dots and dashes; Morse code
Colloquial term for Morse code signals, especially the sound of dots (トン) and dashes (ツー).
radio telegraphy
Colloquial term for radio telegraphy as a communication method, often associated with amateur radio.
See also: 無線電信
I could hear Morse code coming from the radio.
Back in the day, I used to communicate with friends far away via radio telegraphy.
Onomatopoeic from the sounds of Morse code: トン (dot) and ツー (dash).