Hi all!

I've encountered a calibration problem with my NanoVNA V2 Plus4. So far I've been using the calibration set that arrived with the NanoVNA. Checking a simple SMA wire gave a S11 parameter of -20dB around 1-3 GHz which is fairly high. I've checked the same SMA cable in a more professional keysight VNA and found that its S11 values are -35 to -40dB.
This -20dB issue is bothering me since the noise floor for the S11 parameter should be ~-40 to -50 dB. Also the S11 plot looks quite deterministic without any observed noise.

This leads me to believe this is a calibration issue. I've checked the calibration both through the NanoVNA software and my Matlab code, both giving identical results.

Am I missing something? Any help would be appriciated.

Thanks in advance!
Shlomi

Hi, the V2 is a T/R VNA, meaning port 2 can not transmit and so port 2 match error can not be calibrated out. With a cable you will measure the port 2 return loss, which will be around 16 to 20dB. To measure the cable's return loss we recommend terminating the cable with a good quality 50 ohm load. The 50 ohm load provided with the V2 Plus4 will give ~30dB return loss at these frequencies.
Thanks

Hi!

Thank you very much for the fast response.
I have checked your suggestion (cable + 50Ohm cap) and indeed the S11 parameter is less than -30dB.

I'm trying to understand what to expect for S21/S11 measurements on two-terminal transmission lines. If the port 2 match error is around -16 to -20 dB, does it mean that measuring S11 values below this error at a two-terminal measurement is impossible? What would be the best course of action if I want a decent measurement like that?

Best, and again thank you for your quick reply!

Hi, to improve the port matching of port 2, you can add a 6dB attenuator to port 2, which will improve the return loss by up to 12dB while only lowering dynamic range by 6dB.
Thanks

As was previously suggested by support, cable impedance can be measured as
a one-port measurement. Terminate the far end of the cable with a quality
50 Ohm load and read S11. You can also measure the cable loss by
terminating it in a good quality short. The loss will equal 1/2 the
magnitude of S11.

On Thu, Dec 28, 2023 at 11:01 AM nanov2support <edelswartz123@gmail.com>
wrote:

> Hi, to improve the port matching of port 2, you can add a 6dB attenuator
> to port 2, which will improve the return loss by up to 12dB while only
> lowering dynamic range by 6dB.
> Thanks
>
>
>