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I am having different SWR readings between my NanoVNA-H (Not connected to the computer) and NanoVNA saver versions 3.9 and 3.10, NanoVNA-H version 1.0.45

I have followed directions carefully when setting up and verified calibration when the Nano is not connected to the computer.
I don’t believe there is a way to verify calibration when in Nano saver.

This problem appears regardless whether I am using version 3.9 or 3.10 of saver.

An example would be the following:

When Nano is not connected to the computer the SWR for a given VHF frequency would be 1.5.
When connected to Saver it may be 3.4 in saver version 3.9 doing the measurements correctly.
and 4.2 in version 3.10.

When I am thinking about it this is not possible because the SWR is being read off of the Nano unit to the saver.

I have used the manuals for SWR as well as several You Tube videos to verify that I am the measurements correctly.

Thank You,
Steven/kc3dow

Are you measuring a vertical ground plane antenna?
When you connect the nano to the computer, the ground on the cable makes
your computer case and all attached to it part of the local ground plane,
which is much larger than the nano itself. This can cause significant
variations at vhf and above if you are not careful in providing a ground
plane for the antenna in your measurement setup. The cable also provides a
path for electrical noise between the computer and nano. Ferrites on the
USB cable can help with this part of the problem.

On Mon, Jul 31, 2023, 2:49 PM Steven KC3DOW via groups.io <treasurebox7762=
[email protected]> wrote:

I am having different SWR readings between my NanoVNA-H (Not connected to
the computer) and NanoVNA saver versions 3.9 and 3.10, NanoVNA-H version
1.0.45

I have followed directions carefully when setting up and verified
calibration when the Nano is not connected to the computer.
I don’t believe there is a way to verify calibration when in Nano saver.

This problem appears regardless whether I am using version 3.9 or 3.10 of
saver.

An example would be the following:

When Nano is not connected to the computer the SWR for a given VHF
frequency would be 1.5.
When connected to Saver it may be 3.4 in saver version 3.9 doing the
measurements correctly.
and 4.2 in version 3.10.

When I am thinking about it this is not possible because the SWR is being
read off of the Nano unit to the saver.

I have used the manuals for SWR as well as several You Tube videos to
verify that I am the measurements correctly.

Thank You,
Steven/kc3dow

That is very odd indeed, Steven.

Try this:
Connect a 50 ohm dummy load and do an SWR sweep when Nano VNA is not on SAVER.
Take a look at SWR, reflection coefficient, return loss, and Smith Chart.

Then do the same tests with the same dummy load with Nano VNA SAVER software running.
The graphs should be identical

If not, I suspect a “calibration” error when you were doing the Nano SAVE calibrations.

If they are identical with a dummy load - then there is no problem with SAVER.
Then I would check the coax for something “odd”.

Let us know if the dummy load produces a SWR of 1:1 across the band you are testing.

BTW - what antenna ? and what frequencies?

If this is your “end fed” then I would look for RFI leaking back on the outside shield of the coax.
That is often an issue with “end-fed, one-half wave” 130 ft wires with a 49:1 UNUN.

Put some kind of “choke” in the feed line.
The outside shield may be acting like your “counterpoise” inadvertently.

give me a call when you figure it out
k3euibarry@...

barry

Oh…. I just saw you said a VHF antenna.

I’m going to guess —-

Any chance this VHF antenna is a J-Pole?

If so, when measuring SWR with your Nano VNA, rub your hand up/down the coax near the VNA jack and see if the SWR changes as you move your hand over a 1 meter length.

If the SWR changes, we know the problem.
Current on the outside of the coax.

barry
k3eui

Hi Barry,
Not a 'J' pole. It is a Diamond X-50A. My previous antenna was a 'J' pole but did not reach an area that I needed to reach.
This Diamond does the job but I am trying to train myself to use the NanoVNA-H and learn Saver when I ran into the problem. I was trying to check swr to see if it was within specs.
By the way. I did the calibration correctly and by the book and also did the verification which was successful.
I don't see any way to verify calibration with Saver but what I do is setup the frequencies that I want to check before doing calibration.

Thanks for your help,
Steven/kc3dow

QUOTE: I don't see any way to verify calibration with Saver but what I do
is setup the frequencies that I want to check before doing calibration.
..........................................................................................................................

You are correct in setting up your frequency span before doing the cal. in
Saver.

However, it is easy to check cal. once it is run in Saver. Use the same
standards you used for cal. and sweep each one at a time. The short should
show a short - extreme left of the Smith Chart. The open should show an
open - extreme right of the smith Chart. The 50-ohm standard should be
bullseye in the center of the Smith Chart. It's that simple.

Dave - W?LEV

On Wed, Aug 2, 2023 at 7:53?PM Steven KC3DOW via groups.io <treasurebox7762=
[email protected]> wrote:

Hi Barry,
Not a 'J' pole. It is a Diamond X-50A. My previous antenna was a 'J' pole
but did not reach an area that I needed to reach.
This Diamond does the job but I am trying to train myself to use the
NanoVNA-H and learn Saver when I ran into the problem. I was trying to
check swr to see if it was within specs.
By the way. I did the calibration correctly and by the book and also did
the verification which was successful.
I don't see any way to verify calibration with Saver but what I do is
setup the frequencies that I want to check before doing calibration.

Thanks for your help,
Steven/kc3dow

--

*Dave - W?LEV*


--
Dave - W?LEV

Wow, Thanks Dave.
I did not realize I could do that. Just like verifying calibration on the Nano without connecting to the computer.

Steven/kc3dow

Steven
Did you do a CALIBRATION for each band, over a fairly narrow frequency range?
I do that, and SAVE the file: 80m CAL, 40m CAL, etc.
I also did one for HF CAL covering 1-30 MHz with with SAVER I can use thousands of cal points and when I save the file, it is maybe 200 kB.

If your SAVER readings are different from the internal readings, I would first check your CAL files on SAVER.

As mentioned, put the 50 ohm dummy load on and see if the SWR is low (1:1) on each band you test.
2m and 440 MHz has some additional challenges for the leads and adapters.

de k3eui

On 8/3/23 5:06 AM, Barry K3EUI wrote:

Steven
Did you do a CALIBRATION for each band, over a fairly narrow frequency range?
I do that, and SAVE the file: 80m CAL, 40m CAL, etc.
I also did one for HF CAL covering 1-30 MHz with with SAVER I can use thousands of cal points and when I save the file, it is maybe 200 kB.
If your SAVER readings are different from the internal readings, I would first check your CAL files on SAVER.
As mentioned, put the 50 ohm dummy load on and see if the SWR is low (1:1) on each band you test.
2m and 440 MHz has some additional challenges for the leads and adapters.
de k3eui

Just a comment on Calibration - if you are calibrating at the NanoVNA, or with short jumpers, then a single wide band cal is probably sufficient - the interpolation algorithm will find the right values when you're making narrow sweep range measurements.

BUT, if you're calibrating at the end of long coax (e.g. measuring an antenna through the feedline), then you might need narrower calibration ranges, or more properly, more closely spaced calibration points.]

For example if you have 100 ft of coax (call it 30 meters) equivalent free space length, the feedline puts dips and peaks into the reflection values that are spaced every 5 MHz.

A 0-500 MHz sweep with 100 points only measures every 5 MHz, so the interpolation won't necessarily return the right values.

As Barry comments, with NanoVNA Saver (and other tools) you can do a thousand or more points in your cal, so then it works ok.

I'm finding this conversation very interesting. I'm just getting
up-to-speed with the nanoVNA and thought I understood that the best place
to calibrate for SWR measurement would be close to the transceiver,
including all cabling. What would be the advantage of bypassing the
feedline from the calibration?
In summary, it sounds like if one has a 30m feedline, calibration should be
performed in smaller ranges for the best results, right?

On 8/3/23 9:02 AM, Michael Hughes wrote:

I'm finding this conversation very interesting. I'm just getting
up-to-speed with the nanoVNA and thought I understood that the best place
to calibrate for SWR measurement would be close to the transceiver,
including all cabling. What would be the advantage of bypassing the
feedline from the calibration?
In summary, it sounds like if one has a 30m feedline, calibration should be
performed in smaller ranges for the best results, right?

It depends on whether you are interested in the SWR as seen by the transceiver or looking at the antenna.

If you're just looking to "tune" for best match - VNA calibrated at its connectors.

If you're fiddling with the antenna (or with a switch box or something), then calibrating at the end of the feedline might be more useful.

Or, if you're looking at measuring antenna interactions in an array.

It's just a matter of what you want to know.

Hello Michael,

Jim is correct. I will say it in a simpler fashion just so it is clearer, if needed.....

If you are using your nanovna to do antenna fine tuning so that you can hook it up to radio and use it - then do your calibration on nano and then measure at the coax right where it plugs into the radio. This will give you the swr over the coax all the way to the antenna. Do your adjusting on the antenna until you get an acceptable vswr level that you want to hook up to the radio. Then unplug the nano, plug the coax into the radio (or tuner) and away you go.

If you are building an antenna or balun or unun then just measure at the connector of that device and build to what you are looking for.

So, both of you were correct in your statements.

Hope this helped.

73
Mark

Very helpful, both of you. Appreciate it.

I have a NanoVNA-F and went through the calibration process and then was measuring a few of my HT antennas to get comfortable with the VNA. I noticed very different readings if I held the VNA with two hands, one hand, and not touching it on a wooden surface. Is there a specific way to hold or not hold the VNA when doing measurements? Do you need to ground it?

I was getting values like 1.3 with two hands, 1.5 - 2.3 with left or right hand, and 3+ with it resting on a wood table.

Brian
W1BKW