EMI
See also Filters
List
- https://www.eevblog.com/forum/projects/what-fcc-certification-test-that-i-need-to-pass-for-project-that-i-am-working-on/ - links to
- https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15/subpart-C - Has a list of 'not allowed' RF frequencies.
- https://www.eevblog.com/forum/projects/impact-on-emi-due-to-test-points-placed-on-bottom-side-of-pcb/ - Concern about test points going through a 4 layer board to the unshielded bottom (top is shielded).
Tips/Techniques
Spectrum Depends Upon Frequency and Rise/Fall Time
Per hackaday: https://hackaday.com/2024/03/30/how-much-bandwidth-does-cw-really-occupy/ and https://www.youtube.com/watch?v=KEgrTwjWLf0 Ideally a spectrum analyzer will look at both the spectrum and the waveform (oscilloscope), the latter being used for rise/fall time. Also worth noting is the old adage about square waves being made up of sine waves. http://web.archive.org/web/20230711194015/https://www.thepulsar.be/article/generating-sine-wave-from-square-waves/ Of course, rise and fall time is often the highest frequency in your circuit. CW is a type of OOK (on off keying), which he refers to as an extreme example of AM modulation (interesting) often catalogued with FSK (frequency shift keying) where different frequencies take the 1 and 0. OOK is the simplest transceiver and used with the cheap 433 or 900MHz transceivers on ebay which I have played around with but ended up just purchasing some low power labs tx (which ended up not working properly...)
Using Encoding Instead of Binary On/Off or OSK to Reduce EMI
This was used for ethernet. See somewhere in the beginning of the first edition (first 55 pages, I can't find the reference at the moment) of the Switch Book by Rich Seifert. There is an explanation of the types of ethernet signal encoding here (though it doesn't seem to mention emi) http://units.folder101.com/cisco/sem1/Notes/ch7-technologies/encoding.htm.
