Single wire dipole antennas, spot-tuned to the required operating frequency, are the most efficient antennas for use in HF base stations.
They are simple to install and have a relatively narrow bandwidth and require little maintenance.
When several frequencies are required at a base station, several dipoles can be stacked one above the other between two towers.
An antenna switch box BC91600 can be used to switch to the required dipole depending on the channel.