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Hello,

Where can I find latest Nanovna v2 3.2 inch firmware?
On the github repository the latest is dated 20201013, while it looks more recent versions are available, like 20201122.

Thanks,
Simone

Christoph,

Aliexpress, vendor is Deepelec, this is the official vendor, everyone else
is a clone on Aliexpress or anywhere else.

Stay safe.

John
VE7KKQ

Use menu to go to DISPLAY then TRACES then select the other two which are
off.

As a newcomer, is it permissible to ask the question, which has certainly been asked many times, where - from a European perspective - it makes most sense to order a VNA-F? There are so many offers from Ali, ebay and other platforms, you have to know your way around...

Many thanks and greetings from Austria

73 Christoph, OE2CRM

—

The following numbers are from




Return Reflection VSWR Transmitted

Loss Coefficient Power

10 dB 0.316 1.92 90%

20 0.1 1.22 99%

30 0.032 1.07 99.9%

Twenty dB return loss means 99% of the incident power is transmitted,
practically all of it. The payback for working for higher return loss
is very small.

Dave WA8YWQ

On Thu, Jan 28, 2021 at 01:27 PM, Leif M wrote:

I just noticed that I can't get return loss better than about 40dB even with a
30dB attenuator. With 60cm/2 feet of RG58 cable the return loss was wavy like
with impedance missmatch. I have calibrated the VNA from 50k to 300M. I guess
I have to calibrate the VNA again.

40 dB return loss is an SWR of 1.02. If you calibrated with a load that was exactly 50 ohms and the DUT was purely resistive it would be 50.1 ohms at this SWR. However the loads supplied with the NanoVNA's are not near 50ohms. The one supplied with my NanoVNA-H is 49.81 at DC and the nanoVNA-H4 (also supplied with SAA-2) is 50.86 DC. The impedance varies with frequency. So if I calibrate with one of those and then measure a 30 dB attenuator 40 dB of Return Loss would not be much of a surprise.

I get the wavy Return Loss on my RigExpert and NanoVNA's when using typical "nominal impedance" 50 ohm cable. These ripples in the SWR will have a minimum at multiples of 1/4 wavelength and maximum at multiples of 1/2 wavelength. Here is an example with 50 feet of RG-8X with a 75 ohm resistive load at the end.

Roger

Consider the magnitude of that measurement in terms of %.? For practical uses, anything over -40 dB is meaningless unless you are comparing a part specification.? Like it is supposed to be >-45 dB.? ?Yes, my cal gives me >-60 dB, but I don't ever need it.??Please don't get blinded by specifications.
Mel, K6KBE

In theory down to 90dB. If I calibrate and measure with my DIY standard
I get those figures in the HF range. But that's mostly meaningless.
You have to remember that these are relative measurements, you can't
measure over X dB RL if your calibration standard RL is less than X.

Thanks Robin, that is most helpful. After your post I looked around and found a short type C to A cable, and sure enough the VNA was fine. It was just the cable squeezed into the box that must have broken it. Unfortunately I had already arranged to return it, and didn't want to risk fouling up the process by cancelling the return. Hopefully I will get one returned in a week or so with a good cable.
--
Dennis WA5LXS

This is a return loss to VSWR table. At 40 dB return loss the VSWR would be
1.02:1. A return loss of 14dB/VSWR 1.5:1 would be good for a typical filter.
*Clyde K. Spencer*

I just noticed that I can't get return loss better than about 40dB even with a 30dB attenuator. With 60cm/2 feet of RG58 cable the return loss was wavy like with impedance missmatch. I have calibrated the VNA from 50k to 300M. I guess I have to calibrate the VNA again.

FYi: I tried to measure an RF filter, made with an open stub in the middle of cable. It was too broad to be of use.

On Thu, Jan 28, 2021 at 09:03 AM, John Cunliffe W7ZQ wrote:

I assume you are calibrating the nano with the pigtail installed? If not, you
are comparing apples with oranges. Unless the load is a pure restive load with
no inductive or capacitive components the added length of the pigtail will
cause a change in the vswr as it acts like a transformer of the impedance and
can very well result in the different curves you are seeing. If you don't have
a way to calibrate the nano at the end of the pigtail you can add an equal
electrical length of coax cable to the rig expert setup.

Sorry but adding a short pigtail will not be an "apples to ranges" comparison. The complex impedance will change when you add a short pigtail to a long feedline but the VSWR change will be minimal. The reason is that the complex impedance change will result in a phase angle change to the reflection coefficient but the magnitude of the reflection coefficient will only be a tiny fraction smaller. You can easily verify this on a Smith chart or by adding a few feet of coax to a feedline and then measuring VSWR.

Instead of using an antenna which does capture ambient fields as your
comparison standard, find and use non-reactive resistors as you 'gold
standard'. You can also install series/parallel reactive components of
well known values around the resistive elements. That way, the potential
of interfering ambient fields are out of the picture.

Dave - W?LEV

On Thu, Jan 28, 2021 at 5:03 PM John Cunliffe W7ZQ <n2nep@...>
wrote:

I assume you are calibrating the nano with the pigtail installed? If not,
you are comparing apples with oranges. Unless the load is a pure restive
load with no inductive or capacitive components the added length of the
pigtail will cause a change in the vswr as it acts like a transformer of
the impedance and can very well result in the different curves you are
seeing. If you don't have a way to calibrate the nano at the end of the
pigtail you can add an equal electrical length of coax cable to the rig
expert setup.

--
*Dave - W?LEV*
*Just Let Darwin Work*

I assume you are calibrating the nano with the pigtail installed? If not, you are comparing apples with oranges. Unless the load is a pure restive load with no inductive or capacitive components the added length of the pigtail will cause a change in the vswr as it acts like a transformer of the impedance and can very well result in the different curves you are seeing. If you don't have a way to calibrate the nano at the end of the pigtail you can add an equal electrical length of coax cable to the rig expert setup.

John,

if you want to get, say, 3000? choking impedance on UHF, broadband, I can only wish you good luck! Because at 3000? at 500MHz is what a 0.1pF stray capacitance has. So forget about winding multiple turns on a core.

The best thing you ca do, I think, is find out which beads or toroids provide the highest impedance per length over the frequency range you need, and stack as many of them as necessary on your transmission line.

Manfred

I think FairRite makes toroid choke kits that comes with enameled wire and
Teflon tubing that slips over it. Not much more expensive than the bare
toroid.

My W/C is on 40-meters where I measure 1161 - j1110 at 7.0 MHz.

700W on 1161? is a current of 0.776A. The impedance magnitude is 1606?, and so the voltage is 1246V RMS, which is 1762V peak. At 1500W it would be about 50% higher. That's what you have at the input of the CMC, which is where I understand you are measuring. Along the length of the winding the voltage could get higher or lower. By Murphy's Law it will get higher, of course...

Even if the insulation of the magnet wire could take a million volt, it wouldn't be enough. This is because of Corona Effect. Consider a cut view through your bifiliar line: Two round copper wires, with a thin film of insulation around each, in direct contact, and with a wedge of air penetrating between the wires on each side. The problem is this wedge of air. With the insulation material having a dielectric constant of about 4 times that of air, the electric field gradient in the insulation is about 4 times lower than in the air. So, at a place where the air wedge has a suitable thickness, most of the voltage will appear across the air, rather than across the insulation thickness.

Now it happens that air won't break down below roughly 300V, no matter how thin the air layer is. But at voltages above that level it can break down. When the air breaks down, microscopic arcing happens, and most of the voltage moves into the insulation layers, limiting the arcing. But it is there, right at the surface of the insulation, and will erode the insulation over time. Sooner or later it will fail. Depending on how strong the effect it, it might fail after several weeks, or after several milliseconds, or anywhere in between.

So a magnet wire pair in direct contact can certainly work at somewhat more than 300V, because some of the voltage is dropping in the insulation, but not a huge lot more. Even if it has a very good insulation.

The insulation must be thick enough, and its dielectric constant low enough, to never exceed the breakdown voltage of the air wedge. With insulated wires in direct contact, that's about 300V in the air, and if there is a significant spacing it gets higher. With enough spacing, of course, the air alone provides enough insulation.

A better parallel transmission line would have the dielectric material molded around both conductors, filling the space between them, eliminating the air wedges.

A thicker insulation helps a lot, and an insulation having the lowest possible dielectric constant also helps. This is why teflon is so good: It does have a low dielectric constant, so more of the field appears in the teflon and less in the air.

An alternative is inserting a magnet-wire-wound CMC in a can of some suitable oil, and make sure no tiny air bubbles remain lodged between the wires. The downside of oil, of course, is that it increases the stray capacitance...

My lowest impedance is at 2.0 MHz and measures 19 - j288

1500W on 19? is 8.89A. The magnitude of that impedance is 288.6?. So the voltage is 2566V RMS, or 3629V peak. And very likely you could have even higher voltage spots along the line in your CMC!

You could measure the impedances with two different line lengths, both lines being of the same construction, for example using two of your CMCs having very different winding length. Then you can calculate what the highest voltage will be. But even without doing this, it's crystal clear that a CMC used on several bands in a high-SWR line, tuned/matched between the CMC and the transceiver, needs to be able to handle really high voltage, and pretty high current.

Manfred

Create a repo on github, it's free and others can send changes.

Dave - W?LEV

<<Generally, a few clamp-on ferrites of the appropriate material at the feedlint is all you really need. ..ferrites aimed at EMC and RFI control are good for that purpose at VHF/UHF frequencies

Unfortunately the Z of clamp-ons is a couple of hundred R at best; I'm looking for > 10 times that, eg for resonant feedline and end fed 1/2 wave antennae. So clamp on are inadequate

I should have said that I need broadband suppression, so 1/4 and 1/2 wave types are no use.

73
John

.

The document is written in Microsoft Word and printed in PDF with PrimoPDF.
No protection is activated.
If anyone wants a word document I will gladly send to email but the word document
is about 9 MB.

73
Martin 9A2JK