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Radiofrequency fields are usually measured in order to be compared with electromagnetic exposure limits defined by international standardization organizations with the aim of preserving the human health. However, in the case of WiFi technology, accurate measurement of the radiation coming from user terminals and access points is a great challenge due to the nature of these emissions, which are non-continuous signals transmitted in the form of pulses of short duration. Most of the methodologies defined up to now for determining WiFi exposure levels use or take as reference exposimeters, broadband probes and spectrum analyzers without taking into account that WiFi signals are not continuously transmitted. This leads to an overestimation of the radiation level that cannot be considered negligible when data of the actual exposure are needed. To avoid this, other procedures apply empirical weighting factors that account for the actual duration of burst transmissions. However, this implies the implementation of additional measurements for calculating the weighting factors, and thus, increases the complexity of the work. According to this, it was still necessary to define the frequency domain measurement setup that is optimal for obtaining realistic WiFi signal values, without requiring the performance of additional recordings. Thus, the definition of an appropriate methodology to achieve this goal was established as the main objective of this study. The set of tasks carried out to identify such configuration, as well as the limitations obtained for other measurement settings are deeply explained in this paper.

Millington's field strength prediction method is analyzed under different simulation conditions on the basis of the results of a medium waveband (MW or medium wave band extends from 530 to 1600 kHz) digital radio mondiale (DRM) measurement campaign. Millington technique applies the reciprocity condition by simply averaging the forward and reverse field strength values. This simplified approach could be a source of field strength prediction error in the MW planning tools. Critical path features for the fulfillment of the reciprocity condition are identified and their influence on predicted values is stated. Reciprocity effect on the predictions error is evaluated by means of the difference between digital medium wave field strength measured values of certain critical selected paths, and the corresponding Millington's method predicted ones. It has been found that the prediction error can be as high as 15 dB when comparing Millington's method results and measurements but the simple reciprocity approach made by Millington procedure is not the most remarkable source of error.Index Terms-Digital radio mondiale (DRM), field strength prediction, ground wave, medium wave, Millington's method.

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