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From the beginning:

Many of the questions that appear in this forum regarding VNA operation suggest the fundamental premise of the VNA is either missing, misunderstood, assumed, or ignored. Questions elicit a barrage of responses; most of which are appropriately motivated, but not always helpful or instructive.

Often; original posters become silent while threads evolve and drone on until eventually terminating open ended; with final posts sometimes unrelated to the question originally asked. This is common on forums, but it is not efficient toward establishing a knowledge base.

The scope of questions as well as most answers to them overlook the obvious but simple detail that all VNA's only produce one output result per measurement. That result can be presented to a user in a plethora of data formats, with the most common format being a complex number pair referred to as a voltage reflection coefficient or simply reflection coefficient, and only one VNA port is utilized for the measurement. Measurements between ports are called transmission coefficients and are used for insertion loss (gain), delay, isolation, etc. measurements. Armed with the measured coefficient(s), the frequency at which the measurement was made, and an accurately affixed known reference called the characteristic impedance or Z0, all other data formats are derived through mathematical manipulation.

By the above; the entire essence of a VNA is to make one or more complex voltage (amplitude and phase) measurements. It is precisely analogous to an AC voltmeter. Other than the operational tasks of physically connecting to, calibrating, and performing the measurements; knowledge of how the hardware acquires and presents its results neither adds to nor detracts from the instruments capability, utility, and usefulness of the device to a user.

What now becomes glaringly obvious is that beyond the powerful measurement capability and utility of a VNA, modern instruments include an equally powerful embedded feature that performs involved complex mathematical computations in real time with the measurements being made. Analogous to a pre-programmed, fully automatic graphing calculator, the VNA produces a family of tabular and graphical displays of the most common RF parameters and formats of interests to engineers and technicians.

A key point here is that the measured results presented by the VNA are precisely identical, no matter the format in which they are presented. Unless it has been determined that a bug exists in the VNA software/firmware; users can take it on faith that the parameters are accurate as presented; assuming the instrument is being utilized as dictated by its design.

Inasmuch the various data formats are used, related, manipulated, interpreted, etc., operation of the VNA should be and remain transparent to discussions regarding data format relationships. Motivated users can (and should) pursue an understanding of the underlying mathematics of scattering parameters, complex numbers, and linear algebra to the extent required to meet their needs.

In most cases, users are interested in a particular measurement detail; e.g. impedance, VSWR, gain, etc., and alternative data formats have little if any relevance. In other cases they may find utility in the convenience of format conversion; e.g. inductance to reactance, phase to delay, etc.; all being computationally derived from identical measurement.data.

For users who are just becoming familiar with VNAs and their applications; an intuitive understanding and acceptance of the fundamental premise of VNA measurements as described here should sufficiently allow easy access to most of the utility that VNAs provide, and inspire the pursuit of deeper understanding of the relationship and derivation of all the parameters used to define RF networks.

--
73

Gary, N3GO

Andy,

Here is a link to an excellent paper by Olivier Pilloud HB9CEM which describes the relationship between the reflection coefficient Gamma (Γ). complex impedance (R+jX), Return Loss and VSWR. He also shows how the rectangular plot, polar plot and Smith chart are overlaid. He finishes up with an example and plots the results.



IHope it helps you - Roger

Wonderful! Thanks, Jean-Roger

I order here

Andy,

Below is a copy /paste of my answer to another old thread. It could be of interest for your question 3.

REAL and IMAG parameters are not the samething as RESISTANCE and REACTANCE parameters. REAL and IMAG apply to reflection coefficient Γ, in its complex form (a+j.b). That's why values are always in the [-1,1] interval, without any associated unit. When REAL=-1 and IMAG=0, it is the Short circuit situation. When REAL=1 and IMAG=0, it is the Open circuit situation. When REAL=0 and IMAG=0, it is the normal Loaded (50 ohms) situation.

LINEAR is the Γ modulus form of combined REAL and IMAG values, and finally POLAR is the geometric representation of REAL, IMAG and PHASE values. When POLAR is displayed by the NanoVNA, and even if data values are exactly displayed as for Smith Chart, results must not be read in the same way. Have a try by displaying two CH0 traces, POLAR and SMITH.

SWR and LOGMAG (Return Loss) are derivated from Γ modulus (LINEAR). For educational purposes I have created an ods file (see below), showing and calculating NanoVNA parameters. You can play with it by entering values in the blue fields, and also checking what are the arithmetic relations behind the different results. Here Group Delay is not relevant as calculations are done for a discrete (CW) frequency.

A last word about the use of REAL and IMAG parameters. The following case (see attachment) is an opened coaxial cable (length 2 meters), creating a quarter wave stub (at red marker). An opened coaxial cable remains a good use case for education and increase of knowledge. On the NanoVNAsaver snapshot we see clearly that displayed values between RESISTANCE/REACTANCE and REAL/IMAG do not allow an immediate comparison. For example at red marker, R+jX or Smith Chart highlight a value of 0+j0 ohms (short circuit situation), and checking this with REAL/IMAG chart you get -1 (REAL) and 0 (IMAG) which is the same thing. Be careful with REAL and IMAG curves which follow sinus and cosinus rules, it reflects simply a monotonous variation of PHASE.

REAL is also interesting if you want to measure a coaxial cable length, thanks to advanced TDR function.

73 from Jean-Roger / F6EGK

The group has a very well built wiki. Please read it there as well. If this seems like a lot at first reading because your problem is hard to put on any description, set it aside for a while, read it again, and understand what you need to do. It's not such a big deal, believe me.
You should not believe all the answers of your computer regarding the driver. Think and act. When I first installed the DefuSe Demo, I also installed the driver and later there was never an issue with the lack of a driver. Yes, in old age, the human brain has a hard time understanding what others are doing out of routine at a young age. Maybe that’s why they’re looking for template descriptions who run into errors. Each operating system uses a file manager. This file manager should be used to find the required drivers at the DefuSe Demo installation site. Not only does a “good priest learn to his death,” we also need to continually learn in an ever-changing world to understand and follow change.

Gyula HA3HZ
--
*** If you are not part of the solution, then you are the problem. ( ) ***

Thanks, Dave. Note that the images you sent did not come to me, only the place-holders (see below). Also, I may have been unclear. I totally understand that resistance and reactance are quite different, but I am wondering why the Real number on the polar chart is nowhere near the Resistance reported when R is output, and why the imaginary part of the polar chart (dropping off the j) is nowhere near the reactance reported when that is the output. In other words, isn’t the real part of the complex number equal to resistance and the imaginary part equal to reactance? But the nanoVNA gives VERY different values…

Andy

1. “Phase is the relative phase difference between source and received
signals.” What does this really mean? Is it current to voltage phase, or
change in that as influenced by the DUT, or simply phase change of voltage
alone, or…?

The phase represents the voltage/current offset produced by the DUT (Device
Under Test) as measured by the NANOVNA. Generally, voltage is 180-degrees
out of phase with current - high current ===> low voltage and low current
===> high voltage. So the two are 180-degrees, or π-radians, out of phase
with each other. The 180-degree phase difference between current and
voltage applies strictly to resistive loads with no reactance - the ± jX
term in the complete impedance expressioin: Z = R ± jX. Z = total
impdeance, R = resistive term, ± jX = reactive term. Introduction of a
complex portion of the impedance measurement skews the voltage/current
phase relationship to something other than the resistive 180-degree offset.

[image: image.png]

2. “Polar is same as Smith chart but with complex reactance rather than L
or C shown.” Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?

The following two charts from a course I once taught express the mapping
between ± jX and their equivalent lumped equiivalent form. As noted above
and below, they are both frequency dependent, can not dissipate power by
themselves (in the ideal model), and can be associated with external
fields. The resistance term of the impedance expression is frequency
independent, can and does dissipate power, and is not associated with
external fields. Yet another difference: 1) resistance can not modify or
change phase relationships between current and voltage, and 2) reactance
indeed can and does modify or change the phase relationships between
current and voltage.

[image: image.png]

[image: image.png]

3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn’t they be the same?

Absolutely not the same !!! Consider the above two charts. They should
make it clear why resistance and reactance are not the same. iI've also
pointed out the difference between resistance and reactance - the ± jX term
of the total impedance expression.

4. Everyone says that the VNA reports S11 and S21; I get that these are
reflection and transmission, but what are the units (or dimensions)? Is it
voltage, or power, or current…?

S-Parameters in their pure form are vector power measurements. There are a
number of ways they can be reported. For S11: 1) a simple numerical ratio
(in its simplest form) of input vs reflected powers, 2) that numerical
ratio expressed in dB, 3) numerical ratio of the reflection coefficient,
and 4) numerical ratio of the reflection coefficient expressen in dB. dB
is all base 10 as we are dealing with power. For S22: 1) a simple
numerical ratio of input power vs. transmitted power, 2) that numerical
ratio expressed in dB. Note that S22 as measured on the "output" side of
the DUT is the equivalent of S11 on the "input" side of the DUT, both with
the opposite port properly terminated. The transmission measurement for
impedance, S21, really has no meaning (no Smith Chart applicability). The
measurement for the output port of impedance is S22.

Dave - W?LEV

On Thu, Sep 9, 2021 at 3:11 PM Andrew Kurtz via groups.io <adkurtz=
[email protected]> wrote:

I have been through the Wiki and got some answers, but here are some
questions about the output options on the nanoVNA-H4:

1. “Phase is the relative phase difference between source and received
signals.” What does this really mean? Is it current to voltage phase, or
change in that as influenced by the DUT, or simply phase change of voltage
alone, or…?

2. “Polar is same as Smith chart but with complex reactance rather than L
or C shown.” Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?

3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn’t they be the same?

4. Everyone says that the VNA reports S11 and S21; I get that these are
reflection and transmission, but what are the units (or dimensions)? Is it
voltage, or power, or current…?

Thanks!

Andy

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

1. Voltage, Output vs Input
2. Takes more time than I have to explain.
3. Ditto.
4. S11 and S21 are ratios (dB actually, which is really just a ratio) of
voltages. S11 = 20*log(Vreflected/Vincident). S21 = 20*log(Voutput/Vinput)


On Thu, Sep 9, 2021 at 11:11 AM Andrew Kurtz via groups.io <adkurtz=
[email protected]> wrote:

I have been through the Wiki and got some answers, but here are some
questions about the output options on the nanoVNA-H4:

1. “Phase is the relative phase difference between source and received
signals.” What does this really mean? Is it current to voltage phase, or
change in that as influenced by the DUT, or simply phase change of voltage
alone, or…?

2. “Polar is same as Smith chart but with complex reactance rather than L
or C shown.” Yes, the trace is identical to Smith, but why are the real
and imaginary numbers reported nowheres near the R and X reported by
Resistance and Reactance outputs?

3. Likewise, Real and Imaginary have no similarity to Resistance and
Reactance; shouldn’t they be the same?

4. Everyone says that the VNA reports S11 and S21; I get that these are
reflection and transmission, but what are the units (or dimensions)? Is it
voltage, or power, or current…?

Thanks!

Andy

--
Carey Fisher
careyfisher@...

I have been through the Wiki and got some answers, but here are some questions about the output options on the nanoVNA-H4:

1. “Phase is the relative phase difference between source and received signals.” What does this really mean? Is it current to voltage phase, or change in that as influenced by the DUT, or simply phase change of voltage alone, or…?

2. “Polar is same as Smith chart but with complex reactance rather than L or C shown.” Yes, the trace is identical to Smith, but why are the real and imaginary numbers reported nowheres near the R and X reported by Resistance and Reactance outputs?

3. Likewise, Real and Imaginary have no similarity to Resistance and Reactance; shouldn’t they be the same?

4. Everyone says that the VNA reports S11 and S21; I get that these are reflection and transmission, but what are the units (or dimensions)? Is it voltage, or power, or current…?

Thanks!

Andy

I can't write or debug software for units I don't have I'm afraid (I don't have a V2plus4), it's like trying to find faults on a car you don't have or have never seen, you need the car there with you to run tests on.

Anyway, to be honest I've moved on now, am doing other things these days.

Thanks for all the thanks.

Hi,

A great effort, OneOfEleven !
Apologies in advance if this thread isn't the correct place for this question though.

I have a NanoVNA V2Plus4 (build 20101013, v1.2) and cannot successfully run other Apps on any of my laptops (Win-7 old machine & Win-10, new machine), both have Cypress drivers installed. So I was delighted when this version ran (v.1.1208), however ...

The pgm loads OK and most functions (span, number of points etc) can be changed. However the 'Continuous Scan' only runs a single scan. The Nana displays USB mode screen as expected. Selecting Cont Scan a second time causes the Nano to revert to it's normal VNA display and then selecting Cont Scan a third time, updated the v1.1.208 graphs. I can crash/freeze both the Nano and the s/ware v1.1.208 by selecting an invalid value (ie : Number of Points).

Is it finger-trouble or have I missed something obvious ? Appreciate your comments.

Thanks in advance,

Kitski

Very thanks OneOfEleven !!!

Enrique LU8EFF

I

Get Outlook for Android<>
________________________________
From: [email protected] <[email protected]> on behalf of Ray <boxman@...>
Sent: Tuesday, September 7, 2021 9:27:18 AM
To: [email protected] <[email protected]>
Subject: Re: [nanovna-users] nanoVNA developers

Oy. TNX.

From the home of
Prof. Emeritus Raymond (Reuven) Boxman
School of Electrical Engineering
Tel Aviv University
Cell: +972 544 634 217

CEO Clear Wave Ltd.
Scientific Writing Courses:


-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Mike C.
Sent: ??? ? 07 ?????? 2021 05:47
To: [email protected]
Subject: Re: [nanovna-users] nanoVNA developers

Just a heads-up Raymond. Your 2 websites:

CEO Clear Wave Ltd.
Scientific Writing Courses:

are "out to lunch", i.e. 'non-functional', just saying. I do like your "perspective", thanks for your input.
Mike C.
Sand-mountain, Trenton, GA, living on "the brow".




On 9/3/2021 4:57 AM, Ray wrote:

A little perspective:
I bought my nanoVNA V2, and also a spectrum analyzer, on Ali Express, well before I even knew about this user group. I came across it while looking for something else, and it immediately caught my attention. I had used a full feature VNA and spectrum analyzer once (costing about $100,000 and $30,000, respectively, or so I was told), and said to myself: hey, this looks neat and would come in handy for various projects I'm working on. I chose the model and the store on Ali based on getting something that would cover the 2.45 GHz ISM band, at a price less than $70 (to avoid paying customs), and generally at minimum price.

Unfortunately, the hardware arrived with almost 0 documentation. The only thing sent was a menu map, which was more or less useless. I was given a link to website, which had some minimal instructions which could not be carried out for calibrating. Corresponding with the vendor was completely unsatisfactory -- I am sure they have no idea what they are selling. For them if they sell a VNA, a pair of sneakers, or sex toys -- its exactly the same thing -- what is the profit margin. (The 35-4400 MHz Spectrum Analyzer came with even less documentation, and I have not yet managed to get it to work).

I had never heard of OwO, Hugens, or any of the dedicated people who developed firmware or software, or help other people on this group, until I came across this group searching for some kind of manual. All power to all of you! And many thanks!

But everyone should be aware that there is a commercial jungle out there. My suspicion is that many more people buy a nanoVNA because they saw a commercial advertisement, e.g. on Amazon or Ali, rather than from reading this group's discourse. Thus appeals in this group to respect the developers' wishes will probably have little effect. My advice to all developers, of whatever, is to first decide what your motivation is. If it is to profit from your work, which is perfectly legitimate, then you should take all of the legal precautions necessary, e.g. patent protection, secrecy, etc. This can be quite costly - probably a minimum of $10,000 for each country over the lifetime of the patent, if you know enough to file yourself (otherwise twice or thrice this figure). And if you need to defend a patent against infringement, the costs can easily get to the M$ range. Know that Murphy's law applies here - if something can be copied, and if it is worthwhile to copy, then it will be copied.

Or, a developer can decide that his or her motivation is not monetary, but rather helping mankind, helping the profession or the hobby, or even obtaining or strengthening one's reputation in the technical community. Then you might tell all and share all, and feel some satisfaction that others are benefitting from your efforts. In my opinion, any middle ground between these two approaches is apt to be frustrating.

With regards and gratitude,
Ray 4X1RB

From the home of
Prof. Emeritus Raymond (Reuven) Boxman School of Electrical
Engineering Tel Aviv University
Cell: +972 544 634 217

CEO Clear Wave Ltd. Scientific
Writing Courses:


-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of
OwO
Sent: ??? ? 02 ?????? 2021 16:20
To: [email protected]
Subject: Re: [nanovna-users] SAA-2N V2.2 DISPLAY ISSUES

I asked?, not forced, people to not help vendors that are selling copies of my design against my will.

How hard is it to simply STOP producing and selling copies of my design? My request is as simple as it gets. Is it that important to Hugen to make a profit off of my work and screw the original developers over while doing it?

Hi Albert!
Here are some pictures of my test jigs...
Karl

Nano's have very narrow downconversion bandwidth so not too vunerable.

But, do you happen to have a UHF TV ch 33 transmitter nearby.

Works fine !! Thank you so much OneOffEleven.

Jos


Op 8-9-2021 om 18:03 schreef OneOfEleven:

--
Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware.

Thank You OneOfEleven...

Great respect.. Top !!!

JP

v1.1.208 works great ! I love it - it?s the best - thank you OneOfEleven

The wiki page Home has been updated by Larry Rothman <nlroth@...>.

Reason: updated nanovna-app info for release 1.1.208

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