I’m working on an AM transmitter that modulates a digital 1MHz signal by turning it on and off. I need to drive a short (6″ to 9″) antenna with this and need to know how to optimize transmission. I’ve read about using antenna loading coils and found an online calculator that told me to put 10mH in series with a 9 inch antenna but when I do that I still hardly hear anything on the AM radio 5 feet away. Anyone have any ideas?