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S11 or S21 delay?

On S11 2x delay (to cable end and back)
On S21 1x delay (from one port to another(

I am having difficulty constructing a set of phase matched cables using my NanoVNA SAA-2N and the tutorial available at this link .

The cable I am using is Times Microwave LMR-400-LLPX with a nominal length of 20 feet. Manufacturer's specification for time delay is 1.34 nS/ft.

My cables need to be phase matched +/- 5 degrees at 1.1GHz.

The difficulty that I'm having is with the following results returned by the NanoVNA.
Cable 1 measured time delay = 54.35 nS
Cable 2 measured time delay = 52.93 nS
Surprisingly, both values are significantly greater than the calculated delay of 26.8 nS = 1.34 nS/ft x 20 ft
Furthermore, based on the formula in the tutorial, the phase shift appears to be 562 degrees

What am I doing wrong?

Might I suggest that we continue to meet via Zoom on Monday evenings at 7 pm (EST) to share what we know about the VNA?

I don’t see my talk as a “lecture” to record and watch. I’m not a VNA engineer.
But I can see why this technique (record and play back) might work for some who just can’t make the “live” session.


We have met three times now via Zoom and discussed these topics:
1) What is a VNA and in broad strokes how does it work?
I compared the VNA to a dolphin or a bat and SONAR - what do you learn from the reflected SOUND waves

2) Why is CALIBRATING the device over a frequency range important - and how do you do that?
The SAVER software makes this process easy - and I can save a file with thousands of data points.


We then talked about
Why an antenna has a resistance, a reactance, and an impedance?
What kinds of graphs can you plot to understand an antenna?
I did a live demo with my own 80m dipole in my yard.


3) Yesterday we talked about some of the VNA guts
Reflection Coefficient (rho) as a RATIO of reflected voltage to forward voltage and why 0<rho<1
RETURN LOSS - what is it, why is it measured in decibels, and why is it a positive value
SWR - how is this related to reflection coefficient and Return Loss

We ran out of time (8 pm EST) and stopped but there were some good questions and discussions.

Might I suggest we continue to meet via Zoom on Monday evenings at 7 pm EST.
I realize that makes it awful for other time zones distant from N.America

I hinted that I could use my own Nano VNA (model 4 H) to help me adjust my MANUAL antenna tuner for HF antennas.
I then showed how the various graphs (SWR, Return Loss) change as I mess with the capacitor/inductor setting in my “TUNER”.

So come join in on this discussion of Nano VNA next Monday evening.

De k3eui Barry
Philadelphia PA USA

Great, thanks. So you get the same results if the end is either open or shorted right? Reverse the cable and you can confirm where the break is.

With a dummy load the cable length should read very large with no kinks right?

How do I adapt this to other cables? Do I need a balun?

Hello Barry,

Some of us in the NanoVNA community actually live outside continental USA.
Not sure where your QTH is, but there is also a 5 hour time difference across the continental USA as well.

It would be great to have access to your obvious vast experience in RF topics, especially when it shows the application of the fabulous NanoVNA.

Would you reconsider recording? (Even delay access to encourage as much online participation as possible)

73...Bob VK2ZRE (Downunder in Australia)

On Mon, Nov 14, 2022 at 12:53 AM, tuckvk3cca wrote:

When you click on the TDR in Nanovsaver. The length of the cable is already
indicated, which I presume is the physical length once you specify the coax
type or VF. There are two plots on the graph, but what do they show?

One graph shows the Time Domain response of the cable attached to CH0 (port1). The other shows the approximate impedance magnitude |Z|. In the annotated Saver graph below I measured 3M of RG-316 connected to 1.8M of 75 ohm RG-6 with an adapter.

Roger

I have been asked many times if these Zoom sessions on Nano VNA were recorded.
NO. They were not recorded.

The reason is simple: I wanted these sessions to be discussions, not lectures.
Many folks will not ask or answer questions if the session is recorded (from my experience as a teacher/professor).


I will pause during the zoom session and ask folks to contribute (like a live class)
“What is reactance in an antenna?”
And then ask for contributions.
How do you measure reactance with a VNA from inside your shack (at the end of X feet of coaxial feed line)?

“Does SWR change along the feed line if the attenuation is very low?”
That one is interesting.
I suggest you read the Walt Maxwell books on SWR and feed lines from QST articles in the 1970’s.


Sometimes (actually often) an open ended question leads to a lively debate!


I have about 200 slides (PPT) that I made over the past three years covering all aspect of VNA and antennas and Smith charts.
I’d be happy to share those, as a PPT or as a PDF file.
The slides are just key points to get a discussion going.

Learning is an iterative process with a lot of mistakes along the way.

Come join in on the presentation/discussion,

de k3eui. Barry
Philly
Nov 14th

On Sun, Nov 13, 2022 at 10:57 AM, Barry K3EUI wrote:

No, I did not record them because I wanted to encourage questions/comments and
when you record these sessions,
(some) folks are hesitant to ask questions or respond.

That is truly unfortunate. I am sure there are hundreds if not thousands of people including myself who would love to watch the presentation, but who got late notice or were not available at the time. How many viewers fell into the category of too shy to participate? Could you not record the session, maybe have a recorded Q&A, and then have a closed Q&A at the end? I only ask because this Zoom sounds like a great thing you did, but for very limited benefit.
I am reminded of school classes where a few students were too shy to speak up in class, and therefore they fell behind, eventually failing the class. If they were lucky there was a teacher who noticed and took them aside, perhaps arranging private tutoring so they would be more comfortable.

On Sun, Nov 13, 2022 at 09:59 PM, Ho-Ro wrote:

my LCD screens of nano and tiny do not show any artefacts

DiSlord,

Correction: My tinySA shows it on the "VERSION" screen, while the NanoVNA does not.
But this is also more a topic deep in the HW/FW - we should discuss this on GitHub.
Are you still using your repo because there has been no traffic for a long time? Where can we follow your good work?

Martin

When you click on the TDR in Nanovsaver. The length of the cable is already indicated, which I presume is the physical length once you specify the coax type or VF. There are two plots on the graph, but what do they show?

Are there recordings?

On Sun, Nov 13, 2022 at 7:21 AM Barry K3EUI <k3euibarry@...> wrote:

The “Five County Digital Training Net” (Philadelphia region) is hosting a
series of Zoom Workshops on Monday evenings at 7-9 pm. The topic: Nano VNA
Fundamentals
All are welcome to join.
Link:


We have already held two sessions covering the fundamentals of what a VNA
is capable of measuring and the second session covered how to CALIBRATE the
VNA over a frequency range.

The 3rd Zoom session on November 14th will cover what a Nano VNA measures
and what it calculates: the forward and the reflected signals are compared
(S11) and the following are calculated:

1) Reflection Coefficient (rho) - a fraction from 0 to 1.0 representing
the ratio of returning signal to incident signal. In an antenna, you do not
want any reflected (return) signal, so the ideal reflection coefficient is
zero.

2) Return Loss (dB) - this is based on the reflection coefficient and
represents the loss of signal, but measured in decibels (dB) rather than as
a percent or fraction. Hams rarely use this measurement. Why?

3) SWR - standing wave ratio - We all use this term but what does it
mean? What is an “acceptable” SWR in terms of antenna performance.

I will tie these three measurements into what a Smith Chart reveals.

Come join the discussion.
I am not an RF Engineer - so I try to keep this at a moderate level of
mathematics.

De k3eui
Barry (k3euibarry - at - gmail.com)
Five County Digital Net manager
Philadelphia PA
November 13 2022







--

-Chris

On Sun, Nov 13, 2022 at 08:01 PM, DiSlord wrote:

(you can see it also on Nano or Tiny LCD at right bottom)

Strange, my LCD screens of nano and tiny do not show any artefacts, only the captured data on PC. But it's only a minimal issue in any case.

On Sun, Nov 13, 2022 at 06:29 PM, G8DQX list wrote:

*However*, the *H4* variant of the nanoVNA and the new tinySA *Ultra* use 4"
480×320 screens.

Robin,
Good hint, should work for the bigger ones now - untested because of the HW not (yet) available.
Martin

usage: nanovna_remote.py [-h] [-d DEVICE] [-n | --h4 | -t | --ultra] [-z {2,3,4}]

optional arguments:
-h, --help show this help message and exit
-d DEVICE, --device DEVICE
connect to serial usb device
-n, --nanovna use with NanoVNA-H (default)
--h4 use with NanoVNA-H4
-t, --tinysa use with tinySA
--ultra use with tinySA Ultra
-z {2,3,4}, --zoom {2,3,4}

as well as

usage: nanovna_capture.py [-h] [-d DEVICE] [-n | --h4 | -t | --ultra] [-o OUT]

optional arguments:
-h, --help show this help message and exit
-d DEVICE, --device DEVICE
connect to device
-n, --nanovna use with NanoVNA-H (default)
--h4 use with NanoVNA-H4
-t, --tinysa use with tinySA
--ultra use with tinySA Ultra
-o OUT, --out OUT write the data into file OUT

I think this related to LCD driver, on screen capture i read LCD memory and send to CPU (you can see it also on Nano or Tiny LCD at right bottom)

Artefact present on all LCD displays based on ILI9341 driver
On LiteVNA and st7789 LCD driver no visible artefacts.

Martin,

1) thanks for doing this, it's much appreciated.

2) the link below took one straight to the code, where lines 60-64 show:

# The size of the screen
width = 320
height = 240

which is OK for an original nanoVNA(-H) or a tinySA. *However*, the *H4* variant of the nanoVNA and the new tinySA *Ultra* use 4" 480×320 screens.

I've not had a sensible opportunity to check the script out with my own H4 or tinySA, but thought I'd mention it now, to get a view from yourself.

73, Stay Safe,

Robin, G8DQX

On 12/11/2022 09:19, Ho-Ro wrote:

Hi,
as written just around the corner/g/tinysa/topic/tinysa_remote_py_python/94944540 there's a new tool in my toolbox:



Remote control for the NanoVNA or tinySA - mirror the screen to your PC and operate the device with the mouse. The keys + and - zoom in and out, s takes a screenshot with timestamp, ESC quits the program.

usage: nanovna_remote.py [-h] [-d DEVICE] [-t | -n] [-z {2,3,4}]

optional arguments:
-h, --help show this help message and exit
-d DEVICE, --device DEVICE
connect to serial usb device
-n, --nanovna use with NanoVNA (default)
-t, --tinysa use with tinySA
-z {2,3,4}, --zoom {2,3,4}
zoom the screen image

Martin

The screen capture shows artefacts at the bottom of the image in the far right column. This is independent of the respective device and the recording program used; tinySA also shows the same artefacts. NanoVNA version 1.2.15, the issue existed also with versions 1.0.64 and 1.1.x, also latest tinySA version.

see also
and

Another user's tinySA also shows this, so it is obviously a systematic problem.
/g/tinysa/message/7071

Martin

Hi Barry. This sounds like a really invaluable project. It is just too bad that we didn't know about it sooner, so that we could take in all five sessions.

Is there any possibility that any previous viewers might have copied the first two sessions, or even some screen grabs. I always use PrintScreen to keep a record of any Zoom sessions that I view.

Just a hopeful wish.

Thanks again for your hard work.

Doug

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oops
here is the much better Dummy Load trace

Barry k3eui

This is what I see with the NANO VNA standard LOAD (50 ohm dummy load R)
Nothing unusual here.

de k3eui Barry

Nano VNA graphs using VNA SAVER

Lots of folks have asked me how the REFLECTION Coefficient S11 graph, the RETURN LOSS graph (dB) and the SWR graph compare.
Basically they all show similar aspects of the antenna.


This trace around the 80m band, and is AFTER my CLC Antenna Tuner - set up for min SWR around 3600 kHz
The antenna is about 30 ft high, 130 ft long, center-fed with RG213 coax.
It is a great NVIS antenna.

Note the similar shapes of the RETURN LOSS (dB) and the SWR curve (both derived from the reflection coefficient (S11)


de k3eui Barry

November 13 2022