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PROCEDURES for MEASURING DM LOSS and CM ATTENUATION of CMCs


Siegfried Jackstien 2021/02/06 22:23

to compare chokes (when you have made a few and want to see what is best
for what appication) ... maybe put both values in one table?!?

you made one file to measure cm loss (common mode attenuation) and one
file to measure trough loss (differential mode attenuation) ... to see
what choke is best it would be good to see both values in a single file
(table)

but all overall ... GOOD WORK...WELL DONE

(i do know how to measure these things but it is a perfect write up for
a newcomer!!)

dg9bfc sigi

Am 06.02.2021 um 22:00 schrieb David Eckhardt:

David Eckhardt 2021/02/06 22:31

Both were aimed at the newcomers as step-by-step procedures to help get
used to using the NANOs and not be afraid of making a mistake. It's such a
useful instrument, I'll do about anything to encourage its use!
Personally, it belongs in every ham shack and as valuable as a DMM. It
should also find its place in every EE lab in the universities - just my
opinion.

I also have the data from a number of chokes I wound on various materials.
I've sent that out previously, but I've added to it for my own reference.
Siegfried, do you think that would be of any value to the group as well.
It presently is not in PDF format, but I could convert it if you believe it
would be of any aid to this group.

Dave - WØLEV

On Sat, Feb 6, 2021 at 10:23 PM Siegfried Jackstien <
siegfried.jackstien@freenet.de> wrote:

> to compare chokes (when you have made a few and want to see what is best
> for what appication) ... maybe put both values in one table?!?
>
> you made one file to measure cm loss (common mode attenuation) and one
> file to measure trough loss (differential mode attenuation) ... to see what
> choke is best it would be good to see both values in a single file (table)
>
> but all overall ... GOOD WORK...WELL DONE
>
> (i do know how to measure these things but it is a perfect write up for a
> newcomer!!)
>
> dg9bfc sigi
> Am 06.02.2021 um 22:00 schrieb David Eckhardt:
>
> It was requested by a number of responders that I convert to PDF. The
> attachments are in .PDF format which should be able to be read by
> everyone.
>
> There was also a request to place them in the files section of these
> NANOVNA sites. I am a member and will attempt that. However, if the
> moderators don't see them there, please place them there.
>
> Dave - WØLEV
>
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Siegfried Jackstien 2021/02/07 00:22

and you did that well ... a perfect step by step procedure for a newbie :-)

having a bunch of measured data sure is good ... so if you can make ONE
table from your tests that would be superb (cm and dm together) ... as a
third row maybe measure inductance?!? cause the series inductance is
what dampens the common mode current (as we all know a coil is an rf
resistor)

then you can have a rough idea what chokes do what ... have an idea how
many turns to use (depending what donut you find in your junk box) ...

at best an excel table ... cause that can then also brought to a
diagramm (a picture tells more then thousand numbers in a table)

when you measure a choke (dm or cm value) ... you can then see the sweep
from 160m to 10m with saver (or other soft) ... but when you have the
table with a dozen chokes ... and convert that in excel ... you have a
"sweep" for all chokes in a single view

just an idea from a dumb nut :-)

...........................

https://gm3sek.com/

http://www.ifwtech.co.uk/g3sek/in-prac/index.htm

https://www.nonstopsystems.com/radio/pdf-ant/article-cost-effective-chokes.pdf

https://gm3sek.files.wordpress.com/2019/01/G3TXQ-RC.pdf

a nice picture of "a few dozen" chokes on this page (scroll a bit down)
.... and on the bottom end ... a similar test jig like you used :-)

http://www.karinya.net/g3txq/chokes/

some more info?

http://k9yc.com/2018Cookbook.pdf




dg9bfc sigi

Am 06.02.2021 um 22:31 schrieb David Eckhardt:

Leon - NT8B 2021/07/28 10:22

Dave,

Thank you for creating and sharing these documents.  I have been searching for methodology to test the chokes I'm building for use in my radio operations and your documents are very helpful.

I have a newbie question relating to the NANO calibration procedure described in the document on CM attenuation measurement: how do you correctly connect the 51-ohm resistor when doing the load measurement step in the calibration?  I'm assuming the correct procedure is to attach one end of the resistor to the alligator clip that's connected to the CH0 port of the NANO, and the other end of the resistor is connected to the copper cladding on the test fixture.  What is the best way to ensure a good connection between the resistor and the copper surface of the test fixture?  Is it OK to hold it on the surface by hand or do you recommend another connection method, like using an alligator clip?

Again, with great appreciation and 73,

Leon NT8B

David Eckhardt 2021/07/31 14:53

It's generally OK to firmly grip the shield side of the connection to make
a good connection. However, do not get near the center conductor side of
the fixture. If you are doing differential measurements, do not hold
either side of the fixture. In measuring differential loss, you are making
a DM (differential mode) measurement and neither of the connections to/from
the VNA should be grabbed. When making a CM (Common Mode) loss
measurement, only one winding need be connected, and you are making CM
measurement so the coaxial braid side of the fixture side can be grabbed.
One caution when testing above 30 MHz: Do not use alligator clips or
banana jacks/plugs. With *GREAT care*, they can be used, but not above 150
MHz *AT ALL*!!!

I'm glad you found my postings useful. I initially made the measurements
for my own edification because I have the tools. Then I thought I could
help others by putting it all together. Thanks for the complement!

If I can't help others in retirement with the knowledge and common sense
I've gained over some 50 years professionally and in the hobby, it's time
for my own personal pine box.

On Wed, Jul 28, 2021 at 9:15 PM Leon - NT8B <lhb@brunerweb.net> wrote:

> Dave,
>
> Thank you for creating and sharing these documents. I have been searching
> for methodology to test the chokes I'm building for use in my radio
> operations and your documents are very helpful.
>
> I have a newbie question relating to the NANO calibration procedure
> described in the document on CM attenuation measurement: how do you
> correctly connect the 51-ohm resistor when doing the load measurement step
> in the calibration? I'm assuming the correct procedure is to attach one
> end of the resistor to the alligator clip that's connected to the CH0 port
> of the NANO, and the other end of the resistor is connected to the copper
> cladding on the test fixture. What is the best way to ensure a good
> connection between the resistor and the copper surface of the test
> fixture? Is it OK to hold it on the surface by hand or do you recommend
> another connection method, like using an alligator clip?
>
> Again, with great appreciation and 73,
>
> Leon NT8B
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Albert Kleyn 2021/08/01 09:06

I fully echo the sentiments expressed by Leon, NT8B, Dave... THANK YOU for
your encouragement , support and pearls of real life wisdom ! It is people
like you and several others here in this forum that help steer newbies
like me thru the uncharted NanoVNA swamp. We full well know Dave that you
could have chosen to "Sit by the pool, with the beautiful XYL, a Gin and
Tonic in one hand and a Pina Collada in the other, while looking at the
palm trees and the ocean" !!! Instead, you and a handful of others, are
voluntary here, helping/preventing raw novices like me from sinking
slowly under in the NanoVNA swamp.
It is appreciated much more that this short post can hope to express.
Albert. EI7II.

On Sat, 31 Jul 2021 at 21:53, David Eckhardt <davearea51a@gmail.com> wrote:

Wojtek SP9WPN 2021/08/01 03:15

Thanks Dave for the tutorials, great job.

I would like to add three bits on measuring CM suppression:
First, have a look at G3TXQ article (http://www.karinya.net/g3txq/chokes/) about unwanted reactance in chokes. Fortunately, our VNAs can measure these values, too. It's enough to:
1. Select "S21 R+jX series" chart
2. Adjust vertical scales of the chart to be same for R and X (to allow comparisons)
3. Watch for R being below |X|. Unfortunately there's no option to show |X|, so for negative values one it needs some axis-reading.

Second point, which I'm actually still investigating: it is easy to forget that RF connectors (N, SMA and others) are impedance-controlled only with a proper plug attached. Alligator clips are far from that, but I haven't yet determined amount of damage they induce (or capacite, hihi). Just a friendly warning, especially if you're reaching above 30MHz.

Lastly, I would discourage about pressing the foil to the ground plane with a finger. A flat paper clip would do much better. A plastic one even more. It is a good custom to keep your body and any other conductors (mind the tools!) at least few centimeters away from DUT. Touching or even keeping close to any part of RF system may skew results.

73s,
Wojtek SP9WPN

David Eckhardt 2021/08/01 12:04

And don't forget the hams who set up these groups so we could ask questions
and contribute. Without them, we might have our hands tied behind our
backs. Thank you, all of you!!!

Dave - WØLEV

On Sun, Aug 1, 2021 at 2:06 AM Albert Kleyn <ei7ii.ie@gmail.com> wrote:

> I fully echo the sentiments expressed by Leon, NT8B, Dave... THANK YOU for
> your encouragement , support and pearls of real life wisdom ! It is people
> like you and several others here in this forum that help steer newbies
> like me thru the uncharted NanoVNA swamp. We full well know Dave that you
> could have chosen to "Sit by the pool, with the beautiful XYL, a Gin and
> Tonic in one hand and a Pina Collada in the other, while looking at the
> palm trees and the ocean" !!! Instead, you and a handful of others, are
> voluntary here, helping/preventing raw novices like me from sinking
> slowly under in the NanoVNA swamp.
> It is appreciated much more that this short post can hope to express.
> Albert. EI7II.
>
> On Sat, 31 Jul 2021 at 21:53, David Eckhardt <davearea51a@gmail.com>
> wrote:
>
>> It's generally OK to firmly grip the shield side of the connection to
>> make a good connection. However, do not get near the center conductor side
>> of the fixture. If you are doing differential measurements, do not hold
>> either side of the fixture. In measuring differential loss, you are making
>> a DM (differential mode) measurement and neither of the connections to/from
>> the VNA should be grabbed. When making a CM (Common Mode) loss
>> measurement, only one winding need be connected, and you are making CM
>> measurement so the coaxial braid side of the fixture side can be grabbed.
>> One caution when testing above 30 MHz: Do not use alligator clips or
>> banana jacks/plugs. With *GREAT care*, they can be used, but not above
>> 150 MHz *AT ALL*!!!
>>
>> I'm glad you found my postings useful. I initially made the measurements
>> for my own edification because I have the tools. Then I thought I could
>> help others by putting it all together. Thanks for the complement!
>>
>> If I can't help others in retirement with the knowledge and common sense
>> I've gained over some 50 years professionally and in the hobby, it's time
>> for my own personal pine box.
>>
>> On Wed, Jul 28, 2021 at 9:15 PM Leon - NT8B <lhb@brunerweb.net> wrote:
>>
>>> Dave,
>>>
>>> Thank you for creating and sharing these documents. I have been
>>> searching for methodology to test the chokes I'm building for use in my
>>> radio operations and your documents are very helpful.
>>>
>>> I have a newbie question relating to the NANO calibration procedure
>>> described in the document on CM attenuation measurement: how do you
>>> correctly connect the 51-ohm resistor when doing the load measurement step
>>> in the calibration? I'm assuming the correct procedure is to attach one
>>> end of the resistor to the alligator clip that's connected to the CH0 port
>>> of the NANO, and the other end of the resistor is connected to the copper
>>> cladding on the test fixture. What is the best way to ensure a good
>>> connection between the resistor and the copper surface of the test
>>> fixture? Is it OK to hold it on the surface by hand or do you recommend
>>> another connection method, like using an alligator clip?
>>>
>>> Again, with great appreciation and 73,
>>>
>>> Leon NT8B
>>>
>>>
>>
>> --
>> *Dave - WØLEV*
>> *Just Let Darwin Work*
>>
>>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

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