Believe it or not, this VK5JST aerial analyzer kit is going to rickroll you. [Erich] wanted to see if he could use the device in a different way. His adventure led him to use it to feed different tones to an AM radio, producing the all too familiar [Rick Astley] offering.
There’s a fair bit of math that goes into getting the correct signals to generate a given pitch. But it basically boils down to patching into the hardware early in the RF generation. This way an audio signal can be rolled into the carrier frequency. Since this kit uses a PicAXE microcontroller with available source code it is rather easy to add audio input to tweak what the chip is putting out. But there is also some hardware tinkering to be done. Read more about that at the article linked above, and don’t forget to check out the bottom of that page to hear the final results.