While conventional devices of high-frequency power plant telephony were practically uninstalled in the Czech Republic, and replaced by transmission technologies using combined ground cables with built-in optical cables, this change is still in progress especially in countries with vast energy grids, mainly for economic reasons. In these networks it is therefore expected to introduce several “temporary periods” to move to optical transmission systems. That is why in these countries (e.g. The Russian Federation, Ukraine, China, India, etc.), optimizing conventional high-frequency devices is current issue. The progress is towards digitizing the high-frequency transmission channels.