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An easier way to check coax loss is available on the H4 with most recent
firmware. You connect the coax to only the s11 port, and leave the far end
of the coax open. Then from the menu choose measure / coax. The
measurements will appear at the left of the screen, including a loss
measurement at whatever frequency the cursor is at. So you set the
frequency range to include the frequency of interest, and directly read the
loss at that freq.

The nano makes this measurement from the s11 reflected wave, and divides by
2 because the raw measurement is for both up and back along the cable.
It's a nice feature. Not also that the frequency range must include a low
enough frequency to be a quarter wavelength for the length of the cable, so
I often just calibrate for 50kHz - 30MHz when doing this type of measure so
I don't have to think of it. Even with this wide range it gives good
accuracy because the nano firmware does a good job of interpolation between
measurement points (thank you, Hugen!).

(Note that the length measurement shown depends entirely on the accuracy of
the velocity factor - so be careful with that value.)


On Thu, May 5, 2022, 5:48 PM Bob Ecclestone VK2ZRE <becclest@...>
wrote:

don't think it is busted. Your photo shows the port unterminated. Try
terminating both ports in 50 Ohms and rerun the scan.
The Port2 input is pretty sensitive to internal crosstalk (noise), so I
would not be too concerned.
Remember, this is a ~$100 instrument. It performs exceptionally well for
that amount of money:-)

73...Bob VK2ZRE


On 6/05/2022 10:36 am, kosmos wrote:

Very cool tip, thanks for detailing it!

It removed the movement, but it's still not a line, still looks like

noise with inaccurate values unfortunately.

Could the S21 port just be busted?

don't think it is busted. Your photo shows the port unterminated. Try terminating both ports in 50 Ohms and rerun the scan.
The Port2 input is pretty sensitive to internal crosstalk (noise), so I would not be too concerned.
Remember, this is a ~$100 instrument. It performs exceptionally well for that amount of money:-)

73...Bob VK2ZRE

Very cool tip, thanks for detailing it!

It removed the movement, but it's still not a line, still looks like noise with inaccurate values unfortunately.

Could the S21 port just be busted?

Hello,

Try setting the THRESHOLD setting to 280 and do another complete calibration.
Some clock chips are not stable at the default value of 300(MHz). These chips are severely overclocked in the NanoVNA design, their nominal Fmax is 200MHz.
The instability shows up as "noise" in many traces.
This will reduce your "maximum" frequency to 1400MHz using the 5th harmonic, but most manufacturers state a useful maximum up to about 1250MHz anyway.
Make sure you do a RESET and CLEAR ALL to clear all old Calibration data before you do the new cal.
HTH.

73...Bob VK2ZRE

Hello Victor,

I am sure you will get flooded with replies to your question.
The answer is simple, early versions of the nVNA had a nominal Port1 output of -13dBm, later versions had redesigned Port 1/bridge circuitry and the nominal output is now +1dBm.
So your unit measures pretty close to (a very loose) specification for a later design of the NanoVNA.

73...Bob VK2ZRE

Hello all of you,

I am trying to find some authoritative info on the output power of the
NanoVNA.
In several links I see -13dBm (and sometimes even increasing with
frequency: or

).
Anyway -13dBm is not much: some .005mW (
).

So I checked with a scope and did a start-stop from 7MHz to 7.1MHz, and I
see a block function with amplitude of 0.56V (unloaded). When I load with
50ohm load I get 0.28V.
The amplitude of the fundamental freq. of a block is 0.28*4/pi(). And to
get the Vrms value, we divided it with sqrt(2):
0.28*4/pi()/1.4 = 0.25 Vrms
That makes 1.3mW (0.25^2/50) or 1.1 dBm (10*log(1.1mW/1mW))

So where is this -13 dBm coming from?

Can you help?

All the best,

Victor

Hi Torbj?rn,

going back to your coax xable splitter:

When you have a signal source at A and two loads connected to B and C, the circuit works fine, because each 75? cable will transform its 50? load into 112.5?, and the two 112.5? inputs in parallel give 56.25?, close enough to the 50? the source expects.

When you have two phase-synchronous signal sources at B and C, the same will happen in reverse, and the circuit will work fine too.

But when you have a source at B, and loads at A and C, it will not work. The load at C will be transformed to 112.5? by that cable, this will appear in parallel with the load at A, giving 34.6?, and this will be transformed to 162.5? by the other cable.

Very simply said, your circuit isn't 3-way-symmetric. Ports B and C are identical and interchangeable, but port A is different. You always need to have either the source or the load on port A, and put identical things on B and C - two loads or two synchronized sources.

Manfred

This is when I calibrated and left the cable in through, used the thin coax that comes with it.

The value for S11 looks "about" right. Yes, S21 is noisy. Run the same
test with the coax you used for the through cal, of course, after another
complete cal.

Dave - W?LEV

--
Dave - W?LEV

Here's with a reset calibration, I don't think S21 should be noisy like that, should it?

On Wed, May 4, 2022 at 08:36 AM, KENT BRITAIN wrote:

The TV splitters to connect two TV's to the same antenna are very cheap and
work just fine at that frequency.? ? They are a simple transformer, they
have no impedance of their own.? So splitting 75 Ohms or 50 Ohms is no
difference.? ? Don't like the PAL or F connectors, take out the little
transformer and put it in your own box.? Kent

I tested a quality CATV splitter and found it worked quite well for 50 ohm applications. The Return Loss, S21 and Isolation graphs obtained using a NanoVNA are attached. I used F to BNC adapters (from Amazon) for these tests.

Roger

Still new to using a VNA.

I've calibrated my NanoVNA-H4 and double checked the calibration with the 3 tips once again as per hexandflex' guide, with the isolation and through, since I want to measure the coax loss.
So far so good.

Now when I plug in the cable to both S11 and S21, I get some really odd readings that don't seem to match up with what I'm seeing in guides and videos. My logmag is all over the place and nowhere near showing a proper reading.

What is it that I'm missing here? Did I do something wrong?

Regarding power splitters/combiners, check out the Gysel (rhymes with Diesel) combiner; its termination resistors are 50Ω and grounded, much easier to deal with than the floating 100Ω resistor of the Wilkinson type, especially when it comes to high power work.
73, Don N2VGU

Thanks Andy and Kent. Using the Wilkinson approach my splitter gives SWR 1.1 at the design frequency, quite broad. The input from Kent gave me the idea to make a splitter using two ferrite-toroidal transformers, winding prim/sek 5/7 turns would give the correct transformation, root of 2. Then I could place the transformers in a box together with three ccoax connectors. I will experiment with this setup.

73/Torbjorn

On 2022-05-04 17:39:+0100, you wrote:

You're missing the resistor.
73 Andy, G4KNO

Very useful link. Thanks!

~R~
72/73 de Rich NE1EE
The Dusty Key
On the banks of the Piscataqua

You're missing the resistor.
73 Andy, G4KNO.

On Wed, May 4, 2022 at 4:07 PM Torbj?rn Toreson <torbjorn.toreson@...>
wrote:

Hello,

I intend to use the same antenna for two RX-radios. I will lose 3 dB, but
for the sake of the radios RX-input I intended to present each with roughly
50 ohms.

The frequency is about 90 MHz (not HAM-use). I made two 1/4 wave
transformers with RG59 coax, taking VF of 0,66 in consideration. Measuring
each one with the Nano and 50 on the outer side I get as anticipated about
110 ohm. Now the idea is to parallell the two 110 ohm sides and get around
55 ohm, this is where the antenna should be connected. Imagine the
cable-setup as a V, with the vertex (bottom on the V) labeled A and the two
upper parts labeled B and C.

When I connect 50 ohm dummies to B and C then I can measure about 50 ohm
at A for 90 MHz. Now I wanted to see what one of the radios would feel so I
connected 50 ohm dummies (actually 50 ohm pieces from calibration kits) at
A and C. Now measuring at B I was expecting to see about 50 ohm. That was
not the case, the result was about 140 ohm (X about 0) and SWR about 3 (of
course). At about 150 MHz I got a SWR minimum.

Please help me to understand why the setup works one way (as e.g. to
connect two phased antennas) but not the other way to connect one antenna
to two radios.

73/Torbjorn/SM6AYM

The TV splitters to connect two TV's to the same antenna are very cheap and work just fine at that frequency.? ? They are a simple transformer, they have no impedance of their own.? So splitting 75 Ohms or 50 Ohms is no difference.? ? Don't like the PAL or F connectors, take out the little transformer and put it in your own box.? Kent

Hello,

I intend to use the same antenna for two RX-radios. I will lose 3 dB, but for the sake of the radios RX-input I intended to present each with roughly 50 ohms.

The frequency is about 90 MHz (not HAM-use). I made two 1/4 wave transformers with RG59 coax, taking VF of 0,66 in consideration. Measuring each one with the Nano and 50 on the outer side I get as anticipated about 110 ohm. Now the idea is to parallell the two 110 ohm sides and get around 55 ohm, this is where the antenna should be connected. Imagine the cable-setup as a V, with the vertex (bottom on the V) labeled A and the two upper parts labeled B and C.

When I connect 50 ohm dummies to B and C then I can measure about 50 ohm at A for 90 MHz. Now I wanted to see what one of the radios would feel so I connected 50 ohm dummies (actually 50 ohm pieces from calibration kits) at A and C. Now measuring at B I was expecting to see about 50 ohm. That was not the case, the result was about 140 ohm (X about 0) and SWR about 3 (of course). At about 150 MHz I got a SWR minimum.

Please help me to understand why the setup works one way (as e.g. to connect two phased antennas) but not the other way to connect one antenna to two radios.

73/Torbjorn/SM6AYM

On 5/3/22 8:40 AM, Rich NE1EE wrote:

On 2022-05-03 06:45:-0700, you wrote:

This kind of gets to a point - there *are* people who know the answers on this list, but in general, they also have other things to do, so their time is limited. It's great that you're taking on the challenge of writing a book to explain it, but as you know, it's time consuming.

To be honest, a threaded list isn't the best way to explain this kind of thing. The person who wrote the software generally has a good understanding of the theory, but doesn't necessarily have the time to answer it in a 20 questions form, and, it's also possible to be knowledgeable for writing the code, but not such a great explainer.

This gets to the heart of the matter.

there *are* people who know the answers on this list, but in general, they also have other things to do

Good for them. So do I.

It's great that you're taking on the challenge of writing a book to explain it, but as you know, it's time consuming.

All I set out to do is write a user manual for the nVNAs (-H and -H4, though it generally applies to other nVNAs). I figure that if I write down each feature as I learn it, then that will benefit hundreds? thousands? of those to come. Oh, wait, there are already people who know all this, and could have taken 30 minutes to think about the device and jot down some useful things that they know.

Indeed, but sometimes, (and this is particularly so on a forum like this), one doesn't know the desired level of the answer, audience it's intended for.? As an example, we've had a lot of discussions about calibration standards, and simple questions like "should I calibrate with or without the 6" jumper".? Some folks have a background in RF metrology, and want to make sure that we understand that a simple time offset may not be a good model. Others might be looking at an antenna between 5-10 MHz, for which it makes almost no difference.? Others, though, might be measuring phasing jumpers, so that extra 6-12" makes a difference.

This aspect of "finding the right level" is tricky, especially in a forum which is sort of asynchronous.? A person might pose a question and get 2 or 3 answers, all partially answering it, with different levels of rigor or formality. And then, 3 or 4 more others might respond with different aspects.? If we were all standing in a room doing this in real time, you'd pick up on some of the body language to manage the conversation. Likewise in a one-on-one phone call or remote presence - there would be cues to guide the questions, and followups.

I have long history with software engineering. That means writing requirements, a design, then software and software testing. We don't seem to have much of this.

This is definitely true, and it is characteristic of software that is produced to "scratch an itch", as opposed to "develop a product", particularly when it's done by one person. That's sort of a feature, not a bug. The author writes the software to meet some self derived requirements, which evolve based on time available, inclination, etc.? And if they understand it, that is sufficient for them.? In a lot of cases (e.g. NanoVNA and similar products) someone might push their software out for people to use, on a Use As Is basis, and if bugs are reported or features requested, then they may or may not do it, depending on their other desires.

This isn't unusual in volunteer activities - It's easy to find hams for a one time antenna raising party, less easy to find someone willing to drive up a twisty road, through locked gates, to clean the filters and check the battery water every 3 months.

I created the menu map in yEd because it is readily accessible, and anyone can update it from here out. So we have a Russian hacker who creates this stuff. I'm impressed with the talent. I don't speak Russian as well as he speaks English, and that is not very well. What I set out to do is write down what I think will help others new to the technology know what will happen when they press a button. That's why I posted that excerpt, to show what my intent was. I say was, because it didn't take long to exhaust resources. So, since I don't intend to spend hundreds of hours learning all this stuff, and there is not much feedback besides "look it up on the web", I figure /this/ part of the project is stalled.

And that's fine - you've made a contribution, others will extend or revise it, or you'll do it, or it will be like it is.? That's the way it is. The documentation on console commands is about 2 1/2 years old now (at least the version I have), as the result of Larry's significant effort. Unfortunately, it's a pdf, which is universally readable, but also makes it hard for someone to update.

So we fall back on the classic open source technique "read the code" and "rely on background information" - I use Scikit-RF at work, so does some of the NanoVNA software, so even without much in the way of comments, I can figure out what's going on.

I've created lots of requirement docs in the past. Lots of design docs in the past. Lots of programming and software testing. So it's not that I don't get it...I do.

it's also possible to be knowledgeable for writing the code, but not such a great explainer.

This is a good point. But for me, it's a show-stopper. Because when I ask a question, and there is no answer, there is nothing to write down. I assume that no one actually understands what the answer is.

Or, perhaps you can reframe your question, or maybe synthesize all the responses you got, and repose the question in that context.? It's a conversation, after all. This is, for good or ill, a largely text medium, which doesn't help when trying to describe how things are hooked up, especially when there are significant differences in terminology (not including bikeshed stuff like "is return loss negative?").? A lot depends on the background of the specific person. Someone who comes from a precision metrology background might use different terms than someone from a circuit design, or user background.? Little stuff like "uncertainty", "accuracy", "precision.

I've put the user manual aside. Maybe all that I want to know is there in Russian, but that does me no good. I certainly don't fault a Russian for writing in Russian. I actually started learning Russian years ago, because I thought of them as major players in the science field. But then most of the people I worked with spoke pretty good English...not great, but we could have a conversation, and I could connect the dots. So I stopped learning Russian. Rats. Well, too late to start now...

BTW, this discussion is not limited to this device. I spent 10 years working with PhDs who had the same lazy attitude. Too busy getting ahead of the next PhD to write down what they were doing. Before I left that group, they had hired //another// PhD to work in the lab ///// to reconstruct what had happened 10 years earlier /// because they were too lazy to write it down, and then had the misfortune to need it.

Well, perhaps it's not lazy (which is sort of perjorative) - perhaps it's that their requirements and incentives were not aligned with the others.? As a PhD candidate your *job* is to "get that dissertation completed".? It is generally not evaluated on the quality of the software and documentation you leave behind. That's sort of gravy. This is a typical complaint about new PhDs entering the industrial workforce. As a Phd Candidate, you're expected to do your own work. As an employee on a team, you're expected to share the work. As a PhD candidate, you're expected to be rigorous in derivations and references. As an employee in a team in a frenzy to get the "minimum viable product" out the door, you probably don't care as much about making sure the docs cite the seminal paper in the field.

On 5/3/22 8:10 AM, Rich NE1EE wrote:

On 2022-05-03 06:29:-0700, you wrote:

If you're writing a tutorial manual,

I'm not. I'm writing a user manual for the nVNA. I think we could all benefit from tutorials of some sort, but we all have different interests. To me, that means that many people would prepare tutorials, each in their own area of interest or knowledge.

To a certain extent, though, a user manual is tutorial in nature, if you're giving step by step procedures for how to execute some measurement.? Perhaps not to explain the background, but surely we want something more than a "man file" which lists the available options with no information on why you might want to use it.