I've had a little Part 15 beacon in my campervan for a while now. It's running a few mW to an untuned 12 foot length of wire in the fiberglass muffin top of the van. I don't think it gets out very well when parked at home in the city. However, in open flat terrain, I can easily hear the ground wave over a mile away. Have not yet tested the limits of the groundwave.
Am currently traveling south on US395, from the Nevada state line, in the direction of Lone Pine, and maybe even further south than that. My beacon is on all the time 24/7, except for any times I am SWL'ing.
It sends the letters SPT at 6wpm on 13557.89 KHz ± 10 or 20Hz, depending on ambient temperature. SPT stands for Sprout, my little cat, who is traveling with me. I don't imagine anyone will hear SPT, but you never know........