Noise properties are investigated on experimental basis. Typical distribution functions for power levels and various other quantities useful for communication link simulations are investigated. We observe space and temporal variations of the noise phenomena. Regarding correlation with power load of the installation network, we have established that the noise power is not correlated with the daily load profile of the power system on high levels, but rather that there is a quite tight correlation between noise and local power load, i.e. the load of the actual building, reflecting human (technical) activities in the vicinity. We also concluded that narrowband interferences are more correlated with the load profile than the floor noise, and that the noise components are not entirely random, meaning that much of the noise power is actually coming from electronic and other devices in the relatively near proximity. Propagation model is based on the impedance simulations/measurements. It showed much better compliance with directly measured transfer functions, than today's wide-spread time-domain models, described in most relevant and recent literature, not to mention the vast complexity of time domain methods in real-life multi-branched networks. We have developed very simple, practical and straightforward method which enabled the construction of a software tool that can perform complex analyses of the propagation functions, and based on them and on the stochastic numerical experiments, of a number of quantities relevant for the communication properties of the channels analyzed. The same tool is used for the extensive analysis of the impedances present on PLC network ports. We have also experimentally investigated important impedance properties. Comparing to the contemporary literature, we have provided most detailed and extensive data on propagation and impedance characteristics of the power line communications medium, as well as a simple and straightforward method and appropriate software tool for impedance calculations. Impedance properties of PLC networks are important because impedance mismatches affect the signal transmission. Next part of the dissertation is about the capacity analysis of PLC channels. This analysis, too, is based on the software tools we developed, and on the noise samples taken from the real networks. We conclude that in real-life PLC networks, with propagation and noise properties as described in earlier chapters of the dissertation, there is a substantial communication potential, i.e. that one can achieve communication speeds in the range of hundred of megabits per second in intrabuilding networks. There is also an analysis of the basic electromagnetic compatibility considerations regarding PLC communications, as well as a review of the regulation development and its influence on achievable capacities, and normization processes relevant for the PLC technology.