## 3 Time-Frequency Characteristics of Video Signals  
The video signal generated by the graphic card is sent to the monitor in a serial manner. Correct mapping of the video signal into the image is ensured by information that determines the parameters of horizontal and vertical synchronizations (the length of the image line and the number of lines in the image). The historical background related to the principles of operation of cathode ray tubes means that even modern light-emitting diode (LED) monitors operate in accordance with the rules of image framing developed for Cathode-Ray Tube (CRT) monitors, which, in the transmitted video signal require appropriate gaps to be reserved, once necessary for proper positioning of the electron beam. This property can be helpful in determining rasterization parameters with unknown work parameters of the monitor (display), which is an element of electromagnetic eavesdropping. Examples of dependencies for the 640 \(\times\) 480/60 Hz mode are presented in Figure 1. In inactive state, both sync signals are high (logical \"1\"). The display of the line (row) begins with the appearance of the horizontal sync pulse about a duration 3.81 \(\upmu\)s (96 cycles of pixel clock). However, before the transmission of the video signals corresponding to individual pixels in the line begins, it is necessary to return the electron beam to the beginning of the line (48 + 16 clock cycles of the pixel = 1.91 \(\upmu\)s + 0.64 \(\upmu\)s). Each line is displayed in time 25.42 \(\upmu\)s (640 pixel clock cycles). The total time needed to display one line is 31.77 \(\upmu\)s (96 + 48 + 640 + 16 = 800 cycles of the pixel clock). The same applies to the vertical sync signals. The sync pulse itself lasts 63.6 \(\upmu\)s, and the total time needed to display the image once is 16,683 \(\upmu\)s, while the display of 480 image lines alone takes 15,253 \(\upmu\)s. The time to return to the beginning of the image is 1367 \(\upmu\)s. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Operating Mode** & **Pixel Frequency** & **Sampling Rate** & \
\begin{tabular}{c} **Vertical Synchronization** \\ **Frequency** \\ **[kHz]** \\ \end{tabular} &
\begin{tabular}{c} **Estimated Number of** \\ **Pixels on the Line** \\ \end{tabular} \\ \hline
640 \(\times\) 480/60 Hz & 25.175 & 31.25 & 31.500 & **992.0634921** \\ \hline
800 \(\times\) 600/60 Hz & 40.000 & 62.50 & 37.789 & **1653.920453** \\ \hline
1024 \(\times\) 768/60 Hz & 65.000 & 125.00 & 48.363 & **2584.620474** \\ \hline
1280 \(\times\) 1024/60 Hz & 108.000 & 125.00 & 63.981 & **1953.705006** \\ \hline
1366 \(\times\) 768/60 Hz & 85.500 & 125.00 & 47.712 & **2619.885983** \\ \hline
1440 \(\times\) 900/60 Hz & 106.500 & 125.00 & 55.935 & **2234.736748** \\ \hline
1600 \(\times\) 900/60 Hz & 108.000 & 125.00 & 60.000 & **2083.333333** \\ \hline
1600 \(\times\) 1200/60 Hz & 162.000 & 250.00 & 75.000 & **3333.333333** \\ \hline
1920 \(\times\) 1080/60 Hz & 148.500 & 250.00 & 67.500 & **3703.703704** \\ \hline
2048 \(\times\) 1152/60 Hz & 162.000 & 250.00 & 72.000 & **3472.22222** \\ \hline
4096 \(\times\) 2160/60 Hz & 556.744 & 1000.00 & 133.320 & **7500.750075** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Rasterization parameters in the case of signal recording by using an ADC card. Video signals processed in imaging devices using the raster technique are characterized by a characteristic order. Video data are sent from the source to the receiver at strictly defined time intervals and in strictly defined \"portions\". Horizontal and vertical sync data signals form characteristic frames, which are the result of multiplication of signals: sampled information, horizontal sync and vertical sync [2; 32; 33]. The spectrum of the product of the signals is equal to the convolution of the spectra of the component signals. Taking into account the above in the spectrum of the reveal signal coming from the video signal, spectral lines will appear corresponding to the frequencies of the sync signals.