Music and car advertising that was on a few very low powered AM transmitters quite a few years ago. Here in Houston it was heard along a busy freeway (I-45 North) from a transmitter and antenna mounted on a billboard operating on 1500 kHz. Can’t remember the exact timeframe. Signal could be faintly heard several miles away.I'm curious--What was the "Cadillac Radio" ad concept?
Similar effort some years after that with Honda plugging its SUVs from another billboard transmitter on 1660. Discussed on the Houston forum at the time IIRC, but doesn’t come up on a search. Signal could faintly be heard about a mile and a half away.