开云体育

Steve, I completely share our frustration! This is the primary reason I
advise and avoid information by hams and other amateurs in the discipline
presented on YouTuBe. Much of the information presented is just downright
in error. BE CAREFUL!!! In general, the vast majority of the amateur
radio community doing these YouTube presentations truly do not understand
the engineering, technical, and physics of the issues they are attempting
to present. YouTube, in this case, is your enemy. But, you've discovered
that, already!! ???

There are a number of experts within this group who can help you through
your questions. I'll attempt to answer your questions in a rigoruous and
true to best engineering practices as I can. Several years ago, I also
posted several procedures for measuring what you are seeking using the
NANOVNA. I'll attach those at the end of the (likely to get far too long)
email.

<<<<<<<<<<<<<<<<<

QUOTE: " some folks how long leads (12-24") being used to connect the DUT
to the nano, other say you need to minimize these lengths (<4"). Still
other says it doesn't matter because when you calibrate the Nano it all
comes out in the wash."

Not everything comes out in the cal. I have a home brew fixture I use for
evaluating ferrites and other lumped components. The component is
captivated between a couple of alligato clips. Those are attached to the
center pins of two BNC chassis mount connectors which are mounted on a
small chunk of solid ground plane on a sheet of FR-4 board. Even with
calibration, much above 150 MHz, that fixture does not function correctly -
too many parasitics the cal. does not account for. This is common.

When addressing connecting lead lengths to/from a DUT (Device Under Test)
first consider the frequency. Within our 2300-Meter band (135 kHz - that's
KILOHertz!) where a full free space wavelength is about 1.4 MILES, lead
length isn't much of a concern. At HF, even at 10-Meters where the full
free space wavelength is about 33-feet at 30 MHz, I'd be cautious with
anything over 6 or so inches. At our L-Band allocation, 1.296 GHz, where a
full free space wavelength is about 9-INCHES, even a 1-inch piece of wire
is very significant.

There is no hard and fast set-in-concrete answer to the lead length issue.
Maybe a twentieth of a free space wavelength long might be used as a
guideline. But there is no hard-and-fast "rule".


QUOTE: "Some instructions show what appears to be a metal plate
"shielding" the nano from the DUT. Or maybe this is just a convenient
mounting plate for frame-mount connectors? I haven't seen the explanation
for why this plate is used, not everyone has one, but the K9YC Choke
Cookbook shows a picture of it and I think k(YC has put more thought into
baluns/ununs than almost anybody so I value that picture -- still don't
know why to do it, but see that he is using it in his measurement jig."

Another caution: Not everything in K9YC's Choke Cookbook is technically
sound. It's a good guide, but understand what he and you are presenting
and constructing. I've locked horns with that publications a few times
right along with a few other technoids on the internet. For an excellent
understanding of baluns and unnnuns, I strongly recommend the subject as
treated at the following URL:

On this site all the information is well presented with absolutely minimal
math, is true to the engineering and physics of the issues, and is, well,
just golden. While it's not a technician-level how-to-build-the-wiget,
it's sound information!

The function of the metal plate is an attempt to isolate the NANOVNA or
measurement device from the DUT. Again, consider free space wavelengths.
In reality, the conducting plate only adds yet another error source to be
accounted for. Also, with the NANOVNA by itself - not connected to
ANYTHING, no USB, no charger cables... - at HF it is a very small portion
of a free space wavelength. The leads to/from the DUT pretty much negate
any possible decoupling the conducting plate might offer.

QUOTE: "Some guidance uses just one Nano port, others use both. Some have
PL-259's on both coax ends (for coax-wrapped baluns) which they plug into
SO-230-SMA adaptors straight into the Nano."

The source port, S11, souces RF energy and is capable of measuring various
REFLECTED parameters to anything connected to it, along. Possible
measurement examples are SWR, Return Loss (RL), and complex impedance (R ±
jX, or the Smith Chart).

A 2-Port measurement involves both the source port, S11, AND a RECEIVE
port. Is not doing, the 2-port setup is capable of measuring various
CONDUCTED or THROUGH parameters of a network or device. Possible
measurement examples are filter response, attenuator values, and amplifier
gain.

Each has its own application when it comes to the NANOVNA.

QUOTE: "Others demonstrate measurements with single-conductor wire-wrapped
baluns; still others have double triple, or quad wrapped single conductors
-- which wire ends do you connect to in these cases? All of them, or
should each one individually measure the same?"

As the saying goes, "there are many ways to skin a cat" (please, no offense
to you cat lovers!!). As so with baluns, matching transformers (which are
NOT baluns), unnuns, and the like. Common mode choke or current baluns,
unnuns, linear of toroidal, or wider frequency response, or...... All have
different techniques of winding and choices of circuit equivalent
topologies. Each has its strengths and weaknesses. Doing a serious read
of the DJ0IP reference I gave above will answer many of these questions.

I use toroidal bifilar wound common mode chokes (CMCs) in my antenna feed
system. I have a 450 set of wires fed with parallel conductor transmission
line. In the shack I install the CMC choke between the open wire line and
the input of my home brew single ended (common mode) L-network for matching
what the antenna/transmission line present in the shack to 50 ± j0 ohms. I
use similar chokes wound on both 31 and 43 ferrite material. No single
choke, balun, unnun,...... can properly serve 630 through 6-Meters. Again,
don't be misled by the 4:1 "transformers" indluded in many "antenna
tuners". For one, they don't "tune" the antenna. What's more, they are
only a transformer and NOT a balun and do NOT function well to match either
a higher impedance nor accomplish the transitiion from common mode (coax)
to differential mode (parallel conductor transmission line). There is no
such thing as "one size fits all". K9YC addresses this to a limited
extent. In short, if you go with toroidal cores, 43 material is best at
and above 20-meters. 31 material is best at and below 40-meters.

QUOTe: "Some guides show the use of resistors or capacitors in series or
parallel with the DUT -- are they always needed? What values? Most videos
do not show them being used, but enough do that I wonder if they improve
accuracy. (Kill parasitic capacitance or some such.)"

Two Pointers Here:

1) Resistors are linear and passive devices. They can absorb energy and
transform energy to a different form (current through the resistor into
hear - infrared). They do not change phases within a circuit or
measurement setup. Resistors are ideally not frequency dependent. In the
complex expression for impedance, R ± jX, resistors are the "R" term.

2) Capacitors and inductors are reactive. That is to write, they can and
do alter phases within a circuit or measurement setup. They can not absorb
energy or transform energy to a different forms. In the complex expression
for impedance,
R ± jX, reactive components are represented by the " ±jX" term. Capacitive
reactance is designated with the "-" sign and resides in the upper half of
the Smith Chart. Inductive reactance is designated with the "+" sign and
resides in the lower half of the Smith Chart.

Reactances can be used for matching sources/loads to each other. You may
see them in some measurement setups for this reason. Loss elements,
resistors, may be introduced to provide attenuation of a signal (maybe from
the outpout of an amplifier) to keep RF levels within proper ranges of the
RECEIVE, S22) port.


QUOTE: "What Nano menu items are selected for measuring the effectiveness
of a balun/unun? Logmag, phase, smith, resistance, reactance, .... The
thing we're actually looking for is Impedance, but the Nano doesn't offer
that directly. What other nano settings are needed? Range offsets, etc??"

1) The SOLE FUNCTION of a balun or unnun is to provide a bilateral
transition between common mode (CM) and differential mode (DM). Coaxial
cable functions as a CM transmission line. Parallel conductor cable
functions as a DM transmission line. A balun is NOT a transformer or
matching device which the suppliers of "antenna tuners" have you believe.

CM energy on the outside surface of a coaxial cable is, as stated, common
mode. Therefore, a proper balun or common mode choke (CMC) of unnun can
and does function to discourage CM currents from flowing on the coax outer
braid. In so doing it 1) keeps the coaxial feedline from becoming a
portion of the radiating structure and, 2) discourages CM energy from
degrading the received noise floor due to close-by RFI sources.

As such an important parameter to measure for baluns, unnuns, and CMCs is
the CMRR or Common Mode Rejection Ration. This can be measured with the
NANOVNA by measuring the total series inductance presented by the CMC,
balun, or unun. This can be accomplished either as a single (reflection)
or dual (transmission) port measurement. Most baluns, CMCs, and unnuns
form a reflective and absorptive "filter" for CM energy. Therefore, the
series inductance is important. And,....remember, that reflective property
is frequency dependent!

Loss through the CMC, balun, or unnun is also a major consideration.
Therefore, the transmission loss through the DUT should be made. This, as
well, is easily acomplished with the NANOVNAs configured in either the
single port (reflection) or dual port (transmission) port.

This has become WAY TOO LONG, But if you read it as well as the DJ0IP
reference, you will be well on your way. And don't forget my write-ups of
a couple of years ago on using the NANOVNA to make these measurements.

Oh, Yes, another excellent reference is *Reflections II Transmission Lines
and Antennas* by Maxwell, published by WorldRadio Books in paperback hard
print or online. I recently bought my copy for $20 on Amazon. It, as well
as the DJ0IP reference will explain many things all about RF and dispell a
plethora of half-truths and snake oil so prevalent in amateur circles.

Good luck!!!

I'm getting fatigued at typing.......???

Dave - W?LEV






On Thu, Mar 9, 2023 at 8:20?PM Steve Johnson <cascadianroot@...>
wrote:

I've been recently trying to piece together all the various conflicting
information on balun and unun measurement with the NanoVNA. The problem is
not a lack of tutorials, videos, instructions...it is the opposite -- there
are hundreds of such things available. However, they don't agree with each
other. And, even on this one forum (and other NaoVNA forums), when the
question comes up for a definitive guide, different sets of links are
provided! It appears there ISN'T a definitive guide, rather just a growing
assortment of good/bad/ugly opinions. So it becomes a problem of "which
advice should I believe?"

To give some examples:

- some folks how long leads (12-24") being used to connect the DUT to the
nano, other say you need to minimize these lengths (<4"). Still other says
it doesn't matter because when you calibrate the Nano it all comes out in
the wash.
- Some instructions show what appears to be a metal plate "shielding" the
nano from the DUT. Or maybe this is just a convenient mounting plate for
frame-mount connectors? I haven't seen the explanation for why this plate
is used, not everyone has one, but the K9YC Choke Cookbook shows a picture
of it and I think k(YC has put more thought into baluns/ununs than almost
anybody so I value that picture -- still don't know why to do it, but see
that he is using it in his measurement jig.
- Some guidance uses just one Nano port, others use both. Some have
PL-259's on both coax ends (for coax-wrapped baluns) which they plug into
SO-230-SMA adaptors straight into the Nano.
- Others demonstrate measurements with single-conductor wire-wrapped
baluns; still others have double triple, or quad wrapped single conductors
-- which wire ends do you connect to in these cases? All of them, or
should each one individually measure the same?
- Some guides show the use of resistors or capacitors in series or
parallel with the DUT -- are they always needed? What values? Most videos
do not show them being used, but enough do that I wonder if they improve
accuracy. (Kill parasitic capacitance or some such.)
- What Nano menu items are selected for measuring the effectiveness of a
balun/unun? Logmag, phase, smith, resistance, reactance, .... The thing
we're actually looking for is Impedance, but the Nano doesn't offer that
directly. What other nano settings are needed? Range offsets, etc??

So, you see, this is not a simply-answered question. The common
re-occurrence of the question is enough proof of that. And reading thorough
the boatload of possible linked answers is very time-consuming.

If anyone knows of a guide/video that specifically answers each of the
above questions then please share that one, definitive guide. Is there any
plan that shows how to build a generic balun/unun/choke test fixture that
can be re-used time after time on an assortment of such devices? And what
sets this recommendation apart from all the others (showing different
things?) Why should I believe the specifically recommended one?

--
*Dave - W?LEV*


--
Dave - W?LEV