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Hi,
Does anybody use this device to measure common mode choke impedance?
G3TXQ for instance suggested using |S21| and phase angle to recalculate X
and R of the DUT in the spreadsheet.
NANO VNA-F however has a bunch of formats for S21, including Resistance,
reactance, smith chart, etc. So it seems we can get both X and R directly
in traces without any external calculations
However, for instance, resistance and reactance readings of S21 are very
big. For instance, Port A and Port B shortened by kit's cable shows about
1.2 M of resistance and -500K of reactance at 7.2M frequency (CW). Both
values are not stable and actually are infinities...
While phase value looks OK (-0.15¡ã) and complex representation is OK as
well (1-j0).
Probably I miss some basics in understanding of S21....
Would you please (1) suggest the best way of getting common mode choke¡¯s
impedance with the device and (2) explain the S21 readings in different
formats...
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Hi Igor,
I can help with the search by typing the key words "common mode choke impedance" or shorter will result in more results in the Search window.
In the -F group, I see no such match.
Great learning opportunities here: and here:
73, Gyula HA3HZ
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Hi,
I do CMC-measurments by simply connecting the coax outer braid to the center of CH0 and CH1 and then trace 1 on LOGMAG and Channel 1 THROGH, see attached pictures. In my case the CMC is with ferrite mix 31 and intended to be used on HF. So frequency range is 2 MHz to 30 MHz.
73/Torbjorn
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Wouldn't you want to know what the resistive component of S21 is?
Dale W4OP
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Torbj?rn Toreson Sent: Sunday, February 9, 2020 10:52 AM To: [email protected]Subject: Re: [nanovna-users] Measuring CMC and S21 readings Hi, I do CMC-measurments by simply connecting the coax outer braid to the center of CH0 and CH1 and then trace 1 on LOGMAG and Channel 1 THROGH, see attached pictures. In my case the CMC is with ferrite mix 31 and intended to be used on HF. So frequency range is 2 MHz to 30 MHz. 73/Torbjorn
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Hi, Gyula,
Thanks a lot for very interesting links indeed. I need a time to digest it.
However, just interesting, which readings shows a ¡°big¡± VNAs in S21 if
short both ports with previously calibrated coax cable... It¡¯s clear for
logarithmic format and phase but what is about other formats, resistance,
reactance, etc...
Igor
§Ó§ã, 9 §æ§Ö§Ó§â. 2020 §Ô. §Ó 12:07, Gyula Molnar <gyula.ha3hz@...>:
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Hi Igor,
I can help with the search by typing the key words "common mode choke
impedance" or shorter will result in more results in the Search window.
In the -F group, I see no such match.
Great learning opportunities here: and here:
73, Gyula HA3HZ
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Why? The goal of the measurement described is to evaluate the impedance
(L) presented by the CM choke when installed in the feedline. Presuming
#14 or #12 wire is used, the DC (not the same as measured at frequency)
really washes out as its insignificant to the purpose of the choke.
Dave - W?LEV
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On Sun, Feb 9, 2020 at 4:07 PM Dale Parfitt <PARINC1@...> wrote: Wouldn't you want to know what the resistive component of S21 is?
Dale W4OP
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Torbj?rn Toreson
Sent: Sunday, February 9, 2020 10:52 AM
To: [email protected]
Subject: Re: [nanovna-users] Measuring CMC and S21 readings
Hi,
I do CMC-measurments by simply connecting the coax outer braid to the
center of CH0 and CH1 and then trace 1 on LOGMAG and Channel 1 THROGH, see
attached pictures. In my case the CMC is with ferrite mix 31 and intended
to be used on HF. So frequency range is 2 MHz to 30 MHz.
73/Torbjorn
--
*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*
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There is some debate on how the measured S21 common mode choke impedance actually effects the performance of an antenna system.
Here is one viewpoint by Owen Duffy as food for thought.....
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Some interesting thoughts on this subject by K6JCA with an extensive reference list on this topic at the end of his blog post.
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In my opinion the working of a CMC is to stop RF-currents on the outside of the braid, whether it originates from the antenna or from surrounding mostly vertically polarized disturbances. Thus these currents can not reach, or at least will be mitigated, the receiver. And the "return" current from the antenna will be confined inside the coax, so I don't have both a vertical antenna (if the coax is mostly vertical up to the antenna) by the coax and the real antenna. Because of RF skin effect the inside of the coax braid does not know anything about the outside and vice versa (if proper coax). I have made a simple instrument to measure the current on the coax outside, see picture. Without an CMC I can get high readings from currents on the outside, with an CMC there is no indication at all.
73/Torbjorn
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Exactly Roger- ignoring the reactive component and not knowing the resistive component - and also knowing the antenna system' complex Z can lead to worse CM. W8 JI, and Owen Duffy, in addition to the cited papers have also written on this subject.
Dale W4OP
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Roger Need via Groups.Io Sent: Sunday, February 9, 2020 4:05 PM To: [email protected]Subject: Re: [nanovna-users] Measuring CMC and S21 readings Some interesting thoughts on this subject by K6JCA with an extensive reference list on this topic at the end of his blog post.
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Hi Igor and others Just a small note There is a "snag" regarding converting a S21 measurement to impedance because the math used request that both the source and load impedance from both of the two calibration planes, where the DUT is inserted in between, must be pure 50ohm. That is not the case for a NanoVNA but for a VNA running full 12term error correction. Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] < [email protected]> P? vegne af Igor Lapko Sendt: 9. februar 2020 10:13 Til: [email protected]Emne: [nanovna-users] Measuring CMC and S21 readings Hi, Does anybody use this device to measure common mode choke impedance? G3TXQ for instance suggested using |S21| and phase angle to recalculate X and R of the DUT in the spreadsheet. NANO VNA-F however has a bunch of formats for S21, including Resistance, reactance, smith chart, etc. So it seems we can get both X and R directly in traces without any external calculations However, for instance, resistance and reactance readings of S21 are very big. For instance, Port A and Port B shortened by kit's cable shows about 1.2 M of resistance and -500K of reactance at 7.2M frequency (CW). Both values are not stable and actually are infinities... While phase value looks OK (-0.15¡ã) and complex representation is OK as well (1-j0). Probably I miss some basics in understanding of S21.... Would you please (1) suggest the best way of getting common mode choke¡¯s impedance with the device and (2) explain the S21 readings in different formats...
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I tried this connection with full through cal (excluded isolation) with the
HP 8753C. Shields were commoned at the junction of the coax from the two
ports. Choke was inserted between the S11 and S22 center conductors.
Readings were quite believable and reasonable in dB (log Mag). Among my
'collection' of CM chokes, I found one that didn't hit less than -30 dB
until 29 MHz and good to beyond 50 MHz with no resonances - happy camper.
It's now in my HF system between the output of the home brew L-Network and
the open wire feedline with considerably less RFI. I have not tried this
with the NANOVNA or the NANOVNA-F.
Dave - W?LEV
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On Mon, Feb 10, 2020 at 12:31 AM Kurt Poulsen <kurt@...> wrote: Hi Igor and others
Just a small note
There is a "snag" regarding converting a S21 measurement to impedance
because the math used request that both the source and load impedance from
both of the two calibration planes, where the DUT is inserted in between,
must be pure 50ohm. That is not the case for a NanoVNA but for a VNA
running full 12term error correction.
Kind regards
Kurt
-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af Igor
Lapko
Sendt: 9. februar 2020 10:13
Til: [email protected]
Emne: [nanovna-users] Measuring CMC and S21 readings
Hi,
Does anybody use this device to measure common mode choke impedance?
G3TXQ for instance suggested using |S21| and phase angle to recalculate X
and R of the DUT in the spreadsheet.
NANO VNA-F however has a bunch of formats for S21, including Resistance,
reactance, smith chart, etc. So it seems we can get both X and R directly
in traces without any external calculations
However, for instance, resistance and reactance readings of S21 are very
big. For instance, Port A and Port B shortened by kit's cable shows about
1.2 M of resistance and -500K of reactance at 7.2M frequency (CW). Both
values are not stable and actually are infinities...
While phase value looks OK (-0.15¡ã) and complex representation is OK as
well (1-j0).
Probably I miss some basics in understanding of S21....
Would you please (1) suggest the best way of getting common mode choke¡¯s
impedance with the device and (2) explain the S21 readings in different
formats...
--
*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*
|
G3TXQ's spreadsheet works very nicely after converting the format from the Nano to work with the format from the AIM 4170 (model?). I sure miss Steve! Learned a great deal from him over the years.
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That's what I'm trying to do with nanovna....
Which S21 values should i insert in Steve's spreadsheet ?
Which format conversion is needed ?
Federico
ik3umt
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Federico, I am running nanovna-saver-v0.2.0, that export .s2p file using the "RI" format (one column for the real part, another column for the imaginary part).?? I see that Steve's? spreadsheet uses as input the "MA" format (Magnitude in dB and Angle in degs). Delay column is not used by Steve's formulas.
I don't know if more recent versions of nanovna-saver allow to save .s2p file in MA format.? In any case you can modify the spreadsheet in order to use input data in "RI" format.
Best 73
Piero, I0KPT
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Il 29/09/2020 22:38, Federico - ik3umt ha scritto: That's what I'm trying to do with nanovna....
Which S21 values should i insert in Steve's spreadsheet ?
Which format conversion is needed ?
Federico
ik3umt
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Try the attached spreadsheet
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On Tue, 29 Sep 2020 at 22:38, Federico - ik3umt <ik3umt@...> wrote: That's what I'm trying to do with nanovna....
Which S21 values should i insert in Steve's spreadsheet ?
Which format conversion is needed ?
Federico
ik3umt
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Dragan, in the column "G" it is not correct to use ATAN function!??? The correct expression for cell "G3" is =DEGREES(ATAN2(D3;E3)))? The same for the following rows.
Piero, I0KPT
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Il 29/09/2020 23:03, Dragan Milivojevic ha scritto: Try the attached spreadsheet
On Tue, 29 Sep 2020 at 22:38, Federico - ik3umt <ik3umt@...> wrote:
That's what I'm trying to do with nanovna....
Which S21 values should i insert in Steve's spreadsheet ?
Which format conversion is needed ?
Federico
ik3umt
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You are correct, forgot that the equivalence does not hold when the real part is negative. Corrected and cleaned up version is attached. On Tue, 29 Sep 2020 at 23:36, Piero Tognolatti <piero.tognolatti@...> wrote: Dragan, in the column "G" it is not correct to use ATAN function! The
correct expression for cell "G3" is =DEGREES(ATAN2(D3;E3))) The same
for the following rows.
Piero, I0KPT
Il 29/09/2020 23:03, Dragan Milivojevic ha scritto:
Try the attached spreadsheet
On Tue, 29 Sep 2020 at 22:38, Federico - ik3umt <ik3umt@...> wrote:
That's what I'm trying to do with nanovna....
Which S21 values should i insert in Steve's spreadsheet ?
Which format conversion is needed ?
Federico
ik3umt
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Gyula Molnar
Roger Need
Kurt Poulsen