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I'm new to the NanoVNA H-4.? If I calibrate for SWR in the range of 144-174, and then I change the range to, say, 144-148, do I need to re calibrate?

IOW, for the purposes of SWR readings, under what circumstances do I need to re calibrate?

When changing sweep ranges, it's always a good idea to recal.

Dave - W?LEV

On Tue, Apr 22, 2025 at 3:10?PM Kenneth Roberts via groups.io <kenr313=
[email protected]> wrote:

I'm new to the NanoVNA H-4. If I calibrate for SWR in the range of
144-174, and then I change the range to, say, 144-148, do I need to re
calibrate?

IOW, for the purposes of SWR readings, under what circumstances do I
need to re calibrate?

--

*Dave - W?LEV*


--
Dave - W?LEV

As the second range is well within the first range, you may be able to get
away with it, though the ideal way is as Dave has mentioned.

73
Jon, VU2JO

On Tue, Apr 22, 2025 at 8:40?PM Kenneth Roberts via groups.io <kenr313=
[email protected]> wrote:

I'm new to the NanoVNA H-4. If I calibrate for SWR in the range of
144-174, and then I change the range to, say, 144-148, do I need to re
calibrate?

IOW, for the purposes of SWR readings, under what circumstances do I
need to re calibrate?

I myself wouldn't be sure of the results. I would re-calibrate it for
144-148 MHz. Then store in a different memory slot than the one I stored
144-174 MHz in. It only takes a few minutes to calibrate it.

Zack W9SZ

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Virus-free.www.avg.com
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On Tue, Apr 22, 2025 at 11:22?AM Jon via groups.io <vu2jo0=
[email protected]> wrote:

As the second range is well within the first range, you may be able to get
away with it, though the ideal way is as Dave has mentioned.

73
Jon, VU2JO

On Tue, Apr 22, 2025 at 8:40?PM Kenneth Roberts via groups.io <kenr313=
[email protected]> wrote:

I'm new to the NanoVNA H-4. If I calibrate for SWR in the range of
144-174, and then I change the range to, say, 144-148, do I need to re
calibrate?

IOW, for the purposes of SWR readings, under what circumstances do I
need to re calibrate?

On Tue, Apr 22, 2025 at 09:22 AM, Jon wrote:

As the second range is well within the first range

With the second range within the first range, the nanovna does an excellent job of interpolating between the calibration points, and you will get good readings, especially for general tasks like return loss, SWR, attenuation, etc. But if you need the best precision in the results, do a calibration at the new range.

Thanks to all for the advice.

I have a whole load of rubber duck antennas that I'm checking so see at what range they should work best.? Some of them I don't even know what band they're supposed to be designed for.?? Good learning experience for using the Nano.

Ken, W4KRR

QUOTE: Be sure to calibrate to the end of the coax at the antenna. Coax
will influence the measurements, especially if it is longer than a
wavelength. (unless is is electrically an odd multiple of a half wave.) You
will find your measurement make more sense at VHF/UHF frequencies with the
NanoVNA calibrated to the antenna end of the coax.

****

A bit of a correction is in order:

1) COAX WILL NOT INFLUENCE THE MEASUREMAENTS. But if there is a mismatch
at the antenna where the coax connects to the antenna, the COAX WILL ALTER
the IMPEDANCE. That alteration is what you will measure between the
antenna feedpoint and the shack end of the coax.

2) ANY WHOLE NUMBER MULTIPLE of an electrical 1/2-wavelength in the coax
will reflect the actual antenna feedpoint impedance with a bit loss
included. A 1/2-wavelength is also fully around, 360-degrees or
2π-radians, the Smith Chart.

3) Once you calibrate the feed coax at the end where it would connect to
the antenna feedpoint, you will measure the actual antenna feedpoint
impedance at the shack end of the coax regardless of coax length.

Dave - W?LEV

On Tue, Apr 22, 2025 at 10:25?PM Russ via groups.io <u.rusty=
[email protected]> wrote:

On Tue, Apr 22, 2025 at 08:10 AM, Kenneth Roberts wrote:

I'm new to the NanoVNA H-4. If I calibrate for SWR in the range of

144-174,

and then I change the range to, say, 144-148, do I need to re calibrate?

I always do, just to obtain as much accuracy as possible.

Also: Be sure to calibrate to the end of the coax at the antenna. Coax
will influence the measurements, especially if it is longer than a
wavelength. (unless is is electrically an odd multiple of a half wave.) You
will find your measurement make more sense at VHF/UHF frequencies with the
NanoVNA calibrated to the antenna end of the coax.

--

*Dave - W?LEV*


--
Dave - W?LEV

I have a whole load of rubber duck antennas that I'm checking so see at
what range they should work best.

Ken,
the behavior of rubber duckies depends significantly on the radio they are attached to. So, to get reasonably accurate results when measuring them with the nanoVNA, I suggest that you build a metal bracket about the size of a typical HT, covered with some insulation to mimmick the plastic body of an HT, mount the nanoVNA in that bracket, its measuring port bonded to the bracket, and then hold that contraption in your hand like you would hold an HT, while making the measurements.

You could even use a plastic box the size of an HT, covered with aluminium foil on the inside, properly bonded to the nanoVNA's port.

Of course you need to run the nanoVNA without an USB cable connected.

You will see that depending on how you grab that test contraption, the measured values will shift somewhat. If you mount the antenna directly to the nanoVNA, they will shift more, since the nanoVNA is a lot smaller than an HT, at least the 2.8" screen version. I haven't compared the size of the H4 version to that of an HT. It should be closer, but maybe not close enough.

Perhaps someone else can comment on how accurate the measurements come out when mounting a rubber duckie directly on an H4?

Manfred

Yes, I have noted that the SWR changes when holding the VNA vs. not holding it, and touching the SMA connector vs. not touching it. The readings generally are better when touching vs. not touching.

Ken, W4KRR

This can be improved by adding a small Common Mode Choke at the VNA end to
help isolate the coax from the case of the device. The frequency being
measured also has an impact.

*Clyde K. Spencer*



On Wed, Apr 23, 2025 at 1:28?PM Kenneth Roberts via groups.io <kenr313=
[email protected]> wrote:

Yes, I have noted that the SWR changes when holding the VNA vs. not
holding it, and touching the SMA connector vs. not touching it. The
readings generally are better when touching vs. not touching.

Ken, W4KRR


On 4/23/2025 12:20 PM, Manfred Mornhinweg via groups.io wrote:

I have a whole load of rubber duck antennas that I'm checking so see at
what range they should work best.

Ken,
the behavior of rubber duckies depends significantly on the radio they

are attached to. So, to get reasonably accurate results when measuring them
with the nanoVNA, I suggest that you build a metal bracket about the size
of a typical HT, covered with some insulation to mimmick the plastic body
of an HT, mount the nanoVNA in that bracket, its measuring port bonded to
the bracket, and then hold that contraption in your hand like you would
hold an HT, while making the measurements.

You could even use a plastic box the size of an HT, covered with

aluminium foil on the inside, properly bonded to the nanoVNA's port.

Of course you need to run the nanoVNA without an USB cable connected.

You will see that depending on how you grab that test contraption, the

measured values will shift somewhat. If you mount the antenna directly to
the nanoVNA, they will shift more, since the nanoVNA is a lot smaller than
an HT, at least the 2.8" screen version. I haven't compared the size of the
H4 version to that of an HT. It should be closer, but maybe not close
enough.

Perhaps someone else can comment on how accurate the measurements come

out when mounting a rubber duckie directly on an H4?

Manfred

On Wed, Apr 23, 2025 at 06:31 PM, Clyde Spencer wrote:

This can be improved by adding a small Common Mode Choke at the VNA end to
help isolate the coax from the case of the device.

Clyde, in HTs used for their purpose, which is portable communications, the body of the HT, and even the body of the operator are all part of the antenna. If you mount a rubber duckie directly on a NanoVNA, possibly on a metal bracket, and hold it in your hand, you emulate this situation, and get values close to the real thing. But if you isolate the rubber duckie from the instrument by means of a common mode choke, you will create a very different situation, and totally mess up the measurement!

A rubber duckie at the end of a coax cable will behave totally different than when mounted on an HT.

Manfred