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Hi
DiSlord Coax Zc measurement function, already installed on H4 1.2.40 firmware, seems need to measure C0 capacitance @ 100Khz and the f0 first coax resonance frequency (Hz) and then we calculate Zc = 1/(4 x f0 x c0) Ohm , I appreciate it a lot.
Can we do some accuracy correction ? indeed diélectric permittivity of polyethylene diélectric can vary with fréquency , it can decrease slowly up to -4.5% from 100Khz to 14.1Mhz for example , so we can correct C0 value by -4.5% and then ZC should be increased by +4.5% to be more accurate @ 14 Mhz Zc measurement .
if our coax has 22.28 metre long with Vp around 83% , the first resonnance frequency will be around 2.71 Mhz wich still far from 14Mhz and may be some % error may be done , I prefer to measure the resonnance or antiresonance the nearest to the 14Mhz and devide by number for correction to have the more accurate Zc value based on measurement done as near as possible to the desired frequency ..
What you think about all this view , or DiSlord has already taken in consideration all this possible corrections .
73's Nizar .
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Since you asked what we think - I think this:
For amateur radio use, there is no reason that I know of to have high accuracy in the measurement of cable impedance.
It may be fun for an intellectual exercise, but practically, all we need to know is if the coax is 50-ohm, 75-ohm, 92-ohm, etc., with enough accuracy that we can see that it is a good cable. And DiSlord's current algorithm gives at least this level of accuracy.
We combine that measurement of impedance with a loss measurement and perhaps an electrical and physical length measurement to evaluate a cable's suitability for our purpose.
Even the best coax cables are not 'exact' in their impedance, and in fact, due to manufacturing tolerances, may vary a couple of percentage points of impedance along the length of the cable. A 50-ohm cable that measures 49.1 ohms of impedance is just fine. These variations and minor differences from an 'exact' 50-ohms or 75-ohms make almost no difference in actual use of the cable for any practical purpose. (The VSWR resulting from the difference between 49.1 and 50 ohms is only 1.018:1.)
The 'loss' calculation of the cable is of much more practical use than impedance, since it will determine power delivered to the load, extra loss due to SWR, etc. But even that loss measurement only needs to be 'reasonably' accurate, maybe to 10ths of a dB, for almost any practical amateur radio application. And when building matching stubs with coax, we have to measure the electrical length anyway, which measurement includes any variation due to imperfect impedance. So again, I don't put any value on highly-accurate cable impedance measurements.
Stan KC7XE
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Your coax is only going to have a "resonant frequency" if it is terminated in a very high SWR or a load with a very high or low impedance, such as an open or short. If the load is somewhere close to 50 ohms, you aren't going to see any resonant frequency that is worth any concern. Zack W9SZ <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Fri, Mar 21, 2025 at 6:56?AM Team-SIM SIM-Mode via groups.io <sim31_team= [email protected]> wrote: Hi
DiSlord Coax Zc measurement function, already installed on H4 1.2.40
firmware, seems need to measure C0 capacitance @ 100Khz and the f0 first
coax resonance frequency (Hz) and then we calculate Zc = 1/(4 x f0 x c0)
Ohm , I appreciate it a lot.
Can we do some accuracy correction ? indeed diélectric permittivity of
polyethylene diélectric can vary with fréquency , it can decrease slowly up
to -4.5% from 100Khz to 14.1Mhz for example , so we can correct C0 value by
-4.5% and then ZC should be increased by +4.5% to be more accurate @ 14
Mhz Zc measurement .
if our coax has 22.28 metre long with Vp around 83% , the first resonnance
frequency will be around 2.71 Mhz wich still far from 14Mhz and may be
some % error may be done , I prefer to measure the resonnance or
antiresonance the nearest to the 14Mhz and devide by number for correction
to have the more accurate Zc value based on measurement done as near as
possible to the desired frequency ..
What you think about all this view , or DiSlord has already taken in
consideration all this possible corrections .
73's Nizar .
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Hi Zac
Sorry, Here i meant by coax resonant freq the freq that Give 1/4 lamda electrical length or zero impedance on smith diagram , coax supposed without terminaison .
73s
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OK, yes, I can see that. Zack <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Fri, Mar 21, 2025 at 4:17?PM Team-SIM SIM-Mode via groups.io <sim31_team= [email protected]> wrote: Hi Zac
Sorry, Here i meant by coax resonant freq the freq that Give 1/4 lamda
electrical length or zero impedance on smith diagram , coax supposed
without terminaison .
73s
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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
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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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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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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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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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Interesting , the Zo uses to rise a little when the frequency goes down.
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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
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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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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
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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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?
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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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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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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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Hi Patricio
I do not understand this chart, can you explaine it more pse.
73's Nizar
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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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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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Hi Patricio
Thanks for clarification , I do not understand this graphic zone circled on red color below
73's Nizar
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