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QEX #tutorials


Gary W9TD
 

Besides the Steber article on the nanoVNA, there is an article on a "Simple Inexpensive Accurate Vector Impedance Meter" by Koehler on page 23 that describes the design of an instrument nearly identical to the nanoVNA. Good information on the design considerations and how it works, Thirdly, there is a Technical Note on page 32 from Stensby describing a method to determine coax cable losses by making open and short-circuit measurements of reflection coefficients.


hwalker
 

On Sat, Jan 4, 2020 at 11:24 AM, gary wrote:

Besides the Steber article on the nanoVNA, there is an article on a "Simple Inexpensive Accurate Vector Impedance Meter" by Koehler on page 23 that describes the design of an instrument nearly identical to the nanoVNA. Good information on the design considerations and how it works, Thirdly, there is a Technical Note on page 32 from Stensby describing a method to determine coax cable losses by making open and short-circuit measurements of reflection coefficients.
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For those not aware, ARRL has made the associated files for the "Simple Inexpensive Accurate Vector Impedance Meter" article publicly available at, http://www.arrl.org/files/file/QEX%20Binaries/2020/QEXfiles-2001-Koehler-impedance.zip .

As gary noted, the design is built along the lines of the NanoVNA, however; it is a desktop box without a display. An DIY adapter for making coil and capacitor measurements, useable with the NanoVNA, is also included in the file archive.

- Herb


hwalker
 

I finally received my January/February issue of QEX magazine. Below is a synopsis of the 7 page NanoVNA article by Dr. George Steber.
=============================================================

Dr. Steber starts off by noting that an RF vector network analyzer is the instrument of choice for measuring the electrical parameters of antennas, components, filters and more. For most experimenters the prohibitive high cost of a full-featured analyzer has kept it out of their reach.

He states that in recent years several low cost vector network analyzer designs have appeared on the market with prices that are assessible to experimenters, more specifically the NanoVNA.

Dr. Steber explains how the NanoVNA differs from a typical low cost scalar network analyzer (i.e. NWT4000) by having the capability to measure both magnitude and phase. The unit under review appeared to be hugen's original NanoVNA with shielding and older 50k-900M firmware. It also appears that he only had access to the original NanoVNA-Sharp software application when he wrote the article.

He gives a brief historical overview of the NanoVNA from edy555's original kit to hugen's commercially released version. I'm not sure edy555 would agree with his statement that "after he sold all his kits, he lost interest and discontinued the project". Edy555 has continued to provide firmware and software support for the NanoVNA and has assisted hugen with hardware improvements to the NanoVNA-H.

Dr. Steber also briefly discusses the clones on the market and how to decide if a unit is suitable or not. He references the discussions on this forum by our members. Ultimately his advice was caveat emptor.

Like most of us, he was surprised at the open case design of the NanoVNA but noted that it didn't affect his measurements. He was happy with the calibration standards and cables included with his unit at no additional cost.

He compared the operation of the NanoVNA to the well known DG8SAQ design of T.C. Baier and also said it shares heritage with the EU1KY, antenna analyzer V3. A technical discussion follows about the resistive bridge (works well but limited range), SA612 mixer (Not the best choice but works for the NanoVNA, DG8SAQ and EU1KY), Si5351a generator (square wave output has high harmonic content) and STM32 processor.

The firmware section of the article glosses over the upgrade procedure. It basically just describes shorting the boot pads together. The units that I have purchased recently allow you to enter DFU mode from the menu without needing physical access the boot pins. The NanoVNA-H4 uses the multi-function switch to enter DFU mode.

The operation and uses section had the usual complaint about touchscreen operation using your finger. From experience most of us know that a stylus is the only way to go. The 101 point measurement limitation was the next topic. Again, most of us are already aware that if you have a large frequency span, i.e. 300 MHz, your frequency resolution will be every 2.97 MHz (300/101) and points in-between will be missed. Calibration of the unit and use with NanoVNA-Sharp are glossed over.

Practical measurement examples were presented that compared favorably with the HP8753 VNA within the dynamic range of the NanoVNA. S21 low pass filter, S21 bandpass filter, Measurement bandwidth of the NanoVNA (estimated @ 1 kHz by fft analysis), Testing crystals (101 point resolution dependency. Note: He didn't have access to NanoVNA-saver which over comes the 101 point limitation), Impedance measurement, and VSWR measurement.

Conclusions:
1. Works well.
2. Beware of bad clones.
3. Firmware upgrade procedure may be source of frustration for some.
4. Has limitations but great tool for software/hardware experimenters.
5. Does not come with user manual (note: more resources currently available on the web than at the time of the article).
6. Main limitations are 101 measurement point and 70 dB dynamic range.
7. The NanoVNA is more suitable for advanced radio amateurs who understand its strengths and limitations.



- Herb


Nels Nelsen
 

Thank you very much.
Your review of the
QEX review of the nanoVNA
Is very appreciated and very well written. Thanks for taking the time.
Nels


hwalker
 

On Mon, Jan 13, 2020 at 01:05 PM, Nels Nelsen wrote:

" … Your review of the QEX article on the nanoVNA is very appreciated .."
===========================================
Thanks Nels! I don't know what the lead time is for magazine articles, but the NanoVNA's software and firmware had already taken an incremental leap forward by the time the article was published. The newly released NanoVNA-H4 was just a thought exercise at the time.

One of our members told me there was nothing in the article our community didn't already know, but that the article did help to widen the circle of enthusiasts who are now aware of the NanoVNA.

This group continues to standout as the most referenced source for current information on the NanoVNA.

- Herb


Bob Albert
 

I am amazed at the lack of awareness in the general tech community of the nanoVNA.  I am also amazed at the apathy I sense when spreading the word to those who could greatly benefit from it.
A couple of friends have purchased them but mostly people seem content not to know about this.  It's been around for years and even I only first discovered it last year.
I have two of them and have some issues with spurious power loss but otherwise am very satisfied.  Still learning.

On Monday, January 13, 2020, 02:12:37 PM PST, hwalker <herbwalker2476@...> wrote:

On Mon, Jan 13, 2020 at 01:05 PM, Nels Nelsen wrote:

" … Your review of the QEX article on the nanoVNA  is very appreciated .."
===========================================
    Thanks Nels!  I don't know what the lead time is for magazine articles, but the NanoVNA's software and firmware had already taken an incremental leap forward by the time the article was published.  The newly released NanoVNA-H4 was just a thought exercise at  the time.

    One of our members told me there was nothing in the article our community didn't already know, but that the article did help to widen the circle of enthusiasts who are now aware of the NanoVNA.

    This group continues to standout as the most referenced source for current information on the NanoVNA.

- Herb


Dave smith
 

On Mon, 13 Jan 2020 at 22:12, hwalker <herbwalker2476@...> wrote:

On Mon, Jan 13, 2020 at 01:05 PM, Nels Nelsen wrote:

" … Your review of the QEX article on the nanoVNA is very appreciated .."
===========================================
Thanks Nels! I don't know what the lead time is for magazine
articles, but the NanoVNA's software and firmware had already taken an
incremental leap forward by the time the article was published. The newly
released NanoVNA-H4 was just a thought exercise at the time.

One of our members told me there was nothing in the article our
community didn't already know, but that the article did help to widen the
circle of enthusiasts who are now aware of the NanoVNA.

This group continues to standout as the most referenced source for
current information on the NanoVNA.

- Herb