https://en.wikipedia.org/wiki/American_Morse_code says that 'o' was encoded as 'dit <space> dit', whereas 'i' was encoded as 'dit dit'. International Morse Code changes 'o' to be 'dah dah dah'. I cannot see any evidence American Morse was used for radio, though it may have been.
In American Morse, "O" was two dits separated by a space. Intracharacter spaces were eliminated in International Morse Code. "O" became three dahs. "I" is two dits with no space.