Legal Part 15 FM coverage; a typical FM receiver can receive a signal down to 1.9 Microvolts using a 3 foot wire antenna.
A 1.9 microvolt signal is strong enough to cover a 100 acre 1000 home residential development.
Here is a project just under 30 acres; that can easily be covered
with a part 15 FM transmitter with a 3.8microvolt signal
Part 15 FM Coverage