Years ago I was running an AM Broadcast station when a tanker truck explosion knocked out power to the 50 Kw station and several other large AM stations. I grabbed an old Johnson Ranger and modified it to transmit on the AM band. I got it powered up to about 1/2 a watt and used it to get the station back on the air. I used a bunch of 12 V car batteries in series to power the thing up.