We are all used to seeing mobile phone antennas around the countryside. This one is close to our local railway station. The antenna consists of several elements. The top sections are the antennas themselves, but underneath them are the RF Heads. These used to be placed at the bottom of the towers, but the coax feeder between them snd the antenna introduced signal loss. Nowadays greater reliability means they can be placed up the tower. They are much closer to the antenna so the coax is shorter and there is much less signal loss. They go wrong much less, so it is feasible to place them up the tower where maintenance is more difficult.