EM compatibility issues in wireless communications

The wireless communication band of devices of most commonly used by the public extends from about 27 MHz to 2.2 GHz. Recent advances in the technology of “intelligent” magnetic card reading from a distance of several feet have extended the frequency of wireless personal communications down to 0.12 MHz. The traditional wireless portable communication modulation technology has been frequency modulation (FM); few products used single side band (SSB), which entails linear amplification of the carrier. The explosive demand of channels for cellular telephony has caused the application of more sophisticated modulation technologies (pulsed and linear amplitude modulation). The subscriber units of the newer cell phone technologies produce EM fields in the appropriate RF communication band and low frequency magnetic fields in the modulation baseband (11-217 MHz). These low frequency magnetic fields can interfere with proper functions of other electronic equipment in their immediate vicinity. From the above considerations, it is clear that the EM compatibility challenges in wireless communication technologies extend from few Hz to several GHz. In all frequencies, the EMC challenge arises from the need of evaluating the E and H-fields in the immediate vicinity of their sources and must be averaged either over a small volume to detect the source of disturbance fields which have a sphere of influence with an extremely small radius (e.g. 10-12 cm) with respect to the wavelength of the low frequency (<300 Hz) signal