By successive approximation, I found that a for loop that only toggles a port pin can do 1,552,450 square waves per second, which is 3.1236 (hmm, similar to pi) times 497 KHz, the radio frequency CosineKitty picked up this signal on. I tuned in 1550 on the dial of an AM radio and held it nearby but got nothing that changed when I reset the Atmega.