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Hi Ron,
interesting data, and an interesting use case! My limited experience with
antennas for handheld radios indicate, that they do change their impedance
based on whether a person is holding the radio itself, and thus providing a
sort of counterpoise to the antenna. I don't know entirely how much, nor
how to simulate it reliably for measurements, but I look forward to
learning about it :-)

--
Rune / 5Q5R

I am new to playing with any type of antenna analyzer/vector network
analyzer device but decided to get started learning by purchasing the
NanoVNA, as it was relatively inexpensive. The display on the device was
extremely small and my eyes are getting old, so I first wanted to workout
software that allows me to just use my laptop. I started with NanoVNASharp
and then on to Rune’s NanoVNA-Saver. I have been playing with it a while
and I think I’m starting to get the hang of it. I’ve set the sweep count to
100, which I believe gives higher quality readings than a single sweep. I
calibrated using the short SMA cable that came with the device, along with
the double-female connector to calibrate out the short coax. Now, I wanted
to evaluate the antennas that came stock on some of my portable antennas. I
have a Kenwood TK-2180 VHF LMR portable, which I use primarily for the
Placer County Sheriff’s Search and Rescue. My other radio I bought because
it was cheap, a Baofeng UV-82C VHF/UHF dual-band portable.

For SAR, my primary use is on a repeater with an input frequency of 150.790
MHz and output of 155.160 MHz (the National Search and Rescue frequency). I
also work an event each summer doing armed security where we have an input
frequency of 159.885 MHz and output of 155.655 MHz. Basically, my needs
then are between 150-160 MHz. After calibrating my NanoVNA, I did my sweep
with the Kenwood antenna from 130-180 MHz. I exported the data as an S1P
file and then imported it into Zplot in Microsoft Excel. With this, I
created a graph showing SWR and Return Loss. To my understanding, the more
the return loss, the more resonant the antenna is to that frequency,
meaning that it is more efficient operating at that frequency, correct? I
also took notice of the Smith Chart. For the Kenwood antenna, it hits it’s
best at 152.022 MHz with a return loss of -10.682 dB and SWR of 1.826.


[image: KenwoodTK-2180StockAntenna.jpg]
[image: KenwoodTK-2180-Smith.jpg]

or the Baofeng, it appears that the dip is much narrower but has a much
“deeper” return loss at 148.558 MHz with -23.885 dB and SWR of 1.137.


[image: Baofeng VHF Antenna.jpg]
[image: Baofeng VHF-Smith.jpg]


I am trying to compare these antennas as best I can. It appears as if at
around 148 MHz, the Baofeng antenna is significantly better than the
Kenwood but fairly lousy at the frequencies I really need it. The Kenwood
appears to be a little wider bandwidth but not near as much return loss and
higher SWR. First off, are these findings typical and what does it say
about the antennas that came with each radio?

Sorry if you are receiving this as an email and getting multiple copies...
I tried sending it once before and tried to edit it, because it didn't
format correctly and deleted itself when attempting to edit.
_____________________________________
Ron Webb

The "rubber duckie" sort of antennas as well as other shortened antennas for hand-held radios are always difficult to measure because they are sensitive to their surroundings as well as the size of the radio that they are mounted on. The radio case and your hand serves as part of the ground plane for the antenna.
You could take the antenna apart and remove windings (one at a time) to resonate it to the frequency of your choice. Another way is to use a telescopic antenna and mark it at the frequency that you want to use.?
It's my understanding that some very broad-band antennas use a resistor to broaden the response, but at the expense of resonate SWR.

Having an antenna on your hip or near your body, and may really throw off the resonant frequency. A metal hat with an antenna on top, looks ridiculous, but works quite well.
Stuart K6YAZLos Angeles USA

Hi Ron,

Nice results and they look reasonable.

The handheld radio with the unit near or on the body or simply placed on a isolated table would IDEALLY show no difference! Alas, that is NOT the case and handheld (whips or helical) are influenced by the human body. We, the human body are essentially a dielectric slab, somewhat lossy, we are mostly water!

You might run some cases as you bring your hand near the antenna or bend it etc... and note the significant change in SWR. Yes, at 20 dB or better your units were well designed. Yes, they tend to be narrow band. Back in a prior era, we looked at what it would take to broadband these type antenna over a 30% or larger bandwidth. Small auto tune matching networks wer invented and helped quite well.

Alan

Just for additional information, I was doing the testing in a large conference room with very little in the room other than a table with chairs and a video projector pointing at a whiteboard. It isn't quite as acurate as a laboratory that tries to eliminate all RF radiation. On one end of the table was my laptop (nearest the door). I then placed the NanoVNA the distance of the USB cable that came with it away from the laptop. The little SMA cable is only about 6-8 inches long but I took a paper cup and made a small hole, just big enough for the SMA connector to pass through. I connected one connector to S11 and the other to the antenna. By setting the cup lid down, it made the antenna stay vertical with no real ground plane, as on a handheld radio, there really isn't a ground plane. I'm not really looking for absolute perfection, but at least something where I can compare one antenna to another.

Just to confuse matters, I decided to take that same Kenwood antenna and using some metal clamp on a large, random ground plane, I got very different results, where the return loss was larger (-23.734 dB) at a higher frequency (171.704 Mhz) and reached a lower SWR (1.139).

Ron, the "antenna" on a handheld is not the antenna, it is only

/half/ of the antenna. In a Marconi system reliance is placed on
"ground", of whatever character, to be the other half of the antenna.
Exactly as much energy flows into and is radiated by "ground" as flows
into and is radiated by the, in this case, rubber duck type of antenna.
It is the flux of electric and magnetic fields established between the
two that constitute the radiated (and received) signal. The
transceiver's chassis and the hand holding it are half of the antenna
system. The sole merit of flexible antennas on handhelds is convenience.

In the set up described, the "ground" was mostly the braid of the

coaxial cable.

There is much to be said on the topic.

If a fellow is bound and determined to have a resonant rubber

antenna, then a connector to take that antenna must be mounded in the
middle of a conductive, flat surface the minimum dimension of which is a
quarter wavelength in all directions from the connector plus 5% or more.
With that set up, Ron, antennas can be compared with each other to the
standards applicable here.

As others have noted, we are very much dealing with radar

wavelengths. Nearby objects, metal or meat, will establish standing
waves which will upset the purity of your test results.

If you care to experiment when in the field, connect, at the ground

of the antenna connector, a run of light braid cut for a quarter
wavelength at the frequency of interest and simply let it dangle
downwards over your hand. That is your counterpoise and that explicit
counterpoise will do you far more good out there in the real world than
trying to resonate a rubber antenna!

You may contact me off list if would like to pursue the topic.

John

at radio station VE7AOV

+++++


On 2019-09-11 1:36 p.m., Ron Webb wrote:

Just for additional information, I was doing the testing in a large conference room with very little in the room other than a table with chairs and a video projector pointing at a whiteboard. It isn't quite as acurate as a laboratory that tries to eliminate all RF radiation. On one end of the table was my laptop (nearest the door). I then placed the NanoVNA the distance of the USB cable that came with it away from the laptop. The little SMA cable is only about 6-8 inches long but I took a paper cup and made a small hole, just big enough for the SMA connector to pass through. I connected one connector to S11 and the other to the antenna. By setting the cup lid down, it made the antenna stay vertical with no real ground plane, as on a handheld radio, there really isn't a ground plane. I'm not really looking for absolute perfection, but at least something where I can compare one antenna to another.

On Wed, Sep 11, 2019 at 01:04 PM, Rune Broberg wrote:

Hi Ron,
interesting data, and an interesting use case! My limited experience with
antennas for handheld radios indicate, that they do change their impedance
based on whether a person is holding the radio itself, and thus providing a
sort of counterpoise to the antenna. I don't know entirely how much, nor
how to simulate it reliably for measurements, but I look forward to
learning about it :-)

--
Rune / 5Q5R

On Wed, 11 Sep 2019 at 21:55, Ron Webb <bigron@...> wrote:

I'm still new to posting here, so forgive the double graphics and title of
SWR/RL graphs not being seen. ;)

--