Richard Fry wrote:
"Radiator efficiency for Class A stations (other than in Alaska) must be
such as to produce a groundwave of at least 352 mV/m at 1 km for 1kW of
antenna input power. A 90-degree omni radiator cannot do that."

Most such antennas have long been in place. Surely they are
grandfathered until the station is modified.

Best regards, Richard Harrison, KB5WZI