Yes, he has some nice equipment but lives 250Km away.
I came across this VNA demo board on eBay. I has SMA screw connectors and demonstrates the proper response of various component s. A bit expensive but it gives me some ideas.
In the picture, it looks like SMBs. SMA would be much better for this.
2) The yellow line (CH0 LOGMAG reflected signal?) shows significant improvement with each successive build.
Using the commercial 6GHz as reference, it appears that the yellow line should be as low as possible across the frequency sweep.
Try leaving the CH0 cable open on one end, then try adding the 50 ohm terminator. Then try the short. You will find all of signal is reflected back with the short and open, giving a reading near 0. With the 50 ohm terminator, nothing will be returned and the reading will be -infinity. Well, obviously it's not a perfect world but you will get the point.
For the really low cost attenuators, they publish the SWR which is giving you some figure of merit for the match. I think the Nano can read that directly. For a perfect match (like the 50 ohm terminator) it will read 1.0. Try it with the open and short as well. The low cost attenuators were advertised with an SWR of 1.2. They don't show a different SWR for each attenuator.
I have been avoiding showing you the match (reflection) to avoid adding confusion. Up to 2GHz, I can provide some reasonable numbers but moving beyond that requires a higher grade cal kit than I currently have. Hopefully I will have that sorted out soon. When I made the video for the Nano, I measured some resistors to check the SWR. You will find that section here:
https://youtu.be/mKi6s3WvBAM?t=2167You can try these same experiments to help cement some of these concepts.
Too bad your friend is so far away. They could have been a very good resource.