Uncertainty in radio frequency emission measurements due to the effects of electromagnetic ambient

This paper describes the uncertainty in radio frequency emission (RFE) measurements due to the effects of time varying behaviour of electromagnetic ambient (EMA) noise spectrum prevailing in the measuring environment. Reception of unwanted EMA signals (sometimes, unpredictable before starting the measurements), at the time of RFE measurements, interfere with the measuring RFE signals. This results in nonrepeatability in the measurement results. It is shown that if the noise emitted by an equipment under test (EUT) is equal to or more than worst case EMA level allowable as per international EMC standards (i.e. 50% of specified limit) and when this is added with EMA, the measured noise level is increased significantly. This is explained using experimental results. An allowable EMA margin of 10 dB is suggested instead of 6 dB, to overcome the problems due to EMA.