Abstract :
Our results are based on measurements carried out in a residential house in suburban area of Zagreb town, as well as in a medium-size office building (seven stories, approx. 150 offices) in the Zagreb city center, during two moths (late August, September and early October 2003). The noise samples were collected in five whole-day (6 am–10 pm) campaigns. Those five days were equally distributed over the two-month period. Noise was measured with the spectrum analyzer, built in the instrument Anritsu Site Master S114B, between the neutral (N) and protection (PEN) wire, so that virtually no 50 Hz voltage was present on the analyzer port. Anyways, we have provided a simple overvoltage protection for the instrument, in case a temporary network fault occurs. We have studied noise on N-PEN pair because there is a technically well grounded tendency that this wire-pair, and not the neutral-phase or phase-phase, should be utilized for PLC systems, [1]. Beside noise measurements, we also carried out simultaneous measurements of the actual office building electrical load, by periodically reading its meter. This was needed for the investigation of correlation properties between the electrical load and total noise power in the 10 to 30 MHz band. In all measurements we have recorded both noise samples from one analyzer scan (lasting about 5 seconds), thus obtaining "temporary" shots, and 5 minutes maximal values, using max-hold function of the instrument. We found 5 minutes maximums interesting because of rapid temporal fluctuations in noise power levels. Resolution bandwidth of the analyzer was 10 kHz. On all figures in this article we use noise power levels in dBm recorded by the instrument with that resolution.
