VNA resolution

[Bulova]

Hello,
with the VNA program of Pavel I tested a coil on a ferrite rod. The wire is a RF strand with 50 windings. The impedance shows 200 ohms at 200 khz and about 500 ohms at 500 khz. But the realpart of Z (which should show the serial loss resistance) hangs at the value of 9,99 mohms. But in the narrow frequency of 220 khz it goes up to 277 mohms. But I doubt about this value too. In fact after calculations the DC value should go to about 100 mohms, and only with increased frequency it can increase too due to skin effect, maybe capacitve effects also could disturb these values.
I do know, that it can be a result of resolution limitations, because 100 mohms and 500 ohms is already about 12 bits apart.
In fact I wanted to determine quality (Q) of coils.

Thanks
Dieter

[pavel]

But in the narrow frequency of 220 khz it goes up to 277 mohms.

I am not sure that I understand exactly what this phrase means. However, I think that if you change the frequency range from wide to narrow and/or other sweep settings, then you will need to redo the calibration steps.

[Bulova]

Pavel,
no, my frequency range is always the same: from 10 khz to 1000 khz. What I was observing is how the values change, when I am shifting the cursor. I shifted from 200 khz to 220 khz, the measured table is already done. I could send the two screenshots of the VNA program with both cursor positions.

Maybe the method of measuring for this situation is not suitable. I am thinking about to repeat it by using a resonant circuit instead of the coil alone.

Regards
Dieter