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GIN&PEZ;

I have only advanced in my understanding to the extent that I have been able to confirm that the results of complex load measurements using the G-mini equations map virtually 1:1 to those obtained from and computed by the stand-alone NanoVNA. I have not looked at, nor have I attempted to identify and compare differences between the computational processes used to arrive at their respective results.

To obtain the confirmation, required that I perform a single calibration of my NanoVNA using my imperfect set of calibration standards, immediately followed by a single sweep of my DUT*. This exercise yielded a calibrated NanoVNA measurement of my DUT and the set of the 4 raw data files (S, O, L , and DUT) that the NanoVNA used to compute its results, plus the NanoVNA's internally computed results that resulted from those same raw data measurements. All of the above were exported into a spreadsheet where using the G-mini equations I computed a new set of results which I could then compare with those produced by the NanoVNA.

I have done a limited amount of "what-if" experiments to emulate a crude but viable simulated differential analysis, but only to the extent that I was able to confirm that such testing can be performed in a quantifiable manner.

For example; I made the observation that the load value is a single interpolated data point along a logarithmic line that extends from 0 to infinity, and concluded that the accuracy of all measurements made with respect to this single fixed data point are highly dependent on the accuracy of the data point itself. It also appeared obvious (perhaps only to me) that the severity of the inaccuracy in the placement of this single calibrated data point is most critical, and possibly only critical in the immediate vicinity of the data point itself; observing that the extrapolated influence of the absolute error in the load standard compresses in significance as distance from the center of the chart increases. It seems intuitive that the ability to resolve any load standard error contribution erodes rapidly with distance from Z0, and the contribution of other uncertainties (linearity, noise, resolution in the vicinity of the measurement, etc.) would rapidly dominate elsewhere.

I have however only confirmed that the measurements near the value of the load standard being used (Z0) are highly sensitive to differential values (alternative loads) in close proximity to Z0, and the errors do not appear to propagate sufficiently to degrade the DUT measurement results noticeably. More exhaustive testing is required to perform this test in a satisfactorily convincing manner to yield quantifiable results, but I am severely limited in my ability to do so with the instrumentation I have on hand. My hope is that those with capabilities such as near perfect standards, calibrated reference impedance standards, and/or a very well balanced HW bridge are eavesdropping and gaining in their own understanding of what you are doing; and that they will eventually become motivated to chime in and contribute to this exercise.

Whatever the outcome; my ability to contribute is going to be limited to reproducing results that become useful and meaningful FACUPOV. :-)




* The DUT used in my measurements is a 7 foot length of foam RG8X coaxial cable terminated in a 1/10 Watt 3.3 ohms metal film resistor, and yields an approximately 15:1 VSWR collapsing spiral vs. frequency.



--
73

Gary, N3GO

Probably should add Python to the mix as candidate for your own application development..

Matlab is gold standard for college academics but it is more targeted at nuts and bolts simulations. It is expensive and has significant learning curve.

Octave is a great open source Matlab look alike. Most Matlab programs can be run with Octave. Octave has extension libraries for signal processing similar to Matlab. With relatively minor syntax items, a Matlab programmer can ensure their program will run in Octave.

Python was originally used often for test systems, the same group using Labview. It is very well supported open source and is one of the fastest growing programming application. If you plan on playing with Raspberry Pie you will likely be using Python.

#82' : On The Two-Port Sine Qua Non Practical Application - Source and Load
-
REF : 11 December 2019 - /g/nanovna-users/message/8136

Hello,

Allow us, please, to announce that we just uploaded an updated version at:



with slight modifications and added * e x p l a n a t i o n s * on the text.

Sincerely,

gin&pez@arg

:82'

Which had portions derived from a Project STM32-SDR which was developed by
Charlee Hill W5BAA, John Fisher K5JHF, Milt Cram W8NUE and Dave Miller
VE7PKE/VE7HR. The software was released as open source.
The STM32/SDR project has morphed to the IQ32 which is still in production.
Charlie and Milt over the years have created some wonderful things.

Dave
VE7HR


On Wed, Dec 11, 2019 at 12:53 PM Joe St. Clair AF5MH <saintc@...>
wrote:

I think the Texas hams Larry is referring to are Milt Cram (W8NUE) and
Kees Talen (K5BCQ) who once offered the AQRP Vector Impedance Analyzer kit.
The last time I looked that kit was no longer available.

--
72 de Dave
VE7HR

I think the Texas hams Larry is referring to are Milt Cram (W8NUE) and Kees Talen (K5BCQ) who once offered the AQRP Vector Impedance Analyzer kit. The last time I looked that kit was no longer available.

Hello,

This email message is a notification to let you know that the following files have been updated in the Files area of the [email protected] group.

• /NanoVNA_Console_Commands_Dec 9-19.pdf

Uploaded By: Larry Rothman <nlroth@...>

Description:
This is the latest update of the Console Commands for the NanoVNA as of Dec 9th. It replaces the previous version. updated some command descriptions (per QRP's new v0.4.3 F/W) Please let me know of any errors or omissions.

Cheers,
The Groups.io Team

Hello,

This email message is a notification to let you know that the following files have been updated in the Files area of the [email protected] group.

• /NanoVNA-User-Guide-English-reformat-Dec 9-19.pdf

Uploaded By: Larry Rothman <nlroth@...>

Description:
This is a translated, reformatted and edited version of cho45's excellent NanoVNA User Guide. The document is 37 pages and is formatted for printing. Updated Dec 9-2019 - Added new section on Developer Extended Features, general updates.

Cheers,
The Groups.io Team

Gary,

Indeed, the model is precise, and its uncertainty is only based on uncertainty in the measurement of the 3 calibration standards and (this is not stated in their formula's but I assume the extent to which the standards are known . It is stated that G = -1,0,+1 but how about uncertainties in these? Not calibration set is perfect.)
This model allows the analysis of the impact of each uncertainty separate so you can compare calibration standard uncertainty with measurement uncertainty impact.
The derived equations are as far as I can see (but I am no expert) the same as what you get when you ask Maxima to solve the 3 calibration equations for G = -1,0,+1 . Or have they been able to get a additional level of complexity reduction?
Do you already understand to what extent the uncertainty boundary calculations are different from a differential analysis w.r.t o,s and l? Any higher order terms included?
Very interested to see the real test case data. With a very well balanced HW bridge a VNA will get almost perfect o,s and l data and that will imply the calibration uncertainties and measurement uncertainties both have a lineair impact going through a mobius transform.
--
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Erik, PD0EK

Hello again Erik;

I think you are close but not quite precise in your understanding. Or possibly I’m not yet precise in my own. :-)

All uncertainties are embedded in the model as they are uncertain entities that exist in any measurement. There is no attempt here to sort out the uncertainties, much less in any precise manner. The equations are only a compact (minimized) set required to compute the one and/or two port results while attempting to not degrade the integrity of the calculations resulting from mathematical manipulation.

Measurement accuracy is influenced by the known inaccuracies of the standards used, but not defined by them. The true accuracy in the measurement is bounded by the collective contributions of all uncertainties in the measurement, and not simply (and incorrectly) allocated the preciseness of the standards alone.

The uncertainties in the results achieved by the equations are acknowledged; but addressed as an independent and separate but parallel computational process. This is described in terms of a mechanical (graphical) construction of the bounded limits of regions and intervals surrounding each data point independently. The limits used in describing the uncertainty boundaries are user defined, easily or conveniently determined, and are as precise as the user determines to be justifiable. The construction process is illustrated in the animated videos posted in msg # 7235, and articulated in detail in the series of 5 white papers posted at the beginning of this thread. I have only skimmed over these to date, but I believe them to be complete as presented.

I believe the equations derived thus far in this thread are intended to stand on their own as maximally efficient algorithms for both one and two port S-parameter measurements.

The Uncertainty boundary calculations are a second proposed contribution that attempts to bound the region about each measured value to the most relevant and unavoidable real constraints that have the potential of modulating the measurements away from their true and precisely accurate values. These results would be the ones used to define design margins needed to specify limits of guaranteed performance.

My expectation is to discover that the use of expensive characterized standards versus a well designed and fabricated set of nominal standards contribute only minimally toward the achievement of maximally accurate VNA measurements. At the very least, I anticipate this learning exercise to provide clarity with respect to the sensitivity of uncertainties that can be defined and user constrained or controlled.

This has not been a fast paced learning process as much of the material is quite new to me, and I offer my description of this for your consideration in your own pursuit of understanding. On any aspect other than the derivation and verification of the G-min equation, I remain a student of this process.

--
73

Gary, N3GO

Greetings Thomas,
Your best solution for a low-cost scanner is the RTL-SDR dongle, and some scanning software.
The best one (currently) is the RTL-SDR.COM V3, ($23) which has a very good TCXO, software-switchable direct-sampling mode (for freq range DC- 25MHz), input protection (diodes), aluminum case, and SMA input. It will receive in bandwidths up to about 2.56MHz, and there is software that'll step it along, so you can cover a sweep from 25-1800MHz pretty fast.
The only down-side is that rtl-sdr dongles have no bandpass filtering and will show spurious signals, so you just need to keep its RF gain set low enough that they disappear. They are greatly improved with addition of notch filters for AM and FM broadcast bands (~$10-20 each).
For (free) software, SDR# ("SDR Sharp") is probably the most popular, with many plug-ins, including a full-featured scanner plug-in. There is also software that'll step it along and generate RF heat maps.
I'm not advertising for them, but I know what works... I use mine as a "poor man's" spectrum analyzer and freq counter, and after software calibration to a freq standard, it works quite well.
Don't get a cheap plastic DVR-B dongle; they have terrible oscillator that wanders around all over the place.
73, --kv5r

Fully agree
I'm have been supporting public domain SW for more than 15 years (and still am)
The step from having some SW that is usable versus SW that is robust for any usage is rather big and requires a lot of time.
Not sure I will want to do that for all SW's I make.
--
NanoVNA Wiki: /g/nanovna-users/wiki/home
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Erik, PD0EK

On Wed, Dec 11, 2019 at 03:52 AM, Dennis W1UE wrote:

I'm a newbie user- just received one last week. I've downloaded an instruction package on how to use the VNA. I've used a Mini VNA for several years, and have had problems because of its limited 50dB dynamic range.

What software works with the Nanovna? Are there pros or cons with the various packages? Or am I limited to only one? My primary use of the VNA
is to measure BPFs, HF Stubs, and HF antenna parameters.

=========================================================
Dennis,
I'm surprised for its cost that the MiniVNA has only a 50 dB dynamic range. I am assuming you are referring to S21 measurements.

The NanoVNA has nominal S21 dynamic range specifications of: 50k-300MHz better than 70dB; 300M-600MHz better than 50dB; and the 600M-900MHz better than 40dB. You gain about 20 dB more in the 50k-300MHz range but about the same elsewhere.

The "Software" section of this Wiki page, /g/nanovna-users/wiki/home , provides some of the different software applications available for the NanoVNA. As a new user you'll want to explore other offering on the same Wiki page.

Your experience using the MiniVNA should have you up and using the NanoVNA in no time.

- Herb

I agree with Joe's decision to not release his software to anyone. He has already made several great videos on the nanoVNA which I found useful. Some people feel "entitled" to his work and this was expressed in the eevblog thread on this topic. Unfortunately there are individuals who will criticize his code, demand support and claim credit for forked versions of his code. Who needs that kind of aggravation when you have lost interest in the project as he clearly stated?

I appreciate people like Rune who publish their code, offer support and updates because it takes a lot of work to do so. The community needs to respect this kind of work and not become demanding and discourage him.

#82 : On The Two-Port Sine Qua Non Practical Application - Source and Load
-
REF: #81" : update : on the physical expression of two-port s-parameters
10 December 2019 - /g/nanovna-users/message/8076

Hello,

Allow us, please, to announce that we just finished our work on this subject and
uploaded the updated results at the very same address:



Also allow us, please, to say that in our sow, the virtue of this formulation lies
on that : facupov, we are not able to see any simpler way to express it more
completely other than this one - well, at least currently.

Sincerely,

gin&pez@arg

:82#

Hi Dennis,
there's nothing immediately limiting you to using only once package. I can
only speak for NanoVNA-Saver, and it certainly uses industry standard
Touchstone files where possible, and it does not require using specific
firmware on your device - though in general, it works best and gives the
best results using new(ish) firmware.

I hope you enjoy using your NanoVNA, and I'll happily take any feedback you
might have on NanoVNA-Saver!
--
Rune / 5Q5R

I'm a newbie user- just received one last week. I've downloaded an
instruction package on how to use the VNA. I've used a Mini VNA for
several years, and have had problems because of its limited 50dB dynamic
range.

What software works with the Nanovna? Are there pros or cons with the
various packages? Or am I limited to only one? My primary use of the VNA
is to measure BPFs, HF Stubs, and HF antenna parameters.

Dennis W1UE

Thanks, this helps.

As I understand now: they determine the embedded port parameters by using the equivalent of a one-port calibration with 3 known terminations, then express the embedded port parameters in the response measured for these 3 terminations, thus allowing the identification of regions of uncertainties in these measurements so these can be translated into uncertainties of the embedded port parameters (the uncertainty derivations) and this gives the uncertainty of the measurements done with the one port VNA?


--
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Erik, PD0EK

In addition, ISTR that the Gnu Octave development team considers any lack of functionality as compared to MatLab to be a bug.

Sent from a small flat thingy

Eric;

It might be helpful to review msg #6670. GIN&PEZ presents the derivation of the G-mini equation which is the one-port measurement model, which they summarize in msg #6798.

That one port model, based on an embedded S parameter matrix consisting of an (s, o, l, and DUT) terminated LeastVNA (virtual) reflection port, was then rearranged, then presented, and subsequently revised (corrected) in msg #7272 as a derivation, of a two port indirect measurement model that relies only on the single one port set of reflection measurements... not the independent S11, S22, and thru measurements in common use today.

An important component of their work is that all uncertainties are included in the calculations, and the s, o, l standards used are all considered nominal values. Regions of uncertainty are derived from the results but are defined independently, as a graphical mapping surrounding each measurement based on easily defined real boundaries.

This is my understanding to this point subject to forthcoming corrections by GIN&PEZ.

I have not yet studied the uncertainty derivations in detail, but the concept appears to be sound. I have independently coded the G-mini equation, and have found it to be spot on in agreement with the corrected output results of 3 independent analyzers; the NanoVNA, an N2PK VNA, and an AQRP VIA of similar architecture to the NanoVNA.

I personally find it helpful to return to and review previous posts periodically as I begin to sense that I am gaining in my understanding. I find the communications becomes more clear and it often exposes important details I missed altogether. The process does take a lot of additional effort on my part, but I find it beneficial in areas that the language fails to translate precisely.

I hope you find at least some part of this to be helpful.

--
73

Gary, N3GO

Please have a look here:


Quote: "Hardware design material is disclosed to prevent bad quality clone. Please let me know if you would have your own unit."


--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK