Re: Measuring R,X Resonant Frequency
If one measures SWR in the shack considering the antenna plus feedline (assumed coax) as a system, there is a good way to verify there is no standing waves or reflections on the line - A totally matched system. This can occur if the feedline is just the right length to transform the impedance at the antenna feedpoint to 1:1 over its length. Add about an electrical 1/8-lambda of coax to the existing coax. Doing this in the shack is fine. Again measure SWR with the added length of coax. If the SWR is still 1:1, you're correct in that there is no SWR or reflections on the line. If it does not read 1:1, again, with the added coax, there is SWR and reflections on the line. Don't be fooled. Have a read of KL7AJ's, Eric's, "SWR METERS MAKE YOU STUPID". It's tongue-in-cheek, but addresses some very important facts about SWR in a clear no-math manner. I guarantee you'll be smiling by the time you reach even page 3. Dave - W?LEV On Mon, Jan 20, 2025 at 8:33?PM Miro, N9LR via groups.io <m_kisacanin= [email protected]> wrote: On Mon, Jan 20, 2025 at 08:50 AM, Lester Veenstra wrote:
... a case where the VSWR measures at 1:1 and the Smith chart is not on
the zero reactance line.
A simple answer - for VSWR 1:1, X must be 0 and R must be 50. In any other
case you will have "impedance mismatch", that will causes "reflection", and
reflection "causes" VSWR
A bit longer explanation, by the very definition, for VSWR being 1:1 (no
reflection), two impedances you are comparing MUST be identical resistance
to resistance, reactance to reactance
If your "generator is Z1=R+jX, for VSWR to be 1:1 the load must be Z2=R+jX
(R=R and X=X, if not obvious otherwise)
In the Smith chart we usually use, R=50 and X=0 (you can use any impedance
instead, by 50 ohm center is what you will almost always see), so for VSWR
1:1 you can't have any reactance (X=0)
Do a google search for "complex impedance VSWR" for "formula" or use
Owen's online calculator
-- *Dave - W?LEV* -- Dave - W?LEV
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Re: Measuring R,X Resonant Frequency
¡°If your "generator is Z1=R+jX, for VSWR to be 1:1 the load must be Z2=R+jX (R=R and X=X, if not obvious otherwise)¡± Correction - the load impedance must be the complex conjugate of the source impedance so Z2=R-jX On Mon, Jan 20, 2025 at 2:33?PM Miro, N9LR via groups.io <m_kisacanin= [email protected]> wrote: On Mon, Jan 20, 2025 at 08:50 AM, Lester Veenstra wrote:
... a case where the VSWR measures at 1:1 and the Smith chart is not on
the zero reactance line.
A simple answer - for VSWR 1:1, X must be 0 and R must be 50. In any other
case you will have "impedance mismatch", that will causes "reflection", and
reflection "causes" VSWR
A bit longer explanation, by the very definition, for VSWR being 1:1 (no
reflection), two impedances you are comparing MUST be identical resistance
to resistance, reactance to reactance
If your "generator is Z1=R+jX, for VSWR to be 1:1 the load must be Z2=R+jX
(R=R and X=X, if not obvious otherwise)
In the Smith chart we usually use, R=50 and X=0 (you can use any impedance
instead, by 50 ohm center is what you will almost always see), so for VSWR
1:1 you can't have any reactance (X=0)
Do a google search for "complex impedance VSWR" for "formula" or use
Owen's online calculator
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Re: Measuring R,X Resonant Frequency
On Mon, Jan 20, 2025 at 08:50 AM, Lester Veenstra wrote:
... a case where the VSWR measures at 1:1 and the Smith chart is not on the zero reactance line.
A simple answer - for VSWR 1:1, X must be 0 and R must be 50. In any other case you will have "impedance mismatch", that will causes "reflection", and reflection "causes" VSWR A bit longer explanation, by the very definition, for VSWR being 1:1 (no reflection), two impedances you are comparing MUST be identical resistance to resistance, reactance to reactance If your "generator is Z1=R+jX, for VSWR to be 1:1 the load must be Z2=R+jX (R=R and X=X, if not obvious otherwise) In the Smith chart we usually use, R=50 and X=0 (you can use any impedance instead, by 50 ohm center is what you will almost always see), so for VSWR 1:1 you can't have any reactance (X=0) Do a google search for "complex impedance VSWR" for "formula" or use Owen's online calculator
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Re: 40M X 80M NVIS Antenna for WFD event Jan 25th.
Yes the lengths are wrong but the DX Engineering one is even more off
John ve3ips
So 34 ft for 40 and 70 for 80m then tune for resonance
John ve3ips
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Re: Measuring R,X Resonant Frequency
Well, can anyone come up with a case where the VSWR measures at 1:1 and the Smith chart is not on the zero reactance line. And in fact for 1:1 you would have to be dead center, based on analysis performed by the seat of my pants. But I am open to mathematical sets of R+iX that reads 1:1. just too lazy to work it myself. HI
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Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
lester@...
452 Stable Ln
Keyser WV 26726 USA
GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)
Telephones:
Home: +1-304-289-6057
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Jamaica cell: +1-876-456-8898
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of W0LEV via groups.io Sent: Sunday, January 19, 2025 7:37 PM To: [email protected]Subject: Re: [nanovna-users] Measuring R,X Resonant Frequency Any of the NANOVNAs are well suited to make your desired measurements: SWR and R ¡À j X. Minimum or 1:1 SWR is not a good indicator of resonance, regardless of ham "lore" and misinformation. The DEFINITION of antenna or lumped element circuit resonance is the frequency at which the complex portion of the impedance becomes zero leaving only pure resistance. Addressing an antenna, this resistance is a combination of resistive losses in the system and the radiation resistance of the antenna. SWR, alone, is incapable of indicating that condition as SWR is a scalar measurement (amplitude measurement only with no phase information). The total impedance expression requires a vector measurement of the impedance which also expresses the complex portion, the ¡À j X term. Dave - W?LEV <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Sun, Jan 19, 2025 at 7:14?PM Peter Jones via groups.io <jonesypeter= [email protected]> wrote: Greetings, I've recently completed the construction of my first 'home brew' antenna (1/4 wave vertical). A radio friend of mine suggests I should look at resonance as well as SWR. SWR is fine, but I can't see anything online about an R/X chart (similar to that available on the RigExpert). Can I do this on the NanoVNA V4? Thanks Peter M0LMG [img][/img] -- *Dave - W?LEV* -- Dave - W?LEV
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Re: 40M X 80M NVIS Antenna for WFD event Jan 25th.
Hello David,
The 40M leg is too long.
The SWR and RL are rising with the increase in frequency.
The 80M leg is too short.
The SWR and RL are improving with the increase in frequency.
HTH...Bob VK2ZRE
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On 20/01/2025 3:30 pm, David Gerhart wrote: Hey,
I wired up a 118' X 68' crossed dipole antenna per the recipe here . I was able to get very good transmission 5x9 to a collaborator some miles away on 3.190MHz. The 40M leg seemed more difficult. So I hooked up my Nano VNA-H to the Feed Line. I set the calibration plane at the input to the VNA. The network is 75' of RG58 to a 1:1 Unun, then the Antenna.
NVA Sweep Results attached. I didn't fuss with markers, or other settings ...
What do the measurements suggest? I have some opinions, but thought to listen first.
My goal is to tune it up a bit for Winter Field Day...
Enjoy, and thanks in advance for any thoughts you share.
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Re: Measuring R,X Resonant Frequency
William,
As mentioned our local radio club has a copy, but I'm not there for a few weeks. Stan Dye already answered my question, but will still read the book when I'm next at the club.
I've the Radio Today books from the RSGB for my ICOM 705 and FTDX-10. Both good books.
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Re: Touch screen does not respond well.
"Your unit might not be broken, in the conventional sense!"< Maybe, I have more than one complaint, the screen seems insensitive especially when I'm trying to program frequency, those numbers just don't want to respond. Other times the sensitivity is fine except when I hit back, rather than going back, the dropdown just goes away. Another touch to the screen brings back the same dropdown, so I hit back and the dropdown disappears and I'm in a loop. I end up shutting off the unit and starting over. "issues can be corrected by adjusting the screen's positioning or tension in the case."< I'll try it out of the case. "all described in that book mentioned earlier."< What is the "book" Thanks, Mikek
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Re: Touch screen does not respond well.
Your unit might not be broken, in the conventional sense!
Read in this group about adjusting the display. The display on the nanoVNA is resistive, and many times issues can be corrected by adjusting the screen's positioning or tension in the case.
The screen does also have to be calibrated--all described in that book mentioned earlier.
73, Paul -- AI7JR
--
Paul -- AI7JR
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40M X 80M NVIS Antenna for Winter Field Day
Hey,
I wired up a 118' X 68' crossed dipole antenna per the recipe here . I was able to get very good transmission 5x9 to a collaborator some miles away on 3.915MHz. The 40M leg seemed more difficult. So I hooked up my Nano VNA-H to the Feed Line. I set the calibration plane at the input to the VNA. The network is 75' of RG58 to a 1:1 Unun, then the Antenna.
NVA Sweep Results attached. I didn't fuss with markers, or other settings ...
What do the measurements suggest? I have some opinions, but thought to listen first.
My goal is to tune it up a bit for Winter Field Day...
Enjoy, and thanks in advance for any thoughts you share.
|
Re: Touch screen does not respond well.
I borrowed a friends NanoVNA, same model, same reputable seller. The borrowed unit works like my unit never worked.
It was always a bit difficult to get the screen to respond. I wish I had known how it was supposed to work, I would have returned it
just after I received it.
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Re: Measuring R,X Resonant Frequency
Any of the NANOVNAs are well suited to make your desired measurements: SWR and R ¡À j X. Minimum or 1:1 SWR is not a good indicator of resonance, regardless of ham "lore" and misinformation. The DEFINITION of antenna or lumped element circuit resonance is the frequency at which the complex portion of the impedance becomes zero leaving only pure resistance. Addressing an antenna, this resistance is a combination of resistive losses in the system and the radiation resistance of the antenna. SWR, alone, is incapable of indicating that condition as SWR is a scalar measurement (amplitude measurement only with no phase information). The total impedance expression requires a vector measurement of the impedance which also expresses the complex portion, the ¡À j X term. Dave - W?LEV <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Sun, Jan 19, 2025 at 7:14?PM Peter Jones via groups.io <jonesypeter= [email protected]> wrote: Greetings,
I've recently completed the construction of my first 'home brew' antenna
(1/4 wave vertical). A radio friend of mine suggests I should look at
resonance as well as SWR.
SWR is fine, but I can't see anything online about an R/X chart (similar
to that available on the RigExpert).
Can I do this on the NanoVNA V4?
Thanks
Peter M0LMG
[img][/img]
-- *Dave - W?LEV* -- Dave - W?LEV
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Re: Measuring R,X Resonant Frequency
Peter: It really, really is a fantastic book--- The KINDLE digital download version has links, diagrams and explanatory text--- DO THIS: 1. Estimate the price of your ham shack's current equipment. ENTER THE NUMBER HERE 2. Estimate the price of the last restaurant meal you ate. ENTER THE NUMBER HERE 3. Divide cost #2 by cost #1 and express as a percentage. ENTER THE PERCENTAGE HERE 4. The Kindle cost of the NanoVNA Explained downloadable digital version is $18.99 USD as of now 5. Compare Cost #2 with Cost #4. IF #2>>#4, then getting that book is cheaper than your last restaurant 6. Last step: Buy the book; it is "budget dust" compared to the price of your ham gear. On Sun, Jan 19, 2025 at 7:57?PM Peter Jones via groups.io <jonesypeter= [email protected]> wrote: Thanks Bill,
Maybe someone can explain it in a message?
I think our radio club may have a copy, but I'm not visiting for a few
weeks.
Thanks
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Re: Measuring R,X Resonant Frequency
Just remember that if you want to know where the antenna is resonant (reactance = 0) you have to measure at the feedpoint of the antenna NOT at the end of the transmission line in your hamshack.
It is usually not convenient to place the NanoVNA at the antenna feedpoint but you can get the same result by "de-embedding" the transmission line. This requires that you calibrate at the end of the transmission line using your SOL cal loads. If you save the results you only have to do this once.
Warning - If your coaxial cable has common mode current on the outer surface of the coax shield then this "third wire" is forming part of the antenna system and you results will not be the same as if the NanoVNA was directly connected at the antenna feedpoint. You often see common mode current when you connect an unbalanced transmission line to a dipole. This can be reduced considerably by using a current balun at the feedpoint which helps to choke the RF current.
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Re: Measuring R,X Resonant Frequency
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Re: Measuring R,X Resonant Frequency
Thanks Bill,
Maybe someone can explain it in a message?
I think our radio club may have a copy, but I'm not visiting for a few weeks.
Thanks
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Re: Measuring R,X Resonant Frequency
Look at the display options to show R and X traces. But the easiest way to see resonance is on the default smith chart- wherever the trace crosses the horizontal axis is a resonance point. You can move your cursor there, and read the frequency and the corresponding R (X is 0). The closer R is to 50 ohms, the closer your resonance is to the minimum SWR.
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Re: Measuring R,X Resonant Frequency
Peter: Yes. Buy a copy of "NanoVNA EXPLAINED" by Mike Richards, G4WNC. It's a RSGB book. Get it on Amazon. I have the Kindle version downloaded immediately after buying it. Very thorough and easy to follow. And yes, you can use the various tracks to display info. 73 Bill K2TNO On Sun, Jan 19, 2025, 2:38?PM Peter Jones via groups.io <jonesypeter= [email protected]> wrote: Thanks Bill,
Sorry, my image didn't appear as I had planned.
So can resistance and reactance be displayed at the same time (I assume
multiple traces?).
Can anyone direct to a tutorial?
Thanks
Peter
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Re: Measuring R,X Resonant Frequency
Thanks Bill,
Sorry, my image didn't appear as I had planned.
So can resistance and reactance be displayed at the same time (I assume multiple traces?).
Can anyone direct to a tutorial?
Thanks
Peter
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Re: Measuring R,X Resonant Frequency
Yes NanoVNA can measure resistance and reactance as well as a Smith chart. Resonance is the frequency at which the antenna is purely resistive, and no reactance. You seem to be already aware that the "frequency of minimum swr" is not necessarily the "resonant frequency." But, it can be. Read the ARRL Handbook or ARRL Antenna Book for clarification. Bill K2TNO On Sun, Jan 19, 2025, 2:14?PM Peter Jones via groups.io <jonesypeter= [email protected]> wrote: Greetings,
I've recently completed the construction of my first 'home brew' antenna
(1/4 wave vertical). A radio friend of mine suggests I should look at
resonance as well as SWR.
SWR is fine, but I can't see anything online about an R/X chart (similar
to that available on the RigExpert).
Can I do this on the NanoVNA V4?
Thanks
Peter M0LMG
[img][/img]
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John
Paul - AI7JR
David KK7WXV
Roger Need