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Hi qrp.ddc
The way you wrote "by connecting Ch0 with Ch1" it was obvious the you missed the end of cable calibration ?
Always remember a test cable is part of the instrument as you are forced to calibrate at the end of the cable. Doing thu calibration with two test cable the phase for S11 and S21 are in sync at the S11 calibration plane (at the end of the thru adaptor) and if you then measure a DUT with male SMA on input and female SMA on output the you measure accurate and phase sync (0 degree) is maintained but if removing the female female adaptor for measuring a DUT then phase relation ship between S11 and S21 is lost and you measure inside the DUT by the distance/delay of the thru adaptor. The NanoVNA or any of the PC application cannot offset the delay of the thru adaptor during calibration.
Kind regard
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af qrp.ddc@...
Sendt: 23. september 2019 02:25
Til: [email protected]
Emne: Re: [nanovna-users] RX-Port Input Impedance

[Edited Message Follows]

On Sun, Sep 22, 2019 at 11:57 PM, Kurt Poulsen wrote:

Incorrect, that is not a measurement of the CH1 input impedance. The
cable between Ch0 and Ch1 create impedance transformation.

Actually, you're right my previous screenshot was taken with no calibration for cable end plane. :) Previously I already performed this measurement with calibration for cable end and without and didn't found significant difference for VSWR measurement. So I simply repeated measurement with no full calibration for my previous screenshot.

But how did you found that this is not cable end calibration? :)

Here is measurement with full calibration at the end of cable, you can check it on TDR screenshot. As you can see VSWR is almost the same. I'm using good quality 10 cm RG405 cable, so it doesn't affect VSWR measurement much even with no calibration on cable end.

I also tested CH1 with another type VNA and it shows the same result.