Base-fed masts, the most common type, must be insulated from the ground. At its base, the mast is usually mounted on a thick ceramic insulator, which has the compressive strength to support the tower's weight and the dielectric strength to withstand the high voltage applied by the transmitter. The RF power to drive the antenna is supplied by a matching network, usually housed in an antenna tuning hut next to the mast, and the cable supplying the current is simply bolted to the tower. The actual transmitter is usually located in a separate building, which supplies RF power to the antenna tuning hut via a transmission line.