fill-in transmitter

In DC networks, reception of the transmit signals may be restricted by the topology of the terrain, in tunnels or buildings. In these areas, filling transmitters can ensure perfect reception.

In principle, fill-in transmitters are radio repeaters, i.e. transmitters that transmit on the same frequency of the DC network, but only overcast a dedicated transmission range. The fill transmitters receive the DC signal, amplify it and radiate it into the reception-critical areas. Thus, a filler transmitter in front of a tunnel could receive the signals and radiate them into the tunnel at the same frequency.