I have designed an Arduino shield that uses an FCC pre-certified and PTCRB cellular module and I'm wondering about EMC testing and FCC compliance. However, the main concern here is that I am using a different antenna and I read that I have to use the same antenna(e) that the module used during the certification process in order to not have to completely re-certify it for FCC ($10k+ and FCC ID and all that jazz). The weird thing is that Adafruit doesn't certify any of their FONA cellular boards even though they use different antennae from the ones in the module's certification. And how could you possibly get the exact same antenna that was used in the testing anyway? There are so many antenna knock-offs that may or may not even work. Check out this post in which Adafruit explains why they don't have to test their boards. In response to a question why they don't certify their boards Adafruit replies that "Because of our FONA boards, we're officially listed as a cellphone manufacturer" which basically sounds like "because we sell cellular modules we are officially listed as a cellphone manufacturer and therefore we don't have to certify our products" and that simply doesn't make sense to me.

To summarize, my questions are these:

  1. Is it legal to sell these shields without doing EMC testing or by only doing radiated emissions testing, or do I have to get it completely FCC certified with the new antenna?

  2. What about selling the shield to users in other countries? For example, Adafruit sells both an American (SIM5320A) and European (SIM5320A) version of their 3G module. Specifically I'm asking about the case in which the EU module (like SIM5320E) is CE certified. I understand there are specific laws for each country within an overarching region but I also read that you have to pay each country a registration fee? So if you're selling the board all over the world, how on earth would you afford every single country's fee? I notice that Adafruit doesn't mention where to use their product. By not explicitly mentioning specific countries or regions are they getting away with testing?

  3. Can Arduino shields be considered as "subassemblies" like what Sparkfun does to avoid testing? I would be selling the shield as a standalone module and it could be wired externally and not in the sense of a "shield". In fact, as-is it can't even operate on its own without a host, even if you powered it up by itself. I just don't see how doing EMC testing on a complete assembly (host board + shield) could make sense if I don't have control over what host board the user is going to choose. However, the caveat here is that the legal verbage seems to indicate that you can't say it's for Arduino specifically, otherwise it can't be considered a subassembly: "Subassemblies to digital devices are not subject to the technical standards in this part unless they are marketed as part of a system in which case the resulting system must comply with the applicable regulations." So if you say "shield for Arduino" or "works with Arduino Uno, Mega, Leonardo" it's no longer a subassembly? That sounds like rubbish to me and shatters all common sense of the term!

There's so much stuff involved with the certification process, it's driving me insane! Thanks to anyone who can clarify!

  • \$\begingroup\$ So apparently since section 15.101e describing subassemblies is only for unintentional radiators it cannot be applied to things like Bluetooth/WiFi/cellular things which are intentional radiators, so bummer, I'm out of luck and need to get it EMC tested. However, in order to even take advantage of the module's pre-certification the antenna I'm using must be of a lesser gain than those specified in the FCC certification grant. Otherwise the quote is $37k. So yea, if the antenna has too high of a gain I would have to attenuate it and get it EMC tested. \$\endgroup\$ Jan 4, 2018 at 22:39
  • \$\begingroup\$ You have to certify your system (Arduino + shield + antenna + enclosure). Since you are using a precertified module (with its own FCC ID), certain tests might be skipped, but you still have to go through the process. A certification lab can help you with that evaluation process. \$\endgroup\$
    – Lior Bilia
    Mar 8, 2018 at 16:49

1 Answer 1


This is a great article for you on the subject based on Part 15 of Title 47 CFR. I do not have a huge experience on this but when I have dealt with parts that are part of an assembly, such sub assembly was not tested. Why? for example the same board would be use in multiple chassis each one having a different EMI signature and shielding. Also differences in power and clocks.

Given that it is an intended radiator, it rises flags. The end product must have the correct certifications. In order to do that, the owner of such product has a better time using something that has pass certifications in someway, since they do not have control of the product. The main aspect of the certification is that you limit the user to the antenna type and modulations used.

You can ship modules without certification all day long, as long as who is receiving it does not power it up ;) but you should at very least make sure you are not setting someone up for failure.

Shipping to other countries in big quantities have it's own rules as well. Things like RoHS and REACH. Since it is a sub assembly I have not seen many issues unless it carries installed batteries or it has protected IC per ITAR etc.

Again not an expert but some experience of what I have seen.


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