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I have a device for which I want to do FCC Part 15 testing - unintentional radiation. (It includes an ESP WROOM Wifi/Bluetooth module with modular approval).

This device connects to wifi every 20 seconds for 2 seconds, and then moves a motor for 2 seconds, but only sometimes.

So it's:

1. Sleep for 20 seconds
2. Make http request via Wifi (3 secs)
3. Move a step motor (sometimes) (3 secs) 
-> Go back to 1. 

I presume it's not correct if the device is sleeping for the most part during the EMC tests?

But also, if I skip the sleep and just switch between making HTTP requests and moving the motor, I will not do each of these things half the time.

What's the correct procedure here?

(If you can refer me to docs, I am also happy - I could not find anything when I googled.)

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  • \$\begingroup\$ In case the sleep is there to meet a band requirement of not returning to the same channel for a certain amount of time, then it obviously needs to be there and you can then justify it. The test house might however want some option to have continuous transmission when doing various tests though, I'd ask them how they usually do it. \$\endgroup\$
    – Lundin
    Feb 4, 2022 at 14:12
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    \$\begingroup\$ Sorry, but how this fall inside unintentional radiation? It see it clearly as intentional radiator. law.cornell.edu/definitions/… \$\endgroup\$
    – Marcos
    Feb 4, 2022 at 14:18
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    \$\begingroup\$ I presume the module complies as expected with intentional compliance and the unintended noise only comes from hardware with very fast dI/dt currents with large loop area rather than twisted pairs with a possible snubber \$\endgroup\$ Feb 4, 2022 at 14:19
  • \$\begingroup\$ @Marcos Yeah that's a good point and FCC testing will entail both. "Unintentional radiation" being both "out of band emissions" close to the carrier, as well as "spurious emissions" which is everything else. And also radiated susceptibility tests. \$\endgroup\$
    – Lundin
    Feb 4, 2022 at 14:20
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    \$\begingroup\$ The certification lab will ask you to exercise all modes of operation: RX, TX, Idle, Sleep, PWM on, DC2DC on, Crystals on, etc. Make sure your software can get into each mode with a command. Also, make sure you don't have to have the PC connected to it via a cable during the actual test, it makes the technician job more difficult, and you pay for it. \$\endgroup\$
    – Lior Bilia
    Feb 4, 2022 at 17:18

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I presume it's not correct if the device is sleeping for the most part during the EMC tests?

In the past when our group has done unintentional radiator testing, we have had to cycle between all the software/control modes that the product has. This includes turning different loads on and off. The lab doing the FCC testing will probably want to know about the different modes that you have listed, they may ask you to stay in only one mode make it easier to see the radiation.

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  • \$\begingroup\$ If there are no inputs on the device to cycle through the modes, what do I do? It's just a dumb embedded device, if you want to change behaviour you need to flash a different software version. \$\endgroup\$ Feb 4, 2022 at 20:06

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