Design and Evaluation of a Dual Impedance-Adapting Power-Line Communications Coupler

Historically, the unpredictable on-off switching of loads has been a major obstacle to low-voltage power-line communications. Some researchers have gathered valuable data and have proposed statistical models in order to try and mitigate these sudden changes in access impedance. Others have proposed network conditioning in order to “block off” harsh loads from the power-line network by means of series filters. These filters are expensive, as they have to be rated at the typical current that is drawn by the load to be ‘blocked off’. Also, in many cases, these are the very loads than need to be monitored and controlled for home automation. This paper investigates the possibility of utilizing a simple, dual coupler to diminish the impact of switching loads on data transmission. First, the design of a suitable dual coupler is demonstrated, using a commercially available high-frequency transformer. Next, laboratory as well as live 220-V measurements are done for 50-$\Omega$ modems at frequencies below 1 MHz. These measurements confirm that the proposed dual coupler can help to counter the impact of switching power-line loads by means of i) improved transmission when a certain network point is loaded and ii) more predictable (lower) power-line impedance levels—facilitating more accurate overall impedance adaptation.