Local oscilator from a radio would make a nice transmitter back years ago, I could sometimes get them to go 150 meters, on a good day, making a 19khz generator getting the stereo sign to come on, spent hours trying to get stereo separation playing cds mix tapes, a neighbour would listen.
Can’t imagine anyone doing this now, people don’t have to bother, they could get an in car transmitter with a little aerial have the samething.