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/g/nanovna-users/topic/86678150#25341

Roger

Seems to me you are conflating reactance with resistance.

0 reactance by definition is the resonant point.? Has nothing to do with resistance or VSWR directly.? Resistance and subsequently VSWR are dependent on both reactance and resistance

Using EZNEC Pro/2 v7.0 and the Dipole1.ez entry I see Z 70.8 and -j6.577 for minimum SWR of 1.43 at 297MHz (I did adjust the element lengths to 0.24 to match the intended frequency better)
However at 299Mhz it shows Z 71.89 and +j0.345 for an SWR 1.44 with almost no reactance so more "resonant" but a slightly higher Z.
And if you change to 75Om Z0 the minimum VSWR shows at 299 instead of 297 with an SWR of 1.043
So once you know your 0 reactance point is all about matching Z to maximize power to the antenna.

Mike W9MDB

Point well said, bravo, thanks Jim.

Mike C.

On 8/24/22 11:39 AM, TG Frerichs wrote:

I keep seeing the statement that a resonant halfwave center fed dipole has zero reactance at the feed point, and I don't think this is always correct.
For a center-fed dipole that is 1/2 wavelength and where the length/diameter ratio is greater than fifteen (i.e. a wire antenna) in free space, (e.g., no mutual impedance from a ground plane), I found a couple of references that indicate Xl <> -Xc. They agree as to values.
Quoting Blake:
The radiation resistance for an exactly half-wavelength dipole is found ... to be 73.1 ohms, referred to the maximum current point (dipole center). Therefore this is also the resistive component of the input impedance when the dipole is fed at the center. There is also a small reactive component of 42.5 ohms, inductive. This small inductive reactance may be eliminated by shortening the dipole to about 95% of a half-wavelength (i.e., to 0.475 {lamda}) The radiation resistance (and input impedance) is then 67 ohms. The pattern (beamwidth and gain) is not significantly affected by this slight shortening. ---- Blake, L. V., Antennas (Second), Artech House, Dedham, MA, 1984, pp. 175-176
And in the Antenna Engineering Handbook (Third) in the chapter on dipoles and monopoles I found a third-order polynomial that gave the same results given the above limitations. The claimed accuracy of this approximation is 0.5 ohms, and in the table entitled "Functions R(kl) and X(kl) Contained in the Formula of the Input Impedance of a Center-Driven Cylindrical Antenna" the values for pi/2 length (in radians) are R=73.12 and X=42.46. ---- Chen, To Tai and Long, Stuart A.,"Dipoles and Monopoles," Antenna Engineering Handbook (Third), Johnson, Richard C., Editor, McGraw-Hill, New York, NY, 1993, pp. 4-4, 4-5
Of course, if you start to include a ground plane, ideal or otherwise, these numbers go all to hell. But I think it does show that assuming that a resonant dipole has zero input reactance is not necessarily accurate.

In general: resonance => no reactive component (by definition)

In general: an exact half wavelength (or multiple thereof) has a reactive component for the feedpoint impedance (no matter where along the antenna the feedpoint is located).

In general: resonance is NOT an exact multiple of lambda/2 (at any multiple)

None of these are contradicted by the references above, nor any standard references (Kraus, Balanis, Orfanidis), all of which give explanations and derivations (multiple ones in most cases).

The subject of "analytical formulas" for feed point impedance (and mutual coupling) for various configurations (straight, angled, over a ground plane, next to other antennas in echelon, lined up, parallel, skew, non coplanar, you name it) - has been the subject of countless papers. There are formulas which attempt to approximate these things from first principles. There are also formulas which are a "best fit approximation" to measurements or models, and do not claim to be "representative of the actual theory" - just efficient and fast. A lot of these were used in the past for things like Yagi and Phased Array design. (See, e.g., King three term approximation)

Back before computers got fast, these equations were quite useful in design work. Now, though, it's probably easier to run a numerical model. Rather than write a function that calculates a series expansion for Sine or Cosine Integrals, and then figure out how to incorporate skew or images or whatever, it's easier to write a function that takes the parameter of interest, builds a model file, runs the model, and returns the desired parameter parsed from the output.

Hello Everyone,
I was wondering has anyone of you used this product? () My concern is whether this VNA can talk with nanovna saver or may be with some python program? This one looks good and has some review here:

Thank you.
Khalid

I keep seeing the statement that a resonant halfwave center fed dipole has zero reactance at the feed point, and I don't think this is always correct.

For a center-fed dipole that is 1/2 wavelength and where the length/diameter ratio is greater than fifteen (i.e. a wire antenna) in free space, (e.g., no mutual impedance from a ground plane), I found a couple of references that indicate Xl <> -Xc. They agree as to values.

Quoting Blake:

The radiation resistance for an exactly half-wavelength dipole is found ... to be 73.1 ohms, referred to the maximum current point (dipole center). Therefore this is also the resistive component of the input impedance when the dipole is fed at the center. There is also a small reactive component of 42.5 ohms, inductive. This small inductive reactance may be eliminated by shortening the dipole to about 95% of a half-wavelength (i.e., to 0.475 {lamda}) The radiation resistance (and input impedance) is then 67 ohms. The pattern (beamwidth and gain) is not significantly affected by this slight shortening. ---- Blake, L. V., Antennas (Second), Artech House, Dedham, MA, 1984, pp. 175-176

And in the Antenna Engineering Handbook (Third) in the chapter on dipoles and monopoles I found a third-order polynomial that gave the same results given the above limitations. The claimed accuracy of this approximation is 0.5 ohms, and in the table entitled "Functions R(kl) and X(kl) Contained in the Formula of the Input Impedance of a Center-Driven Cylindrical Antenna" the values for pi/2 length (in radians) are R=73.12 and X=42.46. ---- Chen, To Tai and Long, Stuart A.,"Dipoles and Monopoles," Antenna Engineering Handbook (Third), Johnson, Richard C., Editor, McGraw-Hill, New York, NY, 1993, pp. 4-4, 4-5

Of course, if you start to include a ground plane, ideal or otherwise, these numbers go all to hell. But I think it does show that assuming that a resonant dipole has zero input reactance is not necessarily accurate.

Use ST-Link programmer, see /g/nanovna-beta-test/message/3109
Part dump firmware.

Most easy see current version on version screen, and just download current firmware from official page:

For V2Plus4 exist 2 versions:
20220814 - only for last devices
20211227 - only for old?

Does anyone know how to back up the firmware? I want to back my up before I flash

Thanks

Again without the HTML formatting.


Calibration of any VNA is necessary.? You have to use the open'/short/50Ohm plugs along with your adaptor cable to calibrate the VNA "system".

So the proper sequence for any VNA is:

#1 Calibrate VNA with adaptor cable (i.e. any cable that is NOT part of your antenna system) using open/short/50Ohm
#2 Measure/tune antenna (not the coax from your rig).? This will be your VNA + adaptor cable plugged directly into the antenna with no chokes or anything in between.
#3 Tune your antenna to get 0 reactance and ideally 50Ohms.? But whatever 0 reactance point you have that is the resistance you need to match.? You can usually get below VSWR 2.0 with standard BALUNS of 2X, 4X, 8X, 16X if needed but it's much better to tune the antenna to 50 ohms if you can
Note that you can get 0 reactance at multiple points -- especially on 6M and higher.
#4 Measure your coax using the the 50Ohm terminator on the antenna side and ensure you have 50 Ohms and 0 reactance...or real close to that.? Also use the TDR to ensure no breaks in the coax (pretty rare).? You do need to know the velocity factor of your coax in order to use the distance calculation in the VNA TDR.
#5 Measure the complete coax/antenna system.? Should look very close to the same as it did at the antenna.
#6 Add a 1/8th section of coax? to the system and measure again....if there is no common mode the measurement will be very close to #5.? There should be no common mode if the antenna is 50Ohms and 0 reactance.? If the antenna is not 50Ohms (or not matched to 50Ohms) and/or has reactance than extra coax will change the tuned frequency and resistance....this is why you can't really tune at the rig if your system isn't matched near perfectly.? Common mode will modify the VSWR measurement.

Note that nowhere? above do we talk about minimum VSWR -- that's not the goal.? 50Ohm and 0 reactance is minimum VSWR.? Problem is we are rarely exactly on 50/0. And some antennas can never get there without a lot of monkeying around with custom BALUNs and matching networks.? So always measure your antenna system, coax, system, system+1/8th in that order.



Mike W9MDB

Calibration of any VNA is necessary.? You have to use the open'/short/50Ohm plugs along with your adaptor cable to calibrate the VNA "system".
So the proper sequence for any VNA is:
#1 Calibrate VNA with adaptor cable (i.e. any cable that is NOT part of your antenna system) using open/short/50Ohm#2 Measure/tune antenna (not the coax from your rig).? This will be your VNA + adaptor cable plugged directly into the antenna with no chokes or anything in between.#3 Tune your antenna to get 0 reactance and ideally 50Ohms.? But whatever 0 reactance point you have that is the resistance you need to match.? You can usually get below VSWR 2.0 with standard BALUNS of 2X, 4X, 8X, 16X if needed but it's much better to tune the antenna to 50 ohms if you canNote that you can get 0 reactance at multiple points -- especially on 6M and higher.#4 Measure your coax using the the 50Ohm terminator on the antenna side and ensure you have 50 Ohms and 0 reactance...or real close to that.? Also use the TDR to ensure no breaks in the coax (pretty rare).? You do need to know the velocity factor of your coax in order to use the distance calculation in the VNA TDR.#5 Measure the complete coax/antenna system.? Should look very close to the same as it did at the antenna.#6 Add a 1/8th section of coax? to the system and measure again....if there is no common mode the measurement will be very close to #5.? There should be no common mode if the antenna is 50Ohms and 0 reactance.? If the antenna is not 50Ohms (or not matched to 50Ohms) and/or has reactance than extra coax will change the tuned frequency and resistance....this is why you can't really tune at the rig if your system isn't matched near perfectly.? Common mode will modify the VSWR measurement.
Note that nowhere? above do we talk about minimum VSWR -- that's not the goal.? 50Ohm and 0 reactance is minimum VSWR.? Problem is we are rarely exactly on 50/0. And some antennas can never get there without a lot of monkeying around with custom BALUNs and matching networks.? So always measure your antenna system, coax, system, system+1/8th in that order.


Mike W9MDB

On the other hand, there seem to be many different firmware versions, leading
to confusion among the users, and incompatibility with the Windows support
programs.

To read the thread
/g/nanovna-users/message/29427
NanoVNA App - Installation and Use #applications

I believe you are right; it's to die for. Finally I did well to buy a nanoVNA-F.
--
Fran?ois

-----Message d'origine-----

De la part de David J Taylor
lundi 15 ao?t 2022 11:18

No, Gunk = sqrt(M1*M3/M2)

I agree with you

X: gain of antenna 1 under test (what we are looking for)
A1: gain of antenna 1
A2: gain of antenna 2

M13: measurement of link 1 to 3
M12: measurement of link 1 to 2
M23: measurement of link 2 to 3

M13 = X.A3
M12 = X.A2
M23 = A2.A3

A3 = M13/X
A2 = M12/X

M23 = A2.M13/X = M12.M13/X? (that's where my mistake was)
X? = (M12.M13)/M23
--
Fran?ois

-----Message d'origine-----

De la part de Jim Lux
mercredi 24 ao?t 2022 16:23

I thought I read somewhere it should be calibrated using the software if a person is going to be using the software for measurements

Why are you trying to calibrate it using the computer?
You can perform the calibration using the builtin calibration functions that use the three provided plugs (open, short & 50 ohm)

73
David

yes i have to flash dislord but i want to backup my firmware first what is the best program to do that with?

Thanks

Francois,

Sorry for the delay but I've been too busy to pay much attention to this group.

What I quoted was the IARU standard, which manufacturers follow to some extent. It would be better if they all followed it so that comparisons would mean something.

But it's the closest you're going to get to something meaningful.

Jerry, AI0K

Post your issue on his github or group.

Thank-you and I also applied to be part of the beta group but still waiting.

I got my in May, so I wonder if I have the "old" display. I guess my other question is if I have the newer display module and I install firmware that is for the older display modual what will happen to my display? If it don't work right I don't care because I will be using the software I can re-flash it back if I need the display to work right.

What is the best way to back up my firmware that I have on my nanoVNA?

Thanks

i had both found in the nanovna beta test group

dislord uploaded it there (to make it easy for you i add the fw file for the plus4)

and the nano vna app??

you find here



hope that helps you a bit

dg9bfc sigi



Am 24.08.2022 um 19:09 schrieb GMRS_two_way_radio via groups.io:

Siegfried Jackstien - do you have a link to the firmware and that software?? The only version of software i see is 2.09

Thanks