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When using my NanoVNA to adjust length of a 20m hamstick, the readings kept changing depending on what the NanoVNA was sitting on (truck hood, pelican case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly adjusted antenna?
Thanks, Coyote

Sent with [Proton Mail]() secure email.

Put the NanoVNA on a non conductive surface well away from where the antenna is mounted.

The reason you are getting different readings is because you are changing the ground plain of the antenna system with your body or metal surface or non metal surface. I would guess the antenna itself doesn't have a sufficient ground plain to work off of and so any small changes to the ground side of the system, IE where the coax is finding ground, will alter the measurements.

When you say it's changing, how much is the SWR changing? If by a couple points it's not a big deal. If it's changing from say 1.1 to 1 to 3 to 1 or 4 to 1 by placing the NanoVNA on the hood verses in your hand then you've got a antenna ground issue.

You can try connecting a counterpoise to the ground side of the antenna mount if you can't electrically ground it to the vehicle. That would be a quarter wave of wire or so on the band you are trying to tune.

I would say that the most accurate reading will be the one where the NanoVNA is on the insulated pelican case.

Is the radio you are using going to be chassis grounded to the vehicle or floating inside or outside the vehicle during operation? If floating you want the NanoVna to most accurately represent where the radio will be.

You can cross check this by tuning with the NanoVna, then checking the swr with the radio itself. If they are close, within .5 or so,? you'll be good to go on SWR.



73

Colin, VA6GG

I am waiting for NanoVNA to be delivered this week. My FT-710 radio is on a
steel table. I am planning to use an SMA to SO239 patch cable of 1m length
to connect NanoVNA to PL 259 of my antennas.

From this discussion, it seems that I will have to get a wooden table to
keep the NanoVNA?

I have not used NanoVNA yet.

73
Jon, VU2JO

On Mon, Feb 3, 2025 at 6:53?AM Colin McDonald via groups.io <colinrmcdonald=
[email protected]> wrote:

Put the NanoVNA on a non conductive surface well away from where the
antenna is mounted.

The reason you are getting different readings is because you are
changing the ground plain of the antenna system with your body or metal
surface or non metal surface. I would guess the antenna itself doesn't
have a sufficient ground plain to work off of and so any small changes
to the ground side of the system, IE where the coax is finding ground,
will alter the measurements.

When you say it's changing, how much is the SWR changing? If by a couple
points it's not a big deal. If it's changing from say 1.1 to 1 to 3 to 1
or 4 to 1 by placing the NanoVNA on the hood verses in your hand then
you've got a antenna ground issue.

You can try connecting a counterpoise to the ground side of the antenna
mount if you can't electrically ground it to the vehicle. That would be
a quarter wave of wire or so on the band you are trying to tune.

I would say that the most accurate reading will be the one where the
NanoVNA is on the insulated pelican case.

Is the radio you are using going to be chassis grounded to the vehicle
or floating inside or outside the vehicle during operation? If floating
you want the NanoVna to most accurately represent where the radio will be.

You can cross check this by tuning with the NanoVna, then checking the
swr with the radio itself. If they are close, within .5 or so, you'll
be good to go on SWR.



73

Colin, VA6GG

On 2025-02-02 6:04 p.m., Coyote via groups.io wrote:

When using my NanoVNA to adjust length of a 20m hamstick, the readings

kept changing depending on what the NanoVNA was sitting on (truck hood,
pelican case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly

adjusted antenna?

Thanks, Coyote

Sent with [Proton Mail]() secure email.

The steel table may have an effect. But based on your description, the antennas are some distance away from that table. The table will likely not have any impact on the antenna system if it's separated from the antennas by distance.
To prevent any possible interaction just put the NanoVNA on a non conductive insulator or surface like a piece of cardboard or plastic or rubber mat or something.
The radio is insulated from the table by its insulated feet on the case, so you want to mimic that to some extent if you are using the NanoVna to tune the antenna system from the radio end of the coax.
In the previous scenario, the OP was working in a mobile situation which has different variables to a fixed installation at home.

73
Colin, VA6GG

Thanks a lot for the prompt reply Colin. Shall come back to you in case it
doesn't work out.

73
Jon, VU2JO

On Mon, Feb 3, 2025 at 7:13?AM Colin McDonald via groups.io <colinrmcdonald=
[email protected]> wrote:

The steel table may have an effect. But based on your description, the
antennas are some distance away from that table. The table will likely
not have any impact on the antenna system if it's separated from the
antennas by distance.
To prevent any possible interaction just put the NanoVNA on a non
conductive insulator or surface like a piece of cardboard or plastic or
rubber mat or something.
The radio is insulated from the table by its insulated feet on the case,
so you want to mimic that to some extent if you are using the NanoVna to
tune the antenna system from the radio end of the coax.
In the previous scenario, the OP was working in a mobile situation which
has different variables to a fixed installation at home.

73
Colin, VA6GG
On 2025-02-02 6:33 p.m., Jon via groups.io wrote:

I am waiting for NanoVNA to be delivered this week. My FT-710 radio is

on a

steel table. I am planning to use an SMA to SO239 patch cable of 1m

length

to connect NanoVNA to PL 259 of my antennas.

From this discussion, it seems that I will have to get a wooden table to
keep the NanoVNA?

I have not used NanoVNA yet.

73
Jon, VU2JO

On Mon, Feb 3, 2025 at 6:53?AM Colin McDonald via groups.io

<colinrmcdonald=

[email protected]> wrote:

Put the NanoVNA on a non conductive surface well away from where the
antenna is mounted.

The reason you are getting different readings is because you are
changing the ground plain of the antenna system with your body or metal
surface or non metal surface. I would guess the antenna itself doesn't
have a sufficient ground plain to work off of and so any small changes
to the ground side of the system, IE where the coax is finding ground,
will alter the measurements.

When you say it's changing, how much is the SWR changing? If by a couple
points it's not a big deal. If it's changing from say 1.1 to 1 to 3 to 1
or 4 to 1 by placing the NanoVNA on the hood verses in your hand then
you've got a antenna ground issue.

You can try connecting a counterpoise to the ground side of the antenna
mount if you can't electrically ground it to the vehicle. That would be
a quarter wave of wire or so on the band you are trying to tune.

I would say that the most accurate reading will be the one where the
NanoVNA is on the insulated pelican case.

Is the radio you are using going to be chassis grounded to the vehicle
or floating inside or outside the vehicle during operation? If floating
you want the NanoVna to most accurately represent where the radio will

be.

You can cross check this by tuning with the NanoVna, then checking the
swr with the radio itself. If they are close, within .5 or so, you'll
be good to go on SWR.



73

Colin, VA6GG

On 2025-02-02 6:04 p.m., Coyote via groups.io wrote:

When using my NanoVNA to adjust length of a 20m hamstick, the readings

kept changing depending on what the NanoVNA was sitting on (truck hood,
pelican case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly

adjusted antenna?

Thanks, Coyote

Sent with [Proton Mail]() secure email.

The VNA and you, when hold on hand, are part of antenna. You must change the installation, feeder route, ground if possible properly.
Any trick to allow a reliable measure if removed later for normal operation then the SWR will become unstable again.
Usually a line choke isolates the antenna feeder side from outside world (shack...)

On Sun, Feb 2, 2025 at 05:06 PM, Coyote wrote:

When using my NanoVNA to adjust length of a 20m hamstick, the readings kept
changing depending on what the NanoVNA was sitting on (truck hood, pelican
case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly adjusted
antenna?

A hamstick is a helically wound whip antenna with an adjustable stinger for tuning the antenna to a desired frequency. But it is only "one half" of an antenna system. The other half can be another hamstick (which makes a dipole) or some type of ground plane or counterpoise. The vehicle body act as the other half for mobile installations.

What happens if you just connect the coaxial cable and secure the antenna to a non-metallic structure as some posters have suggested? In this case the outer surface of the coaxial cable will become the other half of the antenna and will radiate RF in addition to the hamstick. If you tune using the stinger you will get a minimum SWR point but if you increase the length of the cable, touch the cable or VNA with your hand or put the antenna over something metallic the readings will change.

The proper way to adjust the antenna is to mount it in the way it will be operated and then adjust the stinger. Be aware that the outer surface of the shield will still act as part of the antenna system and will radiate RF. The level of RF will depend on what type of structure the antenna is mounted over. A metal vehicle body acts as a good ground plane and you will have less cable radiation than just a trunk lid.

You can get a significant reduction in the cable radiation by using an RF choke on the coaxial cable like Juan Pablo suggested. You can make your own or buy one from several vendors.

Roger

Hello: I’m reading this topic since a couple of hour. Its clear that NanoVNA has a poor shielding. These instruments are very cheap …the good news is that there are many things to enhance on them. A metallic case would be a good idea with many grounding points, the problem is the display it should be outside the RF sections… enhance the design requires more money so this is . You need first an electrically stable setting prior VNA calibration. I’ve a NanoVNA and let me tell that you are getting everything this tool can give. In other posts some people are trying to measure very low series resistance from an inductor , this is out of NanoVNA possibilities. I measured the RF generator output and this is square wave, another source of error in the instrument.
That it does is the limit of his technology.

Regards, Patricio.

Thank you, Roger! How many times do we (collectively) need to write
something like you (and I) have!!??? The reader evidently doesn't read the
replies.

SUGGESTION to PROVE A POINT: One additional requirement is that the guy or
gal doing the testing of the antenna have a selection of large clamp-on
ferrite beads of either 31 or 43 material for HF. If you're not interested
in 160 or 75/80 meters, go with only 43 material. At least 10 of each is
good.

OK, here goes. Set up your hamstick or equivalent as you normally would.
Connect the NANOVVNA as you normally would to the far end (transceiver end)
of the coax. Go ahead and hold onto the NANOVNA and/or sit it on something
conducting and large. Make measurements as you normally would. Write
down ALL these measurements where you can compare them to what is coming
further.

Next, leave the setup as above, BUT: Install at least five of your
clamp-on ferrites right at the base of the hamstick (or equivalent) right
where the coax feeds the antenna. If the clamp-ons are large enough, make
one additional turn through each bead. After installing the ferrites, make
measurements as you normally would. Go ahead and hold onto the NANOVNA.
Grip it tightly as though your life depended on it. Write down ALL these
measurements.

Compare the two sets of measurements. I'll bet they are quite different.
What you have done with the clamp-on ferrites is isolate the outer surface
of the coax and YOU from the measurements.

POSSIBLE SUBSTITUTE for the FERRITES: Wind a roughly 10 to 12-inch
diameter loose coil of coax of about 10 or so turns and lay the coil
directly on the soil surface. Don't make the coil too tight.

I've done both while camping in the field off grid. Both show quite a
change form allowing the coax, you, and the environment from becoming part
of the antenna.

Dave - W?LEV

On Mon, Feb 3, 2025 at 6:04?PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

On Sun, Feb 2, 2025 at 05:06 PM, Coyote wrote:

When using my NanoVNA to adjust length of a 20m hamstick, the readings

kept

changing depending on what the NanoVNA was sitting on (truck hood,

pelican

case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly

adjusted

antenna?

A hamstick is a helically wound whip antenna with an adjustable stinger
for tuning the antenna to a desired frequency. But it is only "one half"
of an antenna system. The other half can be another hamstick (which makes
a dipole) or some type of ground plane or counterpoise. The vehicle body
act as the other half for mobile installations.

What happens if you just connect the coaxial cable and secure the antenna
to a non-metallic structure as some posters have suggested? In this case
the outer surface of the coaxial cable will become the other half of the
antenna and will radiate RF in addition to the hamstick. If you tune
using the stinger you will get a minimum SWR point but if you increase the
length of the cable, touch the cable or VNA with your hand or put the
antenna over something metallic the readings will change.

The proper way to adjust the antenna is to mount it in the way it will be
operated and then adjust the stinger. Be aware that the outer surface of
the shield will still act as part of the antenna system and will radiate
RF. The level of RF will depend on what type of structure the antenna is
mounted over. A metal vehicle body acts as a good ground plane and you
will have less cable radiation than just a trunk lid.

You can get a significant reduction in the cable radiation by using an RF
choke on the coaxial cable like Juan Pablo suggested. You can make your
own or buy one from several vendors.

Roger

--

*Dave - W?LEV*


--
Dave - W?LEV

BS...... The NANOVNA is well shielded. How many times do we,
collectively, have to remind others that holding onto the VNA while making
measurements is allowing your conductive body to become part of the antenna
and its fields.

READ THE REPLIES, PLEASE. Several of us have made it as clear as we
possibly can that "shielding" or "earthing" IS NOT A SOLUTION!!!! You and
the coax outer surface of the shield are becoming part of the antenna if
means to decouple the coax shield are not taken.

READ THE REPLIES. Several of us have responded in best engineering
practices, not here-say, snake oil, or witchcraft!!!! Read the previous
replies, PLEASE!!!!!!!!!!!!!!!!!!!

Dave - W?LEV

On Mon, Feb 3, 2025 at 6:20?PM Patricio A. Greco via groups.io
<patricio_greco@...> wrote:

Hello: I’m reading this topic since a couple of hour. Its clear that
NanoVNA has a poor shielding. These instruments are very cheap …the good
news is that there are many things to enhance on them. A metallic case
would be a good idea with many grounding points, the problem is the display
it should be outside the RF sections… enhance the design requires more
money so this is . You need first an electrically stable setting prior VNA
calibration. I’ve a NanoVNA and let me tell that you are getting
everything this tool can give. In other posts some people are trying to
measure very low series resistance from an inductor , this is out of
NanoVNA possibilities. I measured the RF generator output and this is
square wave, another source of error in the instrument.
That it does is the limit of his technology.

Regards, Patricio.

On 3 Feb 2025, at 15:04, Roger Need via groups.io <sailtamarack=

[email protected]> wrote:

On Sun, Feb 2, 2025 at 05:06 PM, Coyote wrote:

When using my NanoVNA to adjust length of a 20m hamstick, the readings

kept

changing depending on what the NanoVNA was sitting on (truck hood,

pelican

case, my thigh, or in my hand).

How do I get a reliable reading that I can count on for a properly

adjusted

antenna?

A hamstick is a helically wound whip antenna with an adjustable stinger

for tuning the antenna to a desired frequency. But it is only "one half"
of an antenna system. The other half can be another hamstick (which makes
a dipole) or some type of ground plane or counterpoise. The vehicle body
act as the other half for mobile installations.

What happens if you just connect the coaxial cable and secure the

antenna to a non-metallic structure as some posters have suggested? In
this case the outer surface of the coaxial cable will become the other half
of the antenna and will radiate RF in addition to the hamstick. If you
tune using the stinger you will get a minimum SWR point but if you increase
the length of the cable, touch the cable or VNA with your hand or put the
antenna over something metallic the readings will change.

The proper way to adjust the antenna is to mount it in the way it will

be operated and then adjust the stinger. Be aware that the outer surface
of the shield will still act as part of the antenna system and will radiate
RF. The level of RF will depend on what type of structure the antenna is
mounted over. A metal vehicle body acts as a good ground plane and you
will have less cable radiation than just a trunk lid.

You can get a significant reduction in the cable radiation by using an

RF choke on the coaxial cable like Juan Pablo suggested. You can make your
own or buy one from several vendors.

Roger

--

*Dave - W?LEV*


--
Dave - W?LEV

Dave made some very good points but perhaps some clarification is needed for those new to the topic. What follows is a simplification of the RF theory involved. For more details see any textbook on antennas and transmission lines.

There is a phenomena known as the "skin effect" where at RF frequencies the current flow is present on the surface of a conductor and has a reduced magnitude deeper in the conductor. . The depth depends on several factors with frequency being one of them.

A coaxial cable used as a transmission line consist of an inner conductor and a shield. The transmission of power takes place between the center conductor and the inner surface of the shield because of the skin effect. . The outer surface of the shield acts as a "3rd wire" and if the far end is connected to a resistive dummy load does not have any current on it. Now when you connect the coaxial cable to an antenna like a dipole the leg connected to the shield is in effect connected to two conductors: the inner shield and the outer shield. The outer shield is now an element of the antenna and RF current can flow on it and radiation can occur.

Now what happens if you connect a hamstick to the center conductor and nothing is connected to the shield? Since the inner and the outer shield are connected at the cable end the outer shield will now be the other radiating element. There is an antenna called the "sleeve dipole" which is built using this technique.

The radiation on the shield is usually undesirable because it can lead to radiation in the shack and for receiving purposes it can lead to picking up noise because it is close to RFI generating devices around the home. The other drawback is that the feedpoint impedance of the antenna will change depending on the length of the coax and objects close to the coax cable. Any ground connection at the transmitter end or in the case of a VNA holding it in your hand will also effect results.

The solution to this is an RF choke. This is an inductor, placed inline close to the antenna feedpoint, which puts a high impedance in series to reduce the level of RF current. . The easiest implementation is multiple ferrite toroid cores with a permeability factor that is suitable for the frequency of operation. The coaxial cable passes through or is wrapped around the toroid. Only the outer surface of the shield is affected by this technique.

In summary to install the hamstick on a vehicle mount it in place with a good ground connection at the antenna feedpoint. Use an RF choke suitable for the frequency of operation. Run the coax to the operating position and then use your VNA to measure SWR. Set the marker to the desired operating frequency and then adjust the stinger for lowest SWR. If running you hand along the coax or holding the VNA significantly affect the results your RF choke is inadequate.

Great description, Roger,

A diagram which illustrates your description of the skin effect in coax is attached (hopefully),

73,

Maynard
W6PAP

On Mon, Feb 3, 2025 at 03:56 PM, Maynard Wright, P. E., W6PAP wrote:

A diagram which illustrates your description of the skin effect in coax is
attached (hopefully),

Maynard - Thanks for drawing. Here is another one that illustrates what I was posting.
It is from this site -->>

On 2/3/25 16:24, Roger Need via groups.io wrote:

On Mon, Feb 3, 2025 at 03:56 PM, Maynard Wright, P. E., W6PAP wrote:

A diagram which illustrates your description of the skin effect in coax is
attached (hopefully),

Maynard - Thanks for drawing. Here is another one that illustrates what I was posting.
It is from this site -->>

Hi, Roger,

That is a good diagram. Thanks for pointing that out.

73,

Maynard
W6PAP

Can only imagine from whence DJ0IP lifted the drawing with his name on it,
given the difficulty he has supporting his “material” to an original
source.

Maynard’s diagram certainly covered the concept.

Here is Owen Duffy's more recent view, and another from the dim past of
1985 from W7EL.

73,

Ed McCann
AG6CX

Thanks for all of the responses and the assistance. I haven't tried again, but will soon.
I did put a choke on, and it greatly increased my SWR ---- hmmm.

I'm encouraged from the responses. I thought my Nano was broken.

Thanks, All - Coyote

To state the obvious, the feed line and termination are, in this case, part of the antenna. In some cases an advantage, but not for reliable measurements of an antenna.

Lester B Veenstra K1YCM M?YCM W8YCM 6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)
lester@...

452 Stable Ln
Keyser WV 26726 USA

GPS: 39.336826 N 78.982287 W (Google)
GPS: 39.33682 N 78.9823741 W (GPSDO)


Telephones:
Home: +1-304-289-6057
US cell +1-304-790-9192
Jamaica cell: +1-876-456-8898

Hi Coyote,

As others have already mentioned having a good choke on the feedline is the key.

When operating mobile (40 and 20 meters) with a ham stick or hustler mobile antenna I use approximately 9 of the Fair-Rite 0431167281 clamp on cores and place them on the coax right before it enters the passenger compartment by taping that section of coax to a rail on the roof top luggage rack to keep them from banging around, or I tape them to the coax right after the coax enters the passenger compartment. I have also at times used a single FT240-31 toroid core with at least 8 turns of the coax wound on it. My test to see if I have enough of the clamp on cores on the coax is to touch the NanoVNA while watching the SWR or touch the coax anywhere in the passenger compartment and if the SWR changes drastically (noticeable shift in resonate frequency, etc.) I then add more cores.

Mike (W9RE) and I (WD8DSB) operated CW mobile in the Indiana QSO party last year and we used the 9 clamp on cores as mentioned above on our 40 and 20 meter hustler antenna feedline to stabilize the SWR. We also tried running a trailer hitch mounted 80 meter hustler mobile antenna and without clamp on cores we could only run 30 watts as our keying would lock up (computer running N1MM with a K3 transceiver) so we installed some clamp on cores on the 80 meter antennas coax external of the passenger compartment and that allowed us to run full power (100 watts) without any keying problems.

Using a good choke on the feedline really helps provide a stable and repeatable system and as an example I would never cut the stinger on a mobile antenna based on resonate frequency measurement without first having a good choke on the feedline.

73,
Don (wd8dsb)