We are having trouble with a CISPR-11 (EN55011) Radiated Emissions Class B compliance test in one of our solutions. The troubling part of it is basically an industrial motherboard (with a commercial SSD and commercial RAM) within a well grounded metal enclousure, sharing space with an industrial switch, a switching 12V industrial power supply and a industrial touch panel and monitor. Every single one of these industrial components have its corresponding compliance certificate for CISPR-11. The antenna picks up the following waveform (Vertical orientation, 3mts distance, 30 to 200 MHz bandwidth). Crosses above the threshold are non-compliant peaks.
The main offender is a 60MHz peak that looks like a strong square wave in frequency domain. That is new to me in these tests; I am more used to specific harmonics in the spectrum. If we turn off the motherboard (and thus also the RAM and SSD), the 60MHz and also those crests at ~80MHz dissapear. Turning of the rest of the components (except the 12V PSU) has no effect.
I have the motherboard's compliance test and procedures, and their peaks are nowhere near in power or frequency. They also used commercial RAM and a mechanical commercial hard drive.
Has anyone seen this waveform before for radiated emissions and/or has any idea, given the description of our system, what could be generating it?
EDIT: Based on comments and answers, I will clarify some things. First, I have 1 Ethernet cable (unshielded) inside the case, connected to the switch, also inside, but then 3 Ethernet SSTP cables going out from the switch to 3 ethernet Basler cameras. These 3 do have a ferrite clamp on each, but I haven't fiddled with the one inside. I'll note that down.
The SMPS was our main target for the whole ordeal but I still need to try ferrite beads on its outputs and maybe enhance the shielding around it.
Unfortunately we do not have our own spectrum analyser and our scopes are up to 60MHz. We do not develop high frequency custom electronics, so they were not neccesary. Given the circumstances, we may adquire one and do our own pre-compliance testings, as many of you suggested.
I will keep this updated.
EDIT2: So I tried making a makeshift antenna out of the scope probe, and we identified a single spot in the LCD screen using FFT, which is directly in front of the motherboard, with a peak exactly at 60Mhz. I am quite sure we found the place where the signal is originating, though still couldn't find the culprit. I tried everything suggested here, and altough they didn't quite fix this particular emission, all suggestions are greatly appreciated as the will surely enhance compatibility.
We identified, however that the screen enclousure is plastic and in some spots (including the one with the 60MHz peak), there's no conductor material between the interior and exterior of the whole enclousure, so next step is to place a metal sheet between back of the screen and everything else. I will post the results for anyone interested.