Power line carrier (PLC) is one of the communication and load control (C&LC) techniques employed in direct load control. A PLC is, within itself, a communication system. It utilizes power transmission line as a medium of transmitting control functions, and relaying. High frequencies, in the order of 30 to 300 kHz, are used. Power line carrier systems are, at present, the most attractive C&LC systems. Recently, dispersed generation - photovoltaics, wind energy, small scale hydro - is introduced to power systems. The introduction of small scale dispersed generation sources degrades the performance of PLC systems by injecting dc-ac inverter related harmonics into the distribution lines. These harmonics interfere with PLC signals. Thus load control functions assigned to PLC systems are affected. It is the purpose of this research to study how a PLC signal propagates through the transmission line and how it is affected by the harmonic interference. An experiment is conducted using a distribution network provided by the Jet Propulsion Laboratory discussions, and conclusions are presented. / M.S.