## 4 Results of an Experimental Study with Power-Line Communication and Selected End-User Equipment  
In the conducted experiments, the waveform of supply voltage was shaped by the superposition of harmonics with set amplitudes. Using programmable power supplies and dedicated software, the supply voltage was shaped in three scenarios as follows:  
* Supply voltage scenario 1: pure sinusoidal voltage. * Supply voltage scenario 2: distorted voltage with harmonics according to permissible limits for public networks defined in EN 50160 [3]. * Supply voltage scenario 3: distorted voltage with harmonics used for immunity tests of load according to IEC 61000-4-13 [30]--equipment with the third class of immunity. Selected harmonics contributions represent margin waveform distortion. The total harmonic distortion index (THD) achieved as a sum of permissible harmonics levels defined in EN 50160 equals 11.62%; however, the normal operating condition of the public grid is usually 2-8%.The study aimed to assess the impact of supply voltage distortion on the operation of a commercial PRIME PLC system with the simultaneous presence of non-intentional emission generated by the loads. In point of the load contribution, several load conditions were considered:  
* Load condition 0: no load. * Load condition 1: LED light source. * Load condition 2: compact fluorescent lamp (CFL) light source. * Load condition 3: induction motor powered by a frequency converter. The PRIME PLC system is based on recommendation G.9904 [41,42]. The technology represents narrowband orthogonal frequency division multiplexing power line communication that uses 97 subcarriers, 96 of which are used for data transmission, where: first carrier frequency is 41.99 kHz (41,992.18750 Hz), last carrier frequency is 88.87 kHz (88,867.18750 Hz), the distance between carriers--0.488 kHz (488.28125 Hz). For each scenario of the supply waveform distortion and each group of loads, the investigation caseswere performed in order to express the variability of non-intentional emission affecting intentional emission of the PRIME PLC transmission system. First, characteristic spectra of the background signal and the transmission signal obtained among 20 s of the STFT observation were compared with the normative curves identified in Section 2.2 referring to standards [2; 3; 4; 5; 6]. Second, selected spectrum signal parameters were derived. Over the given frequency interval in the frequency range of the investigated PRIME PLC system, a single local maximum magnitude of a frequency component of the background signal was identified. It can be treated as a maximum noise contribution (\(N_{max}\)). Then, corresponding to the \(N_{max}\) a magnitude of the transmission signal (\(S(N_{max})\)) related to \(N_{max}\) was selected. The parameters are used to derive a local signal-to-noise ratio (\(SNR_{local}\)), which expresses the local minimum SNR in the transmission band due to reference to the maximum noise frequency component:  
\[ \begin{array}{ll}SNR_{local[dB]}=20&log\frac{S(N_{max})_{[V]}}{N_{max[V]}}=2 logS(N_{max})_{[V]}-20 logN_{\max[V]}=S(N_{max})_{[dB]}-N_{\max[dB]}\\ &=S(N_{max})_{[dB\
u]}-N_{\max[dB\
u]}\end{array}  \tag{1}\]  
Additionally, the classical signal-to-noise ratio in the full frequency range of the PRIME PLC band (\(SNR_{band}\)) was calculated using the power of the transmission signal (\(P_{singal}\)) and power of the background signal (\(P_{noise}\)) calculated based on \(M\) frequency components belonging to the transmission band:  
\[SNR_{band[dB]}=10 log\frac{P_{signal}}{P_{noise}}=10 log\frac{\frac{\frac{1}{M }}\sum_{m=1}^{M}s_{m[V]}^{2}}{\frac{1}{M}\sum_{m=1}^{M}N_{m[V]}^{2}}=P_{signal [dB]}-P_{noise[dB]} \tag{2}\]  
Proposed parametrization using the local and broadband SNR aims to represent the variability of transmission conditions in the transmission band. In order to extend the assessment of the communication conditions, the communication statistics were also analysed, considering the intensification of the connection attempts.