So you went to a tradeshow and heard about this cool new idea called the Internet Of Things; now it’s time to build an IoT product of your own. You know that to be IoT, your Widget D’lux® has to have a network connection but which to choose?

You could use WiFi or Bluetooth but that would be gauche. Maybe LoRaWAN? All the cool kids are using LoRa for medium or long range wireless these days, but that still requires a base station and Widget D’lux® will be a worldwide phenomenon. Or at least a phenomenon past your bedroom walls. And you know how much user’s hate setting things up. So a cell modem it is! But what do you have to do to legally include one in your product? Well that’s a little complicated.

We’ve talked about government certification testing before (seriously, go read that article. Bob did a great job!) and it’s entirely relevant here but cell modems add a couple layers to that onion. There are a bunch of entry points to this discussion so let’s pick one and dive in.

Certification: Intentional, Unintentional, Multiple

So what kind of government certification will you need before you can ship your product? There are a few. If you plan to turn your cell radio on the entire device will need to be certified for intentional radiation to make sure that the radios you intend to use are well-behaved (don’t emit too much energy for given frequency bands). If you plan to turn on Widget D’lux® at all than it will also need to be checked for unintentional emissions to make sure there isn’t too much electromagnetic energy you didn’t mean to transmit. If you want to add another radio like Bluetooth or WiFi there’s also multi-radiator certification to look for problems caused by multiple radios operating at once.

Fortunately there are some tricks which might make that process easier. Testing and certification for multiple radiators is only relevant when more than one is on at once. Maybe the application can be adjusted so that you don’t actually need, say, Bluetooth at the same time as the cell connection? Or only turn the WiFi radio on when the cell signal falls below a certain strength and the radio is subsequently disabled? As long as there’s only ever one transmitter on at a time then you shouldn’t need to pursue additional certification. Though if there is ever a case where they can both be on at once it needs to be appropriately certified.

An even more specific exception is using WiFi to gather access ESSID’s and MACs to help with geolocation. Actively scanning for APs might be faster but if you stick to a passive scan the WiFi radio never transmits. No extra certification required.

Alternatively some modular certifications (we’ll get to that in a moment) allow you to avoid dual radiator certification if antennas of different radiators are placed far enough apart (here’s an example with a 20cm separation). Specific …read more

Source:: Hackaday