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

Antenna counterpoise.

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

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:

> 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
>
>
>

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

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
>

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:

> 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
>
>
>
>

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

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.

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.

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:

> 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.
>
>
>

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.

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:

> 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.
>
>
>

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.

_._,_._,_

* * *

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.