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Hi Roger
Using the S21 methods requires that both the source (CH0) and load (CH1) impedance are pure 50 ohm, so you get also errors this way. Have you tried to read the Rp instead of Rs in NanoVNA-saver. That makes a big difference to the R values as it is often forgotten the standard impedance displayed are R+jX and then the R value is frequency dependent due to the X value present. Often the use of port extension can cure the problem if the DUT is mounted to an adaptor introducing a shunt C.
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af Roger Need via Groups.Io
Sendt: 15. marts 2020 00:59
Til: [email protected]
Emne: Re: [nanovna-users] Checking 1:49 UnUn with nanovna #applications

On Sat, Mar 14, 2020 at 04:36 PM, WB2UAQ wrote:

I also measured the feed point impedance of a 67 ft wire at 7 MHz using the
Nanovna and found it to be 3600 to 3900 ohms shunted by about 8 pF. This Z
is about 1250-j1820...way out of the range of the Nanovna (S11)

Yes the S11 bridge method starts to get quite inaccurate after the impedance gets higher than a few hundred ohms. Fortunately the NanoVNA can do S21 measurements and we can determine complex impedance at several thousand ohms using the "Series Method" shown below. The equations are not that complicated and I was hoping Rune could add them to NanoVNA Saver. Presently I do them in a spreadsheet after an import of a S21 Touchstone file.

Roger