I have an old electronic circuit kit that has plans to build your own radio station that casts an AM signal. I included some pictures of the finished circuit as well as the video of me trying to get it to cast a signal. I still haven't found the perfect distance the receiver (in this case my old Walkman chanelled through my computer speakers) needs to be from the transmitter and I'm still working out the frequencies needed, but you can see in the video that changing the tuning of the transmitter and moving the transmitter and receiver farther apart changes the signal received (and it sounds pretty sci-fi-awesome too). At some points, my "testing...testing" actually comes through to the receiver a little, too.