This paper shows experimental results of packet error rates (PERs) in wireless-LAN mounted printed circuit boards and gives a discussion on a mechanism of electromagnetic noise coupling that affects the PER. We utilized the amplitude probability distribution to investigate the noise coupling channel. We measured the magnetic near-field distribution to obtain information about noise sources. Based on measurement results, we also performed parallel plate resonance analysis to find out electromagnetic interference antennas. We confirmed that noise radiates from a power supply system of a digital circuit and its coupling to a receiving antenna causes an increase of the PER.