Carlos
The nanoVNA has about 5 to 10 dB headroom in S21 in alle ranges. This is done by adjusting the gain off the amplifier before the adc to the frequency range
Biggest concern in overloading are the mixers when SI5351 outputpower is boosted in overtone mode. But this does not happen. A filter before the amp in the adc keeps near harmonics out.
So when measuring amplifiers you always should use an attenuator
The design of the nanoVNA is not bad.
