[G0HZU_JMR]

Thanks. The return loss and smith chart plots looking into that Minicircuits amp look to be very dodgy to me.

At 34:40 onwards the ripple in the return loss and the squiggles in the smith chart response look to be caused by a system calibration issue. The TSP presenter thinks this is to do with the way the amplifier is matched but I doubt it. The regular pattern suggests an incorrectly calibrated system at the end of a cable that might be 35cm long. There does appear to be a cable of that length in the video.

Either that or the Siglent VNA has really poor directivity after calibration. The datasheet suggests >40dB directivity so I'd expect to see much better results than what is shown in the video.

A general rule of thumb states that in order to get < +/-1dB uncertainty ripple in the return loss measurement the directivity of the VNA has to be >20dB greater than the return loss being measured.

So if the VNA works as per the datasheet (if calibrated correctly) then there should be less than +/- 1dB ripple on the return loss plots where the return loss is less than 20dB. But the plot shows up to +/- 2.5dB ripple in the circled region below where the RL is about 16dB. This suggests the effective directivity of the VNA is only about 26dB. I strongly suspect that the VNA hasn't been calibrated properly. The regular peaks and troughs do suggest there is a ~35cm long RF cable at the input and this is a strong clue that there is a significant problem with the setup.

There's no way the Minicircuits amplifier will have regular ripple in the return loss like that so either the VNA directivity is really poor or the operator doesn't know how to calibrate the VNA properly. I suspect there is a calibration issue. Maybe the calibration was carried out correctly but it isn't set to be active. Maybe the calibration is disabled in the menu system somewhere.