CIL wrote:
"What do you call these chokes?"

Tower lighting chokes. Every a-c power wire on most AM broadcast towers
is fed through through a high-current r-f choke, beacon, side lights,
and neutral. It avoids shorting out the tower at its base for the r-f
signal.

Another device is used at some stations for the same purpose. It is
called an Austin transformer and consists linked loops to transfer a-c
power while providing little r-f coupling.

Tower lighting chokes must provide better performance for the price
because they seem more prevalent. Tower lighting chokes may all be
wraped around one form or on separate forms. They not only provide good
r-f isolation, but they provide almost complete lightning isolation.
They really keep lightning out of the a-c power circuits on the ground
when used with appropriate bypass capacitors and arresters.

Best regards, Richard Harrison, KB5WZI