开云体育

HI to all
I own a FY6900 device,
a cheap but very complete generator
(mine is the model working up to 60mHz).
Till now I've used it only with an oscilloscope,
but I would like to employ also with a NanoVNA
Anyone has done so?
I think should be very useful for my tests (i.e.
building filters).
Thanks for any suggestion
73
Gabriele, I4JXE

Hello Roger,

I may have missed something here, but it seems to me your trace labels are reversed.
The "top - SMA barrel" trace has much larger SWR ripple and a predominant capacitive reactance loop on the Smith Chart. I suggest this is actually the SO239 barrel.
Also, the markers are at different frequencies which make the upper trace SWR at the marker "look" better.

The lower trace has much lower SWR ripple and a much tighter reactance loop at ~50 Ohms on the Smith trace. More like an SMA barrel.

Cheers...Bob VK2ZRE

Two more pictures using 10 feet of RG58 Coax connected to the vertical. First Picture is with SWR Plot scale set to 0.25 per division and second picture with SWR plot scale set to 1.0 per division.

Here is a picture showing my test vertical mentioned in my above post when I had it connected directly to the NanoVNA-F using just a couple of adapters. Note in this picture the NanoVNA-F was calibrated for and displaying 500 KHz to 1 GHz and displaying 301 points. SWR full scale = 3.5

Don (wd8dsb)

Hi folks,

I somewhat agree with what others have said and Rogers demonstration shows one issue but let me make some additional observations/comments. My comments below ignore some minor effects due to the nature on how the NanoVNA circuit works when measuring impedances that are not close to 50 ohms (example: not close to the center of the Smith Chart).

First off Jeffs antenna only has a feedpoint impedance close to 50 ohms at resonance somewhere in the 400 to 500 MHz range, and you can get close to 50 ohms at resonance by adjusting the angle on the radials. Most importantly feedline loss (attenuation) makes SWR look much better than it really is especially at high frequencies where feedline loss becomes significant, so minor dips in SWR start looking like significant dips due to large feedline attenuation.

Also Jeff used a scale of 1 unit per division on his SWR plot which gives him a full scale reading of 9 on his SWR plot which is zoomed out too much especially considering that feedline loss makes SWR look much better than it really is. I recommend that Jeff set his SWR plot scale to 0.25 per division which would make his full scale plot reading approximately 3.0. If he does this I think he will easily see that his minimum SWR is actually higher than the 406 MHz frequency his marker is set on and his other dips (valleys) that are not at the minimum SWR point will move farther away from his minimum valley making his true resonate point more obvious.

Note: I built an antenna similar to Jeffs this evening as a sanity check and tested it mounted almost directly to the NanoVNA-F using a few adapters. Also connected the antenna to the NanoVNA-F using an 18 inch piece of RG58, and also using 100 feet of RG58, and the differences in the SWR plot between all 3 configurations is very noticeable regarding the generation of multiple dips (valleys) especially when using the very long run of RG58 which is coiled up on a spool that has a lot of loss at 430 MHz.

Also note common mode signal on the feedline did not appear to come into play much during my tests as touching the feedline or NanoVNA-F body had very little impact on the SWR plot (just minor difference).

Just FYI,
Don (wd8dsb)

I suspect some inductance between your metal (?) mount and the feed line running parallel to it. Consider lengthening your feed line by a couple of feet and put a loop in it along the vertical somewhere.

On Thu, Feb 6, 2025 at 03:46 PM, jeffinwa wrote:

In the shop, connecting this device directly to the SO239 connector, the sweep
on the screen is perfect. But in testing with the antenna installed with coax,
and testing at the end of the feed line, the sweep seems strange.

The ripples you are seeing are not unusual. It is not due to the antenna - it is the transmission line and/or adapters being used. . When the impedance of the transmission line is slightly different than the 50 ohm impedance of the NanoVNA you get ripples which give a higher SWR at odd multiples of 1/4 wavelength (1/4, 3/4. 5/4 etc.) and lower at multiples of half wavelength (1/2, 1, 3/2 etc).

Attached are two screenshots. 50 feet of RG213 with 50 ohms at the end was measured. SWR should be close to 1. In one plot a SMA to SO239 adapter was used and in the second a SMA to PL259 adapter with a barrel connector. Those female barrel connectors have about 35 ohms of characteristic impedance. Notice how much more ripple there is with the barrel inline.

Hi,

What you are seeing is perfectly normal and simply represents the fact that the antenna feed impedance (at the antenna feed point) does not exactly match the coax impedance. It's certainly pretty close to matched though because you have a nice dip still - it's just not perfect.? But no need to change anything here.

The coax is acting as an impedance transformer with the impedance transformation cycling every half wavelength of coax.? If you switch on the smith chart trace on the vna you will see a number of circles corresponding to the cycles on your swr trace. Each trip around the smith chart represents one half wavelength of change in the coax's length.

When you did the tests in the shop, the feeder length (from the point on the vna where you did the calibration to the antenna feed point) was very short, much less than a half wavelength - so you didn't see any cycles in the swr. But now that you have a longer coax, you see them.

As an aside, of course the antenna impedance is going to be a bit different in its outside location than it was in the shop just because of the different environment. If you want to see the actual impedance of the antenna then you could do the VNA calibration at the far end of the coax, in situ. That would eliminate the effect of the coax from the readings and you should get a smoother and more accurate reading. But what you have there looks fine for normal operation.

73,

Andrew

VK2EZF

I'm not sure why the ripple is in there. I have never seen that when I do
an SWR measurement. The minimum of 1.2 isn't bad, but the frequency is 406
MHz. What band is the antenna for? Is it a commercially-made antenna?

Zack W9SZ

On Thu, Feb 6, 2025 at 5:47?PM jeffinwa via groups.io <k7jsm=
[email protected]> wrote:

When I am constructing an antenna, I have been using this device to plot
the swr in my shop. I usually set a wide enough bandwidth to easily see
the dip at resonance.

In the shop, connecting this device directly to the SO239 connector, the
sweep on the screen is perfect. But in testing with the antenna installed
with coax, and testing at the end of the feed line, the sweep seems
strange. See attached

That antenna is not the best with only 3 "stingers" as a skeleton image
plane. It's pretty spartan!

The "wiggles" you are seeing at the end of the coax reflect a small SWR on
the coaxial line. The antenna is not strictly 50 ± j 0 ohms. As such, the
wiggles are due to the standing wave within the coax due to a slight
mismatch. But have a look at your cursor at "resonance". The trace is
nearly flat surrounding the cursor. Nothing to be concerned about. Your
NANOVNA is showing you the correct rendition of the response of the antenna
connected to your 50-ohm coaxial line.

Dave - W?LEV

<>
Virus-free.www.avg.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Thu, Feb 6, 2025 at 11:46?PM jeffinwa via groups.io <k7jsm=
[email protected]> wrote:

When I am constructing an antenna, I have been using this device to plot
the swr in my shop. I usually set a wide enough bandwidth to easily see
the dip at resonance.

In the shop, connecting this device directly to the SO239 connector, the
sweep on the screen is perfect. But in testing with the antenna installed
with coax, and testing at the end of the feed line, the sweep seems
strange. See attached

--

*Dave - W?LEV*


--
Dave - W?LEV

When I am constructing an antenna, I have been using this device to plot the swr in my shop. I usually set a wide enough bandwidth to easily see the dip at resonance.

In the shop, connecting this device directly to the SO239 connector, the sweep on the screen is perfect. But in testing with the antenna installed with coax, and testing at the end of the feed line, the sweep seems strange. See attached

any of the nanovna v2 models .. or litevna 62/64

dg9bfc sigi

Am 06.02.2025 um 02:41 schrieb CLIFTON HEAD via groups.io:

If your main application is for ham band use, from HF to VHF/UHF (440MHz), save some money and get the H4.
If you need good accuracy on bands above the 440MHz band, and above 1GHz, I would choose one of the 'liteVNA' or V2 models with extended frequency coverage on the high end.

My Suggestion is
Do your research. you want a device based on the Open Firmware, you want a device that supports the software on GitHub.
Most of the devices are made in China.
The prices are all over the map, research down to who actually manufactures the device.
This takes time, but with internet access you can find and drill down to find what you want and are willing to accept.
OR
Purchase one from Amazon with a return ability. Amazon is good this way. while this is slightly more expensive but gives you time with the actual device to decide to keep or return.

Any of them. The ones with a bigger display are easier to read.
But all of them can do what you’re looking for.
The other thing to look at is frequency range, some have a wider frequency range on the top end.
And connectors and cases - The originals have SMA connectors, some new versions have N connectors and a beefier case. (Which does cost something). I use 6” SMA-UHF and SMA-N jumpers rather than adapters, so the coax doesn’t snap the connector off the NanoVNA.

I changed the driver and problem solved!

??? Thank you!

??? Mark Jordan, PY3SS

What is a good NanoVNA to buy for do antenna reading like SWR, VF and Length of coax cable type work. Also, location of short in the coax..

I made the mistake of going down the measuring Q rabbit hole....

VE2AZX QEX article on different methods -->

VNWA discussion on the topic --> /g/VNWA/topic/96145305#msg21997

Never coming up the rabbit hole after browsing this long report by UK National Physics Lab.

Q-factor Measurement by using a VNA -->

I discovered the problem -- it is my SD card. If I remove the SD card the NanoVNA operates normally (without changing firmware). I tried a different SC card and the problem returned. So, I need to look again at my SC card slot I soldered in last year. It's been working since then up to now. Maybe something came lose, or some particle fell in and shorted something out.

All,

The extra copy of QEX has been spoken for.

DaveD
KC0WJN


On Wed, Feb 5, 2025 at 12:56 Dave Daniel via groups.io <kc0wjn=
[email protected]> wrote:

Does anyone want a copy of the January/February 2025 issue of QEX? The ARRL
sent me two copies. It has the tinySA tracking generator design article in
it.

Of so *respond to me privately* at

kc0wjn at gmail dot com

Responses to the list will be ignored.

The magazine is free; shipping cost from 32754 USA to be paid to me by
PayPal F&F (the shipping cost using USPS Media Mail is probably trivial).

DaveD
KC0WJN