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I have an introduction to the NanoVNA with examples of antenna analysis, component analysis, TDR, and balun impedance measurement. It can be found at



I attempted to put this into the files section but I kept getting server timeout errors. Hopefully this presentation will help hams get more out of their NanoVNAs.

73,
Dan
KW4TI

Link does not work. Asks for sign in to Google.

Roger

I think you need to share it. Requesting that I ask for access.

Hank
W6IR

Here is the link. It should not require permission. Try it again. Apologies.

The link works. It ask for you to send a request. I assume that he'll grant
permission once a request is made.

I'm looking forward in reading through his presentation.


On Sun, May 31, 2020, 5:51 PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

Link does not work. Asks for sign in to Google.

Roger

I began looking through the presentation on the nano,
and immediately caught an error in the table comparing
"ham conventions" versus "More modern conventions".

For "no reflections" the correct return loss expressed in dB
is a positive infinite value, not negative as shown in the table.
More pragmatically, the return loss of any passive device is
a positive number of dB. For example, a "pretty good termination"
might show a return loss of +32 dB.

I know that many people get this wrong. But if you pay attention
to the meaning of the word 'loss', then a negative value in dB
really means a gain (reflected signal more powerful than the
incident signal), which really is possible for active devices like
amplifiers etc.

I once gave a demo of a home brew Time Domain Reflectometer
(TDR) at a club meeting, and finished up with a DUT which I had
lovingly crafted with a tunnel diode to produce return gain over
a wide band. I showed this, pointing out that the reflected signal
was larger than the incident, then challenged the audience to
say what was in the box. Only one guy got it right.

Dana (K8YUM)

Thank You for the share.....WD4PVE

Hi,

thank you, Dana, for that clarification: Return Loss in a passive lumped element circuit is positive, indeed.

I very much agree with that. There are, however, so many opinions and publications around. I think,
that the attached paper from Prof. Dr. Trevor S. Bird, former IEEE chief editor, is a very good one on that
matter. I suggest to earnestly detail seeking, wondering NanoVNA user's to read it. So here it is attached.

The issue, however, goes beyond that. Please have a look at page two, where another very common error
went unnoticed even in the quote used by Trevor S. Bird:



In this quote Trevor missed his article’s main point, that Return loss must be positive in a passive lumped
element circuit, what definitely he tried to show. Enter complex values for some Z1 and Z2 and you can find
by application of complex math, that you easily get negative return loss. I emailed that to him, but he replied
that while obviously my point appeared to be true, at present he didn’t have time to carefully check that.

An obvious example:

(Please also use other, less simple, also non-resonant values for Z1 and Z2 yourself,
and use a math program that can handle complex calculation like EXCEL.)

Think of a simple resonant circuit on your lab table made of (serial) lumped elements only:

Generator (or Thévenin equivalent) impedance: Z2 = R2 + jX2 = 50 +j100 Ohm,
Load impedance: Z1 = R1 + jX1 = 100 –j100 Ohm.



Because of X1 cancelling X2 at resonance, obviously SWR = 100 / 50 = 2.
The Magnitude of the ‘Reflection’ Coefficient = 0,33333.

That’s easy, right? (Then correctly Return Loss = + 9,54 dB)

But if we use the Return Loss formula quoted for the two complex impedances, we would assume
reflection where there is none. By using the formula nevertheless, we will get

Return Loss = - 2,76 dB
(and ‘SWR’ = -6,34) instead.

And that in a simple passive R-C-L circuit !

We probably will agree: That is wrong.


I carefully studied this controversial issue in great detail. So what actually is the reason that so
often this gets wrong?

Here is my answer:

1. The first sentence above is true for transmission lines with a complex characteristic wave impedance Z2,
terminated by a complex load Z1.

2. The last sentence ?More broadly …“, however, makes a wrong assumption that so far never was proven.
I challenge everyone to do this proof. I predict: You will not be able to prove this

wrong assumption:

“More broadly we can set equal the terminated transmission line’s characteristic wave Z2 impedance to a generator’s
internal complex impedance Z2. Both physically are identical or interchangeable and thus the formula applies to both.”

These two values, however, physically are two different things that ever so often are confused – thus falsely allowing
negative return loss for a passive lumped element complex mismatch.

While on a transmission line we have waves traveling in both directions, incident and reflection, along the length of the
line, at the juncture between a complex impedance generator and a complex load there is no such distance, and hence
we also must use a different approach for derivation. There is actually no reflection, as (for simplicity I use a serial circuit)
all parts share one single and thus identical common current in one direction only. So a ?reflection“ factor doesn’t apply.
No real energy actually is reflected – it all flows in one direction from generator to load and is dissipated in the real part of the load
according to R times the square of that common current I. Depending on the mismatch, less power will be transferred than could be
drawn from the generator, if maximum real power transfer is wanted (which in a vast majority of cases applications is aimed at, but
in reality antennas sometimes are used way out of resonance).

It makes me shake my head, how this erroneous assumption became so omnipresent. How could that be?
It even made it into the ATIS standard glossary - and thus spreads like unproven assumptions in fake news do:



But what then is correct?

Here it is, if we keep here – just for comparison purposes – what actually is a misnomer (as there is no reflection) the name “RC” :



With the asterisk meaning conjugate complex.

Should you want the derivation, let me know – I sure have it.

But I don’t want this to get more lengthy than it is already now – forgive me that, please.


Can you agree? Or perhaps Not?

If not:

Would you please prove to be true anyway what above I called a wrong assumption.


73, Hans
DJ7BA


















-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Dana Whitlow
Gesendet: Montag, 1. Juni 2020 12:41
An: [email protected]
Betreff: Re: [nanovna-users] Presentation on the NanoVNA for the Raleigh Amateur Radio Society



I began looking through the presentation on the nano, and immediately caught an error in the table comparing "ham conventions" versus "More modern conventions".



For "no reflections" the correct return loss expressed in dB is a positive infinite value, not negative as shown in the table.

More pragmatically, the return loss of any passive device is a positive number of dB. For example, a "pretty good termination"

might show a return loss of +32 dB.



I know that many people get this wrong. But if you pay attention to the meaning of the word 'loss', then a negative value in dB really means a gain (reflected signal more powerful than the incident signal), which really is possible for active devices like amplifiers etc.



I once gave a demo of a home brew Time Domain Reflectometer

(TDR) at a club meeting, and finished up with a DUT which I had lovingly crafted with a tunnel diode to produce return gain over a wide band. I showed this, pointing out that the reflected signal was larger than the incident, then challenged the audience to say what was in the box. Only one guy got it right.



Dana (K8YUM)







--
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Ditto on thank you for the share. It will make an interesting club presentation.

Link worked for me. Thanks.

Hans, I don't understand your "obvious example" circuit.
Could you please describe it in detail, perhaps expressed
as a spice netlist in the body of your reply, for simplicity?

Thanks,

Dana

Hi Dana,

thanks for your clarification request.
Sorry that I thought it was obvious, I was a bit too short, I think.

The following should take care, hopefully:

On



You can find a circuit diagram, that (disregarding the + and – DC signs) we will use here.

Zs and ZL each are a series of a resistance and a reactance, in the resonance example, XS and XL
are reactances of of equal magnitude but opposite sign – as typical in a resonant serial LC circuit.



Let’s understand ZS as impedance of the source, (in my earlier example it is Z2 = R2 + j X2)
and ZL as impedance of the Load, (in my earlier example it is Z1 = R1 + j X1) .

As was written in the simple resonance example, let be:

Generator (or Thévenin equivalent) impedance: Z2 = R2 + jX2 = 50 +j100 Ohm,
Load impedance: Z1 = R1 + jX1 = 100 –j100 Ohm.

meaning:

R1 = 50 Ohm
X1 = +100 Ohm ( represents omega * L)
R2 = 100 Ohm
X2 = -100 Ohm ( represents 1 / (omega * C)

we can use the (ATIS published) left part “false assumption” formula, neglecting also the magnitude signs, that are falsely arbitrary, too,
as the reflection factor in general has a complex value, of course – just look at any Smith diagram):

as found here:





from this we get: RC = (50 + j100 – (100 – j100)) / (50 + j100 – (100 – j100)) = -50 / (-50 + j 200).

Using EXCEL (because of it’s ability to easily do complex math), this yields:

RC = 0.3333 –j 1.3333

or, if we don’t ignore the magnitude, as ATIS uses it:

RC = | 0.3333 –j 1.3333 | = 1.374

already here we see, that RC (or gamma, as it is sometimes called, too) in a passive lumped element circuit is > 1 ! That is wrong already.

Nevertheless carrying on with it, we get:

SWR = 1 + |RC| / ( 1 - | RC |) = 1 + 1.374 / (1 – 1.374) = -6.342 which, of course, is negative, the fact that the otherwise excellent
article of Trevor S. Bird had quoted, not noticing that it yields a negative result, which he wanted to prove is not correct – just as you had said, too,
as in a passive lumped element circuit RL must be positive.

I don’t know if you can use complex EXCEL, but I hope so.
Feel free to use – besides the simple resonance example – also any other complex values by entering these in the yellow EXCEL fields.

Just in case not - I also add a picture of the EXCEL. In some other work sheet programs, you may be able to make use of that, too.



73, Hans
DJ7BA








-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Dana Whitlow
Gesendet: Dienstag, 2. Juni 2020 01:49
An: [email protected]
Betreff: Re: [nanovna-users] Presentation on the NanoVNA for the Raleigh Amateur Radio Society



Hans, I don't understand your "obvious example" circuit.

Could you please describe it in detail, perhaps expressed as a spice netlist in the body of your reply, for simplicity?



Thanks,



Dana







--
Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft.

I enjoyed your RARS presentation last month Dan. Thanks for taking the time to put it together and present it.

73,
-Rob
N4MN