Another "war story" along similar lines - my ham rig picked up a lot of "hash" on the 20-meter (14 mHz) band, and I was going around trying to find the source. After turning off virtually everything else in the house, and thinking that the noise was coming from the neighbor's house, I eventually found that the noise was coming from a couple of light controllers in our bookshelves, each with a capacitive touch switch level control. The noise occurred even when the lights were off. Unplugging the power cords was the only way of eliminating the noise. A similar issue occurred when transmitting - another "touch switch" fixture would come on from the HF radiation from the antenna, and the resulting hash would swamp signals in the 20 m band. Again, disconnecting the power cord solved the problem.
Makes me wonder how often our unexplained problems might be EMI.
Do installers know not put cables that might have large transients next to cables with low level signal? This is not necessarily EMI, but does your computer have ECC memory, if not you will probably get an error every once in awhile, read the IBM studies. I think Silicon_Smith has the right idea, EMI shielding and testing should probably be a bigger part of all electronic designs. Ever hear your GSM phone buzz in your car speakers, hopefully that is the only problem it is causing. No foil hat for me yet though.
Common culprits! Why wouldnt we have better EMI shielding for equipment susceptible enough. I mean, if the client really wants 100% I bet they dont want it to be just for the approval stage. They should rather, switch on every machine they got and then run the tests!
I'm glad you were able to finally get the environment under control to complete the test successfully. Of all the environments that should be controllable, it is the laboratory environment. I do wonder, however, what the poor manufacturing facility that uses many soldering irons will do when they see all those errors on their DSU.