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Hi Rudi
The ZPlots has facilities as mentioned before to calculate Z0 as function of Frequency base on measurement of an open and shorted cable. Here is the result for the 33cm cable we are discussing. As you see there is interesting "bumps" along the frequency axe due to switching to harmonic modes for the NanoVNA
Kind regards
Kurt

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Fra: [email protected] <[email protected]> P? vegne af reuterr@...
Sendt: 7. december 2019 19:19
Til: [email protected]
Emne: Re: [nanovna-users] New version of NanoVNA-Saver: 0.2.1

On Sat, Dec 7, 2019 at 03:54 PM, Kurt Poulsen wrote:

Regarding the impedance issue i did look at the phase oscillation from
0.5 to 500MHz when I in the ZPLots has subtracted the length where the
Phase approaches a straight line with oscillations. Then I change the
ZO on either side off 50 ohm in steps of 0.1 ohm and for 51.4 ohm the
phase oscillation was minimized. The return loss oscillation is not
changed by changing the Z0 but rather due to port mismatch.

Hello Kurt,

Thank you very much for your quick answer.

I have 3 questions:
1. Where did you subtract the length (20 cm) ?

2. Did you mean that the S11 phase oscillation curve (about sinus) horizontal center line
should be minimised to a straight line and not be bowed?

3. Did you mean with the change of Z0 to connect a resistor of 50 Ohm
at the end of the 22 cm coax cable? And then vary this resistor in 0.1 Ohm steps
to minimise the amplitude of the phase oscillation amplitude?

I mean your file "NanoVNA supplied cable 50K to 500MHz.png" in post 7877 at 2019-12-05 20:10.

In this screen shot there are 2 diagrams with S11 Phase.
When I try to get a similar diagram with a 30 cm RG174 coax cable with open end I get see attached screen shot nanoVNA-saver_RG174-30cm-open-end.png

73, Rudi DL5FA