## 4 Results of an Experimental Study with Power-Line Communication and Selected End-User Equipment
The supply voltage waveform distortion was achieved using the programmable AC source and authorised software for harmonic superposition. The created waveform of the distorted supply voltage is illustrated in Figure 9a. The waveform is characterised by the total harmonic distortion index equals to 11.62%. Figure 8: Case 2: results of the analysis of PRIME PLC system operation with LED light sources at pure sinusoidal voltage supply; (**a**) supply voltage waveform; (**b**) time-frequency representation in the range 2-150 kHz using 100 ms window during the 20 s observation; (**c**) comparison of the spectrum of the corresponding PRIME PLC transmission (black) and the spectrum of the voltage in the connection point of the load and energy meter (grey) with the relation to the normative curves (ul—line voltage in the point of the equipment connection, which is also the point of energy meter connection with PRIME PLC). Spectrum analysis using 200 of 100 ms windows (Figure 9b) allowed identifying the characteristic spectra of non-intentional emission and PRIME PLC transmission. Observing Figure 9c it can be concluded that as it results from the distorted voltage supply waveform \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{4}{c}{**Odd Harmonics**} & \multicolumn{4}{c}{**Even Harmonics**} \\ \hline \multicolumn{4}{c}{**Undividable by 3**} & \multicolumn{4}{c}{**Dividable by 3**} \\ \hline
**Order** & **Amplitude** & **Order** & **Amplitude** & **Order** & **Amplitude** \\ \hline
5 & 6.0\% & 3 & 5.0\% & 2 & 2.0\% \\
7 & 5.0\% & 9 & 1.5\% & 4 & 1.0\% \\
11 & 3.5\% & 15 & 0.5\% & 6... 24 & 0.5\% \\
13 & 3.0\% & 21 & 0.5\% & \textgreater{}24 & 0.5\% \\
17 & 2.0\% & \textgreater{}21 & 0.5\% & & \\
19 & 1.5\% & & & & \\
23 & 1.5\% & & & & \\
25 & 1.5\% & & & & \\ \textgreater{}25 & 1\% & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The magnitude of particular harmonics of the supply voltage according to the permissible values of EN 50160:2015 [3]. Figure 9: Case 3: results of the analysis of PRIME PLC system operation with LED light sources at distorted supply voltage referring to permissible limits for public grid defined in EN 50160:2015 [3]; **(a)** supply voltage waveform; **(b)** time-frequency representation in the range 2-150 kHz using 100 ms window during the 20 s observation; **(c)** comparison of the spectrum of the corresponding PRIME PLC transmission (black) and the spectrum of the voltage in the connection point of the load (grey) with the relation to the normative curves (uL—line voltage in the point of the equipment connection, which is also the point of energy meter connection with PRIME PLC). the voltage spectrum of the non-intentional emission in the connection point of the load and energy meter resulting from the distorted voltage supply waveform is higher than in the case of operation under reference conditions (sinusoidal rated voltage). From the graph in Figure 9c, one can read the following signal parameters in the point of the 42-89 kHz transmission band are expressed by:  
* Local maximum of the non-intentional emission level (noise, background): \(N_{max}\) = 77.08 dB\(\mu\)V.
* The intentional transmission signal level related to \(N_{max}\): \(S(N_{max})\) = 93.55 dB\(\mu\)V.
* Local minimum signal-to-noise ratio: \(SNR_{local}\) = 16.47 dB. * Signal-to-noise ratio in the full transmission band: \(SNR_{band}\) = 23.57 dB. The SNR value in the PRIME PLC communication band proved to be sufficient for the transmission of signals in the majority of trials to be effective, as evidenced by the PLC system statistics. However, going into the details of the statistics it has to be emphasized that in order protect against the potential loss of the transmission the investigated PRIME PLC system increased the number of the connection two times in comparison to reference conditions.