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I had a similar thing happen with the brightness on my H4. I couldn't find any information on adjusting the brightness.

Very detailed and useful work.
It is a pity that the author has not optimized the pdf file, thus reducing the burden on his website.
Thanks Gunthard!

73, Gyula HA3HZ

The spike at 6.5 MHz is due to a resonance of the bypass capacitors and choke supplying power to the SA612s. It's been discussed here, I imagine a search would probably turn it up. A lot of anomalies have been noticed at the change to higher harmonics, mostly at or near 300 MHz.

Folks:
I recently fired up my nanoVNA and was exploring how to integrate basic control into SimSmith. In doing so, I ran across the following behavior.

I did a basic calibration from 50 KHz to 700 MHz. I know that covers an incredible range… I’m not saying it was right, only what I did. (As I understand things, nanoVNAsaver recommends doing this before using its own compensation.)

Then I did scans for ‘short’ and ‘open’ with about 1 foot of what appears to be RG174 type cable. I verified the basic operation using SimSmith and the simulation and measurements correlate well.

Then I used ‘Chipman’ to determine the impedance of the transmission line. (Chipman calculates ‘Zo’ as Sqrt(Zshort*Zopen)’.) I assumed it was close to 50 ohms and, indeed, it was. All well and good.

Then I plotted the calculated Zo on the Smith chart. For the ‘ideal’ case using perfect transmission lines, the result would all be close to 50 ohms. For the vast majority of the spectrum, the results were well behaved. However, at a few frequencies (as shown below) there are anomalies. The frequencies are (around) 315 MHz, 157 MHz, and 475 MHz. (There is also a minor anomaly at around 6.5 MHz.)

I’m hoping these features are familiar to some users and that they can help me determine how to compensate for them. I’m pretty new to the whole discipline so any insight is most welcome.

(I’m wondering if the problem around 315 MHz is related to the transition from the ‘first’ harmonic to the ’third’?)

Here is the plot:



Thanks for any help!

ward
ae6ty

On Sun, Mar 15, 2020 at 03:41 PM, Guillaume Larouche wrote:

"I would like the 4.3 or 4.0 inch display, but it's look like the F and H4 version are not the same processor, so wich one is the more supported model?"

- Up until about a month ago I would definitely have said the NanoVNA-H4 was the better developer supported model. With firmware release 0.1.1, the NanoVNA-F incorporates pretty much all of edy555's 6.0 firmware improvements and adds a few of its own. It proves to me that while the NanoVNA-F may be slower at introducing new firmware updates than the NanoVNA-F that the developer is fully capable of keeping up with any worthwhile new features. This user group beats the NanoVNA-F user group hands down when it comes to support, which adds immeasurable value to the NanoVNA-H4.

"I would like to use TDR one day, any clue if a version running it will be released soon?"

- Both the NanoVNA-H4 and NanoVNA-F already incorporate identical out-of-the-box TDR measurement capability.


I own both models and I am happy with either. They each operate from 10kHz - 1.5GHz with their current firmware, although the performance of the NanoVNA-F starts to get iffy above 1.3 GHz. If you are only going to make measurements up to 1 GHz then you'll be happy with either unit. The NanoVNA-H4 looks like it will actually give usable performance to 2 GHz if the firmware limits are opened up.

A new hardware 3.1 version of the NanoVNA-F has just been released for sell with an improved RF bridge, which may match the NanoVNA-H4's performance above 1.5 GHz. The jury is still out. The 3.1 hardware version also offers the choice of 3 push buttons or a single thumb-wheel. Some user's prefer using push buttons over a thumb-wheel.

The NanoVNA-F is about twice the cost of the NanoVNA-H4 ($60 versus $110) but is packaged better (metal enclosure), has a larger battery, and has an easier firmware update procedure than the NanoVNA-H4 (virtual disk versus third party software).

As I said, I am happy with both units and would buy either again. If cost is not an object and you don't need a lot of user group support, I would go with the ver 3.1 NanoVNA-F. If you just want to have access to a VNA with moderate performance on the cheap, go with the NanoVNA-H4. If you need to make measurements to 3 GHz, then you might consider adding the new NanoVNA V2 (S-A-A-2) to the mix.

- Herb

Yup, the issue with the plastic housing is a 'potenial' problem but almost all H4 units are just fine.?



On Sun, 15 Mar 2020 at 8:14 PM, Ben Yuen<benyuenkc@...> wrote: I have 2.8 and 4.3 inch version. They can do TDR with updated firmware.? Personally I would prefer the F version with metal case which is free from the potential problem of "plastic case" issue at this moment.

VR2XHQ

I have 2.8 and 4.3 inch version. They can do TDR with updated firmware. Personally I would prefer the F version with metal case which is free from the potential problem of "plastic case" issue at this moment.

VR2XHQ

Well,
Everyone has their own personal preference. With that in mind, there is only 1 firmware developer at this time for the F version and 6 developers for the original nanovna-H (4.3). Of the developers for the H, two of those are developing for the H4.?
This means that typically, any new functionality on the H will appear on the H4 (but not the other way round).?

The H and HE versions also have a slightly higher frequency limit.?
In the end, it's still up to you.

On Sun, 15 Mar 2020 at 6:41 PM, Guillaume Larouche<va2na@...> wrote: Hello group,

I would like to get a nano VNA ( already use great VNA at work ) to play with, but i am confusing about wich one to get?

I would like the 4.3 or 4.0 inch display, but it's look like the F and H4 version are not the same processor, so wich one is the more supported model?

Also, i would like to use TDR one day, any clue if a version running it will be released soon?

Thank you
Guillaume

I was hoping that the ground conductivity was different so I did measurements at three places with the wire close to the same angle WRT the ground. The results were very similar so I guess the ground is similar at these locations. In other words, the radiation resistance plus the ground loss resistance was very similar (3600 to 3900 Ohms). The measurements were done over about a 3 month period (last April-June). It might be interesting to note that the feed point Z for a wire cut to 468/7 MHz is resonant a few hundred KHz lower (the above case) BUT this is now a rough estimate because I didn't record where the impedance became only resistive.
For the case in my backyard there is another antenna but the coupling is about 30 dB. A 30 dB separation showed a 1 or 2 ohm shift in the impedance looking in (near 50 ohms) the EFHW when the other antenna was left open-circuit or short-circuit at it's transmission line input end. I did this to address the interaction between these antennas when some one questioned the influence on the measurements. Anyway, I answered the questions that I came up with and then some about 10 months ago. Last June I did ARRL FD running 2 W CW with my old Heathkit HW-8. I worked every station I called on 20 and 40 Meters from ME to S. CA with this same 67 ft EFHW from one of the three test sites. 73

Hello group,

I would like to get a nano VNA ( already use great VNA at work ) to play with, but i am confusing about wich one to get?

I would like the 4.3 or 4.0 inch display, but it's look like the F and H4 version are not the same processor, so wich one is the more supported model?

Also, i would like to use TDR one day, any clue if a version running it will be released soon?

Thank you
Guillaume

WB2UAQ,

Measuring antennas requires knowing what the ground is like.
as it does change the result as well as orientation and height above it.

I know the region and it does change depending on where you are
in that region.

Your trying to answer questions about EFHW antennas. Suggestion do
so at higher frequency like 20m or 10 M as scaling is handy and makes
getting numbers for .1 Lambda height (1meter at 10M) to say .5 lamda
(5M at 10M). Also for orientation and ability to replicate the identical
thing at multiple locations.

Hint it behave much like a dipole.
It as an antenna is the extreme case of an off center fed.

Things going on...

*The impedance of an antenna depends on orientation horizontal sees ground reflections
so there is a pronounced impedance change. (visible with dipoles.)
*Reflections from large bodies (for sloping or vertical) can be seen as modified
impedance as well depending if constructive or destructive.
*Vertical does not have the same interaction with the ground.
See above about large reflective surfaces.
*Also objects like a fence or trees will interact and load (interact with) the wire.
* Resonance effectively changes with height (follows reflected impedance).
* Interaction of the gear attached to the end of it. IF the gear has a cord and
cables it changes the dimension of the antenna as its part of the measurement
plane and the reflection (counterpoise) of it. A case of what you measure and
how can change the measurement.
* Measured impedance at resonance should be Rx, J0, as that changes the
results move around but if you adjust frequency you can see what R is at J0.
WHY? if above resonance it will be inductive or -Jx and below frequency it will
be +jx that colors the result.

This is why everyone has an opinion but authoritative answers are few.
The other part is pick any value and then draw the 1.5:1 or 2:1 circle and
see how much it can vary. For a 1:49 transformer that's about 1250ohms
or 3800 ohms for the 2:1 circle so small errors like accurate to two significant
digits is likely good enough and easily small enough as variation is height
or nearby objects will easily exceed that.

The side effect is someone will argue with you about it as they do not
understand measuring it. For that it must be repeatable and account
for the known variations.

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

That might work if it were a dipole.

for a end fed wire?
The problem then is what represents the ground plane?

An Endfed half wave (or any random wire) is like any antenna
(dipoles for instance) dependent on height above ground and
the ground under it so a point measurement is exactly that.
Since a resonant half wave is also a high impedance typically
greater than 1800 ohms ( to as high as 6000 ohms) direct
attachment is likely not meaningful as the VNA is the counterpoise.
And maybe the hand holding it.

We are also talking about likely 7mhz range so less than an inch
is less significant.

This is where inference substitution is useful, build 1:49 transformer confirm
its behavior with resistors. Place that between the VNA and said wire and
measure impedance. No matter what the wire length will have to be adjusted
for resonance in the measured environment and like a jig in the form of some
many feet of COAX to simulate the antennas interaction with it.

Also how do you put the 67Ft wire that will be fed from only one end in series?
If you touch the far end at all you change the result. That said for a resistor or
cap any small part the techniques work well but a 67 foot in air is not a small
part.

I say this as I once watched an engineer try to measure a 6ft monopole for an
E-field antenna on a PNA indoors. He concluded it could not work despite
a working version outside the window. Much explanation later the light was
seen. Its how antennas behave not the instrument and measurement
technique. They must match to a practical level.

Both can be measured without a VNA using a signal generator, bridge,
RF voltmeter or receiver as null detector plus some sense of the antennas
environment so it will be realistic.

The upside is even if wrong the 2:1 circle is rather large for those trying to
measure a EFHW.

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Allison,

My previous comment to WB2UAQ was not about testing the 49:1 UN-UN wuth S21. It was about measuring the high feedpoint impedance of his 67 ft wire at 7 MHz. For high impedances like this using the Series method with S21 is another way of measuring impedance.

Roger

On Sun, Mar 15, 2020 at 08:11 AM, Larry Benko wrote:

I recently made a video showing how to measure impedance 3 ways with a
VNA including the s11, series sw1, and the shunt s21 methods.
See if interested.

Larry. W0QE

Larry I just watched your video and it does a good job of explaining the three methods. If you are interested in doing a follow-on it would be interesting to see the following:

1. Comparison between SimSmith and NanoVNA using test components on the nanoVNA
2. Investigate what happens as you introduce deviation into the ideal CH0 and CH1 50 ohm impedance as Kurt Poulson discussed above.

Maybe we should move this discussion to a new post so the topic does not get buried in the discussion of 49:1 UN-UN testing.

Roger

Larry,

Impedance measurement is more indirect then measuring the transformer
directly. Both get you to the same point but the big thing is you have to
understand what your measuring and what that means. Easier for people
versed in the theory.

Also some just want to know, does it work as claimed?

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Roger,

S21 to get it right really requires a known transformer or often easier two
of the same back to back. That keep measurement in the 50 ohm
domain and also allows for reasonable accuracy for loss as it should
be twice that of a single transformer.

Its faster and less calculation intense, usually less error.

Allison
-----------------
No direct email, it goes to bit bucket due address harvesting in groups.IO

Hi Rune,
I want to tell you that I have added two parts to my NanoVNA tutorial:

a) Part 2: the NanoVNA-H up to 1500 (1300) MHz with examples

b) Part 3: the NanoVNA als TDR (= Time Domain Reflectometer) with examples

This new tutorial Version can be downloaded from the english section of my Homepage (www.gunthard-kraus.de).

73,s
Gunthard

I recently made a video showing how to measure impedance 3 ways with a VNA including the s11, series sw1, and the shunt s21 methods.
See if interested.

Larry. W0QE

On Sun, Mar 15, 2020 at 05:51 PM, Larry Rothman wrote:

Thank you for the command information, Hugen.
I have a minor H4 firmware enhancement request: is it possible to use the jog
switch to change also brightness when in the brightness config GUI menu?
I'm sure many users would find that method to be preferable.?
Cheers,
Larry



On Sun, 15 Mar 2020 at 12:38 AM, hugen@...<hugen@...> wrote:
hwalker11 is right. The NanoVNA-H4 uses DAC output dimming, so the
brightness can be adjusted using DAC commands. Dac_value = 800 is the minimum
brightness, dac_value = 3300 is the maximum brightness, you can enter any
number between 800-3300 for brightness adjustment.

Yes, the current brightness interface is very primitive. I need to provide a more friendly operation. Thank you for your suggestions.

On Sun, Mar 15, 2020 at 08:00 PM, hwalker wrote:

On Sat, Mar 14, 2020 at 09:38 PM, <hugen@...> wrote:

The NanoVNA-H4 uses DAC output dimming, so the brightness can be adjusted
using DAC commands. Dac_value = 800 is the minimum brightness, dac_value =
3300 is the maximum brightness, you can enter any number between 800-3300 for
brightness adjustment.
================================================================

Note: 1800 is the default, out-of-box, NanoVNA-H4 mid-range brightness
setting. I always wondered about the purpose of the "dac" console command,
although on the 2.8" NanoVNA-H's it's use is evidently reserved for other
(future?) purposes.

- Herb

The NanoVNA originally designed by edy555 allows the use of DAC to adjust VCTCXO, but when I made NanoVNA-H, I thought that adjusting VCTCXO was too much trouble for most users, so I used TCXO. For most VNA users, 2ppm TCXO can fully meet the test requirements. For geeks who may need more accurate frequency calibration, I think they can be easily calibrated by software. Therefore, the DAC on the 2.8-inch NanoVNA-H has no practical use.