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And yet, in real operation these antennas do not have a ground plane
(unless you consider the HT a ground plane, but it's inadequate). So why
not measure the antenna as it's going to be used in the real world?

Zack W9SZ

On Thu, Oct 20, 2022 at 3:28 PM Colin McDonald <colinrmcdonald@...>
wrote:

Most HT antennas are some form of compromised quarter wave radiator.
Meaning they really need a ground plain of some kind to get the correct
feed point impedance.

Not a counter poise, but a ground plain. Remember, you are dealing with
a wave length of 2 meters or so. and once you are beyond a quarter wave
above ground, about 18 inches, a quarter wave radiator needs a ground
plain because the actual ground is no longer providing that.

So, simply connecting the HT antenna to the NanoVNA directly or sticking
the antenna on the end of a cable isn't going to give a very accurate
measurement of the antennas electrical characteristics as far as
impedance and VSWR.


To properly test HT antennas you should have some kind of ground plain
jig to mount the antenna to. You can calibrate the NanoVNA with the
cable and ground plain mount connected to provide a calibrated reference
point for any HT antenna.

I have had some limited success by tightly holding the metal adapter at
the bottom of an HT antenna to provide some form of ground plain to work
with but those results vary quite a bit depending on how tightly I grip
the body of the connector and how far I hold the antenna away from myself.

You will find that even with a proper ground plain, HT antennas are
rarely resonant on the ham bands and impedance can vary wildly depending
on the frequency.


Interestingly enough, out of about 10 different stock rubber duck and
after market whip style antennas that I've tested so far, the original
Nagoya 701 that I bought way back when they were about 3 bucks measures
the lowest SWR on the VHF and UHF ham bands and is the closest to 50
ohms impedance at those frequencies. It's still around 1.5 to 1.7 to
one, but at least it's not 4 or 5 to one with a 80ohm feed point
impedance like most of the stock rubber duck style coil antennas that
come with a handheld.


A large cheap metal baking sheet can suffice as a ground plain for VHF
or UHF. You can mount both types of SMA connectors to it and feed with a
couple pieces of RG174 as long as you keep the run under 10 feet.

If you want to get ambicious you can build a decent ground plain out of
a piece of plywood with 4 20 inch wires at 90 degrees to each other and
a fifth wire circling the perimeter electrically connecting the ends of
the 4 wires. Then a connector of your choice at the center tying the
wires together. You are now looking at a piece at least 40 inches by 40
inches though or a 40 inch circle. Unwieldy for most hobbiests.

But, if you really want to know how the HT antenna is going to measure
when used on a plastic cased HT, probably connecting it directly to the
NanoVNA and holding the Nano it in your hand while conducting the sweep
will give you the closest approximation of real world operation.

Another work around is to get a small magnet mount with the appropriate
SMA antenna mount and do your tests in a vehicle with the antenna stuck
to the roof. This will provide a pretty decent ground plain as well. Or
stick the magnet mount on the top of a fridge or metal stove top etc.
When I test and tune my quarter wave magnet mount antennas I just slap
them on top of my fridge and it seems to work great. Sitting on a wooden
table the same antenna will show a very high swr and feed point
impedance, but once stuck to the fridge those usually drop right down to
expected parameters. Tuned that way, they usually exhibit just about the
same VSWR and impedance when mounted to the vehicle roof.

Lot's of ways to get to the end goal without getting too technical or
fiddly.


Regards

Colin VA6BKX

On 2022-10-20 1:16 p.m., Jim Lux wrote:

On 10/20/22 11:45 AM, Frank wrote:

How To Do A SWR Sweep on 2 Meter HT Antenna ?

Whats better: Should I connect the 2 meter HT antenna directly to the
VNA or should I connect the 2M HT antenna to the end of a SMA cable
then to the VNA ?

The VNA is sort of like an HT and you're holding it in your hand, so
I'd say that's closer.


The other approach is to make a test fixture, use coax with a LOT of
appropriately chosen ferrite beads (probably not 31 for 140 MHz) to
decouple it and put the VNA 10-20 feet away (so the operator is not in
the near field of the antenna.

Test fixture should then replicate the operator's effect. i.e. that
you've got a lossy arm holding the HT next to a lossy body. For what
it's worth human muscle, bone, and vessel tissues are about 1.5 S/m
and epsilon 40. So a bag of salt water with the right conductivity
with some polyester fiber or flakes (fake snow, pillow stuffing)that
is about half the volume (to bring epsilon down from 80 for water))
Sea water is about 3 S/m and about 3.5% salt. So that will get you
started.

(ProTip, add a preservative so mold doesn't grow in your RF simulant -
it's really, really gross)



Or, test in a fixture that replicates "free space" - accept that it's
not what the thing looks like in real life, but does provide something
to compare against.

If you don't care about replicating the human half of the HT antenna, then a pizza pan or large cookie sheet works well. It's repeatable, etc.

FWIW it should be 1/4 lambda *radius* not diameter. so for 70cm band, you're looking at 35cm diameter (call it 14" or so..it's not going to make much difference)

For 2m, that makes your pizza pan a bit bigger than is practical (a 1 meter diameter pizza pan is a specialty item). A big circle cut out of hardware cloth, or a couple pieces of plywood, MDF, or foam core, covered with aluminum foil works.

With all these things, it's the mechanical aspects you'll spend most of your time figuring out.

Understood.

Maybe 1.2.16 is Alpha code.

Maybe DiSlord can comment.

Mike N2MS

Most HT antennas are some form of compromised quarter wave radiator. Meaning they really need a ground plain of some kind to get the correct feed point impedance.

Not a counter poise, but a ground plain. Remember, you are dealing with a wave length of 2 meters or so. and once you are beyond a quarter wave above ground, about 18 inches, a quarter wave radiator needs a ground plain because the actual ground is no longer providing that.

So, simply connecting the HT antenna to the NanoVNA directly or sticking the antenna on the end of a cable isn't going to give a very accurate measurement of the antennas electrical characteristics as far as impedance and VSWR.


To properly test HT antennas you should have some kind of ground plain jig to mount the antenna to. You can calibrate the NanoVNA with the cable and ground plain mount connected to provide a calibrated reference point for any HT antenna.

I have had some limited success by tightly holding the metal adapter at the bottom of an HT antenna to provide some form of ground plain to work with but those results vary quite a bit depending on how tightly I grip the body of the connector and how far I hold the antenna away from myself.

You will find that even with a proper ground plain, HT antennas are rarely resonant on the ham bands and impedance can vary wildly depending on the frequency.


Interestingly enough, out of about 10 different stock rubber duck and after market whip style antennas that I've tested so far, the original Nagoya 701 that I bought way back when they were about 3 bucks measures the lowest SWR on the VHF and UHF ham bands and is the closest to 50 ohms impedance at those frequencies. It's still around 1.5 to 1.7 to one, but at least it's not 4 or 5 to one with a 80ohm feed point impedance like most of the stock rubber duck style coil antennas that come with a handheld.


A large cheap metal baking sheet can suffice as a ground plain for VHF or UHF. You can mount both types of SMA connectors to it and feed with a couple pieces of RG174 as long as you keep the run under 10 feet.

If you want to get ambicious? you can build a decent ground plain out of a piece of plywood with 4 20 inch wires at 90 degrees to each other and a fifth wire circling the perimeter electrically connecting the ends of the 4 wires. Then a connector of your choice at the center tying the wires together. You are now looking at a piece at least 40 inches by 40 inches though or a 40 inch circle. Unwieldy for most hobbiests.

But, if you really want to know how the HT antenna is going to measure when used on a plastic cased HT, probably connecting it directly to the NanoVNA and holding the Nano it in your hand while conducting the sweep will give you the closest approximation of real world operation.

Another work around is to get a small magnet mount with the appropriate SMA antenna mount and do your tests in a vehicle with the antenna stuck to the roof. This will provide a pretty decent ground plain as well. Or stick the magnet mount on the top of a fridge or metal stove top etc. When I test and tune my quarter wave magnet mount antennas I just slap them on top of my fridge and it seems to work great. Sitting on a wooden table the same antenna will show a very high swr and feed point impedance, but once stuck to the fridge those usually drop right down to expected parameters. Tuned that way, they usually exhibit just about the same VSWR and impedance when mounted to the vehicle roof.

Lot's of ways to get to the end goal without getting too technical or fiddly.


Regards

Colin VA6BKX

Thanks for that but please bear with me as I'm not a programmer!
Do I need any other source files to create a dfu file using Dfu File Manager, or just the bin or hex?

--
Mike

100% agree with W0LEV here. That HT antenna wants a ground plane or it's going to read very high. The little VHF/UHF SWR meter I have makes a big point of that in their manual. For a 1/4-wave ground plane at 440MHz, that's a disk about 6.7"/17cm in diameter.

Hi Jim, I believe your are right about it needing a ground..

I just watched a pretty good video on youtube where N0CSM tested several different types of 2 meter HT antenna's using a 18" SMA cable to a test jig that did include a metal "L" shaped mounting bracket to simulate a HT's metal housing. The video is called How To Tune an HT Antenna at

Frank

Hi Dave, Yes I believe your are right about it needing a image plane.

I just watched a pretty good video on youtube where N0CSM tested several different types of 2 meter HT antenna's using a 18" SMA cable to a test jig that did include a metal "L" shaped mounting bracket to simulate a HT's metal housing. The video is called How To Tune an HT Antenna at

Frank

On 10/20/22 11:45 AM, Frank wrote:

How To Do A SWR Sweep on 2 Meter HT Antenna ?
Whats better: Should I connect the 2 meter HT antenna directly to the VNA or should I connect the 2M HT antenna to the end of a SMA cable then to the VNA ?

The VNA is sort of like an HT and you're holding it in your hand, so I'd say that's closer.


The other approach is to make a test fixture, use coax with a LOT of appropriately chosen ferrite beads (probably not 31 for 140 MHz) to decouple it and put the VNA 10-20 feet away (so the operator is not in the near field of the antenna.

Test fixture should then replicate the operator's effect. i.e. that you've got a lossy arm holding the HT next to a lossy body. For what it's worth human muscle, bone, and vessel tissues are about 1.5 S/m and epsilon 40. So a bag of salt water with the right conductivity with some polyester fiber or flakes (fake snow, pillow stuffing)that is about half the volume (to bring epsilon down from 80 for water))
Sea water is about 3 S/m and about 3.5% salt. So that will get you started.

(ProTip, add a preservative so mold doesn't grow in your RF simulant - it's really, really gross)



Or, test in a fixture that replicates "free space" - accept that it's not what the thing looks like in real life, but does provide something to compare against.

If you have strong RF sources - broadcasters or public service -
transmitters - closeby, these can cause erratic and unstable readings when
connected to antennas. After all the cal's are completed, try measuring
known loads without the antennas. These should measure true to the known
loads.

Dave - W?LEV

On Thu, Oct 20, 2022 at 6:56 PM Myroslav Mykhalchuk <samuray7@...>
wrote:

Hello all,

I’m very new to Nano VNA, so my apologies if my question is stupid or is
answered elsewhere. I just bought a new device (the smaller version) from
nanovna.com<> with the main purpose of measuring SWR. I
did follow the instructions for setting the range (stimulus) and
calibrating before the use. I tried the procedure and measurements in
shortwave as well as VHF bands. At all bands the SWR curve is highly
unstable, changing constantly and jumping greatly if I just approach the
device with my hand. On several of my antennas with proven and workable SWR
which should be between 1 and 2, I‘m getting MUCH higher SWR values,
roughly averaging 10 and sometimes approaching 40! or so. However, SWR
reduces sharply if I approach the antenna with my hang.

Does it mean that I‘ve got a defect or fake NanoVNA-H? If so, is it worth
it to try and exchange the device through nanovna.com<>?
I don‘t even see any support contacts there. If exchange is not possible,
would anyone suggest what I can try and fix myself - maybe some HF
shielding?

Many thanks ahead for your thoughts! Cheers,

Myro

--
*Dave - W?LEV*
*Just Let Darwin Work*


--
Dave - W?LEV

Hello all,

I’m very new to Nano VNA, so my apologies if my question is stupid or is answered elsewhere. I just bought a new device (the smaller version) from nanovna.com<> with the main purpose of measuring SWR. I did follow the instructions for setting the range (stimulus) and calibrating before the use. I tried the procedure and measurements in shortwave as well as VHF bands. At all bands the SWR curve is highly unstable, changing constantly and jumping greatly if I just approach the device with my hand. On several of my antennas with proven and workable SWR which should be between 1 and 2, I‘m getting MUCH higher SWR values, roughly averaging 10 and sometimes approaching 40! or so. However, SWR reduces sharply if I approach the antenna with my hang.

Does it mean that I‘ve got a defect or fake NanoVNA-H? If so, is it worth it to try and exchange the device through nanovna.com<>? I don‘t even see any support contacts there. If exchange is not possible, would anyone suggest what I can try and fix myself - maybe some HF shielding?

Many thanks ahead for your thoughts! Cheers,

Myro

Hi, use a cable and calibrate at the end of the cable first. This way you can use any length cable you like as youve calibrated out any differences.

regards Pete

A monopole like an HT antenna requires an image plane. In use, this is a
combination of the HT body and your own body. So, to correctly measure an
HT antenna, this image plane must be replicated. Without that, the data is
somewhat meaningless. I have used a large copper plane with a BNC in the
center to measure these antennas. Not truly the way they are used in
practice, but at least its somewhat rigorous to antenna theory.

Dave - W?LEV

--
Dave - W?LEV

Either way will not help much. An HT antenna is expecting a ground through the radio and your hand. To get anything even remotely effective you would need a piece of metal like a pie pan or pizza pan with the antenna mounted in the middle. Otherwise you will see poor readings

Sent by me

How To Do A SWR Sweep on 2 Meter HT Antenna ?

Whats better: Should I connect the 2 meter HT antenna directly to the VNA or should I connect the 2M HT antenna to the end of a SMA cable then to the VNA ?

hello,
The latest menu map I have seen is for FW 1.2
The FW keeps changes so fast that, so far, no one has taken the time to try and update the menu maps. As soon as one is presented, it's obsolite.
The latest FW is 1.2.16 for the H and H4.
Clyde KC7BJE

Oh yeah. Like the venerable MRF454 with 1 ohm impedances.

But the NanoVNA isn't much worse than any other VNA. And typically, you're looking to optimize a narrow band matching circuit, right?
So you can rig up a jig to measure the matching networks, then put them in the calculation (dembedding). You measure the input to the input network which is connected to the transistor, and from that, you can calculate what the transistor is doing.

This is where a tool like scikit-rf which can import and manipulate all the matrices is nice.

(or ADS)

Careful on spurious oscillations which will blow up port 2 on your VNA - BTDT. The NanoVNA is MUCH cheaper to fix than an 8510.

Thanks PE0CWK, appreciate your help.

Hi Tim,
I have tried both.? With my HW version 4.3_MS NanoVNA the MS file works fine, but with my HW version 4.2 neither the SI hex or binary files will work.? They download fine but the NanoVNA just comes up with a blank, dark screen.
Tom

I have loaded the, iirc, .14 with Cube just fine, but have used the .bin as opposed to .hex images . . . . Have you tried those by chance?

--
Sent from my Android device with K-9 Mail. Please excuse my brevity.