The other kind of low power broadcasting is called "carrier current" because this kind of broadcasting uses wires that are already present as an antenna. To learn more, check out "Carrier Current Broadcasting Theory" by LPB.
One of the requirements of this approach to broadcasting is just a bit more power, something that is almost impossible to do at 100mW on AM.
Happily, a very smart radio engineer created a solution - the AMA 5000 low power transmitter amplifier for 100mW transmitters in the AM band! Most useful for punching another .5 to 3 watts of power into your carrier current system.
Some say the safest approach is the Neutral Loading Option, so check it out. Here's a quick way to get the FCC to come to your house - connect this amplifier to an antenna (don't). With that in mind, take a look at:
AMA 5000 PA Construction plans, including parts layout and PCB foil pattern
And remember, if you can't be good, be careful...