Proliferation of RF ambients threaten the validity of open area test site measurements

The open area test site (OATS) has been in common use for over 20 years since the introduction of electromagnetic interference (EMI) regulations around the world The OATS must have very low RF ambients however the introduction of digital TV broadcasting and the proliferation of mobile telephone transmitters are threatening the validity of the OATS. This paper discusses the increasing difficulties caused by the masking of EMI emissions by new ambient threats at the OATS. The characteristics of ambients are analyzed and recommendations given for EMI measurements in the presence of the more common OATS ambients. Ambient profiles of old and new OATS are compared and the changes discussed. It is shown that validity of OATS in high ambient urban areas is questionable.