Why are digi signals rated to 30w on a 120w antenna

[JACE26]

On a SSB rated to TX at 120w, from an end feed antenna ?

[RobRich]

https://www.pa9x.com/pep-power-and-duty-cycle-in-amateur-radio :)

[Charlie_Dont_Surf]

https://www.pa9x.com/pep-power-and-duty-cycle-in-amateur-radio

While he's not wrong in his basic points, in fact the duty cycle is actually more complicated than his table implies since the duration of an FT8 transmission is always ~12.5 seconds of on time (and FT4 is always ~4.5 seconds) but an AM or FM transmission often is much longer. FM will be "constant envelope" (no amplitude variation), FT8/4 can be close to constant, but AM will necessarily not be constant envelope and power output at 100% modulation will be four times the carrier power, i.e., the power with no modulation.

The overall time scale matters to the heat build up in the PA, baluns, tuners, etc.