For a comparison of rectangular waveform on-times versus spectral
content, the following calculations were done on my WAVESPEC
program for a 0.50 to 0.25 times repetition period and with rise and
fall times equal to 0.02 times repetition period.

If the fundamental energy is the reference, then the harmonics
are down from that 0 db by the values shown:

/------------ width rel. to rep. period -==--------\
Harm 0.50 0.45 0.40 0.35 0.30 0.25
1 0 0 0 0 0 0
3 -6.4 -7.3 -8.4 -9.6 -11.1 -12.8
5 -28.0 -17.8 -15.1 -15.7 -20.3 *
7 -28.1 -20.1 -26.2 -27.7 -26.6 -29.1
9 -28.4 -24.6 -32.1 -44.2 -43.0 *
11 -28.7 -32.7 -42.2 -25.1 -35.8 -28.7
13 -29.1 * -29.1 * -29.1 *

* too far down to matter, not enough there

The above will hold true at any fundamental frequency provided the
rise and fall times are equal and each equal to 0.02 times the
repetition period. Those numbers will change given faster or slower
rise/fall times. All db calculated as 20 x Log (voltage). Width is
determined at the baseline, not the 50% amplitude point.

Len Anderson
retired (from regular hours) electronic engineer person