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Hi Gary,

Regarding fringe capacitance, HP states that fringe capacitance can have an effect on measurement accuracy above about 300 MHz.

This should explain “why” knowing fringe capacitance is important. (And I hope it is already clear why you need to accurately know your standads’ Gammas).

By the way, different types of standards will have different values of fringe capacitance. The Gammas of different Opens aren’t simply a difference in “length change”.

Finally, I would like to add...

Someone once told me that it took HP 10 years to develop VNA error correction. If true, that would have been a tremendous amount of effort by a group of very talented scientists and engineers.

I’m just a retired engineer with a tangential interest in VNA’s. I won’t have the answers to all your questions, but I’ll try to answer what I can.

Best regards,

Jeff, k6jca

On Wed, Jan 8, 2020 at 01:09 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:

Rudi,
The problem is the connector used on that is totally unsuitable. It is not
designed for repeated connections. Even the original manufacturer of the
device, Hirosose, rate it at 20 connections/disconnections. Hirose doesn't
release the diagram of the connector, so every cheap connector is going to
be some variation on that.

I almost choked with laughter when I read the word “knockoffs” being
mentioned by the maker of that board. It just seemed strange to think
anyone would knock off a design that’s so obviously flawed, and so easy to
improve (change connectors to SMA).

You should use a special tool for removing them. This one is made by
Hirose, who designed the U.FL connector.



So the design is so fundamentally flawed it is beyond belief. Anyone that
buys one can expect problems.
Dave

Hello Dave,

Thank you very much for the hint with the *extraction tool* for the U.FL connector.
Unfortunately it is *more expensive* than the *RF Demo Kit*.
I am using a 1.0 mm wide flat screw driver for extracting.
Up to now it works fine, if you press the cable down with your finger,
while you are levering with the screwdriver.

I agree, if you handle the U.FL connector *careless*, you will have sooner or later a *problem*.

By the way the data sheet from Hirose tells about *Durability* the number *30* not 20 cycles.
Compared with normal open milk, which is sour for sure after about a week, if not cooled,
the number of plugging cycles for an U.FL plug is a *minimum of 30*,
with a *good probability of more*, if you handle it *careful*.

For me it is a *learning tool*.
There are 25 connectors on the board, on 18 Test fields.
So, if you test and document each Test field once, including calibration,
you are still under the number of 30 cycles.
Beside that, you have *2 cables*.

Why do you score off a useful cheap learning tool, without trying that yourself?

Have you had a look to my "RF Demo Kit" description at:
/g/nanovna-users/wiki/RF-Demo-Kit-use

73, Rudi DL5FA

On Wed, 8 Jan 2020 at 05:51, Gabriel Tenma White <OwOwOwOwO123@...>
wrote:

Test setup: a slightly higher end VNA was used ;) and set to 10 frequency
points, 50x averaging (so that values are noise free but still updates fast
enough). The pk-pk phase jitter observed after calibration was less than
0.1 degree. The cable under test is then connected to port 1 of the VNA,
and the other end of the cable is left open. I then bend the cable randomly
for 1 minute while keeping to a turn radius limit of 5cm, and record
maximum and minimum observed phase. The resulting (max - min) phase error
is then divided by two (because we are measuring reflection, and signals
travel up and back for 2x phase effect).
The numbers shown below are pk-pk transmission phase variation during the
bend test.

It's good to see some quantitative measurements made, but I believe the
test procedure could be improved.

Essentially it is irrelevant what the peak phase changes are when the
cables are in motion. What is important is what phase changes occur after
they have been moved. I find cables take about 30 seconds to settle back.
So my method would be to make a connection, wait 30 seconds, make another
measurement, wait another 30 seconds etc. Of course, it takes more time,
but is more representative of what one would do in a lab, and should give
better results.

Dave

All,
In a effort to repair my NanoVNA to work above 300 mhz, please see /g/nanovna-users/topic/34518859#4791. So i order a new si5351a chip, and replaced it last night. The new chip did not help solve the issue, i though i had matched the chip to original spec but upon further inspection of the spec sheet show to max freq to be only 200 mhz. The link to what i ordered is below. Can anyone point to the correct chip? or any other tips to make my nanovna work about 300 mhz.

On Tue, 7 Jan 2020 at 15:04, <reuterr@...> wrote:

The RF Demo Kit NWDZ Rev-01-10 is available via Ebay for about 15 EUR.

If you buy one and it fails, I would report via eBay as poor quality. You
will soon get your money back.

Dave

On Wed, 8 Jan 2020 at 10:14, <reuterr@...> wrote:

Hello Klaus,
Could you please tell more details:
1. which Test field do you mean?
2. Do you have a screen shot of a diagram?

I have tested Testfield 1 Low Pass Filter 30 MHz, please see at:
/g/nanovna-users/wiki/RF-Demo-Kit-use
or
Test field 12 Notch filter at about 500 MHz:
RF-Demo-Kit_12-BSF-500MHz_Saver.png

I have not seen any problems.

73, Rudi DL5FA

Rudi,
The problem is the connector used on that is totally unsuitable. It is not
designed for repeated connections. Even the original manufacturer of the
device, Hirosose, rate it at 20 connections/disconnections. Hirose doesn't
release the diagram of the connector, so every cheap connector is going to
be some variation on that.

I almost choked with laughter when I read the word “knockoffs” being
mentioned by the maker of that board. It just seemed strange to think
anyone would knock off a design that’s so obviously flawed, and so easy to
improve (change connectors to SMA).

You should use a special tool for removing them. This one is made by
Hirose, who designed the U.FL connector.



So the design is so fundamentally flawed it is beyond belief. Anyone that
buys one can expect problems.

Dave

Hey Gabriel and hey everyone,

First: Thanks to all of you and of course Gabriel in particular for this really nice and worthwhile discussion! I hope that we can gather some more experiences and ideas. ?

Concerning the caps: compared to 100n or 470nF caps those 4u7 have a lower resonance point and hence are able to filter lower frequencies too. So in total, they are really broadband!

Frankly I never had such radiation problems concerning the ‘normal’ SMA connector type. That’s why I’m a bit astonished that you had one at your design as 4cm distance between 2 SMA connectors (mid to mid) gave me one roughly 90dB isolation. Maybe your connectors are a bit closer…

Funny that we nearly had the same ideas! You surely did a good and detailed prototyping, wow! ?
But concerning the caps between mixer and BB amp: maybe a smaller cap may do the trick? A smaller cap is faster at its charging and discharging but still blocks DC.

I’m sorry that those TC-1-13Ms do not solve your problems. If your looking for a transformer having a compensation for its asymmetry within the component may you can have a look at those:
MABA 011082 or TCM1-63ax. Unfortunately, the S-Parameters are just starting from 5MHz and 1MHz. But within the balun simulation they still had a nice performance at those low frequencies. Of course, they might be a bit more expansive but as they are built up symmetrically you may not need to build in two but just one inside your directive coupler…
May I ask why the OIP3 is important to you? In my opinion to ensure a good performance the system needs to run at the linear region of the amplifier so values like P1dB might be more important than OIP3…?

And Wow to your plans building up a ‘proper’ VNA! That’s amazing! I wish you all the best for it ? But programming (modelling) a FPGA is totally different then a microcontroller. I thought the new SMT32 generation have some specials like higher clock and special filter setup internally etc so maybe those might be already fast enough to shift the IF frequency into a proper value.

As you’ve asked at which project I needed to work on an directional coupler: I did my master thesis at Rohde & Schwarz at their VNA department and developed a directional module from 9kHz to 20GHz (actually it had been more than 30GHz at the end) using PCB material. ?
At the moment I’m just a normal RF-Engineer with several different projects from schematic to layout design and from simulations to antenna setups. But I’m far from being able to lead a whole ne VNA development :’)
Although, maybe I might build up a small directive coupler if I have some spare time just to do some measurements on my one !

And ones more: Thank you very much for sharing your knowledge with us! ?

On Wed, Jan 8, 2020 at 12:26 AM, vincent coppola wrote:

" Here is a screen capture of my 40 m coaxial cable trap. ...'
====================================

Vince,
Screen capture missing.

- Herb

Hello Klaus,
Could you please tell more details:
1. which Test field do you mean?
2. Do you have a screen shot of a diagram?

I have tested Testfield 1 Low Pass Filter 30 MHz, please see at:
/g/nanovna-users/wiki/RF-Demo-Kit-use
or
Test field 12 Notch filter at about 500 MHz:
RF-Demo-Kit_12-BSF-500MHz_Saver.png

I have not seen any problems.

73, Rudi DL5FA

I bought this kit, too. I wondered about the very bad measurements in the inductive part. So I got it to the QRL, where we have a HF-Labor. The results with the Rhode&Schwarz are shattering. I'ts not recommended to buy it.

Here is a screen capture of my 40 m coaxial cable trap. Obviously the center freq is too high but it is work in progress. Roughly one can see that the 3db bandwidth is around 130kHz, Q around 62. Next I ran analysis in band stop mode and it displayed around 1.5mHz BW, and a Q of around 5, which I don't think is correct. Also I tried to up segment count from 1 to 12, but did not help. Finally, in band stop mode it does not tell to place a marker anywhere that I can see. ..Vince

Hi,

Calibration at the far cable end can be difficult at times, as not always
you have easy access to your antenna feedpoint.

An alternative way to get what you want, using easily measured rig side
data and SimSmith, is described in this video:



Simply measure your antenna's impedance response across the band
of interest with NanoVNA at the rig side cable end and save it with
NanoVNA saver as .s1p file. Import the file in SimSmith.

The video explains how to obtain and save the actual feedpoit impedance
response file.

With this, SimSmith makes it easy to optimize your antenna and feed system
without even leaving the shack.

I described an application to this forum. You can find it under:

broadbanding my W3DZZ on 80m

Enjoy.

73, Hans
DJ7BA

-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Chris Keladis
Gesendet: Dienstag, 7. Januar 2020 22:32
An: [email protected]
Betreff: [nanovna-users] Measuring resonance from coax far end.

Hi folks,

This is more a generic VNA question, but thought i'd ask.

I've seen a trick to "eliminate" the coax by calibrating via the OSL on the far end of the coax, rather than having OSL connected directly to the VNA.

Essentially it's re-calibrated with the coax factored into the equation, virtually moving the feedpoint to inside the shack for accurate antenna feedpoint measurement.

If i calibrate the far end, take resonance readings, then recalibrate with the OSL connected directly to the VNA, re-take resonance readings, would it be safe to assume if there is common-mode current interference on the coax it would account for differing results (if there are any)?

If there's no common-mode currents, the coax-length should be invisible.

Just want to make sure i've got my theory correct. :)



Thanks & 73s,

Chris.

And here is another introduction. Read section 2.1.3
This document from 1990 also mentions the ratio of cross ratios and describes various different approaches to calibration next to the well known SOLT

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Attached document should give some answers

The impedance model of the calibration load represents the actual impedance of the load either as it is calculated from theoretical modelling or from measurements like in attached document.

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Interesting.....

My question still doesn't seem to be getting through... Yet it remains a simple one. :-) Let me try this again.

Question: What justifies characterizing the calibration standards?
Answer: Because it improves measurement accuracy.

Question: How does it do that?
Answer: It makes post calibration measurements of the standards plot with the profile of the standards and not plot as though the standards were perfect.

Question: How does doing this make the measurements more accurate?
Answer: Because HP says characterization of the standards improves accuracy, everybody agrees, this is the way it's always been done, and it actually works.

Question: How much more accurate are the measurements after calibrating with the characterized standards?
Answer: Close to absolute.

Question: How do you know the measurements are close to absolutely accurate?
Answer: Because they were characterized by a certified test lab, who provides us with the correction coefficients.

Question: Does the certification lab provide a tolerance on the accuracy of the coefficients they give you?
Answer: I don't know... Probably.

Question: So you are confident that your results are as accurate as you can make them?
Answer: Yes.

Question: Why?
Answer: Whatever do you mean???

Question: Isn't there some degree of uncertainty remaining?
Answer: Well sure...

Question: How much?
Answer: I don't know, but I know its not very much once I've calibrated appropriately with my Characterized calibration standards.

Question: What impedance does the open circuit standard represent?
Answer: Oh I don't know, but it's pretty high... maybe a few k ohms.

Question: I think I read something around 50 femptoFarads being used to compensate for the fringing capacitance of the open standard as a typical correction. Does that sound about right?
Answer: Yeah! I might have heard or read something like that. It's a very small number.

Question: I'll say... but 50 femptoFarads is about 32 ohms at 100 GHz. If the the open circuit impedance drops to 32 ohms, How far does that move the dot?
Answer: I don't know, but it isn't very far?

Question: But it shows that it has a noticeable span on the display. Why is that?
Answer: Because it probably moves that far after it's been calibrated. The open circuit might be offset by the connector length... and it only happens at really high frequencies. In the GHz range maybe.

Question: I'm guessing it's an unavoidable shunt capacitance and maybe there's some angular displacement in play also?
Answer: Probably... Maybe... It has to be something, or else it would be just a dot.

Question; So that isn't an error in the calibration?
Answer: No... It shows that it has been calibrated because it's displaying what the open circuit really looks like.

Question: Then the open circuit doesn't look like a real open circuit?
Answer: Correct. It's not possible to make a perfect open circuit.

Question: So I've been told... That's about as close to an open circuit as we can manufacture though am I right?
Answer: I think so.

Question: Then why isn't the standard used to represent a precise open circuit after calibration? Isn't this a real open circuit in the real world?
Answer: Because then it wouldn't be accurate, and not all open circuits are the same. They might be at a slightly different offset.

Question: That's still just a length change though correct.
Answer: Yes, but now we can measure it and use the data to measure others like it.

Question: You can't manufacture a precise open circuit, but you need to measure them accurately?
Answer: Correct.

Question: Why?
Answer: Huh?

Question: Why? What's the point? How does it manifest its value?

--
73

Gary, N3GO

You would need to have in the ballpark of 80 nH of series inductance due to series parasitics.. Seems a little high but not out of the question.

Measure caps a low freq first to get values with minimum parasitic effects. Don't go below 2 MHz to stay over about 500-800 ohms of reactance as the accuracy gets poorer at higher value of reactance.

If you have access to a good accuracy 10KHz or 100KHz LCR bridge it would give you a good base to work from.

On 1/7/20 6:27 PM, hwalker wrote:

" ..A 100pF silver mica then gives the attached which indicates 105pF at 7MHz, 109pF at 14MHz and 126pF at 28MHz .."
=======================================================

The above frequency dependent impedance effects are why manufacturers specify their component values at specific test frequencies. A dedicated LCR instrument, i.e. the well regarded DE-5000, has five test frequencies 100Hz/120Hz/1kHz/10kHz /100kHz one of which will generally match the manufacturers specified test frequency.

???? Also, they choose lower frequencies not only because it's easier to measure at low frequencies, but also because many components suck at higher frequencies, and by specifying low test frequencies, component manufacturers were able to hide the uselessness of their parts.? Several decades ago I had access to an HP network analyzer, and used it to evaluate components for use in the VHF/UHF radio equipment I was designing.? Among standard ceramic chip capacitors, I found that only Murata and Panasonic were suitable for RF designs.? Pretty much everybody else's "capacitors" were much closer to resistors at those frequencies. But at the specified test frequencies of a few kilohertz to **maybe** a few megahertz, they looked fine, and I assume they would work fine, IF you were only designing audio equipment.

Hi wb2uaq,

Yes - i define resonance as R+j0. I had read that if there are no
common-mode currents on the feedline then length of coax shouldn't matter
as far as swr/resonance is concerned.

If it does change, then chances are there are common-mode currents on the
line affecting the reading.

I understand the basics of smith-charts, i'm a new owner of a nanoVNA but
have an (older) RigExpert as well.

Also understand the 1/4wl or 1/2wl multiples along the length of
transmission-line. I guess i'm a little confused if these will be seen at
the shack-end of the coax, if there was not any common-mode current.

I've read that if there is no common-mode then no change will be seen for
swr or resonance at points along the transmission-line, if there was, there
will be changes at every 1/4wl or 1/2wl point along the transmission-line.

Trying to wrap my head around how coax changes what you see at the
feedpoint. The RigExpert (AntScope2) has a menu to add/subtract/do-nothing
with the transmission-line when taking readings with it and it's always
confused me when taking readings with it.

Anyway, i appreciate your taking the time to reply & best 73s!



Thanks,

Chris.

On Tue, Jan 7, 2020 at 03:43 PM, Brian wrote:

" ..A 100pF silver mica then gives the attached which indicates 105pF at 7MHz, 109pF at 14MHz and 126pF at 28MHz .."
=======================================================

The above frequency dependent impedance effects are why manufacturers specify their component values at specific test frequencies. A dedicated LCR instrument, i.e. the well regarded DE-5000, has five test frequencies 100Hz/120Hz/1kHz/10kHz /100kHz one of which will generally match the manufacturers specified test frequency.

You can judge the accuracy of the NanoVNA at 100 kHz by comparing its results with those of a dedicated instrument like the DE-5000. At HF, you're a bit out of luck unless you have access to something like a high dollar HP 4294A Precision Impedance Analyzer, 40 Hz to 110 MHz. You might start a collection of "golden" components whose impedance values at HF you have determined using other instruments and use those as transfer standards to check the accuracy of the NanoVNA.

For your 100 pf capacitor example, I would expect at 100 kHz for the NanoVNA to measure 100 pf +/- the specified manufacturer's tolerance. At higher frequencies, especially for leaded components, I would expect values similar to what you measured.

- Herb

What is your definition of resonance in this situation? If you measure say R + j0 at the antenna, the Z you measure at the input end will be dependent on the electrical length of the transmission line. Only when it is multiples of quarter waves long or a multiple of half wave long will it look like a resistance again. Any other electrical lengths will result in a resistance plus a reactance. If you are familiar with the Smith Chart, you can see this readily. If not familiar with the Smith Chart. The presence of common mode currents could add more complications but may or may result in a definitive explanation. 73