There are many FM radio transmitters available for use in cars, typically to allow you to use an ipod or similar device to transmit the sound to the car's radio. They have small antennas, and very low power output. But if you add a larger antenna, you can get a bit of range out of them. The problem is you might be violating FCC regulations if you do this. So we'll wait to hear from Alan and Al about what you should really do
As for being Hi-Fi....hmmm.....