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
|
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
|
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
|
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
|
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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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
|
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
|
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
|
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
|
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."
|
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."
|
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
|
Re: NanoVNA H FW 1.0.53 Display Intermittent
William,
This might be due to the case pressing on the touchscreen
Try loosening the mounting screws or perhaps adding thin washers for spacing.
--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."
|
NanoVNA H FW 1.0.53 Display Intermittent
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."
|
Re: NANO VNA H4 , Implausible measurement results?
Hi, Brian,
I still have mine with the matching speaker. Mine is an NC-183, not an NC-183D. Like you, I really loved that thing. Even now, the sight of it here brings back good memories.
But I haven't used it for awhile as I've been using an R-388 I built up from parts in the mid-'70s.
Even more, I use a Halli S-40B, a good compromise between weight and performance. The weight matters more to me at age 82 than is did a few decades ago.
73,
Maynard
W6PAP
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On 4/3/25 08:54, Brian Beezley wrote: On Thu, Apr 3, 2025 at 08:40 AM, Maynard Wright, P. E., W6PAP wrote:
That would have been in 1958 when I bought the NC-183. Before that I had an
S-38E
Maynard, I bought a NC-183 to replace my S-38D in the early 1960s. I just loved that big receiver.
Brian
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Re: NANO VNA H4 , Implausible measurement results?
On Thu, Apr 3, 2025 at 08:40 AM, Maynard Wright, P. E., W6PAP wrote:
That would have been in 1958 when I bought the NC-183. Before that I had an
S-38E
Maynard, I bought a NC-183 to replace my S-38D in the early 1960s. I just loved that big receiver. Brian
|
Re: NANO VNA H4 , Implausible measurement results?
Hi, Ed,
That's true! I remember hearing the phrase "you can work the world with watt and a wet noodle," but I didn't fully understand what was going on at the time.
I did cut an old broadcast receiver chassis in half, use the three tube sockets for a 6AG7, a plate coil, crystals, and leads to the hand key and it put out, I think, about a watt or two and I had fun powering it from my NC-183. I mounted a meter on the chassis for tuning. It's still in the attic somewhere. I used a circuit from the 1952 ARRL Handbook, using a parallel resonant circuit with one variable instead of ARRL's pi-network.
That would have been in 1958 when I bought the NC-183. Before that I had an S-38E and borrowing power from that would have been more difficult. I don't think that I would have been competent enough to build a power supply from scratch so the auxiliary socket on the NC-183 was pretty handy.
73,
Maynard
W6PAP
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On 3/31/25 09:57, AG6CX via groups.io wrote: Maynard and others:
You and we were most fortunate to be initiated with one of the most robust sunspot cycles of modern times in 1957!!
Same story at pre-Nano VNA KN1CJO in southern Maine. Worked all over the place, including all TV sets in the neighborhood.
Antenna was classic Windom, usual length, but fed with 300 feet of single wire to bannana plug into the DX-20 antenna port, me serving as T-R relay.
We are equally fortunate to still be able to remember all that, and be alive to write about
Ed McCann
AG6CX
Sausalito
On Mar 31, 2025, at 8:45?AM, Maynard Wright, P. E., W6PAP via groups.io <ma.wright@...> wrote:
?I got my Novice license in 1957 and used a single wire routed out the window and up to the brick chimney and then across the yard about 100 feet to a pole. It worked fine, with my best DX using a Knight Kit 50 watt (input) transmitter being an Argentine station in Antarctica. I worked a few Japanese stations and some South Americans from my QTH in Northern California, never realizing that my antenna was really awful.
When I upgraded from Novice to Conditional in 1958, I used a 100TH with the same antenna to work folks on AM and CW. With either transmitter, I had to stand up and throw a knife switch on the wall to go from receive to transmit.
I also still have a bunch of QSL cards from that era that bring back nice memories.
The important thing was that my Knight Kit with a pi-network and my 100TH with a swinging link coupler didn't care much about the SWR. I simply tuned for about a 10% drop in plate current and no red glow from the 100TH and everything worked fine. With a modern transmitter that wants something approximating 50 ohms, such an antenna would require a tuner and the losses in the tuner might use up a lot of the generated RF energy.
My most modern rigs here still use pi-networks, which is why I can get away with using a wire in the attic draped over air conditioning ducts and water pipes and work DX, not like a real DXer would want, but enough for a casual guy.
73,
Maynard
W6PAP
On 3/31/25 08:07, Jon via groups.io wrote:
Joe,
I got licensed a decade after you and did not have a chance to use a balun
or 50 ohms coax then. My 40 and 80m dipoles were fed by 75 ohms TV cable. I
did not have an SWR meter either. Still I could work a lot of DX including
a few W land stations with my homebrew 3 x 807 radio, 120W CW and straight
key. I still have a couple of W land QSL cards in my precious collection.
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 7:50?PM Joe WB9SBD via groups.io <nss=
[email protected]> wrote:
Yup!
The Balun Craze is a new Generation thing. Got licensed in 1975, Never
ever heard of a Balun.
All my dipoles were direct feed.
Only till recently has the myth of a dipole without a balun will not work.
just like a 40 meter Dipole will not work on 15 meters!
tell that to all the Novices that got their license in the 70's.
Joe WB9SBD
On 3/31/2025 8:53 AM, Zack Widup via groups.io wrote:
I have never seen a problem feeding a dipole directly with an unbalanced
feedline. The last dipoles I had up (which were for 40 and 30 meters) were
just fed by connecting the two leads of the coax directly to the antenna
wires attached to an insulator at the center of the antenna. SWR in both
cases, when the antenna was trimmed, were around 1.05:1. And I worked 180
countries on 40 m CW with that antenna and Japan fairly often on 30 m CW.
Zack W9SZ
<
Virus-free.www.avg.com
<
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
On Mon, Mar 31, 2025 at 7:59?AM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride= [email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is
~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
|
k6whp
Donald S Brant Jr