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I would suggest one of the small transformers made by Mini-Circuits.
You can get both the unbalanced to balanced transformation and 50 Ohms to
XXX per your needs.
I have been using their 50-75 Ohm transformers for years to test video
products.
Kent

On Monday, August 28, 2023 at 02:01:45 PM CDT, Arun <
arunkumar1@...> wrote:

Has anyone used a NanoVNA to characterize a Twin wire twisted Balanced
line like say a CAN bus line or an ISO-SPI balanced 120 ohm line?
If so what interface hardware has been used or is recomended?

Already understood and thanks. Maybe a better question is: Is there a method to isolate the VNA from the PC when connected via the USB to kill (choke?) the effect. I am just experimenting and learning here, by no means am I a veteran on vna usage.

Thanks Dave.

Thanks to all for their help with this.

Greg, it is not a bad connector, I changed and tested all connection
points, cables, etc. with identical and test units in order to remove those
variables. I always recalibrate for each set of tests. I have removed all
outside interference possibilities that I can. I do not move anything
near the unit, dont touch anything and just take notes on readings. I
attached two pics. One with USB and one without, you can see the changes
clearly. The test rig is 2 identical built unun (haha, well as much as
possible) in a back to back configuration. The secondaries are connected
and the the ground legs are connected. The test is S21 thru displaying
Smith and logmag. I am able to wave hands over everything with no change,
only when I touch something with a fingertip do I see changes (of course).
But it is overall stable. When USB is connected it changes as indicated on
pics. It is not variable unless I change the usb source (laptop vs pc vs
charger etc). As you said, not a laboratory-grade instrument.
Understood. I have not tested anything other circuits yet, only my current
unun config since I noticed this, but I will shortly to see if it happens
during other test and scales. I just wanted to understand if anyone is
seeing this. Not concerned to much yet, but I usually do testing with the
PC apps when working on bench and worried that I may have gotten errors in
my old stuff worked on.

Francious, good to know. I may just be running a sensitive test and I am
hunting efficiency, so I am looking closely and these number changes and
they reflect a lot of change in overall result.

Donald, the test system hopping in could be quite possible. I am testing
the wire wrapped toroids with wires only into screw terminals to bnc and
nanovna.. I am sure the connections are all good and solid while not
optimum. I was testing many configs to search for best results in turns
and caps and toroid materials. Then I noticed the changes in traces and
stopped testing in search of the problem (error introductions). I just
want to make sure that this is small issue and not a power circuit problem
with my unit or a possible issue in the design of the power/charging system
introducing these errors. And how I can isolate my usb connection further.

thanks all!!

On Aug 28, 2023, at 13:01, alan victor <avictor73@...> wrote:

?Spoken for... gone... Thanks!

On Aug 27, 2023, at 21:56, Mark KQ4EKK <kq4ekk+groups@...> wrote:

?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