You're trying to learn an aural language, not a written one, for aviation use. It's the rythm & intonation of the sound that needs to be learnt since that's what you'll hear eg d'dah .......... dah'd'd'dit .......... dah'd'dah'dit NOT dot dash .......... dash dot dot dot ........ dash dot dash dot.
I used an audio cassette while driving to & from work. It started with the teacher's voice pronouncing the letters with the rythm then lated used tones.