Method in an electric net data transmission system for keeping the signal level constant in a coupling furnished with supply cable

Method in low voltage net data transmission system for keeping the signal level of transmission constant on the net voltage rail or for example in wall outlet or in other corresponding connecting point or in sphere of influence by data transmission furnished with a supply cable, in which method the coupling means for making said signal voltage constant comprise:—operating voltage source (Us) for the signal amplifier (10),—signal amplifier (20),—low pass or band pass filter (40), network connecting unit (50),—supply cable, length (LW),—series impedance (ZW)—measuring and handling unit (60) of the transmitted signals for the storage location determination,—electronic unit (70) including sample and holding circuit (S&H) and control circuits (CONTROL) to produce control signal (URC and/or ULC) by means of (ULC) memory map or by means of other type signals, characterized in that in the method the feedback signal(s) is taken wired or wirelessly from one or some locations or sphere of influence of the actual apparatus or supply cable (LW) to the measuring and handling unit (60) of transmitting signals and further to the process unit (70) of sample and holding circuit (S&H) or of corresponding means and control means (CONTROL), by which unit the control signal (URC) and/or ULC) is taken to steer the output signal or output voltage of blocks (10, 20, 40 and/or 50) in a depending way from load impedance (ZLOAD) and from the series impedance (ZW) of supply cable (LW) or possible from frequency, so that the amplitude (ULOAD) of transmission signal level (ULOAD) on voltage rail or some location of the supply cable or on wall outlet or on corresponding connecting point is constant or almost constant.