Testing and calibration laboratories should have a proven competency: they check devices and equipment quality, their generated field level, and whether they fulfill product requirements or safety limits, which means expertizing in applying standardized procedures, in controlling the possible measurement error sources, and in computing their associated uncertainty. This measurement uncertainty comes from different sources (site, equipment, and operator), but there is one factor always present: the environmental conditions. In this paper, we examine the role that fluctuations in temperature and humidity conditions play in the measurement uncertainty of electromagnetic signals. A common issue in all tests is the attenuation of the propagated signal, so we first present the relation between signal attenuation, temperature, and humidity. Then, we quantify the uncertainty in the measured signal for some actual cases at certain conditions, starting by the attenuation effect and then considering other case-specific deviations. We aimed to summarize the steps to compute the uncertainty associated with environmental conditions and to show that the relevance of each factor is case specific. Apparently, low values could contribute to the uncertainty budget. Their relative impact has to be evaluated at least once, to decide if they should be minimized, corrected, or discarded.
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