Communication in the USB 2.0 and USB 3.0 modes was initiated between a PC and hard drive and, in an environment complying with the CISPR25 standard, the noise radiated from the USB cables was evaluated.
As a result, it was found under the condition of using no filters that noise was radiated from the USB cables during both USB 2.0 and USB 3.0 communication.
A high level of harmonic noise—approx. 57 dB (µV/m)—was found at a vertically polarized wave frequency of 240 MHz during USB 2.0 communication.
As a measure taken to suppress the noise, the following components were added to the signal lines:
In this way, it was verified that the noise in both the USB 2.0 and USB 3.0 modes was successfully reduced.
In the USB 2.0 mode, the noise was successfully reduced by a maximum of approx. 37 dB (at a vertically polarized wave frequency of 240 MHz).