1, the input of the device under test is not allowed by the DC potential. Otherwise, it will cause the frequency characteristic analyzer can't work normally.
2, the output impedance of the instrument must be matched with the input impedance on the North side. Otherwise it will cause reflection and inaccurate measurement.
3, RF cable should be as short as possible to avoid unnecessary loss.
4, the instrument output signal is too large, will make the saturation of the active device, measured the distortion of the graph.