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My Antennas also used to sell a high power (5kw 2-30MHz) 1:1 balun using cascaded sections.

Probably two stacked mix 61 on the left and two stacked mix 43 or 52 on the right (but that is just a guess).



--
Regards,

Martin - G8JNJ

Hi Dave,

Interesting stuff, as always a learning experience and as you say very much a work in progress.

Steve, G3TXQ (SK) has some additional charts on his chokes webpage , which are a good starting point for any balun constructors.



These extra charts show the optimum frequency range (black line) for popular ferrite mixes, numbers of cores and numbers of turns.









No single design can provide ideal performance from 1.8 to 30MHz, but you can either choose a design that provides the most useful frequency range, or use multiple chokes to achieve the required characteristic. You can't stack a mixture of cores to achieve this, but you can cascade them.

DX Engineering's "Maxi-Core" method of using multiple ferrite tubes to form large binocular cores, are another method of construction that could be considered.



Regards,

Martin - G8JNJ

Today I wound 18 turns of the DaviswRF superflex #14 wire bifilarly on two
stacked 2.5-inch OD red cores (Type 2 material). The results were as
predicted by Martin:
1) Not much isolation due to series inductance of the windings as a CM
choke - only about 50-ohms. CONCLUSION: No good for a CM choke at HF
2) Nice sharp resonance at about 14 MHz. CONCLUSION: No good for MC
choke at HF.
USES of RED, TYPE 2 MATERIAL: Related to high-Q inductors at HF.

The 2.5" core of 43 material wound in bifilar manner with AWG #12 solid
copper conductor turns capacitive at roughly 22 MHz - hits the real axis of
the Smith Chart - resonance - at that frequency. However, as a CM choke,
it looks pretty good with a 50-ohm non-resistive load and not too bad with
resistive loads of 10, 23.5, 50, 100, and 200 ohms from 0.5 through its
resonance point. It would serve OK as a CM choke from 160 through 18
meters with minimum inductive reactance of 800 ohms over that range.

But, I have a better solution for my applications which I have been using,
but never measured on the VNA. It was chosen for maximum suppression of CM
noise of all the chokes I've wound and tested to date. It is wound in
bifilar manner of DavisRF #14 superflex stranded and insulated wire on two
stacked 3" OD 43 material cores. The stacked cores are 1" thick, total.
Measuring the inductance which is the important factor when used as a CM
choke was quite rewarding. I shorted both ends of the choke and measured
the inductance (inductive reactance) in a single-port series
configuration. Worst case measured in excess of 1.2 kohms while best case
was in excess of 2 kohms over a frequency range of 0.5 through 30.5 MHz.
Connected as a single-port measurement as a CM choke, open circuit just
fills the bottom (capacitive) semicircle of the Smith Chart and short
circuit just fills the upper semicircle (inductive) portion of the Smith
Chart over that frequency range. And..... there were no resonances. I
even checked phase and there was no 'flip' or tangent (45 degrees)-looking
function , again, indicating no resonances over that frequency range. I
couldn't ask for more! So......that will become my CM choke in the antenna
feed system at the output of the matching network from here on. It is
likely an overkill even for 1.5 kW, but I built it from what I had on
hand. With 5-minutes of key-down in CW at 1.5 kW on 14 MHz into a dummy
load (1 kW Bird load), I note a slight amount of heating in the conductors,
but not the core.

Tomorrow: The single one-turn core over both conductors to indicate
balance between the conductors of the open wire feeders.

CURSE OF HAVING GOOD TEST EQUIPMENT (including the NANOVNA's): Nothing is
ever complete and always a work in progress.......????

Dave - W?LEV

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

On 11/9/20 12:51 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:

On Mon, 9 Nov 2020 at 18:03, Barry Feierman <k3euibarry@...> wrote:

Here is my next iteration (PDF) of a summary of "Antenna Fundamentals and
Measurements with a Nano VNA".

Comments are appreciated as I am going to be giving a talk with SOME of
these slides at local radio clubs.

TU
Barry k3eui
Philly region

A couple of comments, after a very quick skim read.
1) You say the loss in a coax is due to I^2 R and V^2 / R. However, it's
not the same value of R. You might consider using Rc for the conductor
losses, and Rd for the dielectric losses, where Rd >> Rc. However, these
are not resistors you would measure on a multimeter. Copper losses will
certainly increase with frequency, which I think you cover, and dielectric
losses may too - it depends on the dielectric.

It's actually I^2*R and V^2*G in the traditional formulation, where G is the dielectric "conductivity" (= 1/R in some sense).
And yes, they are different. G tends to be increasing with frequency linearly.

R increases as 1/sqrt(f) due to skin effect. For most coax, up to 100 MHz, the IR losses are much bigger than the dielectric losses.

That's why the usual transmission loss formula has two coefficients - loss = k1*sqrt(f) + k2*f

2) You talk about efficiency of an antenna, but don't define it. Most
people don't have a clue what efficiency is. The generally accepted
definition amoung professionals comes from IEEE standard 145. Efficiency is
the power radiated divided by the power absorbed by the antenna. Note the
word absorbed - it has nothing to do with the incident power. So if you
have a crap SWR, you transmit 100 W, 99 W gets reflected, and 0.95 W gets
radiated, then the antenna is 95% efficient, despite you would probably not
consider it a very good antenna.

I agree - Efficiency is a tricky word when associated with antennas. I try to stay away from it, and find some other way to describe what it is -
there's "mismatch effects", and "loss effects" - you could have an efficient antenna (low antenna loss) but with system loss because of mismatch and a lossy transmission line.

On Mon, 9 Nov 2020 at 18:03, Barry Feierman <k3euibarry@...> wrote:

Here is my next iteration (PDF) of a summary of "Antenna Fundamentals and
Measurements with a Nano VNA".

Comments are appreciated as I am going to be giving a talk with SOME of
these slides at local radio clubs.

TU
Barry k3eui
Philly region

A couple of comments, after a very quick skim read.

1) You say the loss in a coax is due to I^2 R and V^2 / R. However, it's
not the same value of R. You might consider using Rc for the conductor
losses, and Rd for the dielectric losses, where Rd >> Rc. However, these
are not resistors you would measure on a multimeter. Copper losses will
certainly increase with frequency, which I think you cover, and dielectric
losses may too - it depends on the dielectric.

2) You talk about efficiency of an antenna, but don't define it. Most
people don't have a clue what efficiency is. The generally accepted
definition amoung professionals comes from IEEE standard 145. Efficiency is
the power radiated divided by the power absorbed by the antenna. Note the
word absorbed - it has nothing to do with the incident power. So if you
have a crap SWR, you transmit 100 W, 99 W gets reflected, and 0.95 W gets
radiated, then the antenna is 95% efficient, despite you would probably not
consider it a very good antenna.

I bought one some time ago but never used it much.
Had issues yesterday trying to upgrade the firmware so I ordered a newer one from Amazon.
Should be here today.
I'll take it into the lab tomorrow and see how accurate it is.

Quote (Martin): " More than one choke and different construction may be
required in order to achieve satisfactory operation over a wide frequency
range."

I certainly can confirm that statement from practice. My antenna matching
network is always a work in progress, including the input and output CM
chokes.

More data coming as I wound yet another CM choke yesterday using 3 stacked
2.5" (6.4 cm) #43 material cores with 18 bifilar turns of AWG #12 solid
copper conductor. That took some time with that large gauge conductor
(and less obvious fingerprints as a result)!

That came about after considering my output CM choke on the matching
network (L-Network). I had chosen for that position in the antenna feed
setup a choke (all home made and measured on the HP 8753C) that gave the
best CM rejection from the home appliance SMPS's (with love from China).
I'm in the country and don't even see any city lights at night, so most of
the extraneous noise, other than the usual atmospheric and celestial noise,
is due to the house. Remember, in the good 'ol USofA, FCC excludes home
appliances from any and all regulations addressing conducted and radiated
emissions (good lobby in Congress, I guess). The choke I had in place
measured 500 and 2k ohms over the frequency range of 1.8 to 14.5 MHz.
While that was pretty good, I had the stack of 2.5" 43 material in the
parts cabinet which I had never wound. So, with this discussion, it was
ripe for winding and improvement on the final CM choke in the antenna feed
system. That writeup is coming once I determine and am happy with all the
measurements I can possibly make on that new choke.

Oh, Yes, your suggestion, dahhhh........ (on my part), of passing both
conductors through a common core as a balance monitor for currents in the
two conductors of my open wire feeders will be undertaken and reported on
as well!

Hey, guys and gals, all this would not be possible without the advent of
the NANOVNA's and the moderators having set up this www site (I once worked
with Dave Daniels). THANK YOU!!!

Dave - W?LEV


On Mon, Nov 9, 2020 at 11:08 AM Martin via groups.io <martin_ehrenfried=
[email protected]> wrote:

On Sun, Nov 8, 2020 at 05:24 PM, David Eckhardt wrote:

I could measure total
current on each conductor, and ultimately 'sum' the results to obtain the
expected zero with no CM current.

Hi Dave,

Great stuff, I'm pleased that you have been motivated to make the
measurements, and I'm keen to discover the outcome.

Ideally you would be able to sum the individual amplitudes and phases of
the two conductors forming the transmission line, but it is often easier to
pass both conductors through the same RF current transformer in order to
ensure that you are seeing the true picture.

One of the big Fair-Rite clip-on ferrites is ideal for this purpose.

It has been pointed out to me privately that many of the diagrams that can
be found on-line, showing how common mode current flows and how a choke
balun works, are actually flawed, as the common mode current is shown as
only flowing on one side of the choke, which is impossible. I think this is
simply an illustrative error, made in order to try and simplify the
diagrams, but it can lead to further confusion.

A choke will impede the overall flow of common mode current (on both sides
of the choke) and its reactive component may also lead to phase changes
occurring, which will modify the field radiated by the conductor it is
placed on. So it's not a totally predictable mix, as there are lots of
different interactions going on, especially when the reactance of the choke
is likely to change with frequency, and the conductor common mode standing
wave pattern will also vary with frequency. Which is why it's a good idea
to attempt to quantify the effectiveness of chokes when placed in circuit
at the required frequency(s) of operation. More than one choke and
different construction may be required in order to achieve satisfactory
operation over a wide frequency range.

--
Regards,

Martin - G8JNJ

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

Here is my next iteration (PDF) of a summary of "Antenna Fundamentals and Measurements with a Nano VNA".
I am still learning a lot about this gadget and how to interpret the various graphs.
I've heard you need to do a careful "calibration" to have meaningful results.
I mostly work at HF and mostly on 80m or 20m.

Once you have the fundamentals (new vocabulary) it is rather amazing that a $50 device can tell you so much about
resistance, reactance, impedance, resonance, SWR and phase.

Comments are appreciated as I am going to be giving a talk with SOME of these slides at local radio clubs.

TU
Barry k3eui
Philly region

Dear Marti,

After reading your guide, I have one word for you: it is fantastically well done, a joy to read, and enormously helpful

Well done.

And most importantly, thank you.

Don
Km4udx





Don

On 11/9/20 8:08 AM, Mark Sedutto wrote:

TDR measurments are not significantly affected by wire being coiled. If it had ferrite sleeves on it maybe, but not just coiled, and certainly not a large diameter coil. Youll likely have a greater error from temperature.

I can't imagine anything on the outside of the coax (ferrite sleeves, iron pipe, anything) having an effect unless it's coax with a leaky shield. (they actually make deliberately leaky coax, for things like distributing radio signals in mines and tunnels)

TDR measurments are not significantly affected by wire being coiled. If it had ferrite sleeves on it maybe, but not just coiled, and certainly not a large diameter coil. Youll likely have a greater error from temperature.

On Sun, Nov 8, 2020 at 05:24 PM, David Eckhardt wrote:

I could measure total
current on each conductor, and ultimately 'sum' the results to obtain the
expected zero with no CM current.

Hi Dave,

Great stuff, I'm pleased that you have been motivated to make the measurements, and I'm keen to discover the outcome.

Ideally you would be able to sum the individual amplitudes and phases of the two conductors forming the transmission line, but it is often easier to pass both conductors through the same RF current transformer in order to ensure that you are seeing the true picture.

One of the big Fair-Rite clip-on ferrites is ideal for this purpose.

It has been pointed out to me privately that many of the diagrams that can be found on-line, showing how common mode current flows and how a choke balun works, are actually flawed, as the common mode current is shown as only flowing on one side of the choke, which is impossible. I think this is simply an illustrative error, made in order to try and simplify the diagrams, but it can lead to further confusion.

A choke will impede the overall flow of common mode current (on both sides of the choke) and its reactive component may also lead to phase changes occurring, which will modify the field radiated by the conductor it is placed on. So it's not a totally predictable mix, as there are lots of different interactions going on, especially when the reactance of the choke is likely to change with frequency, and the conductor common mode standing wave pattern will also vary with frequency. Which is why it's a good idea to attempt to quantify the effectiveness of chokes when placed in circuit at the required frequency(s) of operation. More than one choke and different construction may be required in order to achieve satisfactory operation over a wide frequency range.

--
Regards,

Martin - G8JNJ

On Sun, Nov 8, 2020 at 08:23 PM, Stan Dye wrote:

Two simple notes to consider adding:

- The firmware gives reasonable defaults for the scale and reference line
for many use cases, so you only need to set them if you need them to be
different.
- When you save a calibration, it also saves the display settings, so you
can easily recall the whole setup.

(I note these because the list of setup tasks for each measurement seems
long and maybe intimidating if I have to do them for every measurement -
but it's not nearly as bad as it seems.)

Stan KC7XE

Very good idea. I will do that. Thank you Stan.

Also I have corrected some misspelled words - thank you Mike.

Martin 9A2JK

John

You don't state which manufacturer of cable but I know some years ago that Andrew used to number their coax every meter so if you're able to ascertain the right number on the cable [easy] and access the other end, you should be able to confirm your nanoVNA measurement!

Best of luck and I, for one would be interested on how accurate you find the nanoVNA compared to the expensive VNA.

73, Bob
G1ZJP

Thanks for the info, guys. We use heliax to feed a transponder antenna and the indoor end is connected to a special N connector made for the cable. We have a ton of N-to-SMA adapters. We also have a $$$ VNA at work but I also want to test it with the nano for comparison, just didn't know if the cable being coiled would matter.

Thanks again,

--
John AE5X

Yes, at the factory they are typically tested on the spool.
You are looking at internal fields, coiling the coax up makes no difference.
73 Kent WA5VJB

Fantastic job.
I have practicly every manual for the NanoVNA H that I could get my hands on to learn the NanoVNA. Not to degrade the other manuals, but yours seem to be the most useful for a old beginner like me.
Thank you and all others who help us to learn and use the NanoVNA to its fullest.
Now, we need one like yours for the NanoSA.
Again thank you.
73's
Clyde Lambert KC7BJE

On 11/8/20 12:17 PM, John AE5X wrote:

Hello all,
I don't have much experience using TDR's in general and am wondering if they can accurately measure cable length if the cable is coiled rather than deployed in a more typical manner? At my work QTH we have a length of heliax on a big wooden spool and no one knows how much of it there is, nor can we easily count the number of coils on this stuff. It is quite rigid and we'd like to not have to unroll it.
Thanks/73,

that is the perfect use for a TDR.

I am no expert, (I have only used TDR with Nanosaver on short lengths with multiple connections -every single connector showed up with a slight blip) but I see no reason for a TDR measurement not to work. It does not matter that the wire is coiled although there might be some uncertainty at the far end ; hopefully it is open circuit at the far cut end, but the last inch might be crushed. What you hope is that there is not a perfect 50 ohm load at the far end! You need to set the vna to the highest possible upper frequency for short lengths (1mm to a metre) but have the lowest start frequency for long lengths.

The biggest difficulty will be to get a decent connection to the heliax. I do not know how you connect Heliax to sma. I suppose very short wires soldered to the sma connection should be ok for the far end measurement. You might even get a clean enough signal to confirm that there is no damage somewhere on the coil.

Steve L

Hello all,

I don't have much experience using TDR's in general and am wondering if they can accurately measure cable length if the cable is coiled rather than deployed in a more typical manner? At my work QTH we have a length of heliax on a big wooden spool and no one knows how much of it there is, nor can we easily count the number of coils on this stuff. It is quite rigid and we'd like to not have to unroll it.

Thanks/73,
--
John AE5X