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I suggest you use the nanoVNA in stand-alone mode (without a PC) in order to test it out.
Do a calibration over a wide range like 50 kHz. to 900 MHz. and then check it using the cal loads and the Smith Chart.
Short should be a dot on far left of horizontal axis
50 ohm load should be a dot in center of Smith chart
Open should be a dot on far right of horizontal axis

Watch this video for the complete procedure.

Roger