Total posts : 45366
As both of you and I have found, this can get pretty messy when trying to interpret and follow the part 15 rules.
Here’s my take on it.
The 200 foot limit is not writtten into law, it is a illustration cited in a public notice on the subject and states the range one can expect.
There are two governing parts of part 15. One is based on field strength alone. The second part can be used in lieu of the field strength limit.
This second part defines the antenna, ground, transmission line, and power input limits. You may operate under either of these rules, and are not required to operate under both, thus if you are compliant with antenna, power, etc., you do not need to observe the field strength limit.
It appears that through clever engineering of antennas some AM broadcasters have legally extended the range of their signals beyond what was apparently the original intent of the FCC rules.
I don’t know, but I suspect that they are producing field strengths beyond the limits, but they are legal if following the antenna, etc. limit rules.
I don’t have all the part15 numbers before me at present but you can pursue them by reading through the part15 rules which apply to operation in the AM broadcast band.
What do others think?
(BTW I am an also an amateur operator who got started when I was 14 with part 15 AM and still (46 years later) have fun with it.)