Hi @Guillaume -
To use a 500m tether, a more modern 2 wire “homeplug” module may be able to work. I linked this thread in my original response. Here is a link to a potential source for hardware that would work at this distance, but Blue Robotics has not tested this directly.
Note that these systems are not related to VDSL as far as I understand… they can actually interfere with each other it would seem!