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Yes. If we are trying to measure the so called TRUE INSERTION loss... |S21|. And the vna has a reasonable dynamic range, then we could build an appropriate MINIMUM LOSS PAD. It would provide a match between 50 ohms and the UNUN transform ratio. Example, say it was a 9:1. Then I would need a 450 ohm to 50 ohm minimum loss pad. That pad has a minimum loss of ~ 16 dB. Higher loss will result in "nicer R values"... So now measure the pad, then measure the pad + UNUN and find the delta. Yes, something so simple has the devil in the details. And it can be more difficult than first realized!

Alan

Hello again Alan,

Thanks for the detailed answer.

I had to google for the design, I have found this website:

I have made a small screen shot of the T design. If one terminates this circuit with a 50 ohms resistor it will work, correct? Assuming the R T values will convert the input impedance to 50 ohms...

The loss relationship should be written as 1/(1-|s11|^2)...

Need to check, is this a valid form for a passive transformer network?

Here is some info on the MFJ cal loads suggested by W7ZQ. Says rated to 1 GHz. - really?

Roger

Check the calibration load of 50 ohms.

Seems like I got errors very much like that when I installed on Mint 19.3 Cinnamon. However, I am still able to start and run it by navigating in terminal to the nanovna-saver folder and entering "python3.7 nanovna-saver.py". I think with earlier versions I had to use "python3.7 ./nanovna-saver.py" but I could be remembering wrong. I am using nanovna-saver 0.2.2.

Hi Luis. Your query stated BALUN. However, if an UNUN, then a simple R pad, either PI or T with a Z value that matches the UNUN transform ratio is required.

The method in either case requires a measure of only s11 or the return as this is directly tagged back to the insertion loss as loss= 1/(1-s11).

If it is a large transformer ratio, the prior post of measurement of short and open s11 is a method to try.

My VNA doesn't seem to be working but occasionally, I can get a reading on it. Thinking that it might be me, is there a way to reset the nanoVNA back to it's delivered format, in case I have done something that is causing the problem or is there a test that I can do to prove to myself, that the device is actually working?
Any suggestions or help would be appreciated. I have calibrated it a number of times but that didn't seem to make much difference. I have connected to nanoVNA-Saver and can set frequencies etc but still don't get any results if I connect it to an antenna for 2m and set the device to scan from 140mhz to 150mhz. I would have thought that I should see something.
Bill

Very nice. The stylus holder is a great idea. Thanks for sharing.
---?
Ciao baby, catch you on the flip side??
73 de W3AB/GEO ???



You can say "over", you can say "out", you just can't say "over and out".

I have a nanoVNA model H, and I've been several designs that were quite clever. I am looking for an enclosure that would fit the nanoVNA model H with the addition of chassis mount PL-239's to SMA's in a longer case to protect the SMA connectors and to mount the chassis mount PL-239 to the end, thus only exposing the PL-239 connectors. Does anyone have a design for the H model that would provide safety to the SMA's and also mount the PL-239 connectors? If anyone has such a design or one that they have made, I sure would appreciate some pictures and any STL files that I could have the enclosure made locally. Thanks! K5MFP

Luis,

One method: Measure the return loss of the balun with the balun shorted. The return loss should be about twice the balun loss. This is similar to measuring the loss of a shorted or open piece of cable.

--John Gord

On Wed, 20 May 2020 at 02:58, aparent1/kb1gmx <kb1gmx@...> wrote:

Calibrating to the end of a cable was SOP in the lab I ran and every
time some one would tell me it introduces error I'd give them what ever
time they needed to prove it. They all failed in their assertions
as did I when I had that assumption in my head many years before.

Your data is as good as the cal to the plane of the cal. Even with
45ft of RG400 at 400mhz it worked.

The only yabut of it is if the losses are so great and the cable
long enough it will eventually self terminate. At that point its
not useful to do a SOL cal at the far end as the reflections are
absorbed before they reach the instrument.

Allison

There is another thing to be careful of, if using some of the older
professional VNAs, like the 8753. The VNA transmits a signal continuously
during the sweep, changing the frequency during the sweep. If the cables
are long, the transit time can be such that the received signal will be on
a significantly different frequency to that transmitted. It can then fall
outside the passband of the filter. This is well documented in application
notes from HP/Agilent/Keysight, and in the manuals for the VNAs. One just
increases the sweep time.

One thing to be aware of is the phase stability of the cables. Good quality
VNA test port cables are expensive - over $5000 for my VNA.

G8WRB.

Get two of them back to back but at those impedance transformation
ratios you are looking at
~20dB of attenuation per pad so that could be a problem.

Hi Larry

I recommend the BNC 4 part kit from SDR Kits which covers both a male and female calibration kit. The 3 part is male only. You can only find the 4 part kit in the Web shop section. (I have told Jan at SDR Kits that the 4 part is not shown on the sdr kits homepage as such but he has forgotten to change that ? )

<> &path=66_68_90&product_id=181
You will get full documentation for the delays for short and open and for the load both resistance/inductance/and delay. The delays for the thu adaptors are also documented so you can create a calibration kit file in NanoVNA saver. Using the kit on the stand alone NanoVNA is not a good idea as nanoVNA assumes an ideal calibration kit with no delays and a pure 50 ohm load.
I have previously published the calibration kit settings for thus kit, but I am not sure it is fully correct, so "one of these days" I will issue a new document on how to setup the NanoVNA Saver with this kit as each kit is individually measured and characterized by SDR kit and thus a detailed explanation needed.
You may "give me a push" if it takes too long be fore I get this new document done and released ?

Kind regards

Kurt





-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af k4mla via groups.io
Sendt: 20. maj 2020 05:00
Til: [email protected]
Emne: Re: [nanovna-users] Calibration standards - BNC



All,



I'd like an inexpensive calibration set (open, short, 50 ohm load) for BNC (M&F) Any one seen such??



Larry, K4MLA

On Tue, May 19, 2020 at 12:48 PM, <sj@...> wrote:

I would say NO.
Sorry to say, but have worked with VNA's for 30 years and as soon as you come
near 1/8 wavelength the measurement errors are taking over. ...
People believing they can calibrate out 20 meter of coax at any frequency,
does not have any idea what they are talking about.

If that were true, nobody would ever use a VNA above DC, or some frequency very close to it. Like others here, I also have taken measurements at the end of a long coax, with good results.

I've been able to install the NanoVNA-Saver on Ubuntu 20.04 using the attached helper document. I regret to say that I forgot where I found it ... memory loss is the first sign of senility!

The nice thing about this approach is that it can be set up with a script, saved as a desktop icon and run easily. One caveat is that your username must be part of the"dialout" group on your Linux system so that access to the usb port will be allowed to connect the NanoVNA to your computer. As always, your mileage may vary if running other versions of Ubuntu or other distros.

73 Bob KC2JAV

Hi Alan

Thanks for the reply.

You mean like a attenuator circuit made with resistors?

I am not sure if I understood.

If the unun ratio is 49:1 means that the R pad should receive on the input 2450R and the output would be 50R.

How can I measure the R pad loss to subtract it from the unun + R pad loss?

Cheers

Successful solutions should be found here in the forum: call the SEARCH button and then type nanovnasaver ubuntu or similar and there are several descriptions. There are several descriptions.

73, Gyula HA3HZ

--
*** nothing is permanent only change ( ) ***

Very nice....I think I'll follow your lead as the cleanest enclosure solution, Craig. I like the stylus attach too.

73 Kees K5BCQ

Dan,

I didn't get it running either so I am watching this thread. I think I got the nano-saver running in a virtual box under Ubuntu using the instructions for Linux Mint 64 bit which is found in the Wiki on this site under Software at 3.7.2. I just received my nanovna this week and am still in the learning curve also.

David Humphreys KB8LLL