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On Wed, May 14, 2025 at 06:50 AM, Team-SIM SIM-Mode wrote:

Here My message about RG213 coax measurements posted here on Avril 5 2025:

for My RG213 cable (25m length) loaded by a 50.3 Ohm resistor ,
I used the centered impedances circle methode on smith graph with the
renormalized Z0 impedance ( option added by DiSlord) for different ferquency's
band (span always fixed to 4 Mhz) :

2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
50Mhz ---> Zc = 49.0 Ohm
100Mhz ---> Zc = 43.5 Ohm

Your measurements do not agree with the calculated values for typical RG213. The characteristic impedance of Belden coax is around 50.6 ohms at 1 MHz and slowly decreases to about 50 ohms at 100 MHz. You can see that in the attached graph which is based on the parameters for this type of cable. It decreases because the inductance is decreasing with frequency.

The problem with your test method is that you will not have a pure resistance at the end of the cable as the frequency is increased. Any resistor (including SMD) will have some series inductance and there will also be capacitance across the resistance. The reactance associated with these components will be small at low frequencies but will be considerable at your highest measured frequency of 100 MHz. This is particularly true if you try to use any kind of small adjustable potentiometer for your test.

The end result is that your measurements will not be correct because you don't have a pure resistance load to base your measurements on.

Only one of the methods I presented involved a formula. What the dickens
is wrong with a little very simple algebra??

The other two methods are simple and only need a non-reactive
potentiometer, a VNA, or a DMM.

Why have you taken offense to my offering?

Dave - W?LEV

On Wed, May 14, 2025 at 10:58?PM Team-SIM SIM-Mode via groups.io
<sim31_team@...> wrote:

Hi Dave

I believe that everything I have presented here has already been
demonstrated both experimentally and graphically, without relying on
formulas or theoretical estimations. Nevertheless, approximation methods
are always possible, depending on the required level of accuracy."
73s Nizar

--

*Dave - W?LEV*


--
Dave - W?LEV

Hi Dave

I believe that everything I have presented here has already been demonstrated both experimentally and graphically, without relying on formulas or theoretical estimations. Nevertheless, approximation methods are always possible, depending on the required level of accuracy."
73s Nizar

QUOTE: In such a case, the measurements will be distorted by the
transformation introduced by the CRC's twin-lead line.

These CMCs are not made of just "twin lead line". They are intelligently
chosen conductors, ideally insulated with Teflon, and properly wound in
bifilar manner on an appropriate toroidal core.

Opinions don't count in this game of antennas and transmission lines! Real
properly measured data using the correct instruments and techniques are
what's important. In other words, "show me the data" !!!

Measure Z at the antenna. Any, and I do emphasize "any" reactance at that
point when coupled to a good 50-ohm XMSN line will alter the impedance at
the shack end of that line!!! The effect of a short length of transmission
line embodied in the CMC will do typically less than any reactive component
at the antenna. So, again, show me the data before offering "opinions".
Please.....

I'm only attempting to keep this thread on a technical basis and not based
on opinion. Science and engineering rely on hard theory and data to back
up the theories. Antenna and transmission lines rely on hard science and
data, not opinion.

Dave - W ?LEV

On Wed, May 14, 2025 at 9:36?PM Team-SIM SIM-Mode via groups.io <sim31_team=
[email protected]> wrote:

Hi Miro
I believe you asked the right question here.
In my opinion, not having the correct characteristic impedance (Zc) for
the CRC that matches the Coax/Antenna system slightly alters the impedance
seen by the coax from the antenna and also the propor resonnance frequency
, CRC become a part of resonnance frequency . It also affects the impedance
measurements taken at that point, especially if the NanoVNA is calibrated
right at the point just below the antenna. In such a case, the measurements
will be distorted by the transformation introduced by the CRC's twin-lead
line.

For example, consider a CRC with a Zc of 140 Ohms used with a 50 Ohm
coaxial system: the impedance measured with or without the CRC will be
different, and correcting the antenna accordingly becomes much more
difficult. On the other hand, if the CRC has a characteristic impedance
equal to that of the Coax/Antenna system, the measured impedance will be
the same before or after the CRC. This would greatly simplify both the
calculations and the practical adjustments needed to optimize the antenna
system.

73's Nizar

--

*Dave - W?LEV*


--
Dave - W?LEV

QUOTE: ........ but should we ever be concerned that CMC might have fc
different from the rest of the system?

All my CMCs are home brewed and meticulously measured with professional
instruments. My usual frequency sweep runs from 1 MHz through 30 MHz.
They are broadbanded.

Dave - W?LEV

On Wed, May 14, 2025 at 9:16?PM Miro, N9LR via groups.io <m_kisacanin=
[email protected]> wrote:

Assuming that "wires" (transmission line) used to make CMC are much
shorter then "lambda" across useful frequencies, how much impact do you
expect from "mismatched" characteristic impedance of CMC?

It's cool to know how to measure it, but should we ever be concerned that
CMC might have fc different from the rest of the system?

--

*Dave - W?LEV*


--
Dave - W?LEV

Hi Miro
I believe you asked the right question here.
In my opinion, not having the correct characteristic impedance (Zc) for the CRC that matches the Coax/Antenna system slightly alters the impedance seen by the coax from the antenna and also the propor resonnance frequency , CRC become a part of resonnance frequency . It also affects the impedance measurements taken at that point, especially if the NanoVNA is calibrated right at the point just below the antenna. In such a case, the measurements will be distorted by the transformation introduced by the CRC's twin-lead line.

For example, consider a CRC with a Zc of 140 Ohms used with a 50 Ohm coaxial system: the impedance measured with or without the CRC will be different, and correcting the antenna accordingly becomes much more difficult. On the other hand, if the CRC has a characteristic impedance equal to that of the Coax/Antenna system, the measured impedance will be the same before or after the CRC. This would greatly simplify both the calculations and the practical adjustments needed to optimize the antenna system.

73's Nizar

12, 10, and 6 meters might be a bit of concern. But usually these are at
or less than an electrical 0.1 wavelengths long. The characteristic
impedance of all that I've built and measured (well over 20) come in
between 70 and 110 ohms. The Vp measures around 0.55.

Any length of transmission line or reactive circuit element inserted that
has a Zo other than the system impedance will alter the system impedance
coming through that component. Generally, any transmission of less than an
electrical 0.1 wavelength and a Zo within reason is quite acceptable.

No, I'm not concerned. If I were, I have the proper instruments to measure
the results.

Dave - W?LEV

On Wed, May 14, 2025 at 9:16?PM Miro, N9LR via groups.io <m_kisacanin=
[email protected]> wrote:

Assuming that "wires" (transmission line) used to make CMC are much
shorter then "lambda" across useful frequencies, how much impact do you
expect from "mismatched" characteristic impedance of CMC?

It's cool to know how to measure it, but should we ever be concerned that
CMC might have fc different from the rest of the system?

--

*Dave - W?LEV*


--
Dave - W?LEV

Assuming that "wires" (transmission line) used to make CMC are much shorter then "lambda" across useful frequencies, how much impact do you expect from "mismatched" characteristic impedance of CMC?

It's cool to know how to measure it, but should we ever be concerned that CMC might have fc different from the rest of the system?

When using the rectangular display, you can see that results may be compromised by the limited resolution of the magnitude/angle data, which is 0.001 in magnitude. You can see that the magnitude doesn't change between several adjacent points. You might try using an RI Touchstone file. The data is unlikely to be more accurate, but it may have much greater resolution.

I see no problem using the imaginary part of S11 to locate the exact null.

Brian

Thanks, Alan. Using dot mode makes it easy. The upper Q = 1 intersection is between two data points. The lower intersection is close to one point, at which I've put the marker. A little calculation, perhaps interpolating between the upper points, yields the answer.

Here is a resonator s1p file that you can apply to the Q=1 contour. Capture the
Q crossings at upper and lower (XL , XC) positions on the chart along with the zero real crossing. This provides unloaded Q.

Using dots can have a fascinating decorrelation effect. This is group delay for a crystal filter. The response is 80 dB down outside the passband, as shown in the second image. Group delay gets noisy in the stopband, as expected. Using dots visually decorrelates the noise.

Brian

I should have added this file listing to my previous post. The lin/log switch occurs in the middle. It's at 720 MHz, not 7.2 GHz. My ability to count zeros is restricted to "one, two, three, many."

Brian

I'm going to add an option to plot data points without a line connecting them. This is useful for assessing the data density, which is not always evident in a normal curve. The sample below reveals something I hadn't noticed with this lowpass filter. The frequency steps change from linear to logarithmic at 7.2 GHz. It's obvious in the file listing, but it's not evident in the normal curve.

Brian

Excellent.

On Wed, May 14, 2025 at 06:49 AM, alan victor wrote:

Are the data points from the s1p or s2p file highligted on the plot?

No, but clicking the mouse will put a marker at the data point nearest the mouse cursor. Then you can use the mouse wheel to step up and down the curve to the desired point. I'll think about optionally highlighting the data points. I'm not sure it's needed the way marker placement works.

Brian

Hi Dave

Here My message about RG213 coax measurements posted here on Avril 5 2025:

for My RG213 cable (25m length) loaded by a 50.3 Ohm resistor ,
I used the centered impedances circle methode on smith graph with the renormalized Z0 impedance ( option added by DiSlord) for different ferquency's band (span always fixed to 4 Mhz) :

2Mhz ---> Zc = 52.6 Ohm
3Mhz ---> Zc = 52.5 Ohm
7Mhz ---> Zc = 52.0 Ohm
14Mhz ---> Zc = 53.0 Ohm
18Mhz ---> Zc = 53.0 Ohm
21Mhz ---> Zc = 54.0 Ohm
24Mhz ---> Zc = 54.0 Ohm
29Mhz ---> Zc = 52.0 Ohm
50Mhz ---> Zc = 49.0 Ohm
100Mhz ---> Zc = 43.5 Ohm

Same coaxial Zc varie from 43.5 Ohm to 54.0 Ohm depend on the frequency band .

Direct measurement with Dislord "Cable" function gives Zc = 51.77 Ohm with same cable over all the band wich is correct enought but not too accurate depend on the frequency band .

73's Nizar

Thank you. Are the data points from the s1p or s2p file highligted on the plot?
A cursor that is positioned at or near an input file value is needed. For example,
the crossing of a Q contour or SWR circle needs to display a S11 or S21 mag and angle.

Thanks again.

Thanks, Alan. That's what I figured, but I have no experience with Smith charts so I wasn't sure.

I've posted the latest here:



Brian

No.

Two different tools applied as needed, others may have different opinion.