DIY EMI FCC pre-compliance testing advice - Page 1
Forum section: electronics / projects

author: b177
author_rank: Contributor
timestamp: January 31, 2025, 06:27:53 pm
content: Hi all,I expect to submit a product for FCC certification in the next 6 months and looking for advice on if I should do some DIY pre testing myself, perform 'pre-qualification' at actual testing lab, or jump straight to the actual FCC-compliance testing.The product contains a switching power supply and is DC powered (no AC mains), less than 30W max (12V @ 2 amp nominal) -- it would be covered by FCC class B unintentional radiator. I do not anticipate EMI issues but always best to test early.I do not have any RF test equipment, but willing to buy equipment if needed, but not spend more than what a pre-qualification testing service would cost. I do have a function generator with 50 ohm output, could I use this as a semi-calibrated reference source? and then buy a SDR, like RTL-SDR (under $50)?is there another common 'hack' for doing this kind of pre-testing? (like using an AM radio)? Or I am wasting my time doing anything myself? (I do not care to learn about RF testing, just need to get done, economically)thanks,

author: thm_w
author_rank: Super Contributor
timestamp: February 01, 2025, 12:56:35 am
content: Do you have a decent scope? Use that with some cheap probes just to get an idea of what is radiating on your product and where.Its probably just the one switching psu frequency and its harmonics, but, may be a few other frequencies that you see that are worth noting down. Specifically anything seen on cabling.I don't think I would buy RTL-SDR, but tinySA could be good for the higher frequencies. Since average scope is going to be 100-200MHz or so.https://www.eevblog.com/forum/blog/eevblog-548-emc-pre-compliance-conducted-emissions-testing/https://www.eevblog.com/forum/projects/diy-emc-testing-of-simple-devices/https://www.eevblog.com/forum/projects/build-your-own-emc-probes/(you can buy these for $10)https://www.eevblog.com/forum/projects/a-cheap-way-to-perform-conducted-emission-tests-in-house/https://www.eevblog.com/forum/testgear/emc-how-far-can-you-get-with-diy-ham-receiver/https://www.stupid-projects.com/posts/emc-probe-using-rtl-sdr/

author: b177
author_rank: Contributor
timestamp: February 01, 2025, 04:49:59 am
content: I have a Tektronix TDS-3012 (100 Mhz).. with FFT module.The switcher is 500 khz.Thank you for the links. I searched FCC, but EMC would have been more productive.

author: Simmed
author_rank: Frequent Contributor
timestamp: February 01, 2025, 05:23:22 am
content: for reference alsosome of the LISN threadshttps://www.eevblog.com/forum/rf-microwave/50uh-and-250uh-inductor-design-for-lisn/?allhttps://www.eevblog.com/forum/projects/5uh-lisn-for-spectrum-analyzer-emcemi-work/?all

author: jbb
author_rank: Super Contributor
timestamp: February 01, 2025, 07:01:03 am
content: There are definite limits to what you can do in a normal workshop / lab. I remember being quite concerned about a spike at 13.56 MHz… until I turned my test device off and saw the spike was still there. Turns out all the badge readers for security doors work on 13.56 MHz.I am a big fan of ‘pre-compliance’ testing, ie arranging to visit the official test lab with prototypes and have a poke around. Go there as early as you can in the prototyping phase because - and the following example istotally made up- sometimes a 1nF capacitor in the right place will save you from needing two clamp on cable ferrite rings. As a bonus, you’ll learn about how the test lab actually tests things.I am also a fan of making life easy for the test lab. We would provide multiple prototypes, preloaded with EMC test software (if this is different to normal software) plus all cables and a testing laptop itself pre-loaded with a test command and control program. They didn’t have to install drivers or type weird commands or stare at output print lines to see if anything was wonky: just click the go button and read the summary counters. I’m pretty sure that our approach helped us get lab bookings (not always easy!) because the lab techs knew we wouldn’t f**k around wasting their time.