You could probably get by without anything, and just never move enough product that someone notices it's malfunctioning, and that those consequences come back to you. The risk of failure is, whatever it says in this part of course, and if doing a recall and testing and modifications and return would destroy your business... maybe that's a risk you're willing to take, maybe not. The business case could even be made to proceed on a best-efforts basis (perhaps invest in some precompliance testing, or contract/hire someone for same), turn some profit, then go back and do it, and hope that you didn't screw it up the first time (and if you did, you only need to recall those first sales).Basic EMI principles, if you have a device with one connector or less, it's at least very easy to improve it to such point that it passes, and the risk is most likely radiated if anything -- there's no conducted emissions at all without a connector obviously, and with just one, the "reaction mass" can only be the enclosure itself. Two or more connectors, you have risks for EMI going up and down both -- equal and opposite emissions are the most likely case, and so conducted is a strong concern. This is obviously a big problem for power supplies where those two connections are supposed to be isolated so you can't just tie input/output grounds together and be done. If you don't need isolation, conversely, tying grounds -- and ensuring there's no induced voltage in the ground path between them -- gives at the very least a strong starting point forGround is king; if you can extend PCB ground plane up and over the connectors themselves (shielded or metallic connectors, braid cable or coax), you keep whatever nastiness is in the cables, neatly tucked away. You might avoid filtering digital comms with the use of shielded cables (pedestrian example: USB ismostlydifferential, but it also delivers a common mode 1.6V pulse (SE0, both lines low) as part of its protocol, which would be unreadable, and impossible to filter, without the use of shielded cables and connectors). Even with, filtering to the maximum amount permissible given the nature of the signals is always helpful, and without shielding, filtering allows you to use bare naked signals at low bit rates (some kbps, maybe even up to 100s, depending on length) while avoiding emissions and susceptibility problems (similar example: USB HIDs with unshielded cables!).FCC doesn't require susceptibility testing BTW, but does recommend it. CE requires it.I take it, this is just an inline signal processing box, perhaps with an audio port on one end, and serial cable on the other. That's quite good, it means required bandwidth is small. The serial port might even be shielded (DE-9), for which you can recommend the use of a shielded cable in the manual. Even without, I might place a little filtering on RS-232 (more on "TTL level" serial, it needs more help), and a TVS for ESD protection. The audio side, I would not assume shielded cabling, and simply filtering it will do well enough (and a TVS / clamp diode).Tim

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 22, 2023, 12:48:03 pm
content: Provide a few review samples to some amateur radio operators, in particular emphasize that it has not been tested for EMI and that you would like to make sure it won't have any problems regarding that. Most likely if you make a product with EMI problems, amateur radio operators would be the first to notice.

author: lucy.sierra
author_rank: Newbie
timestamp: January 05, 2024, 05:21:09 pm
content: You can ask your EMC questions toKen Wyatt.