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nanoVNA V2 Plus4 measurment accuracy on 7 Mhz band


Lorenzo Simoncello - 2020/12/08 08:28

Hi all!
I've just received the nanoVNA V2 Plus4. I'm a new user.
Measuring my HF antenna, I can see on 40 m band, the minimun SWR is at 7.110 Mhz (measuring with the radio inside VSWR meter).
Using the nanoVNA V2 Plus4, i can see the minimun SWR at 7.050 Mhz (start frequency 6.9 Mhz, stop frequency 7,3 Mhz), right calibrated.

whats wrong? I think it is non the result I expected

It is a frequency sweep problem?
Is there a way to setup a very detailed mesurement on a specific limited frequency rage?

Thanks in advance for all suggestions

73 de Lorenzo iw3her

OwO 2020/12/09 00:31

Antenna counterpoise.

Lorenzo Simoncello - 2020/12/08 08:54

Thanks for your answer.
Could you explain better?
I've just made the same measure also with an external analogic VSWR meter... the minimun SWR is at 7.120 Mhz (quite closed with the internal radio VSWR meter that show minumun at 7.110 Mhz)
The nanoVNA V2 Plus4 show the minumun at 7.050 Mhz....

All measurements made at the end of the cable, near the radio.

Sorry, I'm new at this vna and may be there are some tips to know... any suggestion are welcome

73 Lorenzo iw3her

Dragan Milivojevic 2020/12/08 18:09

Connect the outer shell of the connector to the ground.

On Tue, 8 Dec 2020 at 17:54, Lorenzo Simoncello - IW3HER <
lorenzo.simoncello@gmail.com> wrote:

Tom Paratore 2020/12/08 18:15

Have you performed a calibration on the VNA?

You must do this each time you change the frequency range that you are sweeping.
On Dec 8, 2020, at 12:10 PM, Dragan Milivojevic <d.milivojevic@gmail.com> wrote:


Connect the outer shell of the connector to the ground.

On Tue, 8 Dec 2020 at 17:54, Lorenzo Simoncello - IW3HER <lorenzo.simoncello@gmail.com<mailto:lorenzo.simoncello@gmail.com>> wrote:
Thanks for your answer.
Could you explain better?
I've just made the same measure also with an external analogic VSWR meter... the minimun SWR is at 7.120 Mhz (quite closed with the internal radio VSWR meter that show minumun at 7.110 Mhz)
The nanoVNA V2 Plus4 show the minumun at 7.050 Mhz....

All measurements made at the end of the cable, near the radio.

Sorry, I'm new at this vna and may be there are some tips to know... any suggestion are welcome

73 Lorenzo iw3her

Siegfried Jackstien 2020/12/08 22:42

you have not your cable calibrated out ... so you measure not the
antenna but antenna with cable from feeding pojnt to shack

adding an swr meter changes that cable length ... so another fault added

so you are not measuring ... but "guessing"

greetz sigi dg9bfc

Am 08.12.2020 um 16:54 schrieb Lorenzo Simoncello - IW3HER:

Dragan Milivojevic 2020/12/09 05:17

He is measuring (with other devices) at the end of the cable
so no, he should get the same results.
The only difference is that in the measurement setup is that
other devices (rig, SWR meter) are connected to ground.

On Tue, 8 Dec 2020 at 23:42, Siegfried Jackstien <
siegfried.jackstien@freenet.de> wrote:

Tom Paratore 2020/12/09 12:44

You need to perform a calibration of the unit.
On Dec 8, 2020, at 11:17 PM, Dragan Milivojevic <d.milivojevic@gmail.com> wrote:


He is measuring (with other devices) at the end of the cable
so no, he should get the same results.
The only difference is that in the measurement setup is that
other devices (rig, SWR meter) are connected to ground.

On Tue, 8 Dec 2020 at 23:42, Siegfried Jackstien <siegfried.jackstien@freenet.de<mailto:siegfried.jackstien@freenet.de>> wrote:

you have not your cable calibrated out ... so you measure not the antenna but antenna with cable from feeding pojnt to shack

adding an swr meter changes that cable length ... so another fault added

so you are not measuring ... but "guessing"

greetz sigi dg9bfc

Am 08.12.2020 um 16:54 schrieb Lorenzo Simoncello - IW3HER:
Thanks for your answer.
Could you explain better?
I've just made the same measure also with an external analogic VSWR meter... the minimun SWR is at 7.120 Mhz (quite closed with the internal radio VSWR meter that show minumun at 7.110 Mhz)
The nanoVNA V2 Plus4 show the minumun at 7.050 Mhz....

All measurements made at the end of the cable, near the radio.

Sorry, I'm new at this vna and may be there are some tips to know... any suggestion are welcome

73 Lorenzo iw3her

C.M. 2020/12/11 21:05

I got a similar dilemma. I own quite a number of portable VNA's. I tried to measure a 433MHz rod monopole and here are the results:

Tindie v2:             427.000MHz      VSWR: 1.24
Tindie v2 plus:     431.000MHz      VSWR: 1.22
Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
N1201SA:           428.000MHz       VSWR: 1.42
Arinst VNA:         414.398MHz       VSWR: 1.20

All devices are calibrated against the same standards and each device is placed on a styrofoam support.

C.M. 2020/12/11 21:05

[Edited Message Follows]

I got a similar dilemma. I own quite a number of portable VNA's. I tried to measure a 433MHz rod monopole and here are the results:

Tindie v2:             428.000MHz      VSWR: 1.24
Tindie v2 plus:     431.000MHz      VSWR: 1.22
Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
N1201SA:           428.000MHz       VSWR: 1.42
Arinst VNA:         414.398MHz       VSWR: 1.20

All devices were calibrated against the same standards at port 1 and each device is placed on a styrofoam support. The antenna was directly connected to port 1 for each measurement.

C.M. 2020/12/11 21:05

[Edited Message Follows]

I got a similar dilemma. I own quite a number of portable VNA's. I tried to measure a 433MHz rod monopole and here are the results:

Tindie v2:             428.000MHz      VSWR: 1.24
Tindie v2 plus:     431.000MHz      VSWR: 1.22
Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
N1201SA:           428.000MHz       VSWR: 1.42
Arinst VNA:         414.398MHz       VSWR: 1.20
NanoVNA-Fv2:    424.000MHz      VSWR: 1.08

All devices were calibrated against the same standards at port 1 and each device is placed on a styrofoam support. The antenna was directly connected to port 1 for each measurement.

n2msqrp 2020/12/12 00:33

I believe the lack of a ground plane reference is affecting the measurements.
The body of the analyzer is affecting the resonant length.



CAn you mount the antenna on copper plate and measure?



Mike N2MS

> On 12/12/2020 12:05 AM C.M. <jasoncmcheng@hotmail.com> wrote:

>

>
>

>
>

> [Edited Message Follows]

>

> I got a similar dilemma. I own quite a number of portable VNA's. I tried to
measure a 433MHz rod monopole and here are the results:
>
> Tindie v2: 428.000MHz VSWR: 1.24
> Tindie v2 plus: 431.000MHz VSWR: 1.22
> Tindie v2 plus 4: 418.500MHz VSWR: 1.25
> N1201SA: 428.000MHz VSWR: 1.42
> Arinst VNA: 414.398MHz VSWR: 1.20
> NanoVNA-Fv2: 424.000MHz VSWR: 1.08
>
> All devices were calibrated against the same standards at port 1 and each
device is placed on a styrofoam support. The antenna was directly connected to
port 1 for each measurement.

_._,_._,_

* * *

C.M. 2020/12/12 00:02

Yes it is true that using a ground plane can reduce the discrepancy to within 1.5MHz i.e. 423.5 to 425MHz and VSWR 2.1 to 2.2 for all VNA's.

The problem is that I intend to tune the antenna on the actual device at the point where it is connected. A sufficiently large ground plane does not exist and different readings given by different VNA's lead to different tuning results.

Carlos Cabezas 2020/12/12 10:38

You need a dummy device with a good common mode choke on the coax exiting,
so the measurement reflects the real behaviour of the antenna.

Remember that a monopole is just half of the antenna. The other half being
the device PCB and enclosure. Even your hand holding it or the proximity to
your body will detune it.

El sáb., 12 dic. 2020 9:03, C.M. <jasoncmcheng@hotmail.com> escribió:

C.M. 2020/12/12 03:38

Yes it is logical to mount ferrites on the feed cable to eliminate its influence against the measurement.

I have seen so many videos on Youtube demonstrating direct connection of a whip antenna to the VNA. Now I learn that this will not give a correct measurement, at least not good for 433MHz.

Carlos Cabezas 2020/12/12 13:11

There is nothing like a "correct measurement" for a whip or monopole. The
device is part of the antenna, as It is acting like an imperfect ground
plane or counterpoise.

There is nothing wrong with measuring a whip antenna directly connected to
a VNA. You just must be aware that the measurement just represent the whip
behaviour while connected to that VNA along with power, USB cable or any
conductive structure connected to It.

El sáb., 12 dic. 2020 12:38, C.M. <jasoncmcheng@hotmail.com> escribió:

n2msqrp 2020/12/12 07:22

You would also get different results if you use the antenna on different
radios or if the antenna is near objects such as you body. Fortunately since
the antenna is connected directly to the radio you do not have to worry about
transmission line loss with a marginal SWR.



Mike N2MS

> On 12/12/2020 3:02 AM C.M. <jasoncmcheng@hotmail.com> wrote:

>

>
>

>
>

> Yes it is true that using a ground plane can reduce the discrepancy to
within 1.5MHz i.e. 423.5 to 425MHz and VSWR 2.1 to 2.2 for all VNA's.
>
> The problem is that I intend to tune the antenna on the actual device at the
point where it is connected. A sufficiently large ground plane does not exist
and different readings given by different VNA's lead to different tuning
results.

_._,_._,_

* * *

Jim Lux 2020/12/12 07:48

On 12/11/20 9:05 PM, C.M. wrote:
>
> [Edited Message Follows]
>
> I got a similar dilemma. I own quite a number of portable VNA's. I
> tried to measure a 433MHz rod monopole and here are the results:
>
> Tindie v2:             428.000MHz      VSWR: 1.24
> Tindie v2 plus:     431.000MHz      VSWR: 1.22
> Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
> N1201SA:           428.000MHz       VSWR: 1.42
> Arinst VNA:         414.398MHz       VSWR: 1.20
> NanoVNA-Fv2:    424.000MHz      VSWR: 1.08
>

Welcome to the wild world of antenna metrology !

That's not a huge difference, converting to voltage reflection
coefficient magnitude

1.24 -> 0.107

1.22 -> 0.099

1.25 -> 0.111

1.42 -> 0.174

1.20 -> 0.091

1.08 -> 0.038

With the exception of the two noticeable outliers, you're looking at 5%
sort of variation, which isn't uncommon.


This is a rod monopole, you say? Is it 1/4 wavelength mounted on top of
a large (> 1 lambda in all directions, i.e. about 1.4x1.4 meters, but
preferably more like 2 lambda) metal surface, and then the VNA is
underneath it? You're reading the VNA from a distance (more than 2
meters away)? There's no other power cables, USB cables, etc.  The
environment around the antenna and the ground plane is strictly
controlled - there's nothing within several meters (or at least nothing
that moves)

If you really want to get a handle on measurement uncertainty, you'll
need to make multiple measurements with each device (with a
disconnection and reconnection - since that is often one of sources of
measurement uncertainty. You taking some pains to torque the connector
the same each time to the VNA?

Are some SMA and some N?  Was that factored into the cal strategy?

In real terms, what does 5% mean - these are all around 20 dB RL - that
means the test set is seeing about 1% of the RF power reflecting back at
it. The antenna is radiating the other 99%.  So if there's something in
the vicinity of the antenna that reflects back another 1%, then the
reflection coefficient changes about 10%.  It doesn't take much to
reflect (or scatter, is the usual term) 1%

A person has a scattering cross section of about a 0.5-1 square meter
back towards the source (monostatic cross section) - At a distance of 2
meters, your monopole's field is spread out over about 12 square meters
(really back of the envelope, and 2m is probably actually in the near
field still), so a 1 square meter reflector will send back 1/12th of the
energy (i.e. about -10dB) - yeah the reflector's not a corner cube
(although that's taken into account in the monostatic cross section), so
not all of the energy comes back to the source. And, you don't know what
phase it is. And it's physically large, so the phase of the reflection
from a person's middle comes back at a different phase than a person's
head or arms.

But the point is - it's *really* easy to get a contamination of a
measurement that will show up as a 1 dB change in a reflection magnitude
of -20dB.

For those wanting to set up home antenna ranges (a *great* use of a
nanoVNA) there's a bunch of things you can do.  - get the measurement
equipment away from the AUT - a cable, with lots of the *correct*
ferrite around it (don't just assume any old ferrites are right).  -
have a consistent ground plane and other environment - think in terms of
multiple wavelengths - a good "open air test site" is really open .  Be
able to adjust the height or position of the AUT and its ground plane,
and take a bunch of measurements, and look for a cyclical variation as
you move it (the sure sign of a scattering source somewhere).  Move your
receiving probe (the other port on the VNA) for the same reason.

Good luck.


5-10% on a "backyard range" is doing quite well.

Jim Lux 2020/12/12 07:49

On 12/11/20 9:05 PM, C.M. wrote:
>
> [Edited Message Follows]
>
> I got a similar dilemma. I own quite a number of portable VNA's. I
> tried to measure a 433MHz rod monopole and here are the results:
>
> Tindie v2:             428.000MHz      VSWR: 1.24
> Tindie v2 plus:     431.000MHz      VSWR: 1.22
> Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
> N1201SA:           428.000MHz       VSWR: 1.42
> Arinst VNA:         414.398MHz       VSWR: 1.20
> NanoVNA-Fv2:    424.000MHz      VSWR: 1.08
>

That's not a huge difference, converting to voltage reflection
coefficient magnitude

1.24 -> 0.107

1.22 -> 0.099

1.25 -> 0.111

1.42 -> 0.174

1.20 -> 0.091

1.08 -> 0.038

With the exception of the two noticeable outliers, you're looking at 10%
sort of variation


This is a rod monopole, you say? Is it 1/4 wavelength mounted on top of
a large metal surface, and then the VNA is underneath it?


Jim Lux 2020/12/12 07:50

On 12/11/20 9:05 PM, C.M. wrote:
>
> [Edited Message Follows]
>
> I got a similar dilemma. I own quite a number of portable VNA's. I
> tried to measure a 433MHz rod monopole and here are the results:
>
> Tindie v2:             428.000MHz      VSWR: 1.24
> Tindie v2 plus:     431.000MHz      VSWR: 1.22
> Tindie v2 plus 4:  418.500MHz      VSWR: 1.25
> N1201SA:           428.000MHz       VSWR: 1.42
> Arinst VNA:         414.398MHz       VSWR: 1.20
> NanoVNA-Fv2:    424.000MHz      VSWR: 1.08
>

Welcome to the wild world of antenna metrology !

That's not a huge difference, converting to voltage reflection
coefficient magnitude

1.24 -> 0.107

1.22 -> 0.099

1.25 -> 0.111

1.42 -> 0.174

1.20 -> 0.091

1.08 -> 0.038

With the exception of the two noticeable outliers, you're looking at 5%
sort of variation, which isn't uncommon.


This is a rod monopole, you say? Is it 1/4 wavelength mounted on top of
a large (> 1 lambda in all directions, i.e. about 1.4x1.4 meters, but
preferably more like 2 lambda) metal surface, and then the VNA is
underneath it? You're reading the VNA from a distance (more than 2
meters away)? There's no other power cables, USB cables, etc.  The
environment around the antenna and the ground plane is strictly
controlled - there's nothing within several meters (or at least nothing
that moves)

If you really want to get a handle on measurement uncertainty, you'll
need to make multiple measurements with each device (with a
disconnection and reconnection - since that is often one of sources of
measurement uncertainty. You taking some pains to torque the connector
the same each time to the VNA?

Are some SMA and some N?  Was that factored into the cal strategy?

In real terms, what does 5% mean - these are all around 20 dB RL - that
means the test set is seeing about 1% of the RF power reflecting back at
it. The antenna is radiating the other 99%.  So if there's something in
the vicinity of the antenna that reflects back another 1%, then the
reflection coefficient changes about 10%.  It doesn't take much to
reflect (or scatter, is the usual term) 1%

A person has a scattering cross section of about a 0.5-1 square meter
back towards the source (monostatic cross section) - At a distance of 2
meters, your monopole's field is spread out over about 12 square meters
(really back of the envelope, and 2m is probably actually in the near
field still), so a 1 square meter reflector will send back 1/12th of the
energy (i.e. about -10dB) - yeah the reflector's not a corner cube
(although that's taken into account in the monostatic cross section), so
not all of the energy comes back to the source. And, you don't know what
phase it is. And it's physically large, so the phase of the reflection
from a person's middle comes back at a different phase than a person's
head or arms.

But the point is - it's *really* easy to get a contamination of a
measurement that will show up as a 1 dB change in a reflection magnitude
of -20dB.

For those wanting to set up home antenna ranges (a *great* use of a
nanoVNA) there's a bunch of things you can do.  - get the measurement
equipment away from the AUT - a cable, with lots of the *correct*
ferrite around it (don't just assume any old ferrites are right).  -
have a consistent ground plane and other environment - think in terms of
multiple wavelengths - a good "open air test site" is really open .  Be
able to adjust the height or position of the AUT and its ground plane,
and take a bunch of measurements, and look for a cyclical variation as
you move it (the sure sign of a scattering source somewhere).  Move your
receiving probe (the other port on the VNA) for the same reason.

Good luck.


5-10% on a "backyard range" is doing quite well.




David Eckhardt 2020/12/12 16:28

A 12" diameter pie tin would work well. Strive to have a circle of 12" in
diameter on which you mount the antenna in the center. Them measure
everything again and email backi.

Dave - WØLEV

On Sat, Dec 12, 2020 at 5:33 AM n2msqrp <mstangelo@comcast.net> wrote:

> I believe the lack of a ground plane reference is affecting the
> measurements. The body of the analyzer is affecting the resonant length.
>
> CAn you mount the antenna on copper plate and measure?
>
> Mike N2MS
>
> On 12/12/2020 12:05 AM C.M. <jasoncmcheng@hotmail.com> wrote:
>
>
>
> [Edited Message Follows]
> I got a similar dilemma. I own quite a number of portable VNA's. I tried
> to measure a 433MHz rod monopole and here are the results:
>
> Tindie v2: 428.000MHz VSWR: 1.24
> Tindie v2 plus: 431.000MHz VSWR: 1.22
> Tindie v2 plus 4: 418.500MHz VSWR: 1.25
> N1201SA: 428.000MHz VSWR: 1.42
> Arinst VNA: 414.398MHz VSWR: 1.20
> NanoVNA-Fv2: 424.000MHz VSWR: 1.08
>
> All devices were calibrated against the same standards at port 1 and each
> device is placed on a styrofoam support. The antenna was directly connected
> to port 1 for each measurement.
>
>
>
>

--
*Dave - WØLEV*
*Just Let Darwin Work*

Jim Lux 2020/12/12 10:01

On 12/12/20 8:28 AM, David Eckhardt wrote:
> A 12" diameter pie tin would work well.  Strive to have a circle of
> 12" in diameter on which you mount the antenna in the center.  Them
> measure everything again and email backi.
>
> Dave - WØLEV


12" is about 40% of a wavelength. It might mask some of the "VNA as
other half of antenna", but nowhere near large enough to make accurate
measurements.  A good rule of thumb is that the *radius* of the ground
plane should be somewhat larger than the height of the antenna.  So if
you have a little rubber duck that's 6" tall, the 12" pie plate (I use
pizza pans for this kind of thing) would be a good starting point.  If
it's a mobile 5/8 whip that's 18" tall, you need something a bit bigger.

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