It will transmit as far as the first transformer on the supply system and anybody on the same phase as you will receive the signal.
Some theory:- The transformer output will be 440 volt three phase and neutral and phase to neutral is 240 volt.
If your electrical installation is old then you will possibly have a coloured disc pinned to the board near the incoming supply telling you which phase you are on.
Thus you are warned never take an extention lead, plugged into your supply, next door, because they may be on a different phase, and if you get across both supplies you will be on 440 volts. Could spoil your day.
regards