## 4 Conclusions  
The paper presents a comparative analysis of analog (de)modulation systems employed in maritime communications for search-and-rescue operations. The noise stability of the following systems is investigated: DSB AM (A3X class), SSB AM (J3E class), FM (F1B class), and PM (G3E class). The analysis is carried out through analytical calculation of the improvement factor of the demodulator (IFD), and by implementing the modulator-demodulator systems in the Matlab-Simulink simulation environment. The research method employed in the two-phased analysis is scientifically accurate and thorough. For particular value ranges of the modulation parameters, the two phases of the analysis yield similar results. However, one drawback of the research method employed in the analysis is that it needs to be supplemented by experimental validation. Based on the results discussion in the previous section, several conclusions regarding the deployment of analog communication system in SAR operations communications can be formulated. For radio communications allocated to MF/HF and VHF maritime bands, systems using emission classes related to linear modulations (in amplitude) prove to be more resistant to disturbances than systems using emission classes related to phase and frequency modulations. This is true for all radio communications in environments affected by noise and in which we cannot provide a proper signal-to-noise ratio (over 10 dB). Keeping the J3E emission class for the maritime MF/HF range, both in ordinary communications and especially in distress communications, for the next at least 10 years is a perfectly justified thing due to:  
* The constructive simplicity of the radio stations that use it;
* Resistance to disturbances;
* Very small occupied bandwidth, (default and lower transmission power);
* Efficient use of the electromagnetic spectrum;
* Propagation of HF waves at very long distances and on multiple paths, which leads to the summation at the input terminals of the receiver of both the multiple signals from the transmitter being worked with and from other transmitters;
* The multitude of users of this range and the very high requirement of allocated frequencies/channels. The advantages listed above make the emission classes that use SSB modulation particularly attractive for terrestrial radiocommunications or fiber optic communications [25; 26; 27; 28; 29]. Taking into consideration that in ETSI EN 300 338-1 V1.4.2 (2017-11) standard it is provided that the integrated equipment used for communications in the MF/HF range must be able to operate and in J2B mode, it is very possible that in the future it will be introduced the obligation to transmit distress alerts via DSC in the MF/HF ranges in J2B mode. The use of phase modulation for distress communications is possible only in the VHF range where with the assurance of a higher bandwidth (16 kHz) better performance of this modulation can be obtained and with the imposition of restrictions/communication \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & & & **Stability to Disturbances** & \\ \cline{3-5}
**SNR** & **Emission Classes** & & & **Conclusions from the** \\
**Used in Distress** & **Communications** & **IFD Conclusions** & **Simulink Conclusions** & **Technical** \\  & & & & **Literature/References** \\ \hline  & A3X & Similar to case 3—10 dB. & Good & Unacceptable \\ \cline{2-5}
0–(\(-3\)) & F1B & Similar to case 3—10 dB. & Unacceptable & Unacceptable \\ \cline{2-5} dB & J3E & Similar to case 3—10 dB. & Good & Unacceptable \\ \cline{2-5}  & G3E & Similar to case 3—10 dB. & Unacceptable & Unacceptable \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._disciplines (during communications any other type of communication that may interfere with them is prohibited). Because the impact of the WRC extends over long periods of time, between 10 and 20 years after the conference, the emission classes analysed in this paper will certainly be used for distress maritime communications for at least the next 10 years [30].