Re: Measurement correction for Zc Coax caracteristic Impedance
This is the part of LF model that don’t work basically because is the wrong frequency region…
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On 6 Apr 2025, at 1:49?PM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi Patricio
Thanks for clarification , I do not understand this graphic zone circled on red color below
73's Nizar
<Capture d_????cran 2025-04-06 174532.png>
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Patricio
Thanks for clarification , I do not understand this graphic zone circled on red color below
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
This chart shows the typical behaviour of a loosy coaxial cable over frequency. Basically there are two models , the low frequency model in this case the dielectric loose are very small then G tends to zero and is removed from the Zo formula. The serial equivalent loose resistor this is basically the resistance of the metallic boundary of the cable. It drops to lower frequency to a minimum this is determined by the conductor resistivity and uses to be very small but never zero , L goes up from the High Frequency model because appears magnetic fields inside de conductors… as frequency goes down the Zo goes up. In the other hand on high frequency region L an C are dominant on Zo formula and results on a more stable value. Skin effect reduces de magnetic field inside de conductor and L becomes defined basically by metallic boundaries.
At all this is not a problem in the practical world because the coaxial cables are used on high frequency regions , at audiofrecuencies becomes a shielded cable and Zo concept are irrelevant. In metrology these variations are taken to correct high precision measurements and standards characterization.
At very low frequencies where transmission lines are required usually higher Zo is adopted too . This is the frequency where LF and HF curves crosses are higher as Zo is lower. This is of course with the same materials on each case.
I?m sorry for my engllsh is not very good. If you have any difficulties to understand that I say please let me know.
Regardd, Patricio.
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On 6 Apr 2025, at 5:31?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi Patricio
I do not understand this chart, can you explaine it more pse.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
With same coax, same method, same NanoVNA H4 (1.2.40 DiSlord) surprisingly i have some different Zc values for 50Mhz & 100Mhz
50Mhz ---> Zc = 49.0 Ohm
100Mhz ---> Zc = 43.5 Ohm
73's Nizar
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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Patricio
I do not understand this chart, can you explaine it more pse.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Oops! I should have R >> jwL, not R >> jwC. My error.
73,
Maynard
W6PAP
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On 4/5/25 16:20, Maynard Wright, P. E., W6PAP via groups.io wrote: An interesting chart.? Note that below about 300 kHz, the imaginary component of the characteristic impedance can no longer be ignored and, if you are working on any cables at voice frequencies or where R >> jwC, the angle of the characteristic impedance will be around -45 degrees, which is characteristic of most telephone cable pairs (or any other transmission lines) at voice frequencies.
73,
Maynard
W6PAP
On 4/5/25 12:10, Patricio Greco via groups.io wrote:
?
On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213? cable (25m length) loaded by a 50.3 Ohm resistor
I used the same?? circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's? Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
An interesting chart. Note that below about 300 kHz, the imaginary component of the characteristic impedance can no longer be ignored and, if you are working on any cables at voice frequencies or where R >> jwC, the angle of the characteristic impedance will be around -45 degrees, which is characteristic of most telephone cable pairs (or any other transmission lines) at voice frequencies.
73,
Maynard
W6PAP
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On 4/5/25 12:10, Patricio Greco via groups.io wrote: ?
On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
?
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On 5 Apr 2025, at 12:03?PM, Jim Lux via groups.io <jimlux@...> wrote:
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <> <patricio_greco@... <mailto:patricio_greco@...>> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <> <sim31_team@... <mailto:sim31_team@...>> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Jim Lux
"L , C & R exhibit some frequency-dependent variation; they do not have a perfectly flat response across frequency. This behavior depends on the dielectric material used, skin effect and the physical design of the coaxial cable. so theroritical formula is 1sft order modelisation , NanoVNA mesure them physically, just we should have the good method and practice at a reasonnable accuracy.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Not unexpected
Zc is sqrt( (R+jomegaL)/(G+jomegaC))
Mostly determined by L/C, but the R is in there too, and it goes up as frequency goes up, because of skin effect. For HF the dielectric loss (G) is really tiny, so the R term dominates.
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Show quoted text
On Apr 5, 2025, at 05:34, Patricio Greco via groups.io <patricio_greco@...> wrote:
?Interesting , the Zo uses to rise a little when the frequency goes down.
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Interesting , the Zo uses to rise a little when the frequency goes down.
toggle quoted message
Show quoted text
On 5 Apr 2025, at 6:43?AM, Team-SIM SIM-Mode via groups.io <sim31_team@...> wrote:
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
|
Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
for same RG213 cable (25m length) loaded by a 50.3 Ohm resistor
I used the same circle methode centered 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
Direct measurement with Dislord Coax function gives Zc = 51.77 Ohm with same cable.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi Dave
DiSlord coax function seems using Zc = 1/(4*fr*C0) ,
fr= is the first resonance frequency with open terminaison it's around 1.7Mhz measured by NANoVNA.
C0 = capacitance value at lower frequency around 50Khz to 100Khz measured by NanoVNA.
it gives a good value 51.7 Ohm around 1Mhz ,
but At 14.1 Mhz Zc changes a bit to 53 Ohm , and this impedance circle method seems sligthly better using around 50 Ohm terminaison load and frequency domaine around 14.1Mhz as explained in my last messages.
73's Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
I wonder how the "short / open" method compares using Zc = SQRT [L / C] ? Of course, that will introduce losses due to theoretical infinite SWR. Dave - W?LEV On Fri, Apr 4, 2025 at 2:37?PM Team-SIM SIM-Mode via groups.io <sim31_team= [email protected]> wrote: Hi
below what i have measured on smith graph with my 25m length of RG213
coax cable with a NanoVNA H4
With Dislord function and no terminaison : it gives Z0=51.7 Ohm , it do
not change with frequency's , based on low frequncy's measurement < 1.7 Mhz
with a 50.3 ohm resistor Coax terminaison, Smith graph gives a nice
centered little circle for 53 Ohm renormalized impedance graph, ( 52 Ohm
and 54 Ohm gives sheefted circles of center ) , 53 Ohm seems to be the
good Z0 value for around 14.100 Mhz frequency's and not 51.7 Ohm as
calculated by Dislord function,
This nice and relatively more accurate method need a 6X Zoom on smith
graph , why not to add this option on the future H4 firmware ?
see sceenshoots attached
73's Nizar
-- *Dave - W?LEV* -- Dave - W?LEV
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
I think that this method of small circles centered with the renormalized impedance at the center of the Smith graph, must bring two advantages compared to that used by the DiSlord method:
1) we are rather in progressive wave and almost no standing wave, that is to say our area of ??interest during our antenna measurements close to SWR = 1.0,
2) secondo the measurements are rather made around the frequency of interest 14.100 Mhz a span of 4Mhz.
just it is desirable to have a graphic zoom of 8x of the Smith graph to further refine the value of Z0.
73s Nizar
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Re: Measurement correction for Zc Coax caracteristic Impedance
Hi
below what i have measured on smith graph with my 25m length of RG213 coax cable with a NanoVNA H4
With Dislord function and no terminaison : it gives Z0=51.7 Ohm , it do not change with frequency's , based on low frequncy's measurement < 1.7 Mhz
with a 50.3 ohm resistor Coax terminaison, Smith graph gives a nice centered little circle for 53 Ohm renormalized impedance graph, ( 52 Ohm and 54 Ohm gives sheefted circles of center ) , 53 Ohm seems to be the good Z0 value for around 14.100 Mhz frequency's and not 51.7 Ohm as calculated by Dislord function,
This nice and relatively more accurate method need a 6X Zoom on smith graph , why not to add this option on the future H4 firmware ?
see sceenshoots attached
73's Nizar
|
Re: NanoVNA H FW 1.0.53 Display Intermittent
I have this problem even with my recently purchased NanoVNA. Sometimes when I switch on, the screen is blank. If I switch off and switch on once again, usually it becomes OK. The problem recurs again during the next power on sometimes. Occasionally I have to switch on and off a couple of times or more to get the screen visible. Otherwise there is no problem with the functioning of the NanoVNA. Battery gives good charge retention. 73 Jon, VU2JO On Thu, Apr 3, 2025 at 10:59?PM k6whp via groups.io <k6whp= [email protected]> wrote: Have an old NanoVNA H with the above FW whose display is intermittent.
More specifically, the menu turns off and on or will revert to the main
menu.
I have tried to do the touch cal and touch test with no success.
Appreciate any remarks on the subject; resetting the unit, etc.
Thanks in advance.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."
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Re: NanoVNA H FW 1.0.53 Display Intermittent
John,
Thank you for your advice; I think that is the reason for the fault.
I tried that and operated the unit outside of the case and it seemed to work a little better but the menu still flickered and jittered. I also noted that, after a full charge, the battery discharged rapidly -- after about 10 minutes of use. Apologize for not searching the group for an answer, but what battery could be used and how would it be replaced?
Thank you again.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."
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Re: NanoVNA H FW 1.0.53 Display Intermittent
William,
Also check for battery swelling causing pressure on the display.
--John Gord
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On Thu, Apr 3, 2025 at 10:29 AM, k6whp wrote:
Have an old NanoVNA H with the above FW whose display is intermittent. More
specifically, the menu turns off and on or will revert to the main menu.
I have tried to do the touch cal and touch test with no success. Appreciate
any remarks on the subject; resetting the unit, etc.
Thanks in advance.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."
|
Internally-matched power transistors use the internal bond wires as high-Q inductive elements. In conjunction with MOS capacitors they are used to build matching networks inside the package to bring the sub- to few-Ohm transistor impedances to something more manageable, or in some cases directly to 50 Ohm, at the device leads. The number of wires and their length, height and spacing determine their values, so are tweaked for tuning.
The devices' parasitic capacitances are absorbed into the matching network, making a useful element out of what was a hindrance.
73, Don N2VGU
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k6whp
Donald S Brant Jr