Recently here in the UK
Low power VHF FM Broadcast transmitters
became legal to own and operate.
Thou these devices are intended to provide a radio link between two in Car entertainment devices
( example. Boot mounted CD Changer and Head unit )
These devices operate in the FM VHF Broadcast Band ( 86 - 108 MHZ )
and do not require a licence.
And I have discovered,
that they work equaly well to provide a localised broadcast
if one is connected to your PC's Audio Card speaker socket.
listen to your broadcast in FM Stereo all around your property
with you portable Boom Box
PPS: and yes
connecting a booster ( BURNER )
or external Antenna
or even tamparing with the casing