beetlejuice
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Hi everyone
I recently submitted a new design for emc testing. Its passed all but the radiated emissions testing.
The design incorporates a camera connected to a controller. The camera is powered by 24vdc down a 15 m power cable.
When tested for emissions there are some pretty significant peaks in the results.
The top chart in the above image shows the emissions from just the camera powered via 15m cable.
The bottom chart shows the emissions after placing a ferrite clamp on the DC cable.
From the charts its clear that the noise is at harmonics of the 36MHz clock frequency of the digital video signal. After checking the 24v power rail with an oscilloscope with an FFT function it seems evident that there is a lot of 36 / 72 / 108 ... Mhz noise peaks on the 24v power rail. So i'm assuming that the emission failure is due to this 36Mhz fundamental and harmonics being conducted onto the 15m power cable and then radiated out as RF. I'm assuming that the power cable is the radiator because placing the ferrite on it reduces the emissions.
Am I on the right track with my assumption about the noise radiating from the cable ?
Any suggestions on what type of filter I need to kill these emissions?
I recently submitted a new design for emc testing. Its passed all but the radiated emissions testing.
The design incorporates a camera connected to a controller. The camera is powered by 24vdc down a 15 m power cable.
When tested for emissions there are some pretty significant peaks in the results.
The top chart in the above image shows the emissions from just the camera powered via 15m cable.
The bottom chart shows the emissions after placing a ferrite clamp on the DC cable.
From the charts its clear that the noise is at harmonics of the 36MHz clock frequency of the digital video signal. After checking the 24v power rail with an oscilloscope with an FFT function it seems evident that there is a lot of 36 / 72 / 108 ... Mhz noise peaks on the 24v power rail. So i'm assuming that the emission failure is due to this 36Mhz fundamental and harmonics being conducted onto the 15m power cable and then radiated out as RF. I'm assuming that the power cable is the radiator because placing the ferrite on it reduces the emissions.
Am I on the right track with my assumption about the noise radiating from the cable ?
Any suggestions on what type of filter I need to kill these emissions?