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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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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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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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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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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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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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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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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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Any of the NANOVNAs are well suited to make your desired measurements: SWR and R ± 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 ± 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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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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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)
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Telephones:
Home: +1-304-289-6057
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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 ± 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 ± 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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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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“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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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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On Sun, Jan 19, 2025 at 11:23 AM, William Schrader wrote:
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.
Good point..... I made a measurement of a 2M dipole constructed from some brass rod and suspended about 5 feet of the workshop floor. The NanoVNA-H4 was connected directly at the feedpoint. The results were saved to the SD card and loaded into NanoVNA App for analysis. Note how the frequency with minimum VSWR is different than where resonance occurs (with X=0). Zipped file of graph is also attached since groups.io tends to shrink images. Roger
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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.
If that is the situation then there WILL be standing waves on the line! The fact that the impedance is transformed at the end of the line to 50ohms does not alter what happens on the line at the mismatch to the load. There will still be a reflected signal due to that mismatch. The only way that there can be no reflected signal, and no standing waves on the line, is if the load matches the impedance of the coax. Also with a 50ohm coax it will not be possible to alter the length to achieve a 1:1 match. Changing the length will just cause the observed impedance to travel around a constant VSWR circle on the Smith Chart, (plus or minus a very small deviation due to the changed loss from the different length of coax) ie the same VSWR but with a different phase. It is only if you used a length of coax of a different impedance that you might see a move towards the centre of the chart. 73 Jeff G8HUL
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Good point..... I made a measurement of a 2M dipole constructed from some brass rod and suspended about 5 feet of the workshop
floor. The NanoVNA-H4 was connected directly at the feedpoint. The results were saved to the SD card and loaded into NanoVNA
App for analysis. Note how the frequency with minimum VSWR is different than where resonance occurs (with X=0). Zipped file of
graph is also attached since groups.io tends to shrink images.
An antenna does not have to be resonant to radiate efficiently. It will radiate all of the power that is applied to it, less any resistive losses in the antenna. What is important is getting the power into the antenna from the feeder, and a poor match will reflect power. Most antennas are not 50ohms at resonance, so you will never get a perfect match, either you add some matching at the base of the antenna to match that resistance at resonance to 50 ohms, or you adjust the antenna away from resonance to give the best possible match, something close to 50 ohms but not quite there, and put up with a small mismatch. Which ever you do the object is to get as close to 50 ohms as you can at the base of the antenna. What you don't want to do is try to match at the shack with an ATU as then there will be standing waves on the coax adding to loss and possibly rf on the coax outer. 73 Jeff G8HUL
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This is the best video I've found on the subject. It took a lot of searching, as there is a lot of trash out there!
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On Mon, Jan 20, 2025 at 02:43 PM, Tony Scaminaci wrote: the load impedance must be the complex conjugate of the source impedance so Z2=R-jX Not sure that's true, but I have to admit, that's the part of SWR theory that I struggle the most If you check formula for reflection coefficient ( R = (Z1-Z2)/(Z1+Z2) ) and any random "online calculator, all of them line up with Z1 = Z2, and not the conjugate Conjugate assures max transfer of power as reactance's null each other (kind of a "system's resonance" of some kind). But then, expectation is that the max power transfer happens for SWR 1:1. The reason we don't see that "questioned" more often is because we all start with assumption that Z1=50, so conjugate becomes irrelevant concept :) Hope someone here can clear that up :)
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Roger Need
