On Sun, Dec 29, 2024 at 05:57 PM, Andrew Love wrote:

Of course the real question here is possibly why is there a mismatch  between
the output of the qcx and the input of the amp?

Driving a non-class A amplifier is complicated. For one thing, the input impedance varies significantly with supply voltage and drive/power level, and to some extent the output tuning........
2:1 VSWR is a common spec limit. Consider the situation where the source is 100Ω and the load is 25Ω, there is a 4:1 mismatch yet both are "nominally" 50Ω. Power transfer will clearly not be optimum.

For another, the output impedance also varies and the output power and efficiency varies with the load, even more than just the mismatch loss would suggest.
Even the impedance at the 2nd, 3rd and possibly higher harmonics will have significant effects, at both input and output.

You might get more than power with 50Ω, you might get less, it depends on the amplifier and its tuning and bias conditions.
Many of these same effects will occur with the driving amplifier/transmitter.
Things get complicated when you are driving a dynamic, nonlinear load with a similarly imperfect source.

https://en.wikipedia.org/wiki/Load_pull https://www.everythingrf.com/community/what-are-load-pull-measurements
73, Don N2VGU

Quick question. What nanovna is this https://nanovna.com/?page_id=87
referring to?

Fred
N4CLA

On Sun, Dec 29, 2024 at 6:21 PM Geoff Peters - AB6BT via groups.io <AB6BT=
comcast.net@groups.io> wrote:

Why not buy an " Antenna Analyzer"? That will do what you want.

73,
Geoff --> AB6BT

On 12/28/2024 10:44 PM, aeternus.arcis via groups.io wrote:

Hello.
I just wanted to ask if there is any interest from the community or the

developers to make the menu easy for radio amateurs, for people that are
not engineers? Currently the menu is a big mess with a lot of options and
sub-options and so on. So if you want to make a simple measure, you have to
go in many menus to change many settings. I know this gives a lot of
control, but I will be very nice to have a few buttons on the main screen,
like a main menu, that take you to the most used measurements, with all of
the settings already set, with bigger font and a few buttons to change some
settings only to that current measurement. I also do not know if this is
something that the hardware supports.

Why not buy an " Antenna Analyzer"? That will  do what you want.

73,
Geoff --> AB6BT

Don't you have a few little HT antennas you can attach to the VNA to learn the instrument in the comfort of your home?

If you buy an instrument, you take time to learn how to use it. SWR is a weak measurement on its own. The Smith Chart is your real best friend. There are many YouTube videos on the instrument and the chart. Meanwhile, if you learn a few things and SAVE your settings, you will have 95% of what you want! Turn on VNA, RECALL the setting you want and go measure

Hi Bryan,Of course the real question here is possibly why is there a mismatch  between the output of the qcx and the input of the amp? They are presumably notionally both 50 ohms. Is it really significant? Is there a fault somewhere?But... Depending on the tuner's construction and topology you may be able to get at the individual  components and measure them in place but I suspect the calibration error due to difficult connection into the tuner would be quite large.A more holistic approach would be to simply measure the effective complex impedance of the adjusted tuner as a whole. One way would be to put a 50 ohm dummy load on the output of the tuner and measure the impedance R+jX at the input. This will tell you that the output impedance of the QCX is R-jX (the complex conjugate). Now you can use any of the online pi, L or T match calculators to design a matching network that is the equivalent of the tuner.Hth.Andrew Sent from my Galaxy

Hi Brian,

Indeed if you characterize the impedance you can arrive at a fixed matching network.

If we suppose the QCX requires a 50 Ω load, a reasonable assumption, and the QRP Guys tuner got it matched, you can try the following approach:

Disconnect the tuner and put a "dummy" load of 50 Ω on the _transmitter_ side;
Then measure with nanoVNA the impedance "seen" in the load side of the tuner, note its value.

The input impedance of the 50 W amp will be the conjugate of this measurement, so if you read, for example, 12 resistive and 40 inductive ohms, 12 +j40 Ω, then the input would be 12 -j40 Ω, i.e., 12 resistive and 40 capacitive.

From these numbers you can use the formulas appropriate for the match.

Depending on the values found maybe even a single L network could get the job done, as you intend to use a fixed one.

More details, as the frequency range of the intended match and the real numbers may steer the approach to other designs, but the road map is this.

HTH

--
Cesar, PY2CSH

Is there any way to determine a tuners L and C settings/values such that a fixed PI network could be built to replace the tuner.

Case in point. I have a QCX and the 50w amp which exhibits a mismatch between the two. I have set my qrpguys tuner in between and tuned it. Now I want to build a tuned circuit with a toroid and caps to replace the tuner.

I'm sure there is a better way but ,,,

Bryan N0LUF

Nizar,

Are you trying to use 75 ohm coax with a transmitter designed for 50 ohm? If so you should be not be using the DiSlord impedance setting which changes the system impedance to 75 (or 77) ohms. You want the SWR measurement to be based on what the transmitter will see.

Here is an example for you to consider. Take a 1/4 wave vertical antenna with a very good ground system (multiple radials) cut to resonate at 14 MHz. At resonance the feedpoint impedance will be 36 ohms plus the ground resistance - lets say 4 ohms. So if you measured at the antenna feedpoint with the NanoVNA you would see 40 +j0 at resonance and an SWR of 1.25. Next we add 7 meters (1/2 wavelength) of RG-58A/U coax and measure at the far end. We get an impedance of 40.9 +j0.194 and an SWR on 1.24. Now if the length is increased to 10.5 meters (3/4 wavelength) we get an impedance of 62.2 -j1.97 and an SWR on 1.23. So everything looks good.

Next we try 7m of RG-59 as the coaxial transmission line. We get an impedance of 41.8 -j0.02 and an SWR on 1.20 based on 50 ohm Zo and 1.81 based on a Zo of 75 ohms. This looks good as well. However if the length is increased to 10.5 meters (3/4 wavelength) we get an impedance of 134.2 -j2.7 and SWR of 2.69 based on 50 ohm Zo and 1.77 based on a Zo of 75 ohms. This is not desirable to have the SWR based on 50 ohms get worse because we changed the cable length.

Observations
---------------
- When the SWR is calculated based on the impedance of the coaxial cable it goes down as the length of the cable is increased. This is due to loss in the cable. The Return Loss increases with cable length.
- When the 75 ohm cable is used the SWR based on a 50 ohm Zo calculation increased to 2.69 when we went from a half wavelength (7M) to 3/4 wavelength (10M). This also means that a transmitter designed for 50 ohms would see a higher SWR and the foldback circuitry (most solid state Tx use this) would cut back the power output.

Discussion
------------
A transmission line can be viewed as an impedance transformer. At half wavelength with a lossless line you "see" the impedance at the far end and the SWR will be the same. As the length is changed the impedance will change but the SWR will remain constant IF calculated based on the characteristic impedance of the transmission line used. With a lossy line the SWR will decrease as the line length is increased. If a 75 ohm line is used and the measurements are made using a Zo of 50 ohms there will be a considerable change in SWR as the line length is changed.

I am not suggesting that a 75 ohm transmission line cannot be used with a 50 ohm transmitter. On the contrary. Often times a specific line length can be used to transform a high or low feedpoint impedance to close to 50 ohm at the transmitter end. One can also use a "tuner" with 75, 300 or 450 ohm transmission lines to make an impedance match to 50 ohms.

What I am stating is that it is not a good idea to use a 75 ohm cable of unknown length and then trim the antenna to get close to 50 ohms and a low SWR at the transmitter end of the cable. One should also not change the NanoVNA menu setting to a different system impedance in the NanoVNA and then trim the antenna. The reasons are that the radiation efficiency of the antenna could be reduced and what will happen if you change the transmission line length.

All calculations above were done using TLDetails which is freely available on the Internet. Screenshots of my calculations are below.

Roger

I am looking from a point of view of someone that does not yet understand many technical things. I may not have time or interest to learn them. So for a person that just wants to simply measure let's say SWR, I think this will be easier. I am not saying to remove the other technical options. They need to exist. Just to add simpler ones. It saves time for people that do not use this every day and and do not remember all of the settings, and I think it also saves time for people that use the device every day, but take many different measurements.

My example is something like this - you press "SWR test" - a new screen opens with preselected only 1 trace, format SWR, channel 0. Then there are two buttons to choose start and stop frequency. And a button to instead choose predefined "amateur radio bands". All of this saves time.
Maybe some of this is limited, because of the screen size on some models. I like how that SV4401A model moves some common options outside of the hidden menu, but it is still not what I am imagining. It is also too expensive, but that is a different topic.

Not really . . . apps need to be compatible with the runtime libraries (try to run something too new on a Linux based system, and the errors you getvare almost always symbol errors from libc, not including the newer ones. Running older code rarely fails . . . ) - almost nothing accesses the kernel directly on any Linux based system (and those interfaces are standards driven, and rarely change - mainly things presented as devices.

For instance (no Android, but the Linux foundation is similar), I can boot my systems ino a 3.x, 4.x, 5.x and 6.x family kernel, and absolutely nohing breaks app-wise - libc never changes.

- Tim

--
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Rick,

That's true to a certain point. However, the API is just an interface to the kernel and must be compatible with the kernel. Changes in the kernel often require changes in the API. Perhaps not in the interface but in the implementation.

And I can find the app in the Play Store but an attempt to download it results in the message that the app is not compatible with my Android version.

73,
Jerry, AI0K

I had a hard time determining if the Demo RF Kit was the same as offered by Amazon and other vendors. I think the person who initiated the Post should have first taken a picture of the RF Demo Kit to show the uninitiated first what is being discussed, then go into the how, why ETC. now that I understand what is being talked about I am very interested.
I just received my nanoVNA -F v2 and I expect delivery of the RF Demo Kit on Monday Dec 30
To me this is an obvious place to start. I am not interest in going out side at -20 C to attach my antenna just to begin learning how to use the nanoVNA device.
Thanks to PDXer for posting the picture of the "Frequency Test Board RF Demo Kit VNA RF Test Module Vector Network Analyzer Breadboard Test Protoboard Board"

there seems to be a debate as to where or how to purchase a nanoVNA. They are all made in various factories in Mainland China. the issue is not so much (in my mind) if it is a clone as in reality they are al a clone of the original open source work. It is more of finding and dealing with a reputable source. or use another intermediary such as Amazon where if there is a problem you can return the item to Amazon. this a all beside attempting as a new comer to the technology choosing which of the multiple firmware versions supported or not supported software versions. This is on the nanoVNA.com site they list the vendors they deal with the supply a known product,
Those of us who have worked with the Lab Grade Network Analyzers will be amazed with the actual performance of a similar device we can now hold in our hands that for instance we can use to test our antennas. The lab grade device does not lend itself to working in the field (I actually had one equipped in a purpose built field work case) While the Lab Grade is a wonderful piece of kit you cannot beat the fact you can now hold in you hand a device you can use while at the top of a tower attached directly to the antenna in question.
As long as you obtain one that works and you become accustomed to the controls and learn the techniques of using the device you will be very pleased with have the convenience of delving into the mystery of wonderful world of antennas and how to improve them beyond the simple SWR at the desired operating frequency. I hope that helps. Dave VE6LX

I don't see it being practical. All those options exist because people do so many different things with the instrument. I for example use the same settings 95% of the time, only the start/stop frequencies change. So I calibrate for the half dozen ranges and measurements (S11 or S21) I use and SAVE them with all their settings (points, traces, etc) in place. All I have to do is RECALL one and I'm good to go!

On 29/12/2024 06:44, aeternus.arcis via groups.io wrote:

Hello.
I just wanted to ask if there is any interest from the community or the developers to make the menu easy for radio amateurs, for people that are not engineers? Currently the menu is a big mess with a lot of options and sub-options and so on. So if you want to make a simple measure, you have to go in many menus to change many settings. I know this gives a lot of control, but I will be very nice to have a few buttons on the main screen, like a main menu, that take you to the most used measurements, with all of the settings already set, with bigger font and a few buttons to change some settings only to that current measurement. I also do not know if this is something that the hardware supports.

I take your point, but I feel that for many purposes start and stop frequencies
are all you need to change, perhaps followed by a calibration. I guess the TDR
measurements (find a cable length or a fault) are a little more complex.

What sorts of top-level options would you like to see? What settings to change?

As many of the devices use a similar menu structure it would be a lot of work to
change, and it might make support more difficult!

There are some excellent resources - including books and videos - out there
which may answer your questions:

https://nanovna.com/?page_id=87


https://groups.io/g/nanovna-users/files/Absolute%20Beginner%20Guide%20to%20The%20NanoVNA/Absolute_Beginner_Guide_NanoVNA_v1_6.pdf

https://www.rsgbshop.org/acatalog/NanoVNAs-Explained-2110.html

Cheers,
David
--
SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: davidtaylor@...
BlueSky: @gm8arv.bsky.social, Twitter: @gm8arv

Hello.
I just wanted to ask if there is any interest from the community or the developers to make the menu easy for radio amateurs, for people that are not engineers? Currently the menu is a big mess with a lot of options and sub-options and so on. So if you want to make a simple measure, you have to go in many menus to change many settings. I know this gives a lot of control, but I will be very nice to have a few buttons on the main screen, like a main menu, that take you to the most used measurements, with all of the settings already set, with bigger font and a few buttons to change some settings only to that current measurement. I also do not know if this is something that the hardware supports.

On Sat, Dec 28, 2024 at 1:56 PM Jerry Stuckle via groups.io <ai0k=
ai0k.net@groups.io> wrote:

Peter,

It looks like you have an older version of the kernel, which could
explain why you can download it and I can't.

Nope, it's not the kernel version, it's the version of the Android API that
the application was built under.
Newer API versions don't support very old versions of Android.

https://apilevels.com/ and
https://support.google.com/googleplay/android-developer/answer/11926878

If you don't see it in the Play Store, then the second link provides the
rationale.
73,
-Rick

--
Rick Murphy, D. Sc., CISSP-ISSAP, K1MU/4, Annandale VA USA

Peter,

It looks like you have an older version of the kernel, which could explain why you can download it and I can't.

73,
Jerry, AI0K

Hi Stan

Thank you for your summary of the common sense of an experienced, it is convincing, in fact I have just done the comparative tests of the same dipole antenna with the same coaxial cable Zc = 77.7 Ohm RG59 with and without compensation of calculation of DiSlord of its function Z--> 77.7 Ohm with the same NanoVNA H4 firmware Dislord 1.2.40, the results are as follows:
without Zc compensation: SWR = 1.22 Fr = 14.385 Mhz
With Zc compensation: SWR = 1.16 FR = 14.112 Mhz
there is 0.06 sheeft for SWR and 272 Khz sheeft for Dip frequency

But with DiSlord conversion function it's much better to use and it's a simple and beautiful function .
Thanks
73's Nizar