Measurement of disturbances radiated from personal computers in the WLAN frequency band

Wireless LAN networks have become widely used in various environments. Since WLAN terminals are normally located nearby personal computers (PCs), electromagnetic disturbances emitted from the PCs potentially degrade the quality of the WLAN communication links. To investigate the effects of the PC disturbances on the wireless links, it is necessary to evaluate and model the characteristics of the radiated emissions from the PCs. We have therefore conducted measurements of the PC disturbances in the WLAN frequency band. The experimental results show that the harmonics of the base clock of a PC are major components of the disturbances in the WLAN frequency band above 2 GHz. It is also found that the harmonic spectrum is not a line spectrum but has a certain bandwidth. This is due to dithered clocking, which is a technique for reducing the spectral amplitude of the harmonics by intentionally sweeping the fundamental frequency of the clock signal. These findings imply that the PC disturbance in the WLAN band can be simulated by frequency modulated CW.