[RTTY] 45.45-baud ASCII, 1000-Hz shift.

[Kok Chen]

The part I couldn't figure out is why the 1 kHz tone is pretty clean, harmonics wise, while the 3 kHz tone has a strong 6 kHz component.

In any case, the tones are not square waves.  

Without phase information, it is not possible to know the 3 kHz waveform.  Perhaps recording the audio and playing back the sacalr waveform will show more.

Very curious why they chose 45.45 baud, other than the fact that there are an integral number of cycles per symbol, both for the 1 kHz tone and for the 3 kHz tone.  Less keyclicks that way.

73
Chen, W7AY