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There is some debate on how the measured S21 common mode choke impedance actually effects the performance of an antenna system.

Here is one viewpoint by Owen Duffy as food for thought.....

Why? The goal of the measurement described is to evaluate the impedance
(L) presented by the CM choke when installed in the feedline. Presuming
#14 or #12 wire is used, the DC (not the same as measured at frequency)
really washes out as its insignificant to the purpose of the choke.

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

Hi, Gyula,

Thanks a lot for very interesting links indeed. I need a time to digest it.

However, just interesting, which readings shows a “big” VNAs in S21 if
short both ports with previously calibrated coax cable... It’s clear for
logarithmic format and phase but what is about other formats, resistance,
reactance, etc...

Igor

вс, 9 февр. 2020 г. в 12:07, Gyula Molnar <gyula.ha3hz@...>:

The permeability of most cores can vary (per spec!!) +/- 20%. This
variation, of course, reflects on the inductance of each winding.

Dave - W?LEV

--

*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*

Ok it looks like you have to press "RESET" before you can re-do the calibration?

I was afraid RESET would clear out all the saved calibrations

I think part of the problem is for some reason when I go into calibration, the "Load" item is highlighted still. Don't know why

On Sat, Feb 8, 2020 at 06:12 PM, K9LUC wrote:

The music makes the videos almost unbearable

There seems to be no narration. Can't you just mute the sound?

Gyula, yesterday all was well and I did some calibrations with my new set of cables, SOLT and FF & MM units to save connections. My results compared to pages 19,20,21 are so-so.
Today. no menu. I went back to read this chain again. I gave the cover two turns loose and all is well again. I will hope that this was my problem.

I do need to order a new "GOOD" unit as this one has no shielding and no battery. I was hoping that V2 would be delivering now.
John

Even when I try to do a new calibration using the included calibration kit (that came with the VNA) it still says "open" is 107ohms or such and doesn't go to infinity on the smith chart properly.

Seems like some sort of bug in the software?

When I start the nanovna with default 0 calibration, it works fine and "open" is all the way to infinity on the smith chart

I've been using the NanoVNA for a bit but I've found when calibrating, the "open" value isn't working reliably when using cables or when using extended adapters (like SMA extension for a male to male, for example)

So for example in a sweep from 6Mhz to 40Mhz I had an SMA to BNC adapter, and then an 8" BNC cable, and then alligator clips. It seemed to refuse to compensate "open", Eventually it took it and operated correctly, but I don't know what I did differently.

It exhibited the same issue now when I put on a SMA Female-Female adapter so I could hook up an SMA plug with 75 ohm resistors as a load to test it (I still calibrated with the default open/short/50ohm load that was included with the NanoVna) I just wanted to measure the 75ohm load SMA to see if it would show a pure 75ohm. But the "open" calibration would not operate correctly, when I removed any load, (and left only adapters on) it was hovering around the 105ohm range on the smith chart and not going all the way to infinity.


I run Calibration, then choose "Open", the short the output and choose "Close" and then "Load" I put a load on, if I take the load off, the "short" doesn't go all the way to the right on the smith chart.

I was running a pretty wide sweep like 10Khz to 8Mhz. The same problem happens when I did 6Mhz to 40Mhz.

For some reason, at least one time I did the calibration , it DID work properly and an open was correctly shown on the smith chart. But but it seems very unreliable.

I have an NanoVNA (bought from Amazon) NanoVNA-H , software build date Nov 25, 2019, version 0.4.0-3-ge04d3af...

Yes AL values of commercial toroids do vary quite a bit. I have found the need to add or subtract one or two turns to get the correct inductance values. Each mix is designed for a certain frequency range. The AL values given are usually for the centre of that range I think.

Wouldn't you want to know what the resistive component of S21 is?

Dale W4OP

On Sat, Feb 8, 2020 at 05:40 PM, Kevin B wrote:

I was going to switch them all to N connectors, on that note, is that still
what's recommended?

I was just looking into this the last few days to create a range of equipment I have SOL set and pleasantly see this message thread in my email.

From my understanding, for above UHF work, the symmetrical layout of the resistors for the 50 ohm load is far more critical, i.e. using four instead of one or two. Thinking I'll use the more critical design using SMD's that I measure to match resistance (and will be neat to see how perform on the LCR-T4 also) the best since seems like best practice for RF design in the microwave range.

I ordered another SMA to SO239 adapter as well as five SO239 panel mounts yesterday. I was thinking I had enough PL259 connectors to make 4 (S, O, L (50 & 75ohm))... though that's one of the reasons I came out to get online just now... I only have two.

I was almost going to order a Type N set (4 each male & female), though am thinking I don't need yet and am not sure I'll even require a 75ohm load set.

These two links, along with IMSAI Guy and Joe Smith related youtube videos helped re-enforce the design considerations:



James

Hi,

I do CMC-measurments by simply connecting the coax outer braid to the center of CH0 and CH1 and then trace 1 on LOGMAG and Channel 1 THROGH, see attached pictures. In my case the CMC is with ferrite mix 31 and intended to be used on HF. So frequency range is 2 MHz to 30 MHz.
73/Torbjorn

Clip leads rock — for audio. Larry's advice is excellent.

Bear W5VZB

In the files area, you will find the Console Commands document where the clearconfig command is explained.

In the WIKI area, you will find references to all the firmware developers.
Please refer to this post as well..
/g/nanovna-users/message/9821

Kevin,

Take a look at the photo’s at

Robert PA7RG

Hello Larry,
Firstly I do thank you very much for taking the trouble to reply.
The answer to your first question is that I find nothing in the files area that is later than the versions that I have tried to use. (Except a version for 75 ohm operation that don't need.)
The second answer is that in my user guide (19/11/19) I see no reference to Clear config, and (as yet) I have not found it in the files area either. So no, I have not been using that command. But I have just downloaded a load of stuff to read, so I might find it in there somewhere.
I can go on using the limited version if I must, because I do have an AIM 4170 for anything below 180MHz, and two PHSNAs (one with the sweep mods) which tend to get put on first because they are so easy to use. So I only switch the NanoVNA on for higher frequency use. (So you didn't need to know that, but you might have found it interesting. If it bored you then I apologise.)

I will come back if I find sucess, in case it helps anyone else.

Thanks again Larry. I do appreciate it.

Tony...

Hi Igor,

I can help with the search by typing the key words "common mode choke impedance" or shorter will result in more results in the Search window.
In the -F group, I see no such match.
Great learning opportunities here: and here:

73, Gyula HA3HZ

Hi,

Does anybody use this device to measure common mode choke impedance?

G3TXQ for instance suggested using |S21| and phase angle to recalculate X
and R of the DUT in the spreadsheet.

NANO VNA-F however has a bunch of formats for S21, including Resistance,
reactance, smith chart, etc. So it seems we can get both X and R directly
in traces without any external calculations

However, for instance, resistance and reactance readings of S21 are very
big. For instance, Port A and Port B shortened by kit's cable shows about
1.2 M of resistance and -500K of reactance at 7.2M frequency (CW). Both
values are not stable and actually are infinities...

While phase value looks OK (-0.15°) and complex representation is OK as
well (1-j0).

Probably I miss some basics in understanding of S21....

Would you please (1) suggest the best way of getting common mode choke’s
impedance with the device and (2) explain the S21 readings in different
formats...