All nanoVNA use the internal SI5351 outside the formal supported spec. e.g. upto 300MHz in fundamental mode. Above 300MHz it switches to harmonics mode (till 900 MHz) and even further harmonics modes above 900MHz
Some do work till 300MHz in fundamental mode , others less good
The latest firmware has the "threshold" command to reduce the maximum frequency for fundamental mode.
Setting (as an example) this the threshold to 280MHz will have the nanoVNA switch to harmonics mode above 280MHz. You may not even notice this.
--
Erik, PD0EK
