Whether you're violating the FCC's rules depends on what you mean by
"terrible," and how "effective" you plan on making your transmitter. If
you've got a transmitter that is designed to work in a car, and you
want it to work at home, it's very likely that you can extend the
transmit range to cover the area of your house without breaking any
rules. If you are talking about setting up a little broadcast station
for your neighborhood, well, that's a different story.

I don't know if the FCC requires type acceptance (in other words,
prohibits you from tinkering with the transmitter by principle) for
these fm wireless gadgets. This is the case with FRS; in particular,
you're not allowed to crack open your radio and attach a quarter wave
vertical. You might want to check on that, too.

You can mire through all of the FCC's rules on their web site. But I
would still love to know if those fractal antennas work.