There are many lpfm transmitters advertised on places like trade me with outputs of up to 15 and 20 watts. Unless the output strength is adjustable enabling you to reduce your output from the antenna to 1watt e.r.i.p. stay clear. The lpfm bands in NZ are guard bands that is why they are positioned at the bottom and top ends of the fm band. The top set of frequencies especially are a buffer between high power broadcasters and the aviation band.