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I see this on both devices, and would like to know how to use it. I also see Rj = 50 ohms, and I wonder if these are confused with one another.

~R~

Most things "RF" deal with a 50 ± j0 ohm system impedance. The exception
is the TV industry who go with 75-ohms. All the NANOVNAs and the TinySA
are designed for and present pretty much a system impedance of 50 ±j0.

You may not be familiar with this expression of impedance. Notice, I am
using the term "impedance". That's because there is a real part (the pure
resistance or "R") and a complex portion which represents the frequency
dependent capacitive or inductive reactance (the ±jX term). The "R" term
is frequency independent. The ±jX term is frequency dependent. The
frequency dependent term may be calculated from the following:

X(C) = 1 / [2 x pi x F x C]

X(L) = [2 x pi X F x L]

pi = 3.14159....
F = Frequency in Hz
C = Capacitance in Farads
L = Inductance in Henries

Is this what you are after?

Dave - W?LEV



On Thu, Apr 28, 2022 at 1:20 PM Rich NE1EE <TheDustyKey@...>
wrote:

I see this on both devices, and would like to know how to use it. I also
see Rj = 50 ohms, and I wonder if these are confused with one another.

~R~

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

And the R1 setting lets you change the internal calculations of the nanoVNA
to use a value other than 50 for the nominal impedance, e.g. 75 + j0, which
for many cases works as expected.
Note that it does not change the hardware-based 50 ohm characteristic
impedance; that stays the same. It just corrects the calculations. For
instance, you can set it to 75, then calibrate with a 75-ohm load, then all
of the displayed calculations will be consistent with each other.

On 2022-04-28 10:23:-0700, you wrote:

And the R1 setting lets you change the internal calculations of the nanoVNA
to use a value other than 50 for the nominal impedance, e.g. 75 + j0, which
for many cases works as expected.
Note that it does not change the hardware-based 50 ohm characteristic
impedance; that stays the same. It just corrects the calculations. For
instance, you can set it to 75, then calibrate with a 75-ohm load, then all
of the displayed calculations will be consistent with each other.

So here are some of the issues.
1. This feature (I guess) is described on the published menu as DISPLAY-> PORT Z 50 -> XX, but no such feature exists on my device.
2. PORT Z 50 -> XX is described similar to what you have written, BUT ... Calibrate as usual to 50 ohms, no matching adapters are needed.
Displays data as if the DUT impedance were different from 50 ohms. (I get that...I just want to make sure I am addressing the right menu item. R1 is not Rj is not Z 50 -> XX.) I would not have guessed that R1 = 5o ohms means what you have written, partly because R1 doesn't mean anything to me.

So I am looking for something definitive...I am too new to know.

3. This feature (as you described) is variously written as
MEASURE > Rj = 50 ohms
MEASURE > R1 = 50 ohms
I don't know if one is correct, or if it does not matter, or why it just doesn't say PORT Z Re = 50 ohms (or = 75 ohms, or whatever)
So those are my questions...
Recall that I am doing this because
a. I am just learning the device, and am confused by all the contradictions I see
b. I'd like to make it easier for those who follow, by writing down what I learn as I go, and publishing that

~R~

On 2022-04-28 17:16:+0000, you wrote:

Most things "RF" deal with a 50 ± j0 ohm system impedance.

Is this what you are after?

Dave - W?LEV

No, but thanks for taking the time! I am working on documenting the nVNA, and trying to find an explanation for each menu item that seems like it needs an explanation.

Please see my next port.

~R~

The purpose of PORT Z 50 -> XX is to set the "reference impedance" to XX.

Important: You still must calibrate using a 50 ohm load!!

If I set XX to 75 ohms the origin of the Smith Chart will now be 75 +j0 ohms. VSWR and Return Loss calculations will now be based on 75 +j0 ohms. The R +jX readouts will be the same as when XX = 50 + j0

Users should be aware that the further away you get from 50 ohms the more inaccurate the SWR and RL calculations. The plots on the Smith chart will be off a bit but hard to visually see.

BTW - The PC software Antscope2 by Rig Expert works with the -H and -H4 and has a similar option to change the "reference impedance" for those that need a PC solution.

Roger

Hello again Rich;

To answer your question directly, neither R1 nor Rj is correct. The variable being changed in the Measure menu referred to as R1 defines the characteristic impedance (a complex R + j0 term) of the measurement system (the NanoVNA in this discussion) called Z0. It is a fixed constant in the mathematics used by the measurement system. To my knowledge, Z0 is always specified with an assumed zero value for the imaginary component, and thus only the real term needs to be defined, and R1 would have been better defined (and universally understood) as Z0.

To be clear; Z0 is a defined reference value to which all measurements are compared. In most discussions here, Z0 is considered 50 + j0 ohms, but in reality it is the definition of Z0 that is precise, and all measurements are ratiometric with respect to that definition. The resultant measurements will only be as precise/accurate as the standard that is used to define Z0; making it the first and most critical item of uncertainty in all VNA measurements. Independent of uncertainties; measurement precision and resolution (critical components of accuracy) degrade exponentially with distance from Z0.

Notwithstanding the above; if your goal is to create a more ergonomic/user friendly menu map of one or more of the NanoVNA versions; it would be best to keep the terms between the hardware and your maps consistent, and not alter the menu terms used, or the order in which the menus items are presented.

FWIW... I applaud your passion to take on this task, as it is a daunting one; with revisions and added features making it a constantly moving target.

72

Gary, N3GO









--
73

Gary, N3GO

The resistive (R) term in a complex impedance R +/- jX is not necessarily frequency independent. Both R and jX can change in some complex impedance loads. An example is an antenna operating at either side of its resonant frequency where both R and jX change with frequency.

On 2022-04-29 05:40:-0700, you wrote:

To answer your question directly, neither R1 nor Rj is correct.

This is what I hoped to see...thanks for the notes following, too, though I was generally aware of the material. In earlier DiSlord docs, there is mention of PORT Z 50 -> XX, but it is not on either of my devices. I have upgraded them all now, so I don't want to flash back just to check what it said earlier.

My hope is that this group can reach a consensus, and that DiSlord, reading it, will change back to PORT Z 50 -> XX. But I don't know what influenced the change to R1 and Rj, so there is some discussion missing.

PORT Z0 = xx ohms would also be clear, I think.

Notwithstanding the above; if your goal is to create a more ergonomic/user friendly menu map of one or more of the NanoVNA versions; it would be best to keep the terms between the hardware and your maps consistent, and not alter the menu terms used, or the order in which the menus items are presented.

Agreed. That only makes sense. The benefit of using an open (free) tool to produce the menu map is that anyone can update it, and yEd is an easy tool to learn at the fundamental level I am using it. My intention is that any updates preserve earlier material, so that anyone who has not upgraded can access an accurate map. The same goes for the menu hierarchy doc. Unfortunately, that doc is not doing as well, due to a paucity of information. And my unwillingness to release a doc that likely contains guesses, which will only serve to spread more myths.

~R~

On Fri, Apr 29, 2022 at 08:55 AM, Rich NE1EE wrote:

This is what I hoped to see...thanks for the notes following, too, though I
was generally aware of the material. In earlier DiSlord docs, there is mention
of PORT Z 50 -> XX, but it is not on either of my devices. I have upgraded
them all now, so I don't want to flash back just to check what it said
earlier.

Which version of firmware and what model(s) are you currently using? It is helpful to know because users in this group are running different versions.

Roger

On 2022-04-29 09:40:-0700, you wrote:

Which version of firmware and what model(s) are you currently using? It is helpful to know because users in this group are running different versions.

nVNA-H4 v4.3_MS firmware 1.1
nVNA-H v3.6_MS firmware 1.1.01

Port Z option not public on my github, so not avaible on Hugen firmware.

Only on my tests fw variants.

On Measure page Rl used for XTAL measure

On 2022-04-29 11:33:-0700, you wrote:

On Measure page Rl used for XTAL measure

Thanks for chipping in DiSlord.
If someone here can explain how that is to be used, I'm happy to put it in the docs.

My -H4 has Rj = 50
My -H has R1 = 50

I am guessing those are the same?

We also have a Series XTAL S21.
I have measured crystal filters, but only to see what it looks like. I really don't know much about them. So I'd appreciate hearing a difference between series xtal s21 and R1 or Rj = 50. A link is fine. I can read up on it.

Thanks
~R~

I see only Rl = 50 (not 1 and not j)

You must read how made XTAL measures and another:
/g/nanovna-users/message/25800
/g/nanovna-users/message/25801

On 2022-04-30 04:20:-0700, you wrote:

I see only Rl = 50 (not 1 and not j)

Good point. I was not expecting a lower case letter here, so I interpreted that as a 1 on both the -H and the -H4. Even in email, I can't always tell, depending on how the font is shown. In this case, I copied the text into my text editor, and saw there that it is a lower case "L".

As for the j, I made my first version of the new menu map by reading the one posted on the nanovna site, and it is not very clear. You will see that you can zoom into my menu and it will be very clear. I /guess/ that I interpreted that button as Rj, because even now it is not clear to me. Whoever manages is welcome to use the map from the files section here. When I look at my own map, that I created by reading the one on I see the Rj, so I assume that this is where I misread that. I will correct that today for both the -H and -H4 maps to use a lower case "L".

You must read how made XTAL measures and another:
/g/nanovna-users/message/25800
/g/nanovna-users/message/25801

Thanks for the link. I will read them.

~R~
72/73 de Rich NE1EE
The Dusty Key
On the banks of the Piscataqua

On 2022-04-30 04:20:-0700, you wrote:

I see only Rl = 50 (not 1 and not j)

This is why I generally avoid the use of lower case "L" unless the meaning is clear, or I can use a font that makes s clear distinction. Simliar reasoning applies to the letter "O". In this case, I was hampered because I didn't know the context. I made this clear at the beginning. I don't intend to become a VNA expert. In saying this, I don't imply that anyone has any burden because of my point of view. It might be as simple as saying that I am not the person to document the features of the nVNAs. Finding an easy tool to use to make a menu map is one thing; documenting the nVNA, another.

~R~