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Hi

The choc of john its exactly an 1/1 balun made by a lot of ferrites, measuring a balun with an NanoVNA on a chack its a thing and results of balun mounted with a dipole antenna was a different subject, indeed the efficiency of a balun depend on frequency's , dipole designe and how the external shield was used ... Just an other subject.
Normalised measurement of balun is simplfyed to an S11 IzI or S21 thru measurements
73s Nizar

On Tue, Apr 15, 2025 at 10:44 PM, Team-SIM SIM-Mode wrote:

S21 thru Logmag measurement is prefered to be done with a 150 Ohm renormalized
Z0

I think this is not correct in this case, Nizar. Measuring the choke is not measuring a transmission line with specific characteristic impedance that needs matched; it is more like measuring an inductor - and that should be done at the 50-ohm impedance of the nanovna.

I wouldn't really describe this as a "common mode" (although that is used) - it's really better conceptualized as a third wire which is connected to the feedpoint, as Roger said. As noted, the choke adds an impedance in the wire.

Roger's other comment is well taken - what you measure on the bench may not be what's in practice.

You can play around with this in NEC pretty easily. I just add a wire to represent the coax shield (outside) and throw a lumped load in where needed.

Unfortunately, NEC doesn't have a way to have a frequency varying load, but I've done that in Python to generate NEC input files. 4NEC2 or EZNEC might have a way to do it. FairRite publishes .xls files with the properties of the materials, which you can use to to calculate R and X.



#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
routines to read ferrite data sheets
and calculate series impedance given frequency, etc
Created on Tue Aug 25 15:40:15 2020
@author: jimlux
"""
import matplotlib.pyplot as plt
import os
import numpy as np
""" typical file from FairRite:
77 material,,
Frequency(Hz),µ',µ''
1.00E+04,1989,14
1.00E+05,2001,37
"""

def readdata(filename):
""" encoding needed, because there's a "mu" character in the file, and UTF-8 dies"""
mu = np.genfromtxt(filename,delimiter=',',skip_header=2, encoding='Latin-1')
return (mu)
def toroidLzero(N,OD,ID,Length):
""" returns Lzero in nanoHenry, given dimensions in mm
"""
L0=0.0461 * N**2 * np.log10(OD/ID) * Length * 10
return(L0)

class ferriteloading:
""" class to support generalized management of ferrite properties"""
def __init__(self):
self.datatab={}

def addmix(self, filename,mixid=None):
""" adds a new mix to the library. Mix is specified as a csv file, from FairRite.
if a mix id isn't specified, the first two characters of the filename are used.
mix ids are *strings*
"""
mutab = readdata(filename)
muf = np.array(mutab[:,0])
mu = np.array(mutab[:,1] + 1j * mutab[:,2],dtype=complex)
if not mixid:
mixid = os.path.split(filename[:2])[1]
if not isinstance(mixid,str):
mixid = "%d"%mixid
self.datatab.update({mixid:[muf,mu]}) #if we make this a 2d array, then frequencies are complex


def mu(self,mix,freq):
if not isinstance(mix,str):
mix= "%d"%mix
x=self.datatab[mix]
mu = np.interp(freq,x[0],x[1])
return mu


if __name__ == "__main__":
mixlist = [31,73,75,76,77,78]
OD = 4.0
ID = 3.0
Length = 1000.
Lzero = toroidLzero(1, OD, ID, Length)

for mix in mixlist:
mixfile = "%2d-Material-Fair-Rite.csv"%mix
print(mixfile)
mu = readdata(mixfile)
f = mu[:,0]
muprime = mu[:,1]
mudoubleprime = mu[:,2]
omega = 2 * np.pi * f
R = omega*mudoubleprime * Lzero * 1E-9
X = omega * muprime * Lzero * 1E-9
plt.figure()
plt.semilogx(f,R)
plt.semilogx(f,X)
plt.title(mixfile)
plt.xlabel("Frequency")
plt.ylabel("Ohms")
plt.legend(["Real","Imag"])
plt.grid()
plt.savefig("%2d-mix.png"%mix)


""" now test the class based implementation """

ferrites = ferriteloading()
for mix in mixlist:
mixfile = "%2d-Material-Fair-Rite.csv"%mix
print(mixfile)
ferrites.addmix(mixfile,mix)

for mix in mixlist:
print(mix,ferrites.mu(mix,1e6))

Users of a Maxwell or W2DU choke need to be aware that the effectiveness in reducing common mode current is not directly related to the magnitude of the impedance |Z| or S21 loss that they measure using a VNA.

When a balanced dipole is fed with an unbalanced transmission line, like coaxial cable, there will be RF radiation from the coaxial cable. The reason why requires some explanation. The power fed to the antenna travels along the inner conductor and the inner surface of the coax shield. The outer surface of the shield is separated from the inner surface due to the skin effect which takes place at RF frequencies. In effect the outer surface of the shield is a "third wire" which is connected to the half of the dipole attached to the shield at the feedpoint. So the antenna now consists of one wire connected to the inner conductor and two wires connected to the shield. The end result is that current is flowing on the outer surface of the shield. The common mode current level will depend on many factors such as operating frequency, the antenna geometry, length of the coax and how grounding is done at the transmitter end.

A Maxwell or W2DU ferrite choke effectively places an inductor in series with the outer surface of the shield. This inductor will have a complex impedance (resistive R and reactive X) that is determined by the ferrite mix, physical parameters of the core and the number of turns. The more resistive the better but the value of X can work for or against reducing common mode current. When considering the inductor as a "loading coil" most readers will know that this can make a radiating element have increased current flow (and hence better radiation at a specific frequency) because the inductive reactance can cancel capacitive reactance. So when measuring the Maxwell one needs to aware that measuring |Z| or S21 on the bench and making assumptions can lead to false conclusions. Making S11 measurements of R and X on a NanoVNA can be accurate to 5% or so up to several thousand ohms as I have shown in other measurement posts in this group.

The bottom line is that S11 or S21 measurements can give some insights into choke parameters but the only real test of effectiveness is to build a simple RF current meter that can slope up and down the coax and measure the actual common mode current.

Roger Need

On Tuesday 15 April 2025 03:00:25 pm DouglasK wrote:

I have a NanoVNA (2.8" screen) from about 2020. Overall it works well, but the Jog Switch doesn't do anything.

The touch screen works fine, it calibrates OK and measures SWR with ease... but the jog switch doesn't do anything. Should it do anything?

I had bought one off ebay and it arrived in the smallest possible box, and when I took it out of the box that switch was at a rather odd angle, and did nothing. I returned that one, no issues with the seller, and ultimately bought one from R&L...


--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

Hi

S11 Smith measurements or S11 IZI is also possible , it should have higher then 1500 Ohm as mentionned by the paper , no care with one wire or two wire connected together , it should be very similaire .

S21 thru Logmag measurement is prefered to be done with a 150 Ohm renormalized Z0 and have more then 20db attenuation, this needs Dislord firmware renormalisation function , not all NanoVNA's has this advanced function, NanoVNA-H or H4 , liteVNA. Has it .
73s Nizar

I find the jog wheel quite useful for moving the marker. Alternatively you
can use the Search Minimum function in the menu to find minimum SWR point
in the tracing.

I have not opened the casing for fear of damaging it! Even now, there is
some loose contact somewhere: Sometimes when I switch on, the screen is
blank. Switch off and switch on, the screen comes up well.

73

Jon, VU2JO

On Wed, Apr 16, 2025 at 12:30?AM DouglasK via groups.io <VE3YDK=
[email protected]> wrote:

I have a NanoVNA (2.8" screen) from about 2020. Overall it works well, but
the Jog Switch doesn't do anything.

The touch screen works fine, it calibrates OK and measures SWR with
ease... but the jog switch doesn't do anything. Should it do anything?

Firmware is reasonably current with version 1.2.43 (p: 101 IF: 12k, ADC:
192K, Lcd:320x240)
Build time: Feb 19 2025 - 21:39:08

Am I missing anything by just using it via touch screen? An inquiring
mind wants to know!

--
---
Do Justly Love Mercy. Walk Humbly.

Ooooopps...... I looked at the picture but saw what I expected: Coax.
Thanks, Stan, for bringing this to my attention.

Test just like my common mode chokes on toroids. Either or both wires will
do.

Dave - W?LEV

On Tue, Apr 15, 2025 at 8:28?PM Stan Dye via groups.io <standye=
[email protected]> wrote:

In this case, Dave, if you look at his picture, he is using two wires for
the choke conductors, not a coax. So either or both wires together should
work.

--

*Dave - W?LEV*


--
Dave - W?LEV

The jog wheel is an a control that allows an alternate way to bring up the menu and select the menu items.
So if you are happy with doing it on the touch screen, you are not missing much. There are some things that are (to me) more convenient with the jog wheel, such as moving / positioning the cursor, etc.
You can probably replace the jog wheel if you want to - or maybe just touching up its solder joints to the main board would restore functionality.

In this case, Dave, if you look at his picture, he is using two wires for the choke conductors, not a coax. So either or both wires together should work.

To clarify, it's a NanoVNA H (classic) and matches the image for a good model in the Wiki.

--
---
Do Justly Love Mercy. Walk Humbly.

I have a NanoVNA (2.8" screen) from about 2020. Overall it works well, but the Jog Switch doesn't do anything.

The touch screen works fine, it calibrates OK and measures SWR with ease... but the jog switch doesn't do anything. Should it do anything?

Firmware is reasonably current with version 1.2.43 (p: 101 IF: 12k, ADC: 192K, Lcd:320x240)
Build time: Feb 19 2025 - 21:39:08

Am I missing anything by just using it via touch screen? An inquiring mind wants to know!

--
---
Do Justly Love Mercy. Walk Humbly.

Since the center conductor closes fields to the interior surface of the
coax shield, it does not interact with external fields. Therefore, it's
only necessary to connect the outer shield between the two ports of the
NANOVNA. Don't be concerned about the center conductor.

Yes, you should measure S21 at something greater than -20 dB (more negative
is more better).

Dave - W?LEV

On Mon, Apr 14, 2025 at 12:47?AM Stan Dye via groups.io <standye=
[email protected]> wrote:

I do a 'loss' measurement rather than an impedance measurement. To do
this, do a 'through' measurement (S21), either on a single wire, or both
wires together, connected to the center pins of the nanovna leads - either
measurement method should show you the same results. The ground (shield)
of the leads to the nanovna should be connected together. A good choke
should give >20dB of S21 loss across the frequency range of interest - the
more loss (attenuation) the better.

--

*Dave - W?LEV*


--
Dave - W?LEV

I do a 'loss' measurement rather than an impedance measurement. To do this, do a 'through' measurement (S21), either on a single wire, or both wires together, connected to the center pins of the nanovna leads - either measurement method should show you the same results. The ground (shield) of the leads to the nanovna should be connected together. A good choke should give >20dB of S21 loss across the frequency range of interest - the more loss (attenuation) the better.

I have made a Maxwell choke for my ladder line feed to my doublet. I would like to check the common mode impedance with the nanovna. Do I just use one of the wires for the reading or both? A diagram of it is in the photos section. It looks like this....
/g/nanovna-users/album?id=301856

John K0JHL

On Sun, Apr 13, 2025 at 02:14 PM, CLIFTON HEAD wrote:
Hi you con download the nanovna-App at



some time is sufficient to search on the messages of one of the io.groups devoted to nanovna .
Maurizio IZ1MDJ

I have problems with the NanoVNAsaver this would be helpful. The app that
comes up is under development
I see nothing more. Can you please give a link for what your talking about.

________________________________
From: [email protected] on behalf of Roger Need via groups.io
Sent: Sunday, April 13, 2025 12:47 AM
To: [email protected]
Subject: Re: [nanovna-users] Windows 11 & NanoVNA H4

Mark,
If you use NanoVNA app (not NanoVNA Saver) you can remote the screen to your
PC. If you have a projector or large TV display then your audience can see
what you are doing right on the NanoVNA itself.

Roger

I have problems with the NanoVNAsaver this would be helpful. The app that comes up is under development
I see nothing more. Can you please give a link for what your talking about.

________________________________
From: [email protected] on behalf of Roger Need via groups.io
Sent: Sunday, April 13, 2025 12:47 AM
To: [email protected]
Subject: Re: [nanovna-users] Windows 11 & NanoVNA H4

Mark,
If you use NanoVNA app (not NanoVNA Saver) you can remote the screen to your PC. If you have a projector or large TV display then your audience can see what you are doing right on the NanoVNA itself.

Roger

Mark,
If you use NanoVNA app (not NanoVNA Saver) you can remote the screen to your PC. If you have a projector or large TV display then your audience can see what you are doing right on the NanoVNA itself.

Roger

Dean,

Had a look at the NanoVNAsaver page. The wiki does not seem to have a 'How
to get started page'. Can you please give some tips for getting started?

73

Jon, VU2JO

On Sat, Apr 12, 2025 at 6:45?PM Dean - KC9REN via groups.io <deanberg2044=
[email protected]> wrote:

Mark, I know of NanoVNAsaver as software
to be run on your laptop. There is a little bit of a learning curve using
the software but there are a number of Youtube videos on the subject too.
Once you use it, you will like it even more than just poking at the NanoVNA
screen. So much more info is shown on the computer. There may be other
software packages but I'm not aware of any at this time. Good luck on your
presentation.
Dean - KC9REN

Mark, I know of NanoVNAsaver as software to be run on your laptop. There is a little bit of a learning curve using the software but there are a number of Youtube videos on the subject too. Once you use it, you will like it even more than just poking at the NanoVNA screen. So much more info is shown on the computer. There may be other software packages but I'm not aware of any at this time. Good luck on your presentation.
Dean - KC9REN