I believe the commercial AM radio band starts a 530 KHz. I was wondering what they use for an antenna.
What kind of loading coil do us use for a clear channel 50,000 watt signal?
they radiate from the tower. the whole tower is the antenna. towers are generally isolated on large insulators to the pad, and a lightning ring is mounted on one or more legs of the tower to ground. the lightning ring is two rings, one to the tower, the other at a 90 degree mounting inside and centered in the first goes to ground.
if there are directional requirements at night for the signal, there are additional similar towers and a phasing network located before the primary tower, with coils and capacitors to split the power and generate a directional signal. the details are worked out by consulting engineers generally based in the VA swamp.
AM transmitters do have internal matching networks of appropriate size so they can dial down the SWR to a match.
in olden days, when electrons were rationed, there were all sort and manner of dipoles and zepps used for transmitting on the common 200 meter frequency the Commerce Department had everybody share.