Submitting a brand new system for electromagnetic compatibility (EMC) testing appears a bit of like displaying up for the ultimate examination after skipping all of the lectures. You may get fortunate and move, but it surely actually would have been smarter to take a couple of of the quizzes to see how issues had been going throughout the semester. Equally, it could be good to know you’re not making any boneheaded errors early within the design course of, which is what this DIY TEM cell is all about.
We actually like [Petteri Aimonen]’s clarification of what a TEM cell, or transverse electromagnetic cell, is: he describes it as “an expanded coaxial cable that’s extensive sufficient to place your system inside.” It principally a cage manufactured from conductive materials that encloses an area for the system beneath take a look at, together with a stripline taking place its heart. The outer cage is connected to the outer braid of a coaxial cable, whereas the stripline is linked to the middle conductor. Any electrical or magnetic subject generated by the system contained in the cage goes down the coax into your take a look at instrument, sometimes a spectrum analyzer.
[Petteri]’s homebrew TEM is made out of a typical sufficient materials: copper-clad FR4. You may use double-sided materials, and even sheet copper in case you’re wealthy, however PCB inventory is simple to work with and will get the job carried out. His design is detailed in a second put up, which matches via the method of designing the scale and shapes of all of the elements in addition to CNC milling the sheets of fabric. [Petteri] tried to make the joints by milling part-way via the substrate and bending the sheet into form, however sadly, the copper didn’t need to cooperate along with his PCB origami. Fortunately, copper foil tape and a bit of solder heal all wounds. He additionally included a line impedance stabilization community (LISN) into the construct to offer a constant 50-ohm attribute impedance.
How does it work? Fairly properly, it appears; when linked to a TinySA spectrum analyzer, [Petteri] was capable of finding high-frequency conductive noise coming from the flyback part of a switch-mode energy provide. All it took was a ferrite bead and cap to repair it early within the prototyping part of the venture. Seems like a win to us.