I am building different Un:Uns using different wiring schemes and caps. While testing a config, I noticed that my battery was down to one bar and I did not have the USB cable plugged in at the time. I was not keeping records at the time, just quick tests. So I did not have my nanovna H4 4.3 plugged in, not using Nanovna-App at the time. I just plugged it in and saw the plot change on the nano display. I went HMMMM. was i touching something? did I move something? No.
I started testing by unplugging the usb, and my original plot came back. Then I plugged it back in and back to same "changed" plot. Repeatable and always the same places the changed occurred.
Thought, maybe my cable is bad. Nope tried 3 different higher quality cables and exact same results. Did the same test on PC directly and not on the usb expansion bar (maybe it introduces the problem). Nope, same plot changes on pc directly to nanovna with all 3 cables. OK, maybe some ferrites will help. Put on 2 Fair-rite type 31 beads (purchased from Mouser, not amazon or ebay!), same changes.
ok remove pc from the equation... I tested on a laptop with battery only, no outside electricity. Desktop on laptop has no apps open (nanovna-app) or anything. Simply plugging in the usb cable changes the plot on the nanovna, not the same but very similar change to the pc plugged in change.
I also let the nanovna FULLY charge while turned off and then tested again. Simply plugging into an external power source via the usb is causing the issue.
Has anyone seen this before? Do you think that the battery charging circuit in the vna is causing the issue (before I examine this further)?
Some details about the nanovna. Nanovna H4. HW version 4.3_MS
It was purchased via Amazon from the AURSINC store, which was listed on the nanovna.com site as a authentic seller.
I have looked inside the unit and it is clean and well manufactured. Clean solder points and the unit arrived in the official box with all parts.
I believe this to be an authentic unit and not clone.
The errors are shown across the whole spectrum but are very low at low frequencies and grow exponentially higher with higher frequencies. I am doing a S21 logmag plot from 1MHz to 30MHz. There also seems to be large shift (jump down) around 15MHz.
Any thoughts would be welcomed.
Thanks in advance,
Mark
