Pump Up the Volume (1990) on Netflix

Mark is an intelligent but shy teenager who has just moved to Arizona from the East Coast. His parents give him a short-wave radio so he can talk to his pals, but instead he sets up shop as pirate deejay Hard Harry, who becomes a hero to his peers while inspiring the wrath of the local high school principal. When one of Harry's listeners commits suicide and Harry- inspired chaos breaks out at the school, the authorities are called in to put a stop to Harry's broadcasts.